Experiment 1:
STRUCTURE, INTERMOLECULAR
FORCES AND SOLUBILITY
ROLE OF INTER- AND
INTRAMOLECULAR FORCES

physical state; solid, liquid & gas


solid vs. liquid: (fat vs. oil)
liquid vs. gas: (C2H6O isomers: dimethyl ether vs. ethanol)

distillation; difference in BP (oC)

extraction; difference in solubility and
partition coefficient.


Chromatography: different IMF between
analyte and stationary vs. mobile phase


Oil and vinegar dressing
GC of alkanes, TLC, HPLC of analgesics
Biology


secondary structure of proteins: H-bonding between amino
acids
DNA and DNA-RNA base pairing: H-bonding between base
pairs
INTERMOLECULAR FORCES

London Dispersion Forces: weak attractive
forces caused by instantaneous dipoles in
molecules.

Dipole-Dipole Forces: Electrostatic
attraction between polar molecules.

Ion-Dipole Forces: Electrostatic attraction
between an ion and a polar solvent.

Hydrogen Bonding: (2-3 kcals/mole)
Electrostatic attraction between the very
electropositive H of -O-H and -N-H
bonds with the negative end of other
dipoles, especially with oxygen and nitrogen
atoms.
DIPOLE - DIPOLE FORCES:



Dipole moment m: Electrostatic attraction
between polar molecules.
measure of the unevenness of electron
density in a bond or molecule.
depends on both electronegativity of atoms
and on molecular geometry.
+
H
-
Cl
m = 1.08 D
H +
C
H
-
-
+
-
O
O
C
O
m = 2.33 D
m = 0.00 D
HYDROGEN BONDING
+
 
O H
donor
+
 
N H

O

O
donor
acceptor
donor
acceptor
 +
O H
+
 
N H

N
acceptor
donor

N
acceptor
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
GOALS OF LAB



Introduction to drawing structures.
Introduction to inter- and intra-molecular
forces between organic molecules.
Through solubility testing, discover
relationship between structure,
intermolecular forces and solubility.
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 of Common
Organic Solvents
Solvent
MF
MW
o
Bp ( C)
Density (g/mL)
Hazards*
Hexane
CH3(CH2)4CH3
C6H14
86.17
68.7
0.659
Flammable
Toxic
Toluene
C6H5CH3
C7H8
92.13
110.6
0.867
Flammable
Toxic
Diethyl ether
CH3CH2OCH2CH3
C4H10O
74.12
34.6
0.713
Flammable
Toxic
Dichloromethane
CH2Cl2
CH2Cl2
84.94
39.8
1.326
Ethyl Acetate
CH3CO2CH2CH3
C4H8O2
88.10
77.1
0.901
Toxic, Irritant
Cancer
suspect
Flammable
Irritant
Acetone
CH3COCH3
C3H6O
58.08
56.3
0.790
Flammable
Irritant
1-Butanol
CH3CH2CH2CH2OH
C4H10O
74.12
117.7
0.810
Flammable
Irritant
1-Propanol
CH3CH2CH2OH
C3H8O
60.09
97.0
0.804
Flammable
Irritant
Ethanol
CH3CH2OH
C2H6O
46.07
78.5
0.789
Flammable
Irritant
Methanol
CH3OH
CH4O
32.04
64.7
0.791
Flammable
Toxic
Water
HOH
H2O
18.02
100.0
0.998
SAFETY CONCERNS

All solvents used in today’s lab are
volatile. Wear safety goggles at all
times, and use fume hoods.
WASTE DISPOSAL
All waste from this experiment goes
into the bottle marked:
“Solubility Waste (IMF)”.
