91Ó°ÊÓ

Alkenes add with halogen acids (HI, HCl, HCl). The H⁺ ion adds to the carbon where steric crowding is less, and the chloride ion adds to the crowded carbon by forming a stable carbocation.

The hydroboration reaction occurs between an alkene and an alkyne and gives a less substituted alcohol.

a. The sulfuric acid first protonates the alkene to form a carbocation intermediate that gives a substituted alcohol product. The hydroxide ion attacks from above and below the plane

Stereoisomers obtained from a

b. The halogen acid HI first protonates the alkene to form a carbocation intermediate that gives a substituted alkyl iodide product. The iodide attacks from below the plane and above the plane.

Stereoisomers obtained from b

c. Chlorination enables anti-addition on the double bond. Therefore, enantiomers are formed as shown:

Stereoisomers obtained from c

d. Hydroboration enables syn addition on the double bond. Therefore, the stereochemistry of H and OH is the same as shown

Stereoisomers obtained from d

e. Chlorination enables anti-addition on the double bond. Therefore, enantiomers are formed as shown:

Stereoisomers obtained from e

f. Sulfuric acid first protonates the alkene to form a carbocation intermediate that gives a substituted alcohol product. The hydroxide ion attacks from above and below the plane.

Stereoisomers obtained from f