Advices For Studying Organic Chemistry

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Tertiary > Secondary >Primary >Methyl

C C

C

C

C C

H

C

C C

H

H

H C

H

H

1) The order of stability of alkyl radicals is the same as for carbocations.

i) Although alkyl radicals are uncharged, the carbon that bears the odd electrons

is electron deficient.

ii) Electron-releasing alkyl groups attached to this carbon provide a stabilizing

effect, and more alkyl groups that are attached to this carbon, the more stable

the radical is.

10.3 THE REACTIONS OF ALKANES WITH HALOGENS

1. Methane, ethane, and other alkanes react with fluorine, chlorine, and bromine.
   
   
   1. Alkanes do not react appreciably with iodine.
   
   
   2. With methane the reaction produces a mixture of halomethanes and a HX.
   
   
   
   

HC

H

H

HHC

X

X

X

X

X

X

X 2 X X

H

HC HCXXC X

H

H

+ heator + +++ H

(The sum of the number of moles of each halogenated methane

produced equals the number of moles of methane that reacted.)

light

MethaneHalogen Halo-

methane

Dihalo-

methane

Trihalo-

methane

Tetrahalo-

methane

Hydrogen

halide

2. Halogentaiton of an alkane is a substitution reaction.

R–H + X 2 R–X + H–X

10.3A MULTIPLE SUBSTITUTION REACTIONS VERSUS SELECTIVITY

1. Multiple substitutions almost always occur in the halogenation of alkanes.