Advices For Studying Organic Chemistry

ii) Allylic halides and benzylic halides: A primary allylic or benzylic carbocation

is approximately as stable as a secondary alkyl carbocation (2° allylic or

benzylic carbocation is about as stable as a 3° alkyl carbocation).

iii) The stability of allylic and benzylic carbocations: delocalization.

H 2 CCHCH 2 +

Allyl carbocation

H

C C C H

H

H H

H

C C C H

H

H H

++

C C C

C ++C

C

CH 2 +

Benzyl

carbocation

C+ C C C

+

+

+

+

+

H H H H H H H H

H

H

H

H

Table 10B Relative rates of reaction of some alkyl tosylates with ethanol at 25 °C

Alkyl tosylate^ Product^ Relative rate

CH 3 CH 2 OTos CH 3 CH 2 OCH 2 CH 3 1

(CH 3 ) 2 CHOTos (CH 3 ) 2 CHOCH 2 CH 3 3

H 2 C=CHCH 2 OTos H 2 C=CHCH 2 OCH 2 CH 3 35

C 6 H 5 CH 2 OTos C 6 H 5 CH 2 OCH 2 CH 3 400

(C 6 H 5 ) 2 CHOTos (C 6 H 5 ) 2 CHOCH 2 CH 3 105

(C 6 H 5 ) 3 COTos (C 6 H 5 ) 3 COCH 2 CH 3 1010