Chem 353 Midterm Review
Exam: open book open notes, it is proctored by learning suite( not recording your screen?), 13 multiple
choice question, 6 flow chart questions, 6 Ir matching, 8 Hnmr, 1 deduce the structure question
What to study: purpose of steps, hnmr, cnmr, able to name – flow chart from sydney***





Percent yield: mass of reactant (1 mol reactant/Mw g of reactant)(mw g/1 mol product) =
theoretical yield
o Actual yield/theoretical yield x100 = %yield
o Record your significant figure:
o Ex: 0.24 (1/150.22)(240.22/1 mol) =0.384, percent yeild = .14/.38 = 36.478--- 3
significant figure = 4
o Make sure you find the limiting reactant then solve for percent yeild
o DO NOT ROUND
o If there is no decimal point at the end of 1000 then the 0s aren't significant
Percent recovery: (weight of isolated product/weight of starting material) x100
o Make sure you have correct units
Safety and Msds
o If you get hurt in a lab – make sure you take care of your injuries first Before finding a TA
o Red: fire hazard, blue: heath, yellow: reactivity (explosive), white: specific hazard
Diastereoptopic hydrogens: experience different chemical environments and are usually )not
always) on the same carbon. They can produce two separate signals on hnmr. Deuterium test
produces a pair of diasteromers
o Want one of the stereocenters to change
o Do the test?
o NOT ACROSS A LINE OF SYMMETRY- need to be on the same side?
o Chair conformers, stereochemistry
o
Enantioptic hydrogens: want both stereocenters to change
o Experience the same chemical environment and therefore give the same signal on hnmr.
Deuterium test produces a pair of enantiomers
o ACROSS A LINE OF SYMETRY
o


See picture:
o A: diasteriotipic B: enantiotropic, c: enantiotropic D: diasteriotopic
Application: you reduce a ketone to an alcohol, how many unique hydrogen signals would you
expect to see on an hnmr? How many unique Carbon signals would you expect to see on a cnmr
o Look at reduction of a ketone experienet
o
o
o
For alcohol Hs:
 7 and 8 are different so is 4 and 5
Remember r and s
For alcohol Cs: 1, 2, ..3, 4, 5, 6
Steam Distillation





Works when two liquid compounds are immiscible (organic and aqueuos)
Cant separate organic compounds from each other. Any other organic compound will codistill
with the product and water
Will have extra of non limiting reactant
o If 6 C and 1 oxygen or greaterit is organic (if 5 Hs and 1 C its aqueous ) - if 5 to one it is
less
Both water and organic coumpunds codistill at the same time, decreased temp
Organic comounds can be separated from the water by performind extractions
Chromatography


Gas chromotography
o Gaseous compounds are pushed through a comlum and separaated by their different
polarities
o Column can be polar or non polar
o If the column is polar: non polar compounds will interact less with the silica gel and will
come out of the compound first (smaller retetion time)
o If the column is nonpolar: polar compounds will interact less with the silica gel and will
come out of the column first (smaller retetion time)
o Cyclo hexene alcohol will have partial negative and partial positive, will be more polar vs
cyclohexene ketone cannot hydorgen bond – less polar
 If on graph and the column is polar, the ketone will come out first then the
alcohol
Thin layer chromatography (TLC)
o Aluminum plate coated with silica gel
o Silica gel is polar
 Retains polar molecules
o


Nonpolar coumpounds woll interact less with the silica gell and move father than more
polar coumounds (larger Rf)
 Rf – 0 at where dot is, 1 at where it stops
o Increasing the polarity of the solvent will cause all coumpounds to move farther (larger
Rf)
o If they both go to one they ran the plate
 Use less polar substance
 Redo plate
 Polar solvents push things through a lot fast
o If they are both at 0, use more polar substance
Column chromatography
o Column filled with silica gel (or alumina)
o Silica gel is polar
o Order of elution depends on the polarity of the compounds
o If I want a better separation between two compounds when running a colum: use less
polar solvent
o Non polar compounds will interact less with the silica gel and move quicker through the
column than more polar column than more polar compounds
o Increasing the polarity of the eluent (solvent) will cause all compounds to move quicker
through the column
See picture: elution order fastest to slowest: B<C<D<A
o More polar things will come out slower
Extractions


Orgaic solvent added to an aquesous solution to create a bilayer and extract product out of
aquesous layer
o Always organic to aqueous is sometimes products get trapped in aqueous to pull it out
Know the density of each solvent
o Methlene chlories > water > ether (ethyl/diethyl ether)
 MC is more dense than water
 Ether and MC are both organic
o Acids and bases can be added in order to ionize certain compounds to separate them
from others in the organix phase
o Alohols mix with water because they are polar enough
Flow chart:
Flow Chart:

