Reaction of atomic hydrogen with CH3Br

Callear, A. B.; Smith, Geoffrey Benedict

doi:10.1016/0009-2614(85)80562-5

Cited by 4 publications

(1 citation statement)

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“…A chemical observation is of interest. In the reactions of H atoms with R−X where X is I or Br the only products observed are R • + HX, and all of these reactions have positive activation energies. − , The transition states for these reactions are thus normal, direct metatheses …”

Section: Metatheses Of R• With Hx and X2mentioning

confidence: 99%

Existence of Negative Activation Energies in Simple Bimolecular Metathesis Reactions and Some Observations on Too-Fast Reactions

Benson

Dobis

1998

J. Phys. Chem. A

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A large number of reactions of the type R• + HX and R• + X2 have been reported as having negative activation energies (X = I, Br, Cl). These reactions have none of the behavior of reactions that are expected to have negative activation energies. It is shown that they must be simple metathesis reactions having a single transition state, (R·H·Ẋ)⧧ or (R·X·Ẋ)⧧. It is concluded that the negative activation energies must be artifacts of the experimental techniques employed. Some of what appear to be simple metathesis reactions but which proceed via atom + radical recombination have had rate constants reported, close to the collision limit. When examined from a collisional point of view, it is shown that they require collision diameters from 8 to 25 Å, far in excess of any known long-range interaction at these distances between neutral species. Again, artifacts of the experimental methods may be responsible.

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