Prediction of Mass Spectra from Substituent Constants SIR: Previous mass spectral correlations (5, 6) have shown qualitatively the paths of molecular degradation from electron impact found in various classes of organic compounds. The only previous quantitative predictions of spectra have been for simple niolecules using the statistical theory of mass spectra ( 2 , 7 ) . For chemical reactions, correlations of the effects of particular substituents have made possible the assignment of substituent constants to predict those effects (1, 4, 8). We have sought to extend this to the reactions under electron impact giving rise to the mass spectrum. For benzoyl compoundsJ the effect of substituent 2 on the rate of the reaction (Ph = phenyl) Z-Ph-CO-R++COR+
+ Z-Ph.
(1)
is shown b y the substituent constant u, where u p = log k / k , (4), k a t e = COR+/Z-PhCOR+, and p is a constant Of characteristic of the reaction. course, to describe the abundance of COR+ with a single u value, Equation 1 must he the predominant reaction affecting COR+, unless such reaction does not involve Z, as
Table 1.
A p-CHa m-CH3 p-tert-Bu p-OH m-OH P-CHBO p-NH1 p-NOz m-NOs p-c1 m-C1 m-Br m-Br
k/k,, Where k = Z
-H
- Ph+/Z
- CH,
-CnH5
1.05 0.42
