ORGANIC CHEMISTRY LABORATORY II
CHEMISTRY 3712/3612
Spring 2003 Edition
Neil T. Allison
Department of Chemistry and Biochemistry
University of Arkansas
Fayetteville AR
Contents
CHEMISTRY 3702-3712; ORGANIC CHEMISTRY LABORATORY I-II.......................................... 4
GENERAL INFORMATION......................................................................................................... 4
Course Objectives.................................................................................................................... 4
Background..................................................................................................................................... 4
Laboratory Text and Other Study References ......................................................................... 4
Laboratory Supplies................................................................................................................. 4
Grades...................................................................................................................................... 5
Quizzes .................................................................................................................................... 5
Late Lab Books and Make-Up Labs........................................................................................ 5
Preparation............................................................................................................................... 5
Housekeeping .......................................................................................................................... 5
Safety ....................................................................................................................................... 6
Laboratory Safety Regulations ............................................................................. 7
Cleaning Glassware ................................................................................................................. 9
Waste Disposal ........................................................................................................................ 10
Miscellaneous Practices Specific to this Course...................................................................... 10
BIBLIOGRAPHY........................................................................................................................... 12
LABORATORY NOTEBOOKS .................................................................................................... 13
CHEMISTRY 3712; ORGANIC CHEMISTRY LABORATORY II...................................................... 16
SCHEDULE OF EXPERIMENTAL WORK................................................................................. 16
LABORATORY DRILL ................................................................................................................ 17
SUGGESTIONS ON ORGANIZATION OF LABORATORY WORK ....................................... 17
CHARACTERISTIC IR GROUP FREQUENCIES OF COMMON COMPOUND TYPES ........ 19
BASIC IR REGIONS ..................................................................................................................... 20
SOLUBILITIES OF ORGANIC COMPOUNDS; ORGANIC ACIDS AND BASES ................. 21
Solubility ................................................................................................................................. 21
Acids and Bases....................................................................................................................... 22
SOLUBILITY CLASSIFICATION OF WATER INSOLUBLE COMPOUNDS ......................... 26
QUANTITATIVE ASPECTS OF EXTRACTION; ILLUSTRATIVE EXAMPLES................... 27
CHARACTERISTIC PROTON CHEMICAL SHIFTS ................................................................. 30
BASIC 1H NMR CHEMICAL SHIFTS ......................................................................................... 31
SHOOLERY'S RULES .................................................................................................................. 32
CHARACTERISTIC CARBON-13 CHEMICAL SHIFTS ........................................................... 33
BASIC 13C NMR CHEMICAL SHIFTS........................................................................................ 34
C-13 ADDITIVITY RULES .......................................................................................................... 35
i
Locker List
Chemistry 3602/3612 M and 3702/3712 L Locker Apparatus List (Rev 9/01)
Name
Course
Student ID
Section
Locker Number (#1)
Lock Serial No.
Lock Combination
Locker Number (#2)
Lock Serial No.
Lock Combination
Locker Number (#3)
Lock Serial No.
Lock Combination
Locker Number (#4)
Lock Serial No.
Lock Combination
Ground Glass Standard Taper Ware, 19/22 Joints
( )
1
Glass Thermometer Adapter
( )
1
Condenser, 200 mm
( )
1
Connecting tube, 3-way distillation head
( )
1
Connecting tube, curved vacuum adapter
( )
2
Flask, round bottom, 250 mL
( )
1
Flask, round bottom, 100 mL
( )
2
Flask, round bottom, 50 mL
( )
2
Flask, round bottom, 25 mL
( )
1
Separatory funnel, 125 mL
( )
3
Stopper, glass
Other Glass and Plastic Ware
( )
1
Beaker, 600 mL
( )
1
Beaker, 400 mL
( )
1
Beaker, 250 mL
( )
1
Beaker, 150 mL
( )
1
Beaker, 100 mL
( )
1
Flask, Erlenmeyer, 250 mL
( )
3
Flask, Erlenmeyer, 50 mL
( )
2
Flask, Erlenmeyer, 25 mL
( )
2
Flask, Erlenmeyer, 10 mL
( )
1
Flask, filtering, 250 mL
( )
1
Flask, filtering, 25 mL
( )
1
Funnel, Buchner, 7.5 cm
( )
1
Funnel, Hirsch
( )
1
Funnel, narrow stem, 75 mm
( )
1
Funnel, powder, 65 mm
( )
1
Graduated cylinder, 100 mL
( )
1
Graduated cylinder, 25 mL
( )
1
Graduated cylinder, 10 mL
2
Locker List
( )
( )
( )
1
Test tube, 18 mm x 150 mm
.......continued........
4
Test tube, 13 mm x 100 mm
( )
2
Tube, centrifuge, 12 mL w/cap
2
Tube, NMR w/cap
( )
1
Thermometer, ≥350 oC
( )
2
Vial, conical, 5 mL w/ closure
( )
2
Watch Glass, 100 mm
Miscellaneous Hardware
( )
1
Rubber Thermometer Adapter
( )
1
Cork ring
( )
3
Dropper bulb, 2 mL
( )
4
Joint clip (Keck clamp), 19/22 (blue)
( )
1
Neoprene adapter tube seal, large, gray
( )
1
Fliter adapter tube seal, small yellow
( )
2
Rubber hose, vacuum, 50 cm
( )
1
Scoopula
( )
1
Spatula
( )
1
Stir bar, egg shaped, 1¼ x 5/8”
( )
1
Stir bar, egg shaped, 3/8 x ¾”
( )
1
Stirring rod, glass, 8 mm
( )
2
Stopper, solid, size 0
( )
2
Stopper, solid, size 1
( )
1
Test tube holder, wire
( )
1
Tweezers (forceps)
Beginning of Semester Check In:
Date:
Student Signature:
TA Signature:
End of Semester Check Out:
Date:______________
Student Signature:______________________
TA Signature:__________________________
3
General Information
CHEMISTRY 3702-3712; ORGANIC CHEMISTRY LABORATORY I-II
GENERAL INFORMATION
Course Objectives
This course is designed to provide instruction and experience in many of the common experimental techniques
which are used for isolation, separation, purification, identification, and synthesis of organic compounds and for
examination of their structures and chemical reactivities. Both semesters involve the integration of techniques into
experiments that are related to the lecture material.
Background
Basic information about this course, applicable to Chemistry 3712 as well as its prerequisite Chemistry 3702,
which includes topics such as grading and other course policies, required supplies, safety regulations, the laboratory
text and other study references, laboratory notebooks, and some general laboratory practices, should be reviewed
prior to the first Chemistry 3712 meeting. It is assumed that you have a sound working knowledge of all laboratory
principles and techniques which were covered in Chemistry 3702, and of the theoretical material on which they are
based. If you need to review that material, restudy the 3702 material and the references cited there.
Laboratory Text and Other Study References
The assigned laboratory textbook is Mohrig, J. R.; Hammond, C. N.; Morrill, T. C.; and Neckers, D. C.,
"Experimental Organic Chemistry", W.H. Freeman and Company, 1997, abbreviated "M,H,M & N" throughout this
manual.
Neither the Chemistry 3702/3712 manual (this book) nor the M,H,M & N laboratory text may be brought into
the laboratory except on the first day (check-in). All of the information needed to carry out an experiment
(procedure, diagrams, physical constants of compounds, etc.) should be written in your laboratory notebook before
you come to the laboratory. Xerox copies attached to notebooks are not acceptable except where the instructions
specifically allow them. See pp 7-9 on "Laboratory Notebooks" for further information.
Many experiments require reference to literature other than the M,H,M & N text for data or experimental
procedures or theoretical background on techniques. These references should be consulted before starting the
experiment, and appropriate notes from them should be included in your laboratory notebook in preparation for the
experiment. Most of these sources are on reserve in the Chemistry Library. See p 6 for a list of them and the
abbreviations which are used for them throughout this manual.
Laboratory Supplies
Each student must provide the following supplies. Bring them to the first laboratory meeting (the check-in
period).
Safety goggles (see p 4 for required specifications)
Laboratory notebook (see p 7 for specifications)
Paper towels for drying glassware, etc.
Gloves (nitrile type - available from VWR (CHEM BUILDING-basement floor) or the bookstore.
4
General Information
Grades
Grades will be determined on the following basis:
Results of experiments
Laboratory notebook
Technique and work habits
Quizzes and problem sets
30%
30%
30%
10%
The "Results" portion of the grade will be evaluated from reports, products, and spectra that are turned in. The
final Results grade will be based on the total number of points for all experiments. Since the drill is a required
portion of the laboratory experience, if a person misses drill on a regular basis (2 or more consecutive times or 3
times total) then the grades for that person will be determined by the following scale: Results 20%, Notebook 20%,
Technique and Work Habits 20%, Quizzes/problem sets/other drill materials 40%
Quizzes
Brief written quizzes will be given during some lab lecture periods. They will cover material concerning work
to be done in lab on that day and/or material related to previous laboratories and lectures. During other drill periods
spectral problems will also be given for credit.
Late Lab Books and Make-Up Labs
There will be no opportunity for make-up labs or for experimental work outside of regularly scheduled lab
periods. If through unusual circumstances you are not able to attend the lab, contact the instructor.
Late lab books will be subject to a grade penalty of 10% (one week late) or 20% (two weeks late). Lab
notebooks that are turned in more than two periods late will not be graded.
Preparation
Just some suggestions to make your time go more efficiently: Plan your work carefully before each laboratory
period. Be organized to use the time efficiently. If a mixture must reflux for 45 minutes, plan to do something else
during that time (take a mp, wash dishes, recrystallize another product, prepare materials for a later part of the
experiment, etc.). Dovetail your operations to leave as little slack time as possible. Otherwise you may not find the
periods long enough to finish all assigned work. As the year progresses you will become very proficient at working
efficiently. Note the available working time is from 1:30 to 5:30.
