Reactions of O(3P) with secondary C-H bonds of saturated hydrocarbons in nonequilibrium plasmas

The functionalization of three n-alkanes by means of a low-pressure oxygen plasma has been achieved. The plasma was generated by applying a low-Frequency high-voltage glow discharge through an oxygen flow. bit, activated species so produced have been allowed to interact with the surface of each one of the liquid compounds at a time. The hydrocarbon has been cooled down to a temperature low enough so that its vapor pressure is about 20–100 times lower than the O₂ pressure, this heing of the order of 0.1–0.4 torr. Under these conditions the main products of the reactions have been the alcohols, except for the primary ones, and the corresponding ketones. A remarkable result we have arrived at is that for the first time secondary carbon hydrogen bonds have shown to possess different reactivities withO(³P). The latter has proved to he the most relevant active species of the plasma. A discussion is given to explain this novel result under two theoretical bases recently published: (i) a conformational analysis of the hydrocarbons according to molecular mechanics calculations, and (ii) an analysis of properties of the molecules based on calculations with charge distributions derived from 6–31G^* wave functions.