Presented by
Leticia Bonita Prince
Newcastle University 4th Year MChem Student
Aims of Today
• Increase your understanding of intermolecular
interactions
• Increase your spatial skills and awareness
using software designed by the CCDC
What are Spatial Skills?
• The ability to mentally manipulate 2-dimensional and 3dimensional figures.
• Important in chemistry, biology, medicine, mathematics,
physics and everyday life.
Introduction
• Non-covalent interactions between functional groups in different
molecules:
• Hydrogen Bonding – The attraction between
a hydrogen on one molecule and an
electronegative element on another
• Van der Waals’– Temporary or permanent
dipole-dipole interactions
Where?
Boiling Points
• The stronger intermolecular forces, the higher
the boiling point:
HCl > HBr > HI
• Relative Boiling Points:
Relative Boiling Points:
AMIDE > CARBOXYLIC ACID > NITRILE >> ACYL CHLORIDE ~ ALDEHYDE ~ KETONE
Hydrogen Bonding
Requirements for a Hydrogen Bond:
• An H atom covalently bonded to another
electronegative atom (e.g. O, Cl, N, etc.) i.e a polar
bond where the H has a partial positive charge.
• A second electronegative atom* on a nearby which
can easily access the H atom, and thus can donate
electron density to it.
Properties
Hydrogen bond properties
Strong
Moderate
Weak
Bond Energy (kJ mol-1)
60-120
16-60
<12
Bond Length (Å) H · · · A
1.2-1.5
1.5-2.2
2.2-3.2
Bond Length (Å) D · · · A
2.2-2.5
2.5-3.2
3.2-4.0
Bond Angle (degrees)
175-180
130-180
90-150
Solubility
• Molecules that can form hydrogen bonds are generally soluble
in other molecules that can form hydrogen bonds.
Ethanol is completely miscible in water as the –OH group can be
involved in H bonding with water.
Propane is INSOLUBLE in water because it’s not polar, nor
capable of forming H bonds.
THANK YOU!
ENJOY THE REST OF YOUR
DAY!