Abstract: | CI mass spectra of the five isomeric vicinal d2-decanes have been recorded using methane and d4-methane as reagent gases. In contrast to earlier suggestions, we find that a large fraction of the alkyl fragment ions from n-decane are formed by elimination of olefins from the abundant [M – 1] ion. Only the C9 and C8 fragment ions are produced completely by a one-step reaction between the decanes and the methane reagent ions. Isotope exchange does not occur between the hydrocarbon and the reagent ions derived from d4-methane but extensive scrambling of the deuterium label in the d2-decanes does take place in the [M – 1] ion. |