The application of mass spectrometry to a quantitative characterisation of the electronic and steric effects in organic compounds—I: The transmission of substituent influence through the chain of conjugated double bonds

Abstract

Abstract The mass spectra of polyenic compounds of the type RC 6 H 4 (CH=CH) n COPh, n=1, R=H,p‐NMe 2 ,p‐OH,p‐OMe,p‐Cl,p‐Br,p‐NO 2 ,m‐NO 2 ; n=2, R=H, p‐NMe 2 , p‐OMe,p‐Cl,p‐Br, p‐NO 2 ; n = 3, R = H, p‐OMe,p‐Cl, p‐Br,p‐No 2 have been measured. The ratio of the intensities of the common ion PhCO (m/e 105) to the intensities of the molecular ions for these series is correlated with the Hammett‐Brown equation with reaction constants p = 0.73 (when n = 1), 0.25 (when n =2), 0.11 (when n = 3). The transmission coefficients were calculated as π'=0.72,0.25 and 0.11 respectively [assuming p=1.01 for benzophenone series‐see M. M. Bursey and F. W. McLafferty, J. Am. Chem. Soc. 89 , 1 (1967)]. The contributions of the inductive mesomeric direct polar conjugation and non‐additive interaction were calculated in accordance with the equation log Z/Z 0 = . It was found that the inductive influence as well as the mesomeric influence of substituents decreases rapidly with the increase in the number of double bonds in the chain. The direct polar effect has a very small value in all series for all substituents with the exeption of NMe 2 . Non‐additive interaction effects are large. They probably express the general influence of RC 6 H 4 (CH=CH) n on COPh.