Advices For Studying Organic Chemistry

CH 3 CH CH 2

X

HBr

slow

CH 3 CH 2 CH 2

1 o

+ Br− CH 3 CH 2 CH 2 Br

1-Bromopropane

(little formed)

CH 3 CHCH 3 Br

+ − CH^3 CHCH^3

2 o

Br

Step 1 Step 2

2-Bromopropane

(main product)

2) The more stable 2° carbocation is formed preferentially in the first step ⇒ the

3. T because it is formed faster.

chief product is 2-bromopropane.

he more stable carbocation predominates

Figure 8.2 Free-energy diagrams for the addition of HBr to propene. ∆G‡(2°) is
less than ∆G‡(1°).

1) The transition state resembles the more stable 2° carbocation ⇒ the reaction

leading to the 2° carbocation (and ultimately to 2-bromopropane) has the lower

free energy of activation.