Fluorination, Chlorination and Bromination of Methane.
Transition State Structures for H-Abstraction.The transitions state structures for the H-abstraction from methane by fluorine, chlorine and bromine have been determined with quantum-mechanical methods and the structures can be viewed with CHIME.
Transition States For Hydrogen Abstraction
fluorine radical abstracts from methane
chlorine radical abstracts from methane
bromine radical abstracts from methane
F
Cl
Br
C-H in TS
1.153
1.438
1.600
C-H in CH
41.085
1.085
1.085
delta(C-H)
0.068
0.353
0.515
H-X in TS
1.350
1.431
1.527
H-X in HX
0.934
1.280
1.436
delta(H-X)
0.416
0.151
0.091
<(H'-C-H') in TS
112.1
116.4
117.6
delta(<(H'-C-H'))
2.6
6.9
8.1
<(H-C-H') in TS
106.7
101.2
99.2
delta(<(H-C-H'))
-2.8
-8.3
-10.3
The later the transition state, the more radical character there is in the hydrocarbon fragment. The more radical character, the more differentiation is possible between primary, secondary and tertiary carbons.
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