On the Mass Spectra of Propanes and Butanes Containing C13

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Abstract
A mass spectrometric method of analysis of C13 enriched samples of paraffins, both with respect to the gross concentrations of —C013, —C113, and —C213 species and the concentration of C13 isomeric species is described, with particular reference to samples of propane−1—C13, propane−2—C13, n‐butane−1—C13, n‐butane−2—C13, i‐butane−1—C13, and i‐butane−2—C13 prepared in connection with tracer studies of certain paraffin reactions. With respect to the analysis, the necessary a priori assumptions and a posteriori checks of the assumptions are described. The relative intensities of certain C1 and C2 ion fragments characteristic of the 75‐ev mass spectra of propane—C013, propane−1—C113, and propane−2—C113, and certain C1, C2, and C3 ion fragments characteristic of the 75‐ev mass spectra of the six similar butanes are tabulated. The isotope effects on the dissociation probabilities of certain states of the propane and butane molecule‐ions are discussed in terms of a simple qualitative model. Of particular interest is the observation that in the states of C3H8+ which dissociate into C1 ion fragments, and the states of i‐C4H10+ which dissociate into C1 or C2 ion fragments the carbon atoms become essentially indistinguishable, and the mass spectra of the isomeric C113 compounds become essentially identical as far as the relative intensities of these fragments are concerned.