Experiment 1:
STRUCTURE, INTERMOLECULAR
FORCES AND SOLUBILITY
OBJECTIVES


To learn how to identify which
intermolecular forces (IMF) exist
between organic compounds.
To investigate the relationship
between structure, intermolecular
forces and solubility using solubility
testing.
ROLE OF IMF

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 IMF

London Dispersion Forces

Dipole-Dipole Forces

Hydrogen Bonding



Acceptors
Donors
Ion-dipole Forces
LONDON DISPERSION FORCES

London Dispersion Forces (LDF) = weakest intermolecular
force.

Temporary attractive force.


Electrons are in constant motion, and are at times
distributed unevenly about the nucleus. This results in the
formation of a temporary dipole.
A second atom/molecule can be distorted by the appearance
of the dipole in the first atom/molecule (electrons repel
one another). This leads to an electrostatic attraction
between the two atoms or molecules.
dd+
--------------
d+
d-
LONDON DISPERSION FORCES



Dispersion forces are present between all molecules,
whether they are polar or nonpolar.
The larger/heavier an atom is, the stronger the
dispersion forces are.
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.
Dipole moment = 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.
OVERVIEW




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
Intermolecular Force(s)
(list all present)
Structure
H
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
toluene
C
CH 3
C
C
C
H
C
C
H
Use the following abbreviations:
LDF = London Dispersion
DD = dipole-dipole
HA = Hydrogen bond acceptor
HD = Hydrogen bond donor
Miscibility in
hexane
Miscibility in
water
M
I
H
diethyl
ether
ethyl
acetate
1-butanol
H
H
H
H
H
C
C
H
H
O
H
H
C
C
H
H
H
H
C
C
H
H
H
H
H
H
C
C
C
C
H
H
H
H
O
H
O
H
C
C
H
H
*************************
Always indicate if a molecule is
a hydrogen bond DONOR, or a
hydrogen bond ACCEPTOR
ONLY! Do not just write
“hydrogen bonding” here!
*************************
OH
H
methanol
H
C
OH
H
water
M
O
H
H
Tables 1.2 and 1.3
Solute
Intermolecular
Force(s)
Structure
toluene
1
H
H
C
C
CH 3
C
C
H
# drops
miscible in
1 mL of water
C
C
H
H
ethyl acetate
H
1-butanol
Alcohol
methanol
H
H
H
C
C
H
H
H
H
H
H
C
C
C
C
H
H
H
H
O
O
H
C
C
2
H
H
4
OH
Structure
Boiling
Point
(Co)
CH3OH
64.7
CH3CH2OH
78.5
1-propanol
CH3CH2CH2OH
97.0
1-butanol
CH3CH2CH2CH2OH
117.7
ethanol
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



(Must clearly state…)
What you will evaluate
How you will evaluate it
TABLE OF PHYSICAL DATA
(Complete the following table using MSDS
sheets from a site listed on WWW Links ONLY. Wikipedia is unacceptable)
Compound
Hexane
MW (g/mol)
BP (oC)
Toluene
X
Diethyl ether
X
Ethyl acetate
X
Acetone
X
1-Butanol
X
1-Propanol
X
Ethanol
X
Methanol
X
Hydrochloric acid

MP (oC)
X
d (g/mL)
X
Sodium benzoate
X
X
Benzoic acid
X
X
Sodium bicarbonate
X
X
REFERENCE TO PROCEDURE


HAZARDS
(Must include…)
Full title including edition and 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.