Advices For Studying Organic Chemistry

H 3 CC

CH 3

CH 2

H

H CH 3 CCH 3 H

CH 3

+

tert-Butyl radical (a 3o radical)

∆H° = + 381 kJ mol–1

CH 3 CCH 2

CH 3

H

Isobutyl radical (a 1o radical)

H 3 CC + H

CH 3

CH 2

H

H

∆H° = + 410 kJ mol–1

1 o radical

2 o radical

PE PE

15 kJ mol−^1

CH 3 CH 2 CH 2

3 o radical

∆Ho = +381 kJ mol−^1

∆Ho = +410 kJ mol−^1

CH 3 CHCH 3

CH 3 CCH 3

CH 3 CHCH 2

29 kJ mol−^1

1 o radical

CH 3

CH 3

CH 3

CH 3 CH 2 CH 2 + H

CH 3 CHCH 3 + H

+ H

∆Ho = +410 kJ mol−^1

∆Ho = +395 kJ mol−^1

+ H

Figure 10.1 (a) Comparison of the potential energies of the propyl radical (+H•)
and the isopropyl radical (+H•) relative to propane. The isopropyl
radical –– a 2° radical –– is more stable than the 1° radical by 15 kJ
mole–1. (b) Comparison of the potential energies of the tert-butyl
radical (+H•) and the isobutyl radical (+H•) relative to isobutane. The
3° radical is more stable than the 1° radical by 29 kJ mole–1.

4. The relative stabilities of alkyl radicals: