The reaction of butylamine, CH3(CH2)3 NH2, with 1-bromobutane in 60 % aqueous ethanol follows th

step 1 Okay, let's start with option A. For both the reaction provided in the question follow SN2 mecha

The reaction of butylamine, CH3(CH2)3 NH2, with...

The reaction of butylamine, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{NH}_{2},$ with 1-bromobutane in $60 \%$ aqueous ethanol follows the rate law rate $=k$ [butylamine][1-bromobutane] The product of the reaction is $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}_{2}^{+}$ $\mathrm{Br}^{-}$. The following very similar reaction, however, has a first-order rate law: <smiles>C=CCNCCCC</smiles> Give a mechanism for each reaction that is consistent with its rate law and with the other facts about nucleophilic substitution reactions. Use the curved-arrow notation.

The reaction of butylamine, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{NH}_{2},$ with 1-bromobutane in $60 \%$ aqueous ethanol follows the rate law
rate $=k$ [butylamine][1-bromobutane]
The product of the reaction is $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}_{2}^{+}$
$\mathrm{Br}^{-}$. The following very similar reaction, however, has a first-order rate law:
<smiles>C=CCNCCCC</smiles>
Give a mechanism for each reaction that is consistent with its rate law and with the other facts about nucleophilic substitution reactions. Use the curved-arrow notation.

Key Concepts

SN2 Mechanism

This is a bimolecular nucleophilic substitution reaction in which the nucleophile attacks the substrate from the back side as the leaving group is simultaneously expelled in a single, concerted step. In such reactions, the rate depends on both the nucleophile and the substrate concentrations, as indicated by a second-order rate law. The reaction features a single transition state without any intermediates and is highly sensitive to steric hindrance at the electrophilic center.

SN1 Mechanism

This mechanism proceeds in two distinct steps; first, the leaving group departs to form a carbocation intermediate, and then the nucleophile rapidly attacks the positively charged intermediate. The rate-determining step involves only the substrate, leading to a first-order rate law. The stability of the resulting carbocation is a key factor influencing the feasibility of the SN1 pathway.

Kinetics and Rate Laws

The observed rate law helps distinguish between SN2 and SN1 mechanisms. A second-order rate law, where the rate depends on both the nucleophile and substrate concentrations, is indicative of a bimolecular concerted mechanism (SN2). Conversely, a first-order rate law, dependent only on the substrate concentration, suggests that the slow, rate-determining step involves only the substrate (SN1).

Carbocation Stabilization

In SN1 reactions, the formation of a carbocation intermediate is crucial, and the stability of this intermediate determines the reaction pathway. Structural features such as resonance stabilization, hyperconjugation, or the presence of electron-donating groups can stabilize the positive charge, making the SN1 mechanism more favorable even in cases where a similar reaction might otherwise proceed via an SN2 pathway.

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