The Kinetics of Coordinate Bond Formation. II

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Abstract
The technique of temperature pattern determination, shown previously to be suitable for the measurement of fast gaseous reactions, has been extended to reactions of boron trifluoride with ammonia, dimethylamine, n‐butylamine, t‐butylamine, and pyridine. The bimolecular rate constants of the first two of these show pressure dependence; those of the other three, within experimental error, do not. A comparison with the previously obtained results on methylamine and trimethylamine demonstrates that the lifetime of the ``hot'' quasi‐molecules formed by the addition of boron trifluoride and an amine increases regularly with the number of vibrational degrees of freedom of the quasi molecule. The rates of addition are all substantially smaller than the rate of recombination of methyl radicals. They increase by about a factor of thirty from that of ammonia to those of heavier amines, being then about 1/30 of the collisional frequency. This finding is not consistent with the supposition that steric requirements alone limit the rates of addition and the existence of a small activation energy is clearly suggested, although it could not be observed experimentally. To explain the present results, the activation energy must decrease from ammonia to heavier amines. Such a decrease is found to be consistent with the presently accepted views on the electronic structure of the boron‐nitrogen bond.

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