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Question: 9. $\xrightarrow[\Delta]{K_2Cr_2O_7} (P)$; Product $(P)$ is:...

→ΔK2Cr2O7(P)\xrightarrow[\Delta]{K_2Cr_2O_7} (P); Product (P)(P) is:

A

Cyclopentene

B

Cyclopentanone

C

2-oxocyclopentane-1-carboxylic acid

D

Cyclopentane-1-carboxylic acid

Answer

2-oxocyclopentane-1-carboxylic acid

Explanation

Solution

The given reaction involves the oxidation of 2-hydroxycyclopentane-1-carboxylic acid with potassium dichromate (K2Cr2O7\text{K}_2\text{Cr}_2\text{O}_7) and heat (Δ\Delta).

  1. Identify the functional groups in the reactant:
    The reactant is a cyclic compound containing two functional groups:

    • A secondary alcohol (-OH group attached to a carbon that is bonded to two other carbons).
    • A carboxylic acid (-COOH group).

  2. Understand the role of the reagent (K2Cr2O7/Δ\text{K}_2\text{Cr}_2\text{O}_7/\Delta):
    Potassium dichromate in acidic medium (implied, as it's a common strong oxidizing agent) is a powerful oxidizing agent.

    • It oxidizes primary alcohols to carboxylic acids.
    • It oxidizes secondary alcohols to ketones.
    • It generally does not oxidize tertiary alcohols.
    • Carboxylic acids are already in a high oxidation state and are resistant to further oxidation under these conditions.

  3. Predict the transformation of each functional group:

    • The secondary alcohol group (-CH(OH)-) will be oxidized to a ketone group (-C(=O)-).
    • The carboxylic acid group (-COOH) will remain unchanged.

  4. Draw the structure of the product (P):
    Starting with 2-hydroxycyclopentane-1-carboxylic acid:

          OH
      |
      CH
     /  \
    CH2--CH -- COOH
    |     |
    CH2--CH2

Upon oxidation, the -CH(OH)- group becomes -C(=O)-:

```
      O
      ||
      C
     /  \
    CH2--CH -- COOH
    |     |
    CH2--CH2
```

This product is 2-oxocyclopentane-1-carboxylic acid (or cyclopentanone-2-carboxylic acid).

  1. Compare with the given options:
    • (a) Cyclopentene: This is an alkene, formed by dehydration, not oxidation.
    • (b) Cyclopentanone: This is a ketone, but the carboxylic acid group is missing.
    • (c) 2-oxocyclopentane-1-carboxylic acid: This structure matches our predicted product, where the secondary alcohol is oxidized to a ketone and the carboxylic acid group remains intact.
    • (d) Cyclopentane-1-carboxylic acid: This compound lacks the oxygen at the 2-position, indicating reduction or removal of the alcohol, not oxidation.

Therefore, product (P) is 2-oxocyclopentane-1-carboxylic acid, which corresponds to option (c).