Verified Solution • 2025–26 Session moderate

QNEET-2013-Ch-1551: NEET 2013 Chemistry - Class 11 NEET-2013-Ch-1551 Solution: Homolytic fission of the following alkanes forms free radicals: …

Homolytic fission of the following alkanes forms free radicals: CH3−CH3CH_3-CH_3 CH3−CH2−CH3CH_3-CH_2-CH_3 (CH3)2CH−CH3(CH_3)_2CH-CH_3 CH3−CH2−CH(CH3)2CH_3-CH_2-CH(CH_3)_2.

Multiple Choice Options

  • A (CH3)3C˙<(CH3)2C˙−CH2CH3<CH3−C˙H−CH3<CH3−C˙H2(\text{CH}_3)_3\dot{\text{C}} < (\text{CH}_3)_2\dot{\text{C}}-\text{CH}_2\text{CH}_3 < \text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3 < \text{CH}_3-\dot{\text{C}}\text{H}_2
  • B (CH3)2C˙−CH2CH3<CH3−C˙H−CH3<CH3−C˙H2<(CH3)3C˙(\text{CH}_3)_2\dot{\text{C}}-\text{CH}_2\text{CH}_3 < \text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3 < \text{CH}_3-\dot{\text{C}}\text{H}_2 < (\text{CH}_3)_3\dot{\text{C}}
  • C CH3−C˙H2<CH3−C˙H−CH3<(CH3)2C˙−CH2CH3<(CH3)3C˙\text{CH}_3-\dot{\text{C}}\text{H}_2 < \text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3 < (\text{CH}_3)_2\dot{\text{C}}-\text{CH}_2\text{CH}_3 < (\text{CH}_3)_3\dot{\text{C}}
  • D CH3−C˙H2<CH3−C˙H−CH3<(CH3)3C˙<(CH3)2C˙−CH2CH3\text{CH}_3-\dot{\text{C}}\text{H}_2 < \text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3 < (\text{CH}_3)_3\dot{\text{C}} < (\text{CH}_3)_2\dot{\text{C}}-\text{CH}_2\text{CH}_3

Step-by-Step Verified Solution

Explanation: The stability of alkyl free radicals depends primarily on hyperconjugation (number of α\alpha-hydrogens):CH3−C˙H2\text{CH}_3-\dot{\text{C}}\text{H}_2 (1∘1^\circ radical): 33 α-H\alpha\text{-H} atomsCH3−C˙H−CH3\text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3 (2∘2^\circ radical): 66 α-H\alpha\text{-H} atoms(CH3)2C˙−CH2CH3(\text{CH}_3)_2\dot{\text{C}}-\text{CH}_2\text{CH}_3 (3∘3^\circ radical): 88 α-H\alpha\text{-H} atoms (66 from the two methyl groups and 22 from the ethyl group)(CH3)3C˙(\text{CH}_3)_3\dot{\text{C}} (3∘3^\circ radical): 99 α-H\alpha\text{-H} atomsGreater number of hyperconjugative structures leads to higher stability, giving the order:
CH3−C˙H2<CH3−C˙H−CH3<(CH3)2C˙−CH2CH3<(CH3)3C˙\text{CH}_3-\dot{\text{C}}\text{H}_2 < \text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3 < (\text{CH}_3)_2\dot{\text{C}}-\text{CH}_2\text{CH}_3 < (\text{CH}_3)_3\dot{\text{C}}

Related Learning Resources & Exam Preparation

NEET PYQ Question Bank
Browse year-wise authentic previous years' questions with solutions
Authentic CBT Mock Tests
Simulate official exam environment with live timer and percentile scoring