1. STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY
Experiment 1:
STRUCTURE, INTERMOLECULAR FORCES AND SOLUBILITY

2. 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.

3. ROLE OF INTER- AND INTRAMOLECULAR FORCES
Physical state
solid, liquid & gas
Distillation
difference in BP
Extraction
difference in solubility
Chromatography
different IMF between analyte and stationary vs. mobile phase
Biology
secondary structure of proteins
DNA and DNA-RNA base pairing

4. TYPES OF INTERMOLECULAR FORCES
London Dispersion Forces
Dipole-Dipole Forces
Hydrogen Bonding
Acceptors
Donors
Ion-dipole Forces

5. 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 +

6. 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

7. 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.

8. 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.

9. 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.
Some compounds have a H to donate to hydrogen bonding, while others can only accept a H from other compounds to form hydrogen bonds.

10. HYDROGEN BONDING
*** Notice that compounds containing an O or N with a H DIRECTLY bound to it are donors and acceptors!***

11. 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.

12. 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.

13. Intermolecular Force(s)
Table 1.1
Organic Liquid
Structure
Intermolecular Force(s)
(list all present)
Miscibility in hexane
Miscibility in water
hexane
London dispersion M I
toluene
diethyl ether
ethyl
acetate
1-butanol
methanol
water

14. Intermolecular Force(s)
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)
Miscibility in
hexane
water
methanol
64.7
ethanol
78.5
1-propanol
97.0
1-butanol
117.7

15. Acid-Base Chemistry

16. Avoid contact with skin and eyes
Table 1.4
Organic Solid
Mol. Formula
Mol. Weight
Melting point
Hazards
Structure
Intermolecular
Force(s)
Solubilities
diethyl ether
water
10%
NaHCO3 1M
HCl
benzoic acid
C7H6O2
g/mol oC
Harmful if swallowed
Eye irritant
sodium benzoate
C7H5NaO2
g/mol
>300 oC
Avoid contact with skin and eyes

17. Are polar molecules involved? molecules and ions both present?
IMF FLOW CHART
Interacting molecules
or ions NO NO
YES NO
Are polar molecules involved?
Are ions involved?
Are polar
molecules and ions both present?
YES
DIPOLE-DIPOLE
Ex: CH3Cl
YES NO
YES
Are hydrogen atoms bonded to N, O, or F atoms?
IONIC BONDING
Ex: NaCl
LDF
ONLY
Ex: CH3CH3
ION-DIPOLE
Ex: NaCl in H2O NO
YES
HYDROGEN BOND
Acceptor
Ex: CH3OCH3
HYDROGEN BOND
Donor
Ex: H2O, NH3

18. SAFETY CONCERNS
All solvents used in today’s lab are volatile. Wear safety goggles at all times, and use fume hoods.

19. WASTE DISPOSAL
Pour all liquid waste from this experiment into the container labeled “LIQUID ORGANIC WASTE”.
Do NOT pour any waste down the drain!

20. LABORATORY NOTEBOOK (Pre-lab)
OBJECTIVE (Must clearly state…)
What you will evaluate
How you will evaluate it
TABLE OF PHYSICAL DATA (Single organized table, must include...)
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 (Must include…)
Full title
Edition
Authors
page numbers where actual procedure can be found

21. LABORATORY NOTEBOOK (In-lab)
DATA/CALCULATIONS
Not applicable for this experiment. All observations will be recorded directly onto the Final Lab Report.
EXPERIMENTAL PROCEDURE
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.

22. 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.