Question

The following factors must be taken into consideration when proposing a mechanism for a nucleophilic substitution reaction. Select all that apply.

		nucleophilic
		the overall thermodynamics of the reaction
		basicity
		the solvent
		the structure of the substrate

Answer 1

1. I think first option is Nucleophile, so I will take it as it is.

SN2 reactions are usually faster when a strong nucleophile is used. Nucleophile concentration have no effect on the rate of SN1 reactions.

2. High temperature increase the rates of all types of reaction by increasing energy factor and collision factor.

3. Basicity – Leaving groups are less basic. More the basicity of leaving group, difficult for it to leave.

Nucleophilicity decreases as the Bronsted basicity increases.

4. Solvent - Polar protic solvents give faster SN1 reactions; polar aprotic solvents such as DMSO give faster SN2 reactions.

5. Structure of the substrate –

SN1 reactions are fastest with tertiary substrates due to more stability of carbocation. (FASt-3®>2®>1®>CH3-Slow).

SN2 reactions are fastest with CH3 due to less steric effect )(Fast - CH3<1<2<3- slow)

Vinylic and aromatic substrates are unreactive in both cases.