Experiment 1:
STRUCTURE, INTERMOLECULAR
FORCES AND SOLUBILITY
OBJECTIVES


To learn how to identify which
intermolecular forces exist between
organic compounds.
To investigate the relationship
between structure, intermolecular
forces and solubility using solubility
testing.
ROLE OF INTER- AND
INTRAMOLECULAR FORCES

Physical state


Distillation


difference in solubility
Chromatography


difference in BP
Extraction


solid, liquid & gas
different IMF between analyte and stationary vs.
mobile phase
Biology


secondary structure of proteins
DNA and DNA-RNA base pairing
TYPES OF
INTERMOLECULAR FORCES

London Dispersion Forces

Dipole-Dipole Forces

Hydrogen Bonding



Acceptors
Donors
Ion-dipole Forces
LONDON DISPERSION FORCES




The London dispersion force is the weakest intermolecular
force.
It is a temporary attractive force that results when the
electrons in two neighboring atoms occupy positions that
make the atoms form temporary dipoles.
Since electrons are constantly in motion, they can be
distributed unevenly about the nucleus. This results in the
formation of a temporary dipole.
A second atom or molecule, in turn, can be distorted by the
appearance of the dipole in the first atom or molecule
(because electrons repel one another) which leads to an
electrostatic attraction between the two atoms or
molecules.
d+
d-
--------------
d+
d-
LONDON DISPERSION FORCES


Dispersion forces are present between all molecules,
whether they are polar or nonpolar.
Larger and heavier atoms and molecules exhibit stronger
dispersion forces than smaller and lighter ones.

Compounds which contain carbons and hydrogens ONLY
possess LDF ONLY.
LESS LDF
MORE LDF
DIPOLE - DIPOLE FORCES



Dipole moment (m): Electrostatic attraction between
polar molecules.
It is a measure of the unevenness of electron density
in a bond or molecule.
It depends on both electronegativity of atoms and on
molecular geometry.
d+
H
d-
Cl
m = 1.08 D
H d+
C
H
d-
d-
d+
d-
O
O
C
O
m = 2.33 D
m = 0.00 D
DIPOLE - DIPOLE FORCES


Dipole-dipole forces are present only in polar molecules.
They occur when the d+ end of one polar molecule is
attracted to the d- end of another.
HYDROGEN BONDING


Hydrogen bonds are a result of the large difference in
electronegativity between H and N, O, or F.
They occur when the H of one molecule attached to an O
or N is attracted to an O or N of a different molecule.
+
d d
O H
donor

d
O
acceptor
+
d d
N H
donor
d
O
acceptor
d d+
O H
donor
d
N
acceptor
+
d d
N H
donor
d
N
acceptor
Some compounds have a H to donate to hydrogen
bonding, while others can only accept a H from other
compounds to form hydrogen bonds.
HYDROGEN BONDING
*** Notice that compounds containing an O or N with a H
DIRECTLY bound to it are donors and acceptors!***
H-Bond donors and acceptors
R
H
water
H
alcohols
phenols
R N H
H
R N H
R
O ..
R C O
.. H
1o amines
2o amines
carboxylic
acids
O
..
R C N H
R
..
..
..
..
..
OH
..
..
..
..
O
..
amides
R
ethers
aldehydes
..
..
O
R C H
O
R C
R
ketones
O ..
R C O
.. R
esters
..
R N R
R
3o amines
R
.
.O
..
N .. +
O
..
..
R
..
O
..
..
..
H-Bond acceptors
..
..
H
..
O
..
nitro compounds
ION-DIPOLE


An ion-dipole force exists between an ion and the
partial charge on the end of a polar molecule.
They are especially important for solutions of ionic
substances in polar solvents, such as NaCl in water.
EXPERIMENTAL OUTLINE




A: Test solubility of compounds in
hexane and water.
B: Test solubility of organic liquids in
water.
C: Test solubility of alcohols in hexane
and water.
D: Test solubility of organic solids in
diethyl ether, water, acidic and basic
solutions.
Table 1.1
Organic
Liquid
hexane
Structure
Intermolecular Force(s)
(list all present)
Miscibility in
hexane
Miscibility in
water
London dispersion
M
I
toluene
diethyl
ether
ethyl
acetate
1-butanol
methanol
water
M
Tables 1.2 and 1.3
Solute
Structures
Intermolecular
Force(s)
# drops
miscible in
1 mL of water
toluene
1
ethyl acetate
2
1-butanol
4
Alcohol
Structure
Boiling
Point
(Co)
methanol
64.7
ethanol
78.5
1-propanol
97.0
1-butanol
117.7
Miscibility
in
hexane
Miscibility
in
water
Acid-Base Chemistry
O
R
O
H
O
+
acid
N
base
H O H
base
+
H O H
acid
R
O
conjugate
base
+
N H
+
conjugate
acid
H3O+
conjugate
acid
OH
conjugate
base
Table 1.4
Organic Solid
Mol. Formula
Mol. Weight
Melting point
Hazards
benzoic acid
C7H6O2
122.12 g/mol
122-123 oC
Harmful if
swallowed
Eye irritant
sodium benzoate
C7H5NaO2
144.10 g/mol
>300 oC
Avoid contact
with skin and
eyes
Solubilities
Structure
Intermolecular
Force(s)
diethyl
ether
water
10%
NaHCO3
1M
HCl
IMF FLOW CHART
Interacting molecules
or ions
NO
Are polar molecules
involved?
NO
Are ions involved?
YES
DIPOLEDIPOLE
Ex: CH3Cl
NO
LDF
ONLY
Ex: CH3CH3
HYDROGEN BOND
Acceptor
Ex: CH3OCH3
Are polar
molecules and
ions both
present?
NO
YES
YES
Are hydrogen atoms
bonded to N, O, or F
atoms?
NO
YES
YES
HYDROGEN BOND
Donor
Ex: H2O, NH3
ION-DIPOLE
Ex: NaCl in H2O
IONIC
BONDING
Ex: NaCl
SAFETY CONCERNS

All solvents used in today’s lab are
volatile. Wear safety goggles at all
times, and use fume hoods.
WASTE DISPOSAL


Pour all liquid waste from this
experiment into the container labeled
“LIQUID ORGANIC WASTE”.
Do NOT pour any waste down the
drain!
LABORATORY NOTEBOOK
(Pre-lab)

OBJECTIVE



What you will evaluate
How you will evaluate it
TABLE OF PHYSICAL DATA



(Must clearly state…)
LIQUIDS: (MW, bp, density, hazards) hexane, toluene, diethyl ether,
ethyl acetate, acetone, butanol, propanol, ethanol, methanol, and
hydrochloric acid.
SOLIDS: (MW, mp, hazards) sodium benzoate, sodium bicarbonate, and
benzoic acid.
REFERENCE TO PROCEDURE




(Single organized table, must include...)
(Must include…)
Full title
Edition
Authors
page numbers where actual procedure can be found
LABORATORY NOTEBOOK
(In-lab)
o DATA/CALCULATIONS
o
Not applicable for this experiment. All observations will be recorded
directly onto the Final Lab Report.
o EXPERIMENTAL PROCEDURE
o
o
o
In paragraph form, briefly describe the procedure that you actually
followed during the lab.
Paragraph must be written in PAST TENSE, PASSIVE VOICE.
Include any mistakes, accidents or observations if necessary.
FOR NEXT LAB…



Experiment 1 Final Lab Report due.
Experiment 2 Pre-lab Notebook entry
due.
It is *highly recommended* that you
watch the following video prior to
coming to lab.

http://www.youtube.com/watch?v=3JlIPnyrZMw