Solved: CHEMISTRY Question for NEET

NEET CHEMISTRYMedium

Consider the following reaction. The structure of the major reaction intermediate formed in the above reaction is-

Option 1: Primary radical

Option 2: H3C−CH(D)−Ċ(CH3)−CH3

Option 3: Secondary radical

Option 4: Secondary radical

Reaction Context: The question refers to a reaction involving the formation of a free radical intermediate, typical of free radical halogenation of alkanes (e.g., bromination) .
Stability of Free Radicals: The stability of alkyl free radicals follows the order: Tertiary ( $3^\circ$ ) > Secondary ( $2^\circ$ ) > Primary ( $1^\circ$ ). This stability order is due to the hyperconjugation effect and the inductive effect of the alkyl groups attached to the carbon bearing the unpaired electron .
Selectivity: In free radical substitution reactions (especially bromination), the major product is derived from the most stable intermediate.
Analysis of Options:

The reactant appears to be an isomer of a deuterated alkane, likely 2-methyl-3-deuterobutane ( $H_3C-CH(D)-CH(CH_3)_2$ ).
Option 2 represents a tertiary ( $3^\circ$ ) free radical ( $H_3C-CH(D)-\dot{C}(CH_3)-CH_3$ ), formed by the abstraction of the hydrogen atom from the tertiary carbon.
Other options represent primary or secondary radicals, which are energetically less stable.

Conclusion: Since the tertiary radical is the most stable, it will be the major reaction intermediate, leading to the major product.

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