Housekeeping
Keep your laboratory station neat. Assemble all apparatus in a neat and orderly manner. Do not have
extraneous pieces of equipment lying about. Keep the bench top clean. Clean up spills at once. This is not only
important for the sake of appearance, it is an important part of accident prevention and it facilitates carrying out
experiments efficiently, correctly, and precisely. A sloppy bench usually indicates a sloppy experiment.
When you use materials at the balances, the side shelves, in the hood, or in the instrument rooms, always leave
those areas clean and neat. Any disorder you create or mess you make is your responsibility.
At the end of each period clean and wipe off your bench top area, be sure that all equipment you used has been
put away properly, and be sure that all of the utilities are turned off at your area. Check the sink trough to be sure it
contains no rubbish which could wash into the drain and clog it, causing a flood.
5
Safety
Safety
Chemists must sometimes work with materials or techniques which are dangerous if not used properly. A
laboratory worker must therefore be continually alert to the potential hazards associated with the substances and
procedures he or she is using. Certain safety precautions must be regularly observed to minimize the probability
and the consequences of laboratory accidents.
Every person in a laboratory must be safety conscious. In advance of every laboratory operation one must
know the potentially dangerous properties of the materials to be used and consider the kinds of accidents which
could occur. The laboratory manipulation should then be carried out in a way which will reduce the probability of
an accident as much as possible, and will prevent harm to persons if an accident even then does occur. In short, one
must always think ahead about safety. Know not only what you are doing, but what you are about to do. Be aware
of what your neighbors are doing. Be sure that your work is not endangering either yourself or others, and that the
work of your neighbors is not creating a hazard to you. If you see another student engaging in an unsafe practice,
do not hesitate to point it out. Safety is everybody's business. If hazard to life and limb is not sufficient motivation,
note that safety violations will result in a lower grade.
You must be intimately familiar with the Departmental Safety Regulations, which are given below. They must
be followed at all times. Before you start any laboratory work in this course you must pass a written test to show
that you know these regulations. A grade of 100% is required. The test will be given in the first lab period (the
check-in period) after a discussion of the safety rules.
In any circumstances where Departmental regulations and instructions in M,H,M & N or any other laboratory
text are in conflict, the Departmental rules take precedence. If the instructions in this manual seem to conflict with
the general Departmental regulations, follow the instructions in this manual; the difference has been approved, for
that specific experiment only, by the Departmental Safety Committee.
Safety goggles meeting current OSHA "Chemical Splash" standards must be worn at all times in the laboratory.
Ordinary eye glasses are not acceptable. See the Departmental Safety Regulations for further information.
Unauthorized experiments are not allowed under any circumstances.
Before coming to the first laboratory meeting (the check-in period), you should study the section on safety in
M,H,M & N pp 1-2, and 689-706. As part of the advance preparation for every experiment, potentially dangerous
properties of each compound which will be used should be noted in the laboratory notebook, together with special
safety precautions which should be observed in handling it. A list of the most common hazardous compounds is
given on the wall chart in the corridor opposite the Chemistry Library. It also lists dangerous properties of many
common substances. Additional safety information on those and other compounds may be found the books on the
special "Safety" shelves in the Chemistry Library. The "Merck Index" and the "Sigma-Aldrich Library of Chemical
Safety Data", on reserve in the Chemistry Library, are especially recommended.
6
Safety
UNIVERSITY OF ARKANSAS
DEPARTMENT OF CHEMISTRY & BIOCHEMISTRY
Laboratory Safety Regulations
Laboratory Safety Equipment
Know the location and operation of the fire extinguishers, fire alarm, safety shower,
eyewash, and fire blanket, and two exits from your laboratory. You will be asked to
show these on the safety quiz!
Personal Safety Equipment
Everyone in the laboratory must always wear safety eye goggles (NOT safety
glasses) whenever chemicals are in use. Students who do not follow this requirement
during any experiment will be told to leave the lab. Goggles must meet current
departmental chemical splash standards. Side shields, top vents, or other parts of
goggles may not be altered in any way.
Everyone in the lab must have nitrile gloves at their disposal to wear when instructed
by the Teaching Assistant (TA) or when handling chemicals whose Material Safety Data
Sheet (MSDS) indicates wearing gloves. Be aware that gloves, like clothes and shoes,
are a first line of defense and are not impervious to all chemicals.
Clothing should cover as much of the body as practical. A lab coat or apron is highly
recommended. Clothing that protects the individual’s body from the neck to mid-calf is
required. Sleeveless shirts, tank tops or other clothing that does not cover the
shoulders or abdominal area is not allowed. Shorts or short skirts are not acceptable
except under a full-length lab coat or apron.
Persons with long hair or beards should recognize that these constitute fire
hazards. Hair beyond shoulder length should be tied back.
Shoes covering the entire foot (including the heel) are required.
Laboratory Accidents - Emergency Action
If anyone is splashed with a burning solvent or corrosive chemical or has any
clothing on fire, the affected area must be doused quickly with running water. Use
laboratory water taps or the safety shower (whichever is appropriate). For corrosive
chemical spills on clothing, the contaminated clothing must be removed as quickly as
possible so water flushes the skin directly.
For chemicals in the eye, immediately help the injured person to the nearest
eyewash and copiously irrigate the eye with water for at least 15 minutes. Hold the
eye(s) open to allow water to cleanse the eye and eyelid. If the injured person is
wearing contact lenses, wash for several minutes, have the wearer remove the lens,
and continue washing.
Laboratory Accidents - Emergency Action (continued)
7
Safety
Minor cuts and thermal burns should be flushed with water.
Report any accident, injury, or chemical spill IMMEDIATELY to your Teaching
Assistant (TA) as soon as emergency action is taken.
General Rules
•
Laboratory work is restricted to established, supervised periods.
•
Only experiments authorized by the TA are permitted.
• Smoking, drinking, or eating is not permitted in the lab. Do not taste any food or
chemical that is in the laboratory.
• Hoods in the labs should never be turned off. Hoods should always be kept
clean and free from any mess (paper towels, dirty glassware, etc.) The hood sash
should be at or below the red arrow at all times especially when in use. The TA will
instruct you when certain chemicals must remain and specific chemical reactions must
be done in the hoods.
• All spills anywhere in the lab (including hoods) must be cleaned up and reported
to the TA immediately.
• Keep bench top, shelves, and floor uncluttered. Leave your work area, sink,
and reagent bench clean after each period. Pay special attention to keeping the
balance and other community areas clean.
• Syringes and needles should never be discarded in the trashcans. Dispose only
in specially marked “Sharps” containers.
• Broken glass should be placed in “Broken Glass” container not in the trashcans.
A special container is provided for broken thermometers. Broken thermometers should
not be placed in the broken glass container.
• Chemical waste should be discarded as directed by your TA. Specific waste
containers will be provided for proper disposal of all hazardous materials.
8
Cleaning and miscellaneous
Cleaning Glassware
Always clean glassware as soon as possible after use. Fresh residues, which are still wet, are much easier to
remove than residues which have had time to harden.
Always clean all dirty glassware before leaving the laboratory at the end of a period. If it is put away dirty it
will be harder to clean later. Furthermore, you will have to waste time cleaning it at the beginning of the next
period, and will get a late start on that experiment. Washing glassware at the start of a period is considered in
determining the "work habits" portion of the lab grade.
Before using glassware in an experiment be sure it is not only clean, but also that it is not wet with a solvent
which should not be part of its contents during the experiment. If you are going to use a flask for an aqueous
solution, it is all right for it to be wet with water but it should not be wet with acetone. If you will use it for a nonaqueous mixture, it must not be wet with water.
If a dirty flask contains a substantial amount of solid or tarry matter, as much of the residue as possible should
be rinsed out with water or scraped out with a spatula before any other cleaning is attempted. This will always be
easier if done promptly, before the residue has had time to solidify or adhere to the glass. Such solid or gummy
residues should be placed in the waste cans, not the sinks.
If most of the solid or tar is too intractible to be removed by rinsing or scraping, try adding either water (if the
residue is mainly inorganic) or 5-10 mL of acetone (if it is an organic tar or resin). Let this mixture stand for 5-10
minutes to loosen the residue.
After most of the bulky contents have been removed, thorough rinsing with water may remove most of the
remaining residue from a flask which initially contained an aqueous or partly aqueous mixture. If the flask
contained a largely organic mixture, rinsing with one or two small portions of acetone (5-10 mL) may help.
If the flask is not completely clean after these operations, scrub it using a test tube brush with water and a high
grade washing powder or scouring powder. Bend the brush as necessary to reach all walls of the flask. Washing
powders which contain fine abrasives to help physically loosen tarry matter are far superior to liquid dishwashing
detergents for this job; the latter are not good for much except making already clean glassware sparkle. Finally,
rinse thoroughly with water to remove all traces of soap, which would contaminate the next mixture you put into the
flask.
With really stubborn traces of organic tars which resist all of these efforts, try a brush and some of the washing
powder with a little acetone instead of water, followed by re-washing and rinsing with water.
Glassware which is clean but still wet should be drained as well as possible and then simply allowed to dry by
evaporation in your locker between periods. If an item must be dried more quickly, rinse out the water with a little
acetone, which will evaporate more rapidly; a stream of air drawn through the flask by holding its mouth to the
vacuum outlet can be used to hasten evaporation if very rapid drying is necessary. Place clean paper towels under
items which are being allowed to air-dry after being rinsed with organic solvents, because the solvent may dissolve
oils and residues from surfaces it contacts (particularly the bench top), and these substances will re-contaminate the
glassware. Do not put glassware which is wet into the kit container; acetone dissolves the foam padding.
