Transcript Diapositive 1 - Jagiellonian University

Solubility,
Polarity
and
Interactions
London force
Solubility
The maximum amount of a solute that dissolves in a given solvent
Depends on the interactions between the solute and solvent
General rule: like dissolves like
A solute is better dissolved in a solvent if it can establish
positive interactions with this solvent
Factors affecting solubility:
Temperature, pressure, polarity
London force
Non polar
molecule
δ-
δ-
δ+
δ+
δ+
δ-
Random electron
motion results in a
temporary dipole
(instantaneous dipole)
Two temporary dipoles
interact
δ+ and δ- ends are
attracted to each other
Relatively weak interaction
Hydrocarbon chains attract each
other mainly by London interactions
Dipole-dipole interaction
When electrons that make up a bond are not
equally shared because of a difference in
electronegativity, a permanent dipole exists in
the molecule
δ+
δ-
δ-
δ+
δ+
δ-
Permanent dipoles
attract each other
Relatively strong interaction
Dipoles interact in a head-to-tail manner
between the polar centres
Electrostatic interaction
+
-
A molecule possessing a
positive charge is attracted to a
molecule possessing a
negative charge
Strong interaction
π-π interaction
Molecule possessing
π electrons
(Aromatic, doublebonds…)
Two molecules
possessing π electrons
interact by sharing these
electrons
Relatively weak interaction
Hydrogen bonding
H
H
Molecule possessing
H linked to a highly
electronegative atom
(O, N, S)
H
The electronegative atom
possesses non-binding
electrons that can be shared
with H of another molecule
Strong interaction
Hydrogen bonding
Each water molecule can bind four other
water molecules.
This fact constitutes the very special
properties of water
and makes it an excellent solvent for polar
substances
Responsible for certain characteristics of water such as:
Surface tension
Viscosity
Cohesiveness
Vapor pressure
Solubilising properties of water
The solubilising properties of water resides
in its ability to interact with dipoles and to
form hydrogen bonds with acidic-proton-containing molecules
Hydrophobic interaction
Oil droplets dispersed in water will join to form larger and
larger droplets, which eventually form two continuous phases over time
Water « pushes away » the molecules it cannot interact with
Hydrophobic interaction
Hydrophobic surfaces in water are surrounded by a shell of highly
ordered water
The system strives to minimize the total area of such shells in order to
gain in entropy and forces hydrophobic substances to merge
Solubilising properties of water
Polarity of Analytes
Salts
Alcohols
Acids
Ethers
Ketones
Halogenated
Aromatic
Hydrocarbons
Aliphatic
Hydrocarbons
Fluorinated
Hydrocarbons
Polarity of Solvents
Water
Alcohols
Acetonitrile
THF
Hydrocarbons
Polarity of Solids
Silica gel
Polar-bonded silica
Short-chain
bonded silica
C18-bonded
silica