Chem 261

Difference between a sigma (σ) bond and a pi (π) bond

Sigma (σ) bond: End-to-end orbital overlap
Pi (π) bond: Sideways orbital overlap

Main types of intermolecular forces

• London Dispersion

• Dipole-dipole

• Hydrogen bonding

• Ion-dipole forces

What does a broad IR peak around 3200-3600 cm^-1 indicate?

O-H stretch (commonly found in alcohols)

Constitutional isomers vs Conformers

Constitutional isomers: Different atom connectivity

Constitutional isomers: Differ by rotation around single bonds

What makes carbon a stereogenic centre?

A carbon bonded to four different groups.

S_N1 vs S_N2

S_N1:

• Unimolecular (substrate only)

• Carbocation stability

• Weak (neutral)

• Polar protic (eg. water, alcohols)

• Retention and inversion

S_N2:

• Bimolecular (substrate and nucleophile)

• Steric hinderance

• Strong (negative)

• Polar aprotic (eg. DMSO, acetone)

• Inversion only

Markovnikov's Rule

In typical HX addition, H adds to the alkene carbon with more H atoms.

S_N1 vs S_N2 in stereochemistry

S_N1: Racemization

S_N2: Inversion of configuration

Enantiomers vs Diastereomers

Enantiomers: Non-superimposable mirror images
Diastereomers: Not mirror images