Free Radicals by Mass Spectrometry. XLV. Ionization Potentials and Heats of Formation of C3H3, C3H5, and C4H7 Radicals and Ions

Abstract

Using an energy-resolved electron beam, appearance potentials for[Formula: see text],[Formula: see text], and [Formula: see text] fragment ions from hydrocarbons of formula C3H4, C3H6, C4H6, C4H8, and C5H10 have been measured. In each case the fragment appears to have a common structure, corresponding to [Formula: see text], [Formula: see text], and [Formula: see text]. Ionization potentials have been measured for propargyl radical (8.68 V), methallyl radical (7.54 V), and 2-methylallyl radical (7.89 V). Corresponding ionic heats of formation are propargyl 281 ± 3 kcal/mol, methallyl 204 ± 3 kcal/mol, and 2-methylallyl 211 ± 5 kcal/mol. The [Formula: see text] fragment ion is 25 kcal/mol more stable than propargyl ion, and is almost certainly cyclopropenyl ion. Ionization potentials for propyne, allene, cyclopropene, 1- and 2-butyne, and fifteen isomers of formula CnH2n have also been measured by monoenergetic electron impact.