Transcript Experiment 1 PowerPoint

Experiment 1:
STRUCTURE, INTERMOLECULAR FORCES,
AND SOLUBILITY
OBJECTIVES

To investigate the effect of intermolecular forces
(IMF) on the solubility of organic compounds in
water using solubility testing.

To study the polarity and solubility of various
alcohols based on carbon chain length.

To understand how acid-base chemistry can affect
the solubility of various organic solids.
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 organic solvents in water.

B: Test solubility of alcohols in hexane and
water.

C: Test solubility of organic solids in hexane,
water, aqueous acidic, and aqueous basic
solutions.
Table 1.1: Miscibility of
Organic Liquids and Water
Solvent
Identity
Solvent
Structure
IMF
(circle all that
apply)
A
methanol
LDF
HBA
D-D
HBD
B
ethyl acetate
LDF
HBA
D-D
HBD
C
dichloromethane
LDF
HBA
D-D
HBD
D
toluene
LDF
HBA
D-D
HBD
E
hexane
LDF
HBA
D-D
HBD
H2O Miscibility
(M or IM)
Organic
Layer
(Top or Bottom)
Table 1.2: Structure and Miscibility
of Alcohols in hexane and water
Alcohol
methanol
F
ethanol
G
1-propanol
H
1-butanol
I
Structure
IMF
Hexane
Boiling
(circle all Miscibility
Point (Co)
that
(M or IM)
apply)
LDF D-D
HBA HBD
LDF D-D
HBA HBD
LDF D-D
HBA HBD
LDF D-D
HBA HBD
H2O
Miscibility
(M or IM)
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 1.3: Structure and
Solubility of Organic Solids
Organic
Solid
J
K
L
benzoic
acid
sodium
benzoate
naphthalene
Structure
IMF
(circle all
that apply)
LDF
HBA
D-D
HBD
I-D
LDF
HBA
D-D
HBD
I-D
LDF
HBA
D-D
HBD
I-D
M
p-nitroaniline
LDF
HBA
D-D
HBD
I-D
hexane
Solubility
(Sol or Insol)
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.

Dichloromethane is carcinogenic in large
amounts.
WASTE DISPOSAL

Pour all liquid waste from this experiment
into the container labeled “LIQUID
ORGANIC WASTE”.

Do NOT pour any waste down the drain!