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 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

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.

+ - --------------- +

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 (): 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.

H Cl C O+ -

= 1.08 D = 0.00 D

O C O

= 2.33 D

- - -+ +H

H

DIPOLE - DIPOLE FORCES

Dipole-dipole forces are present only in polar molecules.

They occur when the + end of one polar molecule is attracted to the - 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.

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

O H O N H O+ +

N H N +

O H N+

donor donor donor donor acceptoracceptoracceptor acceptor

HYDROGEN BONDING

H O H R O H

water alcohols

OH....

..

......

phenols

R N

H

H R N

R

HR C

O

O H R C

O

N

R

H

.. .. ....

... . . . . . . .

1o amines 2o aminescarboxylic acids amides

H-Bond donors and acceptors

H-Bond acceptors

R C

O

O R....

. . . . R N

R

R..

R O R.... R C

O. . . .

R C

O. . . .

H RR N

O

O+ ..

..

.. -

ethers aldehydes ketones esters 3o amines nitro compounds

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

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 Structure

Intermolecular Force(s) (list all present)

Miscibility in hexane

Miscibility in water

hexaneLondon dispersion M I

toluene

diethyl ether

ethylacetate

1-butanol

methanol

waterM

Tables 1.2 and 1.3

Solute StructuresIntermolecular

Force(s)# drops

miscible in 1 mL of water

toluene 1

ethyl acetate

2

1-butanol 4

Alcohol StructureBoiling Point (Co)

Miscibility in

hexane

Miscibility in

water

methanol

64.7

ethanol 78.5

1-propanol

97.0

1-butanol

117.7

Acid-Base Chemistry

OH + H O H + H3O+

acid base conjugate base

conjugate acid

N +H O H

+ OH

base conjugate base

conjugate acid

acid

N H

O

R O

O

R

Table 1.4

Organic SolidMol. FormulaMol. Weight

Melting pointHazards

Structure

Intermolecular

Force(s)

 Solubilities

diethyl ether

water 10% NaHCO3

1M HCl

benzoic acidC7H6O2

122.12 g/mol122-123 oCHarmful if swallowedEye irritant

sodium benzoateC7H5NaO2

144.10 g/mol>300 oC

Avoid contact with skin and

eyes

IMF FLOW CHARTInteracting molecules

or ions

Are ions involved?

YESNO Are polar molecules and

ions both present?

Are polar molecules involved?

NONO

YES

Are hydrogen atoms bonded to N, O, or F atoms?LDF

ONLYEx: CH3CH3

DIPOLE-DIPOLE

Ex: CH3Cl

HYDROGEN BOND

AcceptorEx: CH3OCH3

IONIC BONDINGEx: NaCl

ION-DIPOLEEx: NaCl in H2O

NO YES

YES

HYDROGEN BONDDonor

Ex: H2O, NH3

NO YES

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 (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

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 PROCEDUREo In paragraph form, briefly describe the procedure that you actually

followed during the lab. o Paragraph must be written in PAST TENSE, PASSIVE VOICE.o 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