THERMAL ISOMERIZATION OF ISOCYANIDES . VARIATION OF MOLECULAR PARAMETERS . ETHYL ISOCYANIDE

The thermal unimolecular isomerization of ethyl isocyanide to propionitrile has been investigated as part of a continuing study of this reaction type, and the effects of the variation of molecular parameters on the fall-off behavior were determined. Fall-off has been studied at three temperatures and from the high-pressure limit down to pressures (≳ 10-3 mm) at which k/k∞ is between 10-2 and 10-3, but where the corrections to the data due to heterogeneity become excessive. The Arrhenius parameters have been measured over a wide range of pressure; the high-pressure limiting values are A∞ = 1013.8; Ea∞ = 38.24 kcal mol-1. The difference between Ea∞ for methyl and ethyl isocyanides was determined by internal comparison to be 0.1 kcal mol-1. The data have been treated on the basis of the RRKM formulation. Accuracy requirements for use of consistency tests have been examined. Anharmonicity effects are unimportant. The effects of over-all rotational degrees of freedom on the calculated fall-off behavior are delineated. Good agreement between theory and experiment for the first two members of the homologous series has been found.