Hyperconjugation and Spectrum of the Benzenium Ion, Prototype of Aromatic Carbonium Ions¹

Discrimination among geometrical isomers of α-linolenic acid methyl ester using low energy electron ionization mass spectrometry

“…In other studies, the benzenium ion is shown to be stabilized via hyperconjugation [40,[45][46][47], where the overlap between the bonds of CH 2 and the bonds of remaining carbons in the ring creates cyclic delocalization. Muller et al have reported a hyperconjugation contribution to the resonance energy of ϳ14 kcal/mol and an overall resonance energy that is larger than the conjugation energy of benzene [47]. Their calculations predicted two electronic transitions in the visible region, which was in good agreement with their experimental results.…”

“…Instead, it is a classic carbenium ion [40] with an allylic system [32,33] and minimal, if any, homoallylic delocalization nature [32]. In other studies, the benzenium ion is shown to be stabilized via hyperconjugation [40,[45][46][47], where the overlap between the bonds of CH 2 and the bonds of remaining carbons in the ring creates cyclic delocalization. Muller et al have reported a hyperconjugation contribution to the resonance energy of ϳ14 kcal/mol and an overall resonance energy that is larger