The diol shown is treated with dilute acid. Water is lost from the carbon that gives the diphenyl-stabilised cation. Use the convention that hydride migrates in preference to methyl. Which structure is the major product?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: A

The diol is 1,1-diphenylpropane-1,2-diol. The cation forms at the diphenyl carbon, and the neighbouring carbinol carbon bears H and

CH X_{3}

; by the stated convention hydride migrates, so that carbon becomes the carbonyl of a methyl ketone. The product is 1,1-diphenylpropan-2-one. Methyl migration would give an aldehyde, and the phenyl-shift ketone needs the less stable secondary cation.

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The diol shown is treated with dilute acid. Water is lost from the carbon that gives the diphenyl-stabilised cation. Use the convention that hydride migrates in preference to methyl. Which structure is the major product?

Answer: A

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