Diastereogenic Reactions of Alkenes

Question 1

Alkenes allylic strain

Answer 1

have A1,2 and A1,3 strain

Question 2

predicting stereochemistry of a-stereogenic cis-alkenes

Answer 2

decide favoured conformer with smallest group eclipsing alkene, E+ approaches anti to best s-donor, has good stereoselectivity as only one conformer available to react

Question 3

predicting stereochemistry of a-stereogenic trans-alkenes

Answer 3

may be more than one conformer, E+ approaches anti to best s-donor, poor selectivity due to more than one conformer available to react

Question 4

why does E+ approach anti to best s-donor?

Answer 4

orbital overlap gives smaller HOMO-LUMO gap due to hyperconjugation which is strongest when E+ and C-s are perpendicular