overall outline of the reaction:

benzaldehyde => benzoin => 1,2-diphenyl-1,2-ethanediol => 1,2-diphenyl-1,2-ethanediol + 2,2-dimethoxypropane => 2,2-dimethyl-4,5-diphenyl-[1,3]dioxolane.

1) Use the H NMR spectrum of the purified cyclic acetal to identify the major diastereomer From borohydride reduction. There are no minor diastereomers. Draw its structure including stereochemistry. Determine the ratio between major:minor.

2) Explain the stereoselectivity from the crude H NMR of the cyclic acetal.