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EEJ MAIN Chemistry QUESTION #7130
Question 1
Consider the compound 4-methylpent-1-ene ($CH_{3}-CH(CH_{3})-CH_{2}-CH=CH_{2}$). Which hydrogen atom is most easily replaced during a photochemical bromination reaction?
  • $\alpha$-hydrogen
  • $\gamma$-hydrogen✔️
  • $\delta$-hydrogen
  • $\beta$-hydrogen
Correct Answer Explanation
In free radical bromination, the stability of the radical intermediate determines the ease of replacement. The hydrogen on the third carbon (the allylic position relative to the double bond) forms a resonance-stabilized allylic radical. Additionally, if the position is tertiary, it is even more stable. In 4-methylpent-1-ene, the $\gamma$ position (relative to the substituent or chain end depending on numbering context in the paper) refers to the tertiary/allylic site which is most reactive.