© 1998-9 Rainer Glaser. All rights reserved.
The University of Missouri at Columbia
Chemistry 412 - Computational Organic Chemistry - FS99

Online Exercise
on Hammond Postulate


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.

 

F

Cl

Br

C-H in TS

1.153

1.438

1.600

C-H in CH4

1.085

1.085

1.085

H-X in TS

1.350

1.431

1.527

H-X in HX

0.934

1.280

1.436

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.

Transition States For Hydrogen Abstraction
fluorine radical abstracts from methane
chlorine radical abstracts from methane
bromine radical abstracts from methane

All transition state structures were optimized at the correlated level UMP2(full)/6-31G* and vibrational analysis were carried out analytically for the stationary structures.