Remember that most organic solvent vapors are heavier than air, so evaporation will be faster if flasks are turned on
their sides or securely propped upside down to let solvent vapors flow out.
The ovens in the laboratory will not dry glassware rapidly. Items must be left in them for 24 hours or more to
dry. Never put items wet with a flammable solvent into the ovens; the electric elements might ignite the vapors.
Acetone, like nearly all organic solvents, is highly flammable. Do not use it in any way which might let its
vapors be ignited by a nearby flame. Use acetone sparingly for cleaning; it is expensive. In 1998, acetone cost
about $8.80 per liter, water about $0.0025 per liter.
Additional advice on care and cleaning of glassware is provided in each experiment in M,H,M & N.
9
Waste and Miscellaneous
Waste Disposal
Wastebaskets are for all non-hazardous solid waste, including paper, but not glass.
A special plastic bucket is for sharp waste: all glass (broken or not) except thermometers.
A special bottle is for broken thermometers and other mercury waste.
Syringe needles which cannot be cleaned and re-used must checked back into the stock room for replacement.
Specially labelled waste bottles are provided for organic liquids and other materials which are not to be flushed
down the sink or put into wastebaskets for safety reasons. One bottle is for halogenated organic solvents and
another is for all non-halogenated organic solvents (except small amounts of water-soluble ethanol, acetone, and
methanol, which can go down the sink). Before disposing of any liquid except water through the sinks, check to see
if a special waste container is available for it. Special bottles will also be provided for specific hazardous solids and
solutions containing hazardous materials from certain experiments.
Sinks are only for water and small amounts of the water-miscible solvents ethanol, acetone, and methanol. If
the liquid is a solution, flush it down the sink with plenty of running water. If it has an unpleasant odor, use the sink
in the hood rather than that in the open lab.
Sink troughs are not for waste disposal of any kind.
See each experiment in M,H,M & N for additional information on waste disposal.
Miscellaneous Practices Specific to this Course
1. An initial supply of sample vials is part of your locker equipment. Each time you turn in a sample, you
should obtain a replacement vial from the TA. These replacement vials may need to be cleaned before use.
2. Pasteur pipets, although described as "disposable" by supply houses, should be cleaned and re-used for as
long as possible.
3. Community apparatus such as condenser and vacuum tubing, clamps, steam baths, heating mantles, etc., are
to be stored in the proper drawers or cabinets between periods. Under no circumstances may such items be kept in
individual student lockers.
4. Standard taper glass joints and glass stopcocks should always be lightly greased before use, to prevent them
from "freezing". See the technique section in M,H,M & N p 708 for discussion of the care and use of such ground
glass equipment. Silicone stopcock greases are not to be used for this purpose, because they are almost impossible
to remove when glassware is subsequently cleaned, and they spread a film which contaminates much of the glass
surface beyond the joint. Only hydrocarbon greases such as "Lubriseal" are acceptable in this course. Silicone
greases are rarely needed in general organic work, even at the research level.
5. Teflon stopcocks should never be greased at all. The big advantage of Teflon is that it needs no additional
lubricant. However, Teflon is very soft and easily scratched. Be careful not to let a grain of sand, alumina, or any
other hard material get into the barrel of a Teflon stopcock, because it will score a groove in the Teflon plug when
the stopcock is turned and that groove creates a leak. The other disadvantage of Teflon is its cost; a stopcock plug
alone is about $20.00 (1990 price).
6. Dilute acids, bases, and other common aqueous solutions will be available in this laboratory as stock
solutions at the following concentrations: 3 M hydrochloric acid, 3 M sulfuric acid, 3 M sodium hydroxide, 5%
sodium bicarbonate, 1 M sodium carbonate, saturated sodium chloride (brine). If an experiment calls for a different
concentration, you will need to prepare it by dilution of these solutions. For example, 1.5 M HCl can be prepared
by diluting the 3 M solution with an equal volume of water, 1 M HCl by diluting the 3 M acid with twice its volume
of water. Note that 10% HCl and 10% NaOH are nearly 3 M (really 2.9 M and 2.8 M respectively), so the stock 3
M solutions can be used directly whenever instructions call for a 10% solution of them. This small difference is
insignificant for qualitative and most synthetic work. See the Tables inside the front cover of M,H,M & N for other
% vs molarity concentration relationships.
10
Cleaning and miscellaneous
7. IR and/or NMR spectra of some compounds given as unknowns in this course are published in various
reference works which are in the Chemistry Library. Students are on their honor not to refer to these published
spectra in trying to decide the structures of their unknowns.
11
Biblliography
BIBLIOGRAPHY
In addition to the material in this manual and the M,H,M & N labotatory text, study reference material on
laboratory procedures, techniques, and theory and some experimental procedures themselves are assigned from
other laboratory manuals and textbooks of organic chemistry. These books are referred to throughout this manual
by the following short abbreviations. All except M,H,M & N and Vollhardt (the lecture course textbook) are kept
on reserve in the Chemistry Library for use of Chemistry 3702-3712 students.
Abbreviation
Full Reference
Aldrich
"Aldrich Catalog Handbook of Fine Chemicals"; various editions, Aldrich Chemical Co.,
Milwaukee, WI.
"Handbook of Chemistry and Physics", various editions, Chemical Rubber Publishing Co.,
Sandusky, OH.
"The Merck Index of Chemicals and Drugs", various editions, Merck & Co., Rahway, NJ.
B. S. Furniss et al., "Vogel's Textbook of Practical Organic Chemistry", 4th ed., Longman,
London, 1978.
K. P. C. Vollhardt and N. E. Schore, "Organic Chemistry", 3rd ed., W. H. Freeman, New York,
1998.
W. L. Meyer and N. T.Allison, "Chemistry 3702; Organic Chemistry I Manual", University of
Arkansas, Fayetteville, 2000 (relative sections will be passed out during drill).
W. L. Meyer, M. A. Sturgess, and N. T. Allison, "Guide to Instrument Operation", University
of Arkansas, Fayetteville, 2000 (relative sections will be passed out during drill).
CRC
Merck
Vogel
Vollhardt
3702
IG
12
Notebooks
LABORATORY NOTEBOOKS
Your laboratory notebook should be a complete record of all the laboratory work you do and any conclusions,
etc., which you draw from the experimental data. It should contain all of the information you need to conduct an
experiment without reference to your laboratory textbook, this manual, or other sources, and all of the information
needed to describe the way you actually carried out the experiment, observations you made, and conclusions you
drew. In essence, the notebook should be complete enough so that another student could carry out the experiment
exactly as you did, and know exactly what to expect at each point, by reference to your notebook alone. See
M,H,M & N pp 9-11 for additional advice on notebook records.
General Requirements
1. The notebook must have duplicate pages to make carbon copies.
2. Notes must be kept in ink. Erasures are not permitted. If an error is made in recording information, cross
it out in a way which leaves it readable and write the correct information beside the error.
3. Data must be recorded directly in the notebook, not on scraps of paper for later transfer to the notebook.
4. Data must be recorded as soon as it is obtained. Do not trust to memory, with the intention of adding some
information later.
5. Start each experiment on a new page. Only notes from that experiment should be kept on that page.
6. Date the notebook entry at the start of each experiment. If work on the experiment continues through more
than one period, enter the date where work starts on each new day. At the end of your writeup for each experiment,
date and sign the notebook.
7. The laboratory notebook should not contain lecture notes or other miscellaneous material. It should
contain only the records of your preparation for and conduct of the specific laboratory experiments.
Pre-Laboratory Outline
You may not bring the M,H,M & N text or this manual into the laboratory. Therefore, in preparation for an
experiment you must organize in your notebook all of the information you will need to carry out the experiment
correctly and safely, and all of the information you will need to draw conclusions and answer assigned questions.
The nature of this information will vary from experiment to experiment, but may include the following points:
1. Title of experiment. Date it is to be done.
2. Purpose of experiment. Nature of conclusions to be sought.
3. Balanced equations for all reactions which are involved.
4. Important data about starting materials to be used (molecular weights, densities, mp's or bp's, molecular
and structural formulas, hazardous properties and precautions which they require, etc.).
5. Quantities of materials to be used, in grams and moles, also in mL if liquids.
6. Expected properties of product (molecular weight, formula, mp or bp, etc.).
7. Sketch of equipment set-up, if not trivial.
8. Outline of procedure to be followed, step by step. This should be a summary in your own words, not a
verbatim copy of the laboratory text. Make it as brief as possible, as long as you can interpret it to know what to do.
Xerox copies of the lab text or this manual are not permitted.
9. Potentially hazardous points in the experiment and special safety precautions to be observed.
10. Notes on the theory of the experiment or technique which will be necessary to draw conclusions or answer
questions before you leave the lab after the experiment.
11. Answers to any assigned pre-lab questions.
13
Notebooks
Your pre-laboratory outline will be briefly checked for content and organization by the TA early in the period.
If it is particularly deficient you may be denied permission to start the experiment. The TA's acceptance of your
write-up at this point does not constitute approval of its accuracy, however. The TA will asssign the grade for
completeness and accuracy of this part of the notebook when it is turned in later for grading.
Data During Laboratory
1. Quantities of materials actually used (volumes, weights, and moles).
2. Procedure actually followed. Comment on reasons for any changes in set-up or procedures from those
which were planned.
3. Times, temperatures, etc. actually used or observed.
4. All pertinent observations (color changes, precipitation, etc.).
5. Actual yield of product (weight, moles, and percentage).
6. Actual properties of product (mp, bp, spectral properties, etc.).
7. Show all necessary calculations.
8. At the end of the experiment write out all required conclusions, draw graphs if necessary, and answer all
assigned questions.