You are given 3 compinds In 1,3 dicholorbenze, 3,5 dimethylaniline and propanoic acid. You
need to first dissolve the mixture in methylene chloride. (solution) Once they are dissolved in
methylene chloride add 3 N naOh to form a bilayer. Isolate propanoic acid by removing and
neutralize the aqueous layer. After remoing this layer, you are left with your other two products
in the organic layer. TO recreate the bilayer add 3 HCL.(acid) remove the layer on top and
nueralize it with 3 NAOh in order to precipitate dimethylaniline (base) out of solution. Now dry
the organic phase with anhydrous sodium sulfate and evaporate the remaining organic solvent
to leave 1,3 dichlorobenzene (neutral)
o Label each as acid, nuetral or base
o Anything that ends in benze – nuetral
o Anything with N – will be base
o When see neutralize think – aqueous
o To remove bilayer add acid
o When you add a base, the acid will become chaged and the acid will float to the
aqueous layer

o
KNOW THIS
o If removing aquous layer on top – in methylene chloride, if removing aquouslayer on
bottom – ethyl
o Alchohols don’t make a bilayer
o ******where is product
Flowchart Concepts to Remmeber: picture*******




For carboxiylic Acids
o Use a base to ionize/deprotonate (naOH)
o Later use an ac
Alcholgs:
o Alcohols are nuetral
Only nietralize the aquous layer
Only use organic solvesnts that ar enot miscible with water so you can create a bilayer
Recrystalization:




You should never use ice to make your final crystal because it will have imourities
o Crystals should come out of solution slowlu in order to avoid impurities
Impurities will cause
If your cyrstals : let it sit at room temp
If your crystals: scratch the glass, add a seed crystals
Characterization


Boiking points
o What might cause a boiling point to be inaccurate – altitude (high elevation = low bp)
Melting point
o How do impurities affect the melting points? (make melting point go down)
Ir Spectroscopy










Sp3 C- h : right of 3000cm –1 ,
Sp2 (double bonds – to H): left of 3000cm
Allkene: 1600 (1650-1580)
Carbonyl (C=o) - 1700 cm
Anhydride – 1700 cm and 1800 (two carbonyl peaks)
Alchohol (O-H) – 3500 – 3200cm
o Big dip - Unsterically hindered
o Little sharp peak – sterically hindered
Alcohol (C_O-H) 10501degree, 1100 2Degree, 11503 degree
Carboxylic acid Oh – 3500-2500 funnel
Aldehyde – 2800 and 2700 – need 2 peaks – daggers – short
Ethers c-o-c : 1150-1060
o 1050
Other spectroscy:



Purpose is to find molecular weight
How to use it
o Look to the furthest right grouping of peaks
o Find the tallest peak within that group
o Find mass of the tallest peak = MW of volecule
o Look at number on x axis NOT Y
Odd molecular weigh is an indication of
HNMR:



Know general shifts of functional groups (HS
Strategy:
o Resonance: carboxylic acids and ketones nect to conjugated will electron withdraw
o Ns next to doubld bond will electron donate
o Deshielded is left
Approach:
o Right down list and write splitting
 If across double bonds – and 2 neighbors doublet of dobublet
 Aroamtic double bonds don’t count
 Expected triplet, double bond, onl two neighbors
o
o
Right down integration
 Black line that’s going across
 1cm = 1 H, 2cm = 2H
 One type of H = Icm
 2 types of H = line will go up by 2cm
Partial charge
 Based off of resonace
CNMR
Formate:
Practice – See pictures
Sydney's Review:
Acetone and isopentyl alcohol


Coating is nonpolar
Isopental comes out first – more polar

How does a really polar solvent affect the Rf?:
o Most nonpolar will be at the top (tlc plates are very polar)
o Rf = 1 when its where it stops
Why doesn’t the product reverse back to the reactant?
Why do we grow crystals slowly at room temp
What sort of solvent do we want for good recrystallization
TLC



CNMR:



Will not always have the same amount of carbons as on a cnmr
Some carbons give same signal
Benzene ring + ketone = only 5 carbon signals
Student got boilinh point of 63 but literature got boiling point of 68

Literature boiling point value will always be higher than actual becayse of altitude
Don’t worry about diastereotopic hydrogens?
If a molecule is planar – Hs are in the same chemical environment – enantiotopic
If not planar – different chemical environemtn – diastereotopic
Which layer a molecule is in:


Ethyl ether< water <methyl chloride
o Ethy ether will be on top of water
Have octanol, added ethyl ether (will be with added ethyl ether)– layer with octanol will be on
top- organic layer, bottom will be aqueous layer
o Will only move to aquous layer if has a charge on it – add base or acid
o Extract bottom layer (aqueous layer) if you want to isolate the octanol
#7 - What problem would potentially arise if octanol

Any left over starting material would also distill off
If you splash in your eye - don’t go to TA go to wash it off
#10 – isopropyl alcohol ----> missible with water
Have ketone and ruduce with nabh4 ----> goes to alcohol



How many carbon signals would you have
Going from planar to sp3 hybridized
Go from 4 to 5 – End ones that go off (isopropyl) change to diff
#12 – match the compound:




For second one – funnel would get skinner because of steric hindrance
3rd one would have fat funnel
2nd one is correct ************
Recrystallization – identify missing step





Have crude product – dissolve it in ligroin
Put into hot water bath
Ice water bath
Redissolve hot water bath
Recrystalze at room temp
14-21 NMR matching


Integration
Splitting
o Singlets and doublets
o Partial positive
o
o
o
o
o
o


THIS IS THE MOLECULE
look it up
The more partial positive the more deshieled
Taking electron density away
Nitrogen is a donating
 Going to have partial negative on other side – more shielded
Shift
Resonance, induction
Mixture separation:
IR SPECS:
See pics
On hnmr near 7.3 it’s a solvent