The Mercury Sensitized Photolysis of Tetramethylsilane in the Temperature Range 650 K – 800 K. The Heat of Formation of 2‐Methyl‐2‐Silapropene

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Abstract
(CH3)3SiCH2 radicals, formed in the primary process (1) magnified image decompose according to (4) magnified image in the temperature range 650 K ‐ 800 K. The activation energy for process (4) has been measured to be 170 ± 8 kJ/mol. This value allows one to calculate an upper limit for the heat of formation of 2‐methyl‐2‐silapropene ΔHf0 ≤ ‐2 kJ/mol which is in very good agreement with other values calculated from literature data and supports earlier findings that the back reaction (‐4) has a negligible activation energy. The combined average from our results and the literature is ΔHf0 ((CH3)2Si = CH2) = 2−13+9 kJ/mol.—Furthermore it is shown that 2‐methyl‐2‐silapropene is more stable than the corresponding silylene and carbene isomers. The ζ bond energy has been estimated to be 189 kJ/mol, in excellent agreement with calculations by Ahlrichs and Heinzmann [20].

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