9. Sign and date the notebook. Turn in orignals each day for grading.
10. Spectra or other assigned data should be turned in within one class period of after they are obtained.
Original copies of spectra, etc., should be turned in if you have them. You may want to make a copy to retain in
your notebook. Spectra and any other materials should be clearly labeled with your name, the experiment number,
and the compound they represent, so they can be completely identified even when they are separated from the report
form. In addition, each important peak on every GC or spectrum should be identified by indicating which
compound or part of a compound is responsible for it.
If the experiment calls for a product to be turned in, the compound should be properly bottled and neatly
labeled. The label should contain the name of the compound or its molecular structure; the experiment number;
your name; the tare, gross, and net weights of sample and bottle; and the observed mp or bp of the sample.
Examples of proper labels are posted in the laboratory.
Data must also be recorded in the notebook. You should enter in your notebook all of the important features of
this data (GC retention times, peak areas, and operating conditions; NMR chemical shifts, multiplicities, coupling
constants, peak areas, and the solvent used; important IR frequencies, intensities, and peak shapes as well as the
sampling method, KBr pellet, mull, film, etc.). See the section in this manual on "Laboratory Notebooks" (pp XX)
for additional points on keeping proper laboratory notes.
When you start each experiment check its report form to see what data will be required, so you are sure to
obtain it as you conduct the experiment.
Notebook grades will be based on the completeness and accuracy of the results entered and on the quality of the
results as evaluated from data and from the samples and spectra which are turned in (yields and purities of products,
correct identification of unknowns, quality of attached spectral data, etc.).
Products which are turned in will not be returned. Some spectra will be returned with graded reports; others
will not be returned.
Continued Experiments
Occasionally you may start a new experiment before all preceding experiments have been completed, and must
decide how much notebook space to leave for additional notes on the incomplete experiment. The answer is: leave
only as much space as remains on the last page which contains notes from that experiment. Start the new
14
Notebooks
experiment on the next available page. Continue taking notes for the old experiment on the old page as long as
space is available there. (Because you date each notebook entry it is easy to see from the dates that the last work on
p 37 was done after the first work on p 38.) If the old page fills up before the old experiment is completed, simply
continue notes from the old experiment on the next vacant page which is available; as a heading on that page put
"Experiment 6, continued from page 37", and at the bottom of the old page note "continued on page 41". This way,
each notebook page deals with only one experiment and it is easy to find and follow all of the work on a given
experiment, just as it is easy to find all of a newspaper or magazine article even when it is not all on consecutive
pages.
Instrument Work
The notebook should contain information about all work you do in the instrument rooms as well as in the
laboratory. A dated entry should be made each time you take a mp or run a GC or spectrum. Record the sample
which was used as well as the mp or other data. For IR spectra record the sampling technique (Nujol mull, KBr
pellet, liquid film, solution and solvent, etc.), for UV spectra record the solvent, sample weight, and dilutions, and
for NMR spectra record the solvent. These data must be noted both on the spectrum and in the notebook. In GC
work both the notebook and recorder trace should contain notations of the sample which was used, quantity
injected, and all instrument parameters (temperatures, flow rate, instrument and column used, recorder speed, etc.).
Each spectrum or GC trace should be marked with a code number corresponding to 1) your initials followed by
a dash (-) then 2) the instrument (GC, NMR, IR) followed by a dash (-) and then 3) the lab notebook used (I or II)
followed by a dash (-) then 4) page number in this notebook (page 13, for example) followed by another dash (-)
and a final number corresponding to the 1st, 2nd, etc. of that type of spectra taken. For instance Jane Z. Doe took
two NMR spectra and referred to them in her first (I) lab notebook on page 45. These spectra would thus be
numbered as JZD-NMR-I-45-1 and JZD-NMR-I-45-2.. The formula for the reactions and/or structure of the
compound(s) being analyzed should be clearly written on the spectrum. The spectrum number should be recorded
in the notebook so it is possible to later match the spectra to the notebook. Although you may prefer to keep the GC
traces and original spectra separate from the notebook, all important data from them should also be written in the
notebook (GC retention times and peak areas, frequencies and intensities of important IR peaks, chemical shifts and
areas and multiplicities of all NMR peaks, etc.). The interpretation of each important spectral or GC peak (the
compound or part of a compound responsible for it) should also be entered in the notebook.
Steps in the Instrument Authorization Procedure
1. You must attend a demonstration on proper use of the instrument by the 3702-3712 Assistant. A
demonstration by some other person is not acceptable. These demonstrations are scheduled during regular lab
periods and attendance is recorded by the Assistant.
2. Your first and second uses of an instrument (only the first use in the case of the mp apparatus) must be
scheduled in advance at a time that the Assistant will be present to observe your technique. This may be during a
regular lab period or at a suitable time outside of lab hours. If the Assistant approves your work, you have passed
your "driving tests" on the instrument. If he does not, further driving tests in the presence of the Assistant will be
required.
3. The use of the high field NMR spectrometer must always be carried out in the presence of an Assistant.
4. Except for use of the mp apparatus, authorizations from Chem 3702 do not carry over to Chem 3712. Chem
3712 students must re-demonstrate their ability to use the IR, NMR, and GC in the presence of the supervising 3712
Assistant before using the instruments alone for that course. It will not be necessary to re-take the written tests.
15
Schedule of Experiments
CHEMISTRY 3712; ORGANIC CHEMISTRY LABORATORY II
SCHEDULE OF EXPERIMENTAL WORK
Date
(Friday)
Drill Tentative Schedule
MMHN Experiment (macro except where
noted), these are carried out the week after
scheduled drill except for spring holidays. Lab
book due at beginning lab period of next week.
2
1/17
Introduction, E1 reaction background)
check in, safety
3
1/24
Expt 9.3 background.
Expt 9.3 (Br2 addition to C=C) (book 1)
4
1/31
Expt 9.1 background
Expt 9.1 Ionic vs free radical addition to
alkenes [GC] (book 2)
5
2/7
Finish Expt 9.1 [GC]
6
2/14
NMR/IR/MS problem solving in
groups
Expt 16.1 background
7
2/21
Expt 17.2 background
Expt 17.2 (EAS) [NMR] (book 1)
8
2/28
NMR/IR/MS problem solving in
groups
Finish Spectra, etc for Expt 16.1 and 17.2
[NMR] (book 1)
9
3/7
Expt 23 background
10
3/14
Expt 24.1 background
11
3/28
Expt 22 background
12
13
4/4
4/11
Expt 25.1 background
Expt 28 background
14
4/18
Expt 23 (Horner-Emmons-Wittig Rxn) [NMR]
(book 2)
Spring Break 3/18-3/22; For week 3/25-3/29:
Expt 24.1 (Semicarbazones, kinetic,
thermodynamic) [NMR] (book 2)
Expt 22 (Aldol Condensation) [UV-VIS] (book
1)
Expt 25.1 (Ester Synthesis) [GC] (book 1)
Expt 28 (Cyclopropanes via enolate chemistry)
[NMR] (book 2)
Tie up loose ends
Week
Expt 16.1 (Diels-Alder Rxn) [NMR] (book 1)
NMR/IR/MS problem solving in
groups
15
4/25
Student Evaluations
Clean up - checkout
16
5/2
Dead Day
An additional experiment, for extra credit, may be made available for students who finish all of the foregoing
assigned work and have additional laboratory time available.
16
Drill and Organization
LABORATORY DRILL
In order to carry out laboratory operations effectively, one must not only be familiar with the manipulations
which are involved but also understand the reasons for these manipulations, i.e. the theory upon which the
techniques are based. Therefore, in addition to laboratory work which provides instruction and experience with a
variety of important techniques, this course includes lectures and discussions dealing with the underlying theory.
Reading assignments for each topic should be studied before that drill. Drill material is designed to supplement
and clarify the material in the reading assignments, not just to repeat it, and will therefore assume that you have
some familiarity with the topic in advance. Quizzes will also be prepared on the assumption that you have studied
the reading assignments in advance. Page numbers preceded by "IG" are in the Instrument Guide.
The final laboratory examination will be given during the final examination period, at the regularly scheduled
time for this course.
SUGGESTIONS ON ORGANIZATION OF LABORATORY WORK
A chemist must learn to organize operations in the laboratory to make efficient use of the available time. Each
day's work must be planned in advance. Consider all of the experiments to be done, the approximate time each part
of an experiment will require, and the points at which each experiment can be conveniently interrupted. Then plan
how to best combine all of the work.
For example, if the work involves a recrystallization, it will first be necessary to prepare the hot saturated
solution and possibly decolorize and filter it. Then the solution will be allowed to cool to room temperature, which
will take 10-20 minutes. No harm will be done by allowing even longer for it to cool. During that time one can
profitably work on a different experiment: run a mp, take an IR spectrum, prepare a hot solution for another
recrystallization, or even wash a few dishes if there is nothing else to do. Then one can return to the first
recrystallization, chill the mixture in ice, and filter or centrifuge it. Etc. An accomplished research chemist always
has several experiments in progress simultaneously, so as to be able to take advantage of the slack periods which
occur in almost any experiment. Almost never does he or she wait to finish everything on the current experiment
before starting the next one.
It is valuable to also look ahead to the following period in planning a day's work. Time can often be saved at
the start of a period by weighing out materials at the end of the preceding lab. Especially look at the glassware that
will be needed and be sure it is clean so you needn't waste time washing and drying it at the start of the next period.
The experiments in this course are designed to develop your ability to plan laboratory work, as well as to
develop your proficiency in carrying out laboratory manipulations. They are not the kind of experiments where one
starts Experiment 1, finishes it and then starts Experiment 2, finishes it and then starts Experiment 3, etc. They are
not the kind of experiment in which each laboratory period is devoted to a specific experiment which should be
finished by the end of that period. Rather, they are experiments which will take several periods to finish, and you
will need to regularly combine work on two or more experiments in the same period in order to finish all of them,
just as the research chemist does.
