The study of cis - and trans -2 butene using mass spectrometry

Using mass spectrometric technique, the effect of geometrical isomerism on the first and higher appearance energy values for C₄H₃ ⁺, C₄H₇ ⁺ and C₃H,₃ ⁺ ions obtained from cis-2-butene andtrans-2-butene is reported. The structure in the ionization efficiency curves (studied for 9 eV above threshold) for the same ions obtained from the two isomers is reported and compared. It is believed that at threshold C₄H₇ ⁺ fragment is formed from the two isomers as methallyl ion. For C₃H₃ ⁺ fragment formed from the cw-isomer at threshold the proposed structure is the propargyl ion with ΔH_f equal to 279-4 kcal/mole while for that ion obtained fromtransisomer the proposed structure is the allenyl ion with ΔH_f equal to 296.6 kcal/mole.