Photolysis of Methyl Iodide in Matrices of Organic Compounds at 20° and 77°K. Reactions of Hot Methyl Radicals

Abstract

Methyl iodide‐hydrocarbon and methyl iodide‐alcohol matrices have been photolyzed with 2537‐Å radiation both at 20° and 77°K. The probability of abstraction of an H atom by the hot CH₃ radical formed upon photodissociation of CH₃I is at least a factor of 10 larger in the solid phase than in the gas phase. However, the relative probabilities of abstracting an H atom from various organic compounds are about the same in both phases. Also, hot CH₃ radicals are more reactive than CD₃ radicals in both phases. Photolysis of CH₃I or CD₃I in the presence of (a) equimolar mixtures of perprotonated and perdeuterated hydrocarbons and (b) partially deuterium labeled hydrocarbons shows that the hot methyl radical abstracts an H atom or D atom with equal probability. The hot methyl radical does, however, exhibit a certain selectivity in the site of reaction. For instance, a secondary H atom is abstracted more readily than a primary H atom. This nonstatistical behavior is, however, less important in the solid phase than in the gas phase. When the matrix consists of an unsaturated hydrocarbon, the hot methyl radical can add to the double bond as well as abstract a H atom. It is shown that a hot methyl radical adds to ethylene to form a ${\mathrm{n‐C}}_3{H}_7$ radical which subsequently reacts with the I atom with which it is in juxtaposition. At 20°K about one‐fourth of the hot methyl radicals add to C₂H₄.