Week 3

Question 1

How to make alcohols into good leaving groups

Answer 1

Multiple ways. 1. By using a strong acid which converts the OH into H2O, which then leaves (vulnerable to rearrangements)

2. By converting the OH group into a sulfonate (cannot be used to create grignards)
3. Using PBr3 or SOCl2

Question 2

Using a strong acid to convert an OH into a good leaving group

Answer 2

In secondary and tertiary alcohols, leads to an SN1 pathway, which (in the case of secondary) is very vulnerable to rearrangement (alkyl and hydride shifts) . It also does not preserve stereochemistry.

Question 3

Using sulfonates to make OH a good leaving group

Answer 3

Alcohols can be converted to sulfonates by treating them with sulfonyl chlorides. Common reagents are MsCL (mesyl chloride – OMs) and TsCL (tosyl chloride – OTs). This makes the OH group into a sulfonate, which is a good leaving group. It DOES NOT change the stereochemistry!

Question 4

Using PBr3 and SOCl2 to make OH into a good leaving group

Answer 4

Results in an alkyl halide with either chlorine or bromine. There is inversion of stereochemistry, but there is no rearrangement! The resulting alkyl halides can be used with grignard reagents.

Question 5

What does m-CPBA do?

Answer 5

Forms epoxides when added to alkenes. Maintains cis and trans relationships.