Q.Assertion: Hydrolysis of (–)-2-bromooctane proceeds with inversion of configuration.
Reason: This reaction proceeds through the formation of a carbocation.

The key idea is that SN2 reactions proceed with inversion of configuration, while SN1 reactions proceed via a carbocation intermediate (leading to racemisation).

Reasoning:

1. (–)-2-Bromooctane is a secondary alkyl halide. In a hydrolysis reaction (with a weak nucleophile like water under neutral/basic conditions), it typically follows an SN2 mechanism because the carbon skeleton is sterically unhindered. …

1. Identify the substrate and the reaction type.

   (–)-2-Bromooctane is a secondary alkyl halide. Secondary halides can react by either SN1 or SN2, depending on conditions. Here, the reaction is hydrolysis (with water as the nucleophile). Water is a weak nucleophile, but in a polar protic solvent (typical for hydrolysis), the SN1 pathway is possible. However, the key clue is the inversion of configuration mentioned in the assertion.

2. What does inversion of configuration tell us?

   Inversion is the hallmark of an SN2 mechanism. In SN2, the nucleophile attacks from the back side, directly displacing the leaving group. This flips the stereochemistry at the carbon centre — like an umbrella turning inside out. If the starting material is (–)-2-bromooctane (a single enantiomer), the product will be the opposite enantiomer, i.e., (+)-2-octanol.

3. Why can’t the reason (carbocation formation) explain inversion?

   A carbocation intermediate is planar (sp² hybridised). Attack by water on a planar carbocation can occur from either face, giving a racemic mixture — not inversion. So if the reaction truly went via a carbocation (SN1), you would lose optical activity, not get clean inversion. The reason given is therefore inconsistent with the observed result.

4. Is SN2 plausible for a secondary halide with water?

   Water is a comparatively weak nucleophile, and SN2 is usually favoured by strong nucleophiles, but experimental evidence for this specific reaction shows that hydrolysis of optically active 2-bromooctane gives an inverted product with high optical purity. This confirms an SN2 mechanism, not SN1, for this substrate under these conditions. …

Method: Stereochemical Analysis of SN1 vs SN2 Reactions

Concept

The stereochemical outcome of a nucleophilic substitution reaction depends on the mechanism — whether it proceeds via an SN1 (carbocation intermediate) or SN2 (concerted backside attack) pathway.

Steps

1. Identify the substrate

   (–)-2-bromooctane is a secondary alkyl halide. Secondary substrates can react via either SN1 or SN2, depending on conditions.

2. Analyze the assertion

   Assertion: Hydrolysis of (–)-2-bromooctane proceeds with inversion of configuration.

   • Inversion is the hallmark of an SN2 mechanism (backside attack).
   • So the assertion implies an SN2 pathway.

3. Analyze the reason

   Reason: This reaction proceeds through the formation of a carbocation.

   • Carbocation formation is characteristic of SN1 (or E1) reactions, which lead to racemization (loss of optical activity), not inversion.

4. Check consistency …

Common Mistakes & How to Avoid Them

Mistake 1: Assuming hydrolysis of a secondary halide is automatically SN1

The error: Students see "secondary alkyl halide" + "hydrolysis" and assume SN1/racemisation by default.

Why it's wrong:

Hydrolysis of (–)-2-bromooctane is actually the textbook example of an SN2 reaction — this exact experiment (an optically active secondary halide reacting with hydroxide, monitored by the change in optical rotation) is the classical Hughes-Ingold demonstration that SN2 proceeds via a single concerted backside attack, inverting configuration. If it went through a carbocation (SN1), the product would be racemic — but that is NOT what's observed here.

How to avoid:

• Don't default to "secondary = SN1." Secondary substrates can go either way depending on conditions — and this specific, famous experiment is the SN2 case.
• Remember: SN2 = inversion; SN1 = racemisation. The assertion states inversion is observed, which is the SN2 signature.

Mistake 2: Confusing "inversion" with "racemisation"

The error: Students treat "inversion" and "racemisation" as interchangeable.

Why it's wrong:

• Inversion means the product has the opposite absolute configuration (a single, stereochemically pure outcome).
• Racemisation means a 50:50 mixture of both enantiomers — net optical activity becomes zero.

How to avoid:

• Draw the mechanism:
  • SN2: backside attack → one product, inverted.
  • SN1: planar carbocation → attack from top or bottom → both enantiomers formed (racemic).
• Since the assertion specifically says "inversion" (not "loss of optical activity"), that points to SN2, not SN1.

Mistake 3: Assuming any mention of "hydrolysis" implies a carbocation

The error: Students think "hydrolysis" automatically means SN1/carbocation formation.

Why it's wrong:

Hydrolysis of secondary alkyl halides can proceed via SN2 (concerted, no carbocation) when the assertion/observed outcome is inversion, as here. The Reason's claim that a carbocation forms is what makes it the FALSE part of this question — the observed inversion is direct evidence AGAINST a carbocation intermediate.

How to avoid:

• Let the observed stereochemical OUTCOME tell you the mechanism, not the word "hydrolysis" alone: inversion → SN2 (no carbocation); racemisation → SN1 (carbocation).
• For this question: the assertion says inversion, so the reason (carbocation) must be false.

Mistake 4: Misreading the Assertion-Reason pair

The error: Students pick (iv) — assuming the assertion is false and the reason is true — by defaulting to "secondary = SN1 = carbocation."

Why it's wrong: …