After the first few weeks, all of the planning for your daily work will be left up to you, and you will need to
plan effectively if you are to finish on schedule. However, to serve as a guide while you begin to learn how to
organize such work, the following suggestions are offered regarding the first few lab periods. Please note that you
are not required to arrange your work this way; you may decide that some other plan will work better. The key
points to keep in mind are (a) your plan must allow you to meet the assigned schedule for instrument
demonstrations and driving tests (pp 16-17), and (b) your plan must allow you to complete experiments or parts of
experiments by the assigned deadlines for submitting reports (pp 13-14).
A plan which will work well for one student may be very bad for another. Scheduled times to use the
instruments differ, and a work plan which provides a convenient instrument interruption early in the period might be
incompatible with such an interruption later in the period. Thus, in this course students will not be doing exactly the
same things at the same time or in the same order, and each student will have to plan his or her own schedule rather
than relying on that of someone else.
17
Drill and Organization
Summary. You will find that laboratory periods contain plenty of time to conduct all of the assigned
experimental work if it is well organized through careful advance planning. On the other hand, without such
planning and organization you will probably feel very pressed for time. In planning a given day's schedule you will
also find it useful to look ahead at the following week's work, to see what opportunities it provides for completion
of things you don't finish as fast as you hope to and what preparations for it or short experiments from it you can
shift to the present period if extra time becomes available. Don't assume that it is better to finish a current
experiment before starting the next one; it may be more efficient in the long run to do just the reverse. As the
semester progresses, you will find that you will become very proficient at utilizing laboratory time efficiently by
working on parts of several experiments in the same period.
18
REPORTS
CHARACTERISTIC IR GROUP FREQUENCIES OF COMMON COMPOUND TYPES
Bond
Compound Type (see p 70)
Usual Range, cm-1
Intensity
and Shape*
I. 4000−2500 cm-1 Region (C−H, O−H, N−H)
−C−H
Alkane (sp3 C)
2850−2960
m−s
=C−H
Alkene or aromatic (sp2 C)
3000−3100
w−m
≡C−H
Alkyne (sp C)
ca. 3300
m
O−H
Alcohol or phenol (monomeric)**
3600−3650
m
O−H
Alcohol or phenol (H-bonded)**
3200−3600
m−s; br
O−H
Carboxylic acid
2500−3100
very br
N−H
Amine or amide (monomeric)**
3300−3500
w−m
N−H
Amine or amide (H-bonded)**
3200−3350
w−m; br
II. 2500−1900 cm-1 Region (triple bonds)
C≡C
Alkyne
2100−2260
w
C≡N
Nitrile
2200−2260
m
III. 1900−1550 cm-1 Region (double bonds)
C=O
Ketone or aldehyde
1665−1760
s
C=O
Ester
1720−1790
s
C=O
Carboxylic acid
1690−1730
s
C=O
Amide
1635−1710
s
C=O
Anhydride (2 bands)
1725−1865
s and w−m
C=O
Acid chloride
1750−1800
s
C=C
Alkene
1600−1680
w−m
C=C
Aromatic
1600, 1580,
1500, 1450
v, v,
m−s, s
* s = strong; m = medium; w = weak; v = variable intensity; br = broad. Bands are fairly sharp unless
indicated broad.
** These O−H and N−H compounds are usually H-bonded in condensed phases such as neat liquids or
solids (KBr pellets or Nujol mulls). They are usually monomeric in dilute solution in solvents which
do not H-bond, such as CCl4 or CHCl3.
This very condensed group frequency table and the corresponding chart on the next page are intended primarily
for students who are just beginning the study of organic chemistry and infrared spectroscopy. It should suffice for
all of the IR interpretations needed in Chemistry 3702. However, more detailed frequency:structure correlations can
be made, so for advanced work more extensive tables should be used. Such tables may be found in MMHN pages
593-603.
This introductory list has also been limited to only the most common organic functional groups, the structures
of which are shown on the next page. A number of additional functional groups will be encountered as your study
of organic chemistry progresses (see Vollhardt, section 2-3, for example), and most of them will also have one or
more characteristic group frequencies.
19
REPORTS
Compound Types
Unless specified otherwise, groups shown as R may be H, an alkyl group, or an aromatic ring.
R
R
C
R
C
R
C
R
C
R
H
O
R
Alkene
Alkyne
Alcohol(R = alkyl)
Aromatic Ring
Phenol(R = aromatic ring)
O
R
C
H
R
O
(Phenyl)
O
N
C
R
R
R
R
R
C
N
N
R
Carboxylic Acid
A mine
Nitrile
A mide
O
O
C
O
C
R
R
Ketone (neither R = H)
Aldehyde (one R = H)
R'
R
O
C
R
O
Ester (R' not H)
O
C
C
R
O
R
Anhydride
Cl
Acid Chloride
BASIC IR REGIONS
O
H
C
N
C
O
N
H
C
C
C
N
C
H
C
C
FIN G E R P RINT
Stretch
Phenyl
4000
2500
1900
W avenumber, cm-1
20
1500
Bend (to 1550)
C
O
O
H
C
N
N
H
C
C
C
H
700
REPORTS
SOLUBILITIES OF ORGANIC COMPOUNDS; ORGANIC ACIDS AND BASES
Solubility
The process which occurs when a compound dissolves in a solvent may be depicted in the following way, with
open circles representing solvent molecules and shaded circles representing solute molecules:
+
Solvent
Solute
Solution
A particular solute will dissolve in a given solvent if the overall free energy of the solvent and solute molecules
as they are arranged in solution is lower than the free energy they have as the pure separated solvent and solute. In
other words, one can examine this physical equilibrium just as one treates a chemical equilibrium reaction; the
equilibrium will lie to the right (the compound will dissolve) if the solution represents a more stable system than the
pure components, and it will lie to the left (the compound will not dissolve) if the solution represents a less stable
system.
The relative free energies of the two systems, separated solute and solvent on the one hand and their solution on
the other, depend in the usual way on their relative enthalpies and entropies. The solution is clearly the more
disordered system, so it is inherently favored by entropy. Thus, a given solute will dissolve in a given solvent
unless the enthalpy difference distinctly favors the separated solvent and solute over the solution.
The relative enthalpy of each species (solvent, solute, and solution) depends largely on the attractive forces
between molecular neighbors in it. If these attractions are strong, the system is quite stable and resists change, but if
they are weak the system is less stable and easier to change. From this standpoint the main difference between the
separated solvent and solute and the solution lies in the fact that in the former system the only kind of neighbor
which any molecule has is another molecule of the same kind, solvent:solvent or solute:solute, whereas in the
solution some of these next-neighbor relations have been replaced by solvent:solute contacts.
These intermolecular interactions are largely polar in origin. In a molecule with highly polar bonds some
regions are relatively electron-rich and others are relatively electron-poor. This uneven electron distribution
produces sites of partial negative charge and partial positive charge within the molecule. Although the magnitudes
of these partial charges are far less than the full unit charges of anions or cations, they are still large enough to
produce a substantial electrostatic attraction between a positive site in one molecule and a negative site in a
neighboring molecule. Thus, when all other factors are equal, intermolecular attraction will be greater between
polar molecules than between non-polar molecules, in which the only attractive forces are of the weak van der
Waals type. Forces between oppositely charged ions, with their full unit charges, will be greatest of all. Finally,
one must recognize that both molecules of the neighboring pair must be polar for a strong attraction to occur,
because it results from the interaction of a charged site in one molecule with a charged site in the other. The
attractive force between a polar molecule and a non-polar one will be little more than that between two non-polar
molecules.
With this background, let us return to our picture of the dissolution process. The main factor in determining
whether a given solute will or will not dissolve in a given solvent is how the intermolecular solvent:solute
attractions which would exist in the solution compare with the solvent:solvent and solute:solute attractions which
would be present if the compound does not dissolve. Suppose one has a very polar compound, for example an ionic
salt, and a very polar solvent such as water. Although both the solvent:solvent attractions and the solute:solute
attractions are large, solvent:solute attractions will also be large. There is no substantial loss of attractive forces
upon dissolution, so the salt is soluble in water. On the other hand suppose the same compound were treated with a
non-polar solvent like hexane. The weak solvent:solvent forces in hexane are about like the weak solvent:solute
forces which would exist if the salt dissolved, so little or nothing would be lost upon solution from the standpoint of
the solvent. But the strong solute:solute attractions in the pure salt would not be replaced by equivalent attractions
in the solution. Therefore the salt does not dissolve.
21
REPORTS
One can also consider the converse situation, a non-polar compound such as naphthalene with a polar solvent
or a non-polar solvent respectively. Strong solvent:solvent attractions in the pure polar solvent cannot be balanced
by the weak solvent:solute attractions in a solution, so the non-polar compound does not dissolve in the polar
solvent. With the non-polar solvent, however, weak solvent:solute interactions are no worse than similarly weak
solvent:solvent and solute:solute interactions, so in this case the compound does dissolve.
This is the basis for the often-heard generalization "like dissolves like". Polar compounds dissolve in polar
solvents but not in non-polar ones and vice versa. Very highly polar substances like ionic salts are soluble in very
highly polar solvents like water, but not in non-polar or slightly polar solvents like hexane, ether, or
dichloromethane. Hydrocarbons and other non-polar compounds dissolve in non-polar solvents but not in water.
