Before You Begin

Question #44438

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of 2,2-dimethylpentanedioyl dichloride with one equivalent of diethylamine ( $\ce{Et2NH}$ ) in dry ether at 298 K to form a major mono-amide product, $P$ .

The mechanism of nucleophilic acyl substitution (NAS) involves a tetrahedral intermediate. Kinetic studies on acyl chlorides reveal that steric bulk at the $\alpha$ -carbon significantly alters the reaction coordinate energy profile.

Identify the correct IUPAC name of the major product $P$ and the correct mechanistic description of the rate-determining step (RDS) for the NAS at the unhindered and hindered acyl sites, respectively.

Options

A.
$P$ is 5-(diethylamino)-2,2-dimethyl-5-oxopentanoyl chloride. The RDS for the unhindered site is the collapse of the tetrahedral intermediate, whereas for the hindered site, it is the initial nucleophilic attack.
B.
$P$ is 5-(diethylamino)-4,4-dimethyl-5-oxopentanoyl chloride. The RDS for the unhindered site is the initial nucleophilic attack, whereas for the hindered site, it is the collapse of the tetrahedral intermediate.
C.
$P$ is 5-(diethylamino)-2,2-dimethyl-5-oxopentanoyl chloride. The RDS for both the unhindered and hindered sites is the initial nucleophilic attack.
D.
$P$ is 5-(diethylamino)-4,4-dimethyl-5-oxopentanoyl chloride. The RDS for both the unhindered and hindered sites is the collapse of the tetrahedral intermediate.

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Nucleophilic Addition Sterics|Nucleophilic Acyl Substitution|Ammonolysis Complexity

Why This Question Is Tricky

Common Mistakes

The question tests the intersection of regioselectivity driven by steric hindrance and the nuanced kinetic shifts in reaction mechanisms.

Students often memorize a single RDS for all acyl chlorides.

The 'Hidden Variable' here is the steric destabilization of the transition state during the formation of the tetrahedral intermediate.

By increasing bulk (transitioning from an unhindered to a hindered $\alpha$ -carbon), the activation energy for the initial attack ( $k_1$ ) surpasses that of the intermediate's collapse ( $k_2$ ), inverting the standard kinetic profile.

Furthermore, the question traps students who fail to re-number the carbon chain according to IUPAC priority rules after the regioselective reaction, which would incorrectly lead to the 4,4-dimethyl locant.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Nucleophilic Addition Sterics
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free