2,3-Dimethylbutane-2,3-diol (pinacol) is warmed with dilute H2SO4. The major product is:

JEE Advanced levelSingle correct optionDifficulty 3 of 3o4215

2,3-Dimethylbutane-2,3-diol (pinacol) is warmed with dilute $H X_{2} SO X_{4}$ . The major product is:

Protonation of one OH and loss of water gives the tertiary cation

(CH X_{3}) X_{2} C X^{+} - C (OH) (CH X_{3}) X_{2}

. A 1,2-methyl shift gives a cation stabilised by the OH oxygen,

(CH X_{3}) X_{3} C - C (CH X_{3}) = OH X^{+}

, and loss of

H X^{+}

gives pinacolone,

(CH X_{3}) X_{3} C - CO - CH X_{3}