Pathways for nucleophilic substitution
The fact that there are multiple nucleophilic substitution pathways is signalled by the observation that the rate of reaction depends on
The two main mechanisms for substitution at saturated carbon are referred to as SN2 and SN1.
SN1
(Substitution, Nucleophilic, 1 means unimolecular)
The rate law for unimolecular reactions shows that their rate depends on the concentration of one species (in this case the substrate). This implies that the nucleophile is not involved in the rate-determining step.
the nature of the halide (primary, secondary, tertiary)
the reaction conditions (solvent and temperature)
the reaction conditions (solvent and temperature)
The two main mechanisms for substitution at saturated carbon are referred to as SN2 and SN1.
SN2
(Substitution, Nucleophilic, 2 means bimolecular)
The rate law for bimolecular reactions shows that their rate depends on the concentration of both the nucleophile and the substrate. This implies that both the nucleophile and the substrate are involved in the rate-determining step of the mechanism.
CH3CH2Br + –OH
CH3CH2OH + Br–
rate = k[CH3CH2Br][–OH]
(Substitution, Nucleophilic, 2 means bimolecular)
The rate law for bimolecular reactions shows that their rate depends on the concentration of both the nucleophile and the substrate. This implies that both the nucleophile and the substrate are involved in the rate-determining step of the mechanism.
CH3CH2Br + –OH
CH3CH2OH + Br–rate = k[CH3CH2Br][–OH]
SN1
(Substitution, Nucleophilic, 1 means unimolecular)
The rate law for unimolecular reactions shows that their rate depends on the concentration of one species (in this case the substrate). This implies that the nucleophile is not involved in the rate-determining step.
(CH3)3CBr + –OH (CH3)3COH + Br–
rate = k[(CH3)3CBr]
(CH3)3COH + Br–rate = k[(CH3)3CBr]