Question

1.) What is the order of reactivity of the following reagents under S_N1 conditions? Under S_N2 conditions? Draw the structures of each using the bond line method and explain your answers.

1-methyl-1-bromocyclohexane, 1-bromopropane, 2-bromohexane

2.) What is the order of reactivity of the following reagents under S_N1 conditions? Under S_N2 conditions? Explain your answers.

CH₃CH=CHBr, CH₃CH=CHCH₂Br, CH₃CH₂CH₂Br

3.) We did not use crotyl chloride in this experiment. However, based on your knowledge of S_N1 and S_N2 predict the behavior of crotyl chloride with both sets of reagents.

4.) With the addition of NaI in acetone to the various alkyl halides, how would the results have been affected if water had been present in the test tube during the reaction?

Answer 1

The question concerns about the effect of steric hindrance on the nucleophilic substitution reactions. The explanation is as follows:

Solid We are given following reagents for conside DV (a) I-methyl-I brome cyclohexane (6) I- bromo (C) 2- bromolecane é e, By als I T CH, CH2-CH, Br CH-CH-CHECHE-CHE Now, let us discuss each one by one- Bt Cuz La for snt reaction, the reactant should be 3 alkyl I halide and for SN2 reaction, I alkyl halide is s preferred. 0 TO Here, on removal of leaving group er eg Br, the intermediate is a gol carbocation. I If we somehow consider it to be loccur with son 2 mechanism; there will be a lot of steric hinder ance for nucleophile such that :) CH3 1 I No scope for SN? mechanism due to hinderen

Therefore, to avoid steric hinderance; substitution only occur via Snt mechanism we (6) CH3-CH-Br . It is a 1 alkyl halide and is now steric hinderance there Tale allacks before the deaving group leaves. sance, if nucleophe- However, SNE is also less steric hinderance possible but due to SN2 is preferred. 40) CH3-CH-CH2-CH2-CH-CH3 - It is a 2° alkyl halide and snt as well as SN? both are possible ; but due to long carbon chain on another side; S Nt és Umore pref- Lerred to avoid henderance. Thus, for SN I reaction the order becomes i ca) > C) >66) SNI SN? reaction the order becomes (6) > C > @ SNE