It is important to emphasize that a compound dissolves not only when the intermolecular attractions in the
solution are greater than those in the separated solvent and solute, but also when these attractions are about equally
strong or weak in the two systems. In other words, for a compound to be soluble the intermolecular forces in
solution do not need to exceed those in the separated solvent and solute, they only need to approximately balance
them. As was pointed out earlier, the solution is inherently a more favorable system because it is more disordered
(favored by entropy), so, in fact, the most accurate generalization about solubility would be that the intermolecular
forces in the separated solvent and/or solute must significantly exceed those in the solution to prevent the compound
from dissolving.
The molecular structure of most organic compounds consists of a hydrocarbon framework which carries one or
more non-ionic functional groups. The hydrocarbon portion is non-polar in nature, but the functional groups
contain polar covalent bonds which confer some polar character on the molecule. Thus these compounds lie
somewhere between the two extremes of polarity represented by hydrocarbons and ionic substances. Their
solubility properties depend on the balance between polar and non-polar features in the molecule. If the functional
part is quite polar and makes up a relatively large portion of the structure, the compound may be water soluble. For
example, small molecules with only one polar functional group, like ethanol and acetic acid, dissolve in water
because even that one polar group is a large fraction of the entire molecule. In some cases much higher molecular
weight compounds may be water soluble, provided they contain a large number of polar groups so that again a large
part of the total molecule is polar in nature; sugars are good examples. But if an organic compound contains more
than about four carbon atoms, a single polar functional group is too small a portion of the molecule to make it water
soluble. Such compounds may be too polar to dissolve in completely non-polar hydrocarbon solvents, but they are
not polar enough to dissolve in water. The majority of simple organic compounds are in this category. They
dissolve best in organic solvents of moderate polarity such as ether, dichloromethane, and acetone, which are
approximately similar in polarity to the organic solutes. These same solvents, being not very polar, also dissolve
many hydrocarbons, but rarely will they dissolve highly polar compounds like ionic salts or sugars.
Acids and Bases
A Bronsted acid is a compound which can donate a proton, and a base is a compound which can accept a
proton. Thus the generalized acid:base reaction can be written as follows, where A−H represents the acid and B–
represents the base:
A-H
+
_
B
_
A
+
H-B
(1)
Whether any given acid (HA) does indeed transfer its acidic proton to a given base depends on the relative base
strengths of the original base (B–) and the conjugate base (A–) of the original acid, which is produced by the proton
transfer. The reaction proceeds if B– is a stronger base than A–, but does not proceed if A– is stronger base than B–
. In other words, an acid:base equilibrium always proceeds in the direction which produces the weaker of two
competing bases, A– and B–, and the weaker of two competing acids, AH and BH.
A variety of water-soluble inorganic bases are available, with a variety of different base strengths. We will
consider only two of them here, hydroxide ion (OH–) and bicarbonate ion (HCO3–). Hydroxide ion is the strongest
base which can be used in aqueous solution, because if any stronger base were put into water an acid:base reaction
like equation 1 would occur to convert that base to its conjugate acid and produce OH– (equation 2). Bicarbonate
ion is a substantially weaker base than hydroxide ion.
22
REPORTS
_
B
+
_
H-O H
B-H
+
OH
(2)
Certain organic functional groups contain protons which are sufficiently acidic to be abstracted by hydroxide
ion or even bicarbonate ion. In this introductory discussion we will consider only two of them, but you will learn
about others as your study of organic chemistry progresses. Those two are the carboxyl group of carboxylic acids
and the hydroxyl group of phenols, shown below with the acidic proton underlined.
O
O
R C O H
C O H
Carboxyl
Carboxylic Acid
(R = H, an alkyl group,
or an aromatic ring)
O H
Ar O H
Hydroxyl
Phenol
(Ar = an aromatic ring
but not an alkyl group)
Note especially that in this context the proton of an organic OH group is acidic if the OH is attached to the
carbon of a carbonyl group (O=C−) or the carbon of an aromatic ring (benzene, naphthalene, etc.), but not if it is
attached to an alkyl carbon in an alcohol.
Although carboxylic acids are weak acids in comparison with the common strong inorganic acids like
hydrochloric and sulfuric acid, they are substantially stronger acids than phenols. Both bicarbonate ion and
hydroxide ion are sufficiently basic to deprotonate a carboxylic acid.
O
O
R C O-H
_
+
OH
+
_
H C O3
_
R C O
O
+
H-O H
(3)
+
H2C O 3
(4)
O
R C O-H
R C O
_
The more weakly acid phenols will react with the strong base hydroxide but not the weaker base bicarbonate.
Ar-O-H
Ar-O-H
+
+
OH
_
H C O3
Ar-O
_
Ar-O
_
_
+
H-O H
(5)
+
H2C O 3
(6)
(Note: For the sake of simplicity, no cation has been shown in equations 1-6, for it is not involved in the
acid:base process. However, one must remember that a cation must always be present to balance the anionic
charges, so that in equations 3 and 4, for example, if one used sodium or potassium hydroxide or bicarbonate as the
base the organic product is the sodium or potassium salt of the carboxylic acid.)
When their acidic proton is still attached, both carboxylic acids and phenols are typical covalent organic
compounds of moderate polarity. Thus for the reasons discussed in the previous section they are typically insoluble
in water and soluble in various moderately polar organic solvents such as ether, dichloromethane, etc. (Just which
solvents dissolve a particular compound will depend on the nature of its R or Ar group.) However, in the presence
of aqueous sodium hydroxide the acid:base reactions shown in equations 3 and 5 will occur very rapidly, and the
organic acids will almost immediately be converted to their sodium salts. Those salts are ionic compounds (Na+
RCOO– or Na+ ArO–) just like sodium chloride, and have solubility properties typical of ionic substances. They
dissolve in water but not in moderately polar organic solvents. Thus, whereas a carboxylic acid or a phenol will not
dissolve in water, it will dissolve in aqueous NaOH. Non-acidic organic compounds will be just as insoluble in
aqueous NaOH as they are in water, for NaOH does not convert them to salts.
For similar reasons carboxylic acids which are water-insoluble will dissolve in aqueous sodium bicarbonate,
because it is basic enough to convert them to their salts. However, water-insoluble phenols will not dissolve in
aqueous bicarbonate as they do in aqueous hydroxide, because bicarbonate is too weak a base to deprotonate them.
Consider now what happens if a sodium hydroxide solution of a phenol or a carboxylic acid or a sodium
bicarbonate solution of a carboxylic acid (which is really an aqueous solution of the sodium salt of the acid or
phenol plus some excess hydroxide or bicarbonate) is treated with an excess of a strong aqueous inorganic acid like
23
REPORTS
HCl or H2SO4 (in which the acidic species is really hydronium ion, H3O+). Again acid:base reactions will occur,
and the acidic protons will be distributed among the various basic species so as to produce the weakest acids which
can be formed (equation 1). Hydronium ion is a much stronger acid than water, carbonic acid, a phenol, or a
carboxylic acid, so the following equilibria all lie far to the right at low pH. The carboxylic acid salt or phenol salt
which had been in solution is converted to the free covalent acid or phenol. The latter is not water-soluble, so it
precipitates.
H3 O+ +
H3 O+ +
H 3 O+ +
H3 O+ +
OH
_
HOH
+
HOH
(7)
HOH
+
H2C O 3
(8)
HOH
+
RCO OH
(9)
HOH
+
ArO H
(10)
_
H C O3
RCO O
_
ArO
_
Organic bases can be considered in an entirely analogous manner. Just as a transferable proton is the crucial
structural feature a compound needs in order to be an acid, the feature it needs to be a base is an unshared electron
pair to which a transferred proton can become bonded. If we temporarily restrict attention to aqueous systems, a
compound with such a lone pair will act as a base if it is considerably more basic than water, so that the following
equilibrium will lie far to the right.
H 3 O + + :B
H2 O
+
H-B+
(11)
The most common types of non-ionic organic compounds which fall in this category are the amines, in which
the lone pair is on a nitrogen atom which is singly bonded to three other groups made up of some combination of
hydrogens, alkyl groups, and/or one aromatic ring (but not more than one aromatic ring), e.g.:
..
R N H
..
R N R
..
R N R
..
Ar N H
..
Ar N R
..
Ar N R
H
H
R
H
H
R
A mines, basic in water (R = an alkyl group; Ar = an aromatic ring)
Note that many other compounds with a lone pair on nitrogen are less basic than water and thus will not act as
bases in aqueous systems because the equilibrium in equation 11 lies to the left rather than to the right. Amides, in
which one substituent on nitrogen is a C=O group, and nitriles, in which the nitrogen is multiply bonded to carbon,
are the most common examples of such non-basic nitrogen types.
O
..
R C N H (or R or Ar)
R C N:
H (or R or Ar)
A mide, not basic in water
Nitrile, not basic in water
Amines themselves, being typically moderately-polar organic compounds, are water-insoluble and soluble in
moderately polar organic solvents. However, upon treatment with an aqueous solution of a strong inorganic acid
they will be protonated to form a cation which is like the ammonium ion with some alkyl groups and/or an aromatic
ring in place of some of its hydrogens:
H3 O+ +
..
R N H (or R)
H2 O
H (or R or Ar)
+
H
+
R N H (or R)
(12)
H (or R or Ar)
This product is a salt of the amine, just as ammonium chloride is a salt of ammonia. Its counter-anion, not
shown in equation 12, is whatever anion accompanied hydronium ion in the aqueous acid (chloride, sulfate, etc.).
The salt is a typical water-soluble ionic substance. Thus, whereas an amine does not dissolve in water unless its R
24
REPORTS
groups are very small, it does dissolve in aqueous acid solutions of low pH. A non-basic organic compound would
not be protonated and converted to an ion under such conditions, so it would be no more soluble in aqueous acid
than it was in water alone.
Hydroxide ion is a stronger base than any of these amines or other non-ionic organic compounds.
