JAMB Chemistry 2019 Objective — Question 23

Question 23 of 40 from the Joint Admissions and Matriculation Board (JAMB) Chemistry 2019 Objective paper, with the correct answer and a full explanation.

The major product of the reaction between one mole of H₃C–C≡CH and two moles of HBr is

A. CH₃CBr₂CH₃Correct
B. CH₃CH₂CHBr₂
C. CH₃CHBrCHBr
D. CH₂BrCH₂CH₂Br

Explanation

By Markovnikoff's rule, in an addition of HX to an unsymmetrical alkyne/alkene, the positive part (H) adds to the carbon with more hydrogens. Adding HBr twice to propyne: H₃C–C≡CH + HBr → H₃C–CBr=CH₂, then + HBr → H₃C–CBr₂–CH₃.

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