Advices For Studying Organic Chemistry

(R)-(–)-2-butanol and (S)-(+)-2-butanol are produced in equal amounts,

as a racemate.

4. Addition of HBr to 1-butene:

CH 3 CH 2 +

*

CH 3 CH 2 CHCH 2

BrH

HBr

1-Butene (±)-2-Bromobutane
(chiral) (achiral)

CH 3 CH 2

CC

H H

H

H Br

CH 3 CH 2

H

CH 3

Br

CH 3 CH 2

Br

CH 3

H

H 3 CH 2 C CH

3

H (S)-2-Bromobutane

Top

Bottom

+ (50%)

(50%)

(R)-2-Bromobutane

1-butene Carbocation

intermediate

(achiral) Br

−

Br −

Figure 5. Stereochemistry of the addition of HBr to 1-butene: the intermediate
achiral carbocation is attacked equally well from both top and bottom, leading to a
racemic product mixture.

HCH 3 CH

CH 3

H 3 CH 2 CCH 2 CHCH 3

Br

+ HBr

**

(R)-4-Methyl-1-hexene 2-Bromo-4-methylhexane

*