Consequently, if an excess of aqueous sodium hydroxide is added to the solution of an amine in aqueous acid
(which is actually an aqueous solution of the substituted ammonium salt plus excess hydronium ion), the following
acid:base reactions occur with equilibria which lie far to the right The amine which is formed by reaction 14
(RNH2, etc.) is water-insoluble and precipitates.
H3 O+
_
H2 O
+ :O H
H
+
_
R N H (or R) + :O H
+
H2 O
..
R N H (or R)
(13)
+
H2 O
(14)
H (or R or Ar)
H (or R or Ar)
Hydronium ion is the strongest acid which can exist in aqueous solution, because if any stronger acid were put
into water it would react with water to form the weaker acid, hydronium ion, and its own conjugate base. Thus,
only bases considerably stronger than water can be completely converted to their salts in that solvent. However, in
the absence of water stronger acids are available, and concentrated sulfuric acid represents one such substance. It is
also a highly polar solvent, an excellent solvent for ionic substances but a very poor solvent for non-polar
compounds.
Owing to its very high acidity, concentrated sulfuric acid will protonate almost any organic compound with a
lone electron pair on oxygen or nitrogen. The protonated species, being ionic, then dissolves. Thus compounds like
aldehydes, ketones, esters, alcohols, ethers, amides, nitriles, etc., which have O or N lone pairs too weakly basic to
be protonated in aqueous acid, are protonated by concentrated sulfuric acid and therefore dissolve in it (equations
15-17 etc.).
:O :
(Ar) R C H
(Ar) R C R (Ar)
Aldehyde
Ketone
:O :
..
(Ar) R C N H (R or Ar)
:O :
..
(Ar) R C .O. R (Ar)
:O :
H (R or Ar)
A mide
Ester
..
R .O. H
..
(Ar) R .O. R (Ar)
Alcohol
Ether
R C N:
Nitrile
+
H O:
:O :
R C R
+
H 2S O 4
R C R
+
_
HS O4
(15)
+
_
HS O4
(16)
+
_
HS O4
(17)
..
R .O. H
+
H 2S O 4
H
+
R .O. H
R C
+
H 2S O 4
+
R C N H
N:
Compounds without O or N lone pairs, like hydrocarbons, have no basic site and thus are insoluble even in very
strong acids like concentrated sulfuric acid. Thus a solubility test in this reagent is one way to distinguish O- and
N-containing compounds (soluble) from hydrocarbons and halides (insoluble).
(Note: Some hydrocarbons, including most alkenes and alkynes and some highly reactive aromatics react fairly
rapidly with concentrated sulfuric acid to form soluble addition or substitution products, so they also dissolve in the
concentrated acid, albeit for different reasons than those discussed here. You will learn about those reactions as
your study of organic chemistry progresses. Such compounds will not be used as knowns or unknowns in the
Chemistry 3702 solubility experiment.)
25
REPORTS
SOLUBILITY CLASSIFICATION OF WATER INSOLUBLE COMPOUNDS
The principles of solubility, acidity, and basicity discussed on pp 76-80 lead to the following logical scheme for
testing the solubility of a water-insoluble organic compound to learn what functional groups it may contain and
what groups are not present. A compound will be found to fall into one of five solubility classes: A-1 (moderately
acidic, a carboxylic acid), A-2 (weakly acidic, a phenol), B (basic, an amine), N (neutral in water, a compound
containing N or O in a group which is not acidic or basic enough to form a salt in aqueous solution), or I (inert, a
compound containing no N or O so it cannot form a salt even with concentrated H2SO4). The scheme given here
includes only the functional groups which will be encountered in Chemistry 3702; in more advanced work you will
learn about additional functional groups which fall into some of these classes.
Compound
NaO H (aq)
Insoluble
(B or N orI)
Soluble
(A-1 or A-2)
Compound
Compound
H Cl(aq)
Soluble
(B)
NaH C O 3 (aq)
Insoluble
(N orI)
Insoluble
R N H2
(A-2)
Soluble
(A-1)
Ar-O H
O
R2N H
C
R
R3N
ArN H 2
O
ArN H R
C
ArN R 2
Ar
Compound
H 2 S O 4 (conc)
Soluble
(N)
Contains N or O, but
not a B, A-1, or A-2
functional group
OH
Insoluble
(I)
Contains no N or O
26
OH
REPORTS
QUANTITATIVE ASPECTS OF EXTRACTION; ILLUSTRATIVE EXAMPLES
Normal procedures for separating compounds by liquid-liquid extraction, as in Chemistry 3702 Experiment 5
and in isolation of the products from many synthetic reactions, use successive extractions with several small
portions of a solvent rather than a single extraction with one large portion. They also usually include a final
"backwash" of the combined organic extracts with water before the organic solution is dried and evaporated to
obtain the product. These details are important, but the reasons for them are not necessarily obvious to the
beginning student. They can only be appreciated by considering the quantitative aspects of the extraction process,
as the following examples are intended to demonstrate. Consider extractive separation of a mixture of compounds
A and B which have the following solubilities:
Compound A:
Compound B:
Solubility in Water
Solubility in Ether
SAW = 8.0 g/100 mL
SBW = 1.0 g/100 mL
SAE = 2.0 g/100 mL
SBE = 5.0 g/100 mL
1. Several extractions with small portions of a solvent are more efficient than one extraction with the
same total volume of solvent.
Single Extraction. Suppose a solution of 2.0 g of A and 2.0 g of B in 200 mL of water is extracted with 200
mL of ether. How much of each compound is in each layer?
Compound A:
Let grams of A in the ether layer = gAE
Then grams of A in the water layer = (2.0 − gAE)
Concentration = weight/volume, so:
Concentration of A in ether = CAE = gAE / 200
Concentration of A in water = CAW = (2.0 − gAE) / 200
The extraction law says CAE / CAW = SAE / SAW
Thus (gAE / 200) / [(2.0 − gAE) / 200] = (2.0 / 100) / (8.0 / 100)
Solving for gAE :
gAE
2.0 − gAE
=
=
0.40 g of A in ether
1.60 g of A in water
Compound B (same calculation):
grams of B in the ether layer = gBE
grams of B in the water layer = (2.0 − gBE)
CBE / CBW = SBE / SBW
(gBE / 200) / [(2.0 − gBE) / 200] = (5.0 / 100) / (1.0 / 100)
gBE
2.0 − gBE
=
=
1.67 g of B in ether
0.33 g of B in water
Multiple Extraction. Suppose the same mixture in 200 mL of water is extracted with two 100-mL portions of
ether. How much of each is in the water and in the combined ether extracts?
a. First Extraction. The calculation is the same as above except now CAE = gAE / 100 and CBE = gBE / 100
So [gAE / 100] / [(2.0 − gAE) / 200] = (2.0 / 100) / (8.0 / 100)
gAE
2.0 − gAE
=
=
0.22 g of A in ether
1.78 g of A in water
and [gBE / 100] / [(2.0 − gBE) / 200] = (5.0 / 100) / (1.0 / 100)
gBE
2.0 − gBE
27
=
=
1.43 g of B in ether
0.57 g of B in water
REPORTS
b. Second extraction. The calculation is the same as part "a" except now the starting water contains 1.78 g of A
and 0.57 g of B instead of 2.0 g of each. Thus gAW = (1.78 − gAE) and gBW = (0.57 − gBE).
So [gAE / 100] / [(1.78 − gAE) / 200] = (2.0 / 100) / (8.0 / 100)
gAE
1.78 − gAE
=
=
0.20 g of A in ether
1.58 g of A in water
and [gBE / 200] / [(0.57 − gBE) / 200] = (5.0 / 100) / (1.0 / 100)
gBE
0.57 − gBE
=
=
0.41 g of B in ether
0.16 g of B in water
The net result after two extractions is thus as follows:
Total A in ether
Total B in ether
Total A in water
Total B in water
=
=
=
=
0.22 g in 1st 100 mL + 0.20 g in 2nd 100 mL = 0.42 g
1.43 g in 1st 100 mL + 0.41 g in 2nd 100 mL = 1.84 g
1.58 g
0.16 g
Comparing the results of these two examples in terms of the quantities of A that can be obtained from the water
layer and B from the ether layer, one finds that two 100-mL extractions bring much more B into the ether than does
one 200-mL extraction:
After Extraction With:
Wt of A in water
Wt of B in ether
1 × 200 mL
1.60 g
1.67 g
2 × 100 mL
1.58 g
1.84 g
Comparing the two results in terms of the purity of the A left in water and the B extracted into ether:
% Purity = (wt of desired compound / wt of total sample) × 100
Purity of
A in water
B in ether
Extracted with 1 × 200 mL
[1.60 / (1.60 + 0.33)] × 100 = 80%
[1.67 / (1.67 + 0.40)] × 100 = 81%
Extracted with 2 × 100 mL
[1.58 / (1.58 + 0.16)] × 100 = 92%
[1.84 / (1.84 + 0.42)] × 100 = 81%
The amount of A is about the same from both examples, but the A from multiple extraction is much purer. The
purity of B is about the same from both examples, but the multiple extraction affords much more B. In general,
multiple extractions give either more product or purer product or both.
2. Backwashing the combined organic layers with water can improve purity of the product in the
organic layer without much loss of that product.
Suppose you backwash the above ether solution from the two 100-mL extractions with 100 mL of water and
combine that water with the original water layer. How much of each compound is in each layer and how pure is the
A in water and the B in ether?
The 200 mL of ether contains 0.42 g of A and 1.84 g of B. After backwash:
Compound A:
This leaves
and takes
(gAE / 200) / [(0.42 − gAE) / 100] = (2.0 / 100) / (8.0 / 100)
gAE = 0.12 g of A in ether
0.42 − gAE = 0.30 g of A into backwash water.
