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1.Given the substrate,Select the choice for the most likely substitution mechani

ID: 503559 • Letter: 1

Question

1.Given the substrate,Select the choice for the most likely substitution mechanism and the reason for that mechanism.

2.Select the dominant mechanistic pathway when 2-bromobutane is treated with sodium amide (NaNH2) in DMSO

(pKa of NH3 ~ 36)

Options:

E1

E2    

SN1

SN2

Given the substrate, Select the choice for the most likely substitution mechanism and the reason for that mechanism. A) 3-chloro-3-methyloctane S_N1 since this mechanism is governed by sterics S_N1 since this mechanism is governed by electronics S_N2 since this mechanism is governed by sterics S_N2 since this mechanism is governed by electronics B) 1-chloro-5-methyloctane S_N1 since this mechanism is governed by sterics S_N1 since this mechanism is governed by electronics S_N2 since this mechanism is governed by sterics S_N2 since this mechanism is governed by electronics Select the dominant mechanistic pathway when 2-bromobutane is treated with sodium amide (NaNH_2) in DMSO

Explanation / Answer

A) 3-Chloro-3-methyloctane is a tertairy alkyl halide . It can form more stable tertiary carbocation , stabilised by inductive effect(elelcotronic effect)

thus the right optionis

SN1 as it is govenrned by electronics.

B) the alkyl halide is a primary alkyl halide which can not form stable carbocation(no electronic effect). But the nucelophile can apprach from back side (SN2) due to less steric effect (two small H atoms)

Thus the right choice is

SN2 as it is governed by steric s.

2) 2-bromobutane is a secondary alkyl halide which can undergo SN1/E1 or SN2/E2 depending upon the solvent and the nucleophile used.

here the nucleophile is strong NH2- which is also a strong base, thus E2 is more favored than SN2

The solvent is polar aprotic solvent which favors SN2/E2 mechanism.

Overall the dominant mechanism is E2 elimination.

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