A compound that undergoes substitution by S N 1 mechanism at the fastest rate is to be determined. Concept introduction: For S N 1 reactions, the rate determining step is the formation of the intermediate carbocation. The order of stability of carbocations is: primary < secondary < tertiary More stable carbocations are formed faster than less stable carbocations. Thus, tertiary alkyl halides react fastest while primary alkyl halides react slowest for S N 1 reactions

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Chapter 6, Problem 41DSP

Interpretation Introduction

Interpretation:

A compound that undergoes substitution by SN1 mechanism at the fastest rate is to be determined.

Concept introduction:

For SN1 reactions, the rate determining step is the formation of the intermediate carbocation.

The order of stability of carbocations is: primary < secondary < tertiary

More stable carbocations are formed faster than less stable carbocations. Thus, tertiary alkyl halides react fastest while primary alkyl halides react slowest for SN1 reactions

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Alkyl halides undergo nucleophilic substitution and elimination reactions. When the kinetics of the reaction are measured, if the rate of the reaction is found to be dependent only upon the concentration of the alkyl halide the reaction is first order. The substitution reaction is thus termed SN1, and the elimination reaction is termed E1. These reactions are unimolecular and occur in two steps. The first step is rate-limiting and involves the loss of the leaving group to form a carbocation. In the second, fast, step the nucleophile adds to the carbocation in the SN1 reaction or elimination occurs to give an alkene in the E1 reaction. Because the carbocation is planar, the nucleophile can add to either face and therefore racemization is usually observed although solvent effects can influence this somewhat. E1 elimination follows Zaitsev’s rule and typically yields the most substituted alkene as the major product. Conditions which favor the SN1/E1 pathway include the use of a weak…

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