SN2
1. Occurs most readily on methyl and 1o alkyl halides, however can occur on 2o halides.
2. Works best in polar aprotic solvents.
3. Good nucleophiles work best.
4. Follows second order kinetics, i.e. Rate = k [Base][Substrate]
5. Definite geometric arrangement: gives inversion of configuration

SN1
1. Occurs under Solvolysis Conditions (see below)
2. Occurs with 2o and 3o alkyl halides never with 1o substrates.
3. Follows 1st order kinetics i.e. Rate = k [RX]

E2 Reactions:
1. Occur with 1o, 2o or 3o alkyl halides.
2. Needs a strong (hindered) base. For example Na Ethoxide or Na t-butoxide normally in protic solvents (EtOH).
3. Follows second order kinetics, i.e. Rate = k [Base][Substrate]
4. More stable alkene formed in greater preference.
5. Definite geometric requirement: antiperiplanar geometry required.

E1 Reactions:
1. Occur under Solvolysis Conditions
2. Occurs with 2o and 3o alkyl halides never with 1o substrates.
3. Follows 1st order kinetics i.e. Rate = k [RX]
4. More stable alkene formed in greater preference.
5. No geometric requirement.

Solvolysis Conditions: conditions under which spontaneous disassociation of leaving group occurs (normally this means polar protic solvent and heat)