ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The endoergic substitution reactions Br+R–Cl→Cl+R–Br (R=o-, m-, and p-CH3C6H4, C6H5, C6F5; ΔH°(approximately-equal-to)15 kcal/mol) have been studied using the crossed molecular beams method in the collision energy (Ec ) range 20–35 kcal/mol. The CH3C6H4Br and C6F5Br products were found to be mostly forward scattered with respect to the incident Br beam indicating that the lifetimes of the Br–R–Cl collision complexes are short compared to their rotational periods. The product translational energy distributions and excitation functions for these reactions are well reproduced by statistical calculations that assume that only a few vibrational modes in the collision complexes participate in intramolecular energy redistribution prior to Cl elimination. Ring substituents are found to affect both the extent of energy redistribution in the complexes and the probability of Br addition. For example, no substitution product was observed with m-CH3C6H4Cl or C6H5Cl. The relative magnitudes of the cross sections are explained in terms of possible features of the potential energy surfaces along their reaction coordinates.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.455439
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