There was 1.58 g of A in the original water, so now there is 1.88 g of A in the total water.
Compound B:
This leaves
and takes
(gBE / 200) / [(1.84 − gBE) / 100] = (5.0 / 100) / (1.0 / 100)
gBE = 1.61 g of B in ether
1.84 − gBE = 0.23 g of B into backwash water.
There was 0.16 g of B in the original water, so now there is 0.39 g of B in the total water.
28
REPORTS
Purity of A in water = 1.88 / (1.88 + 0.39) × 100 = 83% pure
Purity of B in ether = 1.61 / (1.61 + 0.12) × 100 = 93% pure
Before backwash the ether contained 2.26 g of 81% pure B (1.84 g of B). After backwash it contains 1.83 g of
93% pure B (1.61 g of B). Purity is improved considerably, and only 0.23 g of B has been lost.
Note that the water-soluble compound is less pure than before. The original water contained 1.74 g of 92%
pure A (1.58 g A). The original water plus the backwash contains 2.27 g of 83% pure A (1.88 g A). From the
standpoint of purity it would have been better to not combine the backwash water with the original water.
29
REPORTS
CHARACTERISTIC PROTON CHEMICAL SHIFTS
Proton Type*
δ, ppm
Proton Type*
δ, ppm
I. sp3 Hybrid C−H
R−CHn
0.9−1.6
R2N−CHn
2.2−3.2
C=C−CHn
1.8−2.6
I−CHn
2.2−4.2
C≡C−CHn
2.0−2.7
Br−CHn
2.6−4.1
N≡C−CHn
2.0−2.7
Cl−CHn
3.0−4.0
Z−C(=O)−CHn
2.0−3.4
O−CHn
3.3−5.1
Ar−CHn
2.3−2.9
F−CHn
4.2−4.5
S−CHn
2.1−2.9
O2N−CHn
4.3−4.7
II.
sp2
Hybrid C−H
R2C=CR−H
4.6−6.3
R−C(=O)−H
9.5−10.1
CZ=C−H or
C=CZ−H
4.6−7.5
R2N−C(=O)−H or
RO−C(=O)−H
7.9-8.2
Ar−H
6.5−8.5
III. sp Hybrid C−H
C≡C−H
2.3−3.2
IV. O−H and N−H
R−OH
0.5−5.5
C(=O)−OH
9−12
Ar−OH
4−8
C(=O)−NH
7−8
Ar−NH or R−NH
1−5
* CHn indicates CH3, CH2R, or CHR2.
Substituents not shown are H or C (alkyl, aryl, C=C, or C=O).
R indicates H or alkyl.
Ar indicates aryl (phenyl or substituted phenyl).
Z indicates H, C, O, or N.
This condensed chemical shift table and the corresponding charts are designed for students who are just
beginning the study of NMR spectroscopy. They should suffice for all of the interpretations which are required in
Chemistry 3702 and most of them in Chemistry 3712. Much more extensive and detailed structure:chemical shift
correlations are available.
30
REPORTS
BASIC 1H NMR CHEMICAL SHIFTS
12
10
8
6
4
2
0
sp3 & sp C H
sp2 C H
R-C H n
C=C-C Hn
R 2 C=C R-H
CZ=C-H; C=CZ-H
C C-C Hn
N C-C H n
pi bond
effects
O=CZ-C Hn
Ar-C Hn
Ar-H
N R-C H=O
O-C H=O
C H=O
S-C Hn
CH
N R-C Hn
Br-C H n
electronegativity
effects
Cl-C Hn
O-C Hn
F-C Hn
O 2 N-C H n
C C-H
C6 H6
C H Cl3
Me2 C O T M S
D MSO
Et2 O(q)
dioxane
S OLVENTS & R EFE RE N C ES:
C H 2 Cl2
Et2 O(t)
R-O H
C(=O)O H
Ar-O H
OH
NH
C(=O)N H
12
10
Ar-N H; R-N H
8
6
δ, ppm
4
2
0
R indicates alkyl or H. Substituents not shown are H or C (alkyl, aryl, C=C, or C=O). CHn indicates CH3,
CH2R, or CHR2. Ar indicates aryl (phenyl or substituted phenyl). Z indicates H, C, O, or N.
31
REPORTS
SHOOLERY'S RULES
The chemical shift of CH2 protons in a compound XCH2Y can be approximately predicted from the following
relationship, in which the σ's are empirical values derived from examination of the spectra of many known
compounds. The same σ values can be used to predict the chemical shift of the proton in a CHXYZ unit, but the
result is much less reliable.
δ = 0.23 + σX + σY
σ
Substituent (X or Y)
σ
Substituent (X or Y)
−Cl
2.53
−CR=CR2 (R = H or alkyl)
1.32
−Br
2.33
−C6H5
1.85
−I
1.82
−C≡C−R (R = H or alkyl)
1.44
−OH
2.56
−C(=O)R (R = alkyl)
1.70
−OR (Alkyl)
2.36
−C(=O)OR (R = alkyl)
1.55
−OAr (Aryl)
3.23
−C(=O)NR2 (R = H or alkyl)
1.59
−O−C(=O)R
3.13
−C≡N
1.70
−SR
1.64
−CF3
1.14
−NR2 (R = H or alkyl)
1.57
−CH3
0.47
Examples of the Use of Shoolery's Rules
Calculated δ
Compound
Observed δ
Br−CH2−Cl
5.09
5.16
I−CH2−I
3.87
4.09
C6H5−CH2−OCH3
4.44
4.41
C6H5−CH2−CH3
2.52
2.55
C6H5−CH2−C6H5
3.91
3.92
CH2=CH−CH2−OH
3.92
3.91
CH2=CH−CH2−CH=CH2
2.87
2.91
CH3−CH2−C(=O)−CH3
2.40
2.47
(C2H5O)3CH
7.31
4.96
(CH3)2CH−I
2.99
4.24
32
REPORTS
CHARACTERISTIC CARBON-13 CHEMICAL SHIFTS
δ, ppm
Carbon Type*
I. sp3 Hybrid C
−C−C
5−55
−C−Br (excluding CH3)
25−65
−C−N
30−70
−C−Cl (excluding CH3)
40−80
−C−O
40−85
II. sp2 Hybrid C
−C=C−
105−150
Phenyl
115−150
−C=O (ketone)
190−220
−CH=O (aldehyde)
180−205
−C(=O)−OH (acid)
165−180
−C(=O)−OR (ester)
160−180
−C(=O)−N (amide)
150−180
III. sp Hybrid C
−C≡C−
65−90
−C≡N
110−125
* Substituents not shown may be H or C (alkyl, aryl, C=C, or C=O).
This very condensed chemical shift table and the corresponding chart are designed to be only a brief
introduction to 13C NMR spectroscopy. They will suffice for all of the interpretations required in Chemistry 3702
and 3712. Much more detailed structure:chemical shift correlations are available and should be used for more
advanced work. A particularly convenient advanced chart can be found in F. W. Wehrli and T. Wirthlin,
"Interpretation of Carbon-13 NMR Spectra", Heyden, London, 1976.
33
REPORTS
BASIC 13C NMR CHEMICAL SHIFTS
240
220
200
180
160
140
120
100
80
60
40
sp2 C
20
0
sp3 C
C C
C=C
Phenyl
C Br
C=O
C N
Acid
Ketone
Aldehyde
C Cl
Ester
A mide
C O
sp C
C N
S OLVE NTS, etc:
Me2 C O
240
220
200
C6D6
180
160
140
120
δ, ppm
Substituents not shown are H or C (alkyl, aryl, C=C, or C=O).
34
C C
C Cl4
C D Cl3
100
80
Me2 S O
60
40
Me2 C O
20
TMS
0
REPORTS
C-13 ADDITIVITY RULES
Approximate carbon chemical shifts in some types of compounds can be predicted to within a few ppm from
empirical additivity relationships which resemble the Shoolery Rules for 1H spectra (see p 87). One example, for
substituted benzenes, is shown below. Analogous additivity rules have also been developed for alkanes, for
alkenes, for substituted cyclohexanes, etc. For details the interested student should consult a text on 13C NMR
spectroscopy such as F. W. Wehrli and T. Wirthlin, "Interpretation of Carbon-13 NMR Spectra", Heyden, London,
1976.
The Substituted Benzene Rule
δC = 128.5 + σi + σo + σm + σp
Where:
δC = calculated chemical shift of the desired carbon, in ppm from TMS.
σi = substituent constant for the group attached to the desired carbon (the "ipso" carbon).
σo / σm / σp = substituent constants for the groups at positions ortho, meta, and para to the desired carbon.
Substituent Constants*
σi
σo
σm
σp
0
0
0
0
CH3
+9.3
+0.8
0
−2.9
C(=O)OH
+2.1
+1.5
0
+5.1
C(=O)CH3
+9.1
+0.1
0
+4.2
CH=O
+8.6
+1.3
+0.6
+5.5
CN
−15.4
+3.6
+0.6
+3.9
Cl
+6.2
+0.4
+1.3
−1.9
Br
−5.5
+3.4
+1.7
−1.6
OH
+26.9
−12.7
+1.4
−7.3
NO2
+20.0
−4.8
+0.9
+5.8
NH2
+18.0
−13.3
+0.9
−9.8
Substituent
H
* σ's for many other groups are also available.
Example
N H2
C H3
C H3
Calculated:
δC-1
Observed:
= 128.5 + σi(NH2) + σm(CH3) + σp(CH3)
= 128.5 + 18.0 + 0 − 2.9
δC-2
=
143.6 ppm
143.5 ppm
=
116.0 ppm
115.6 ppm
= 128.5 + σo(NH2) + σo(CH3) + σm(CH3)
= 128.5 − 13.3 + 0.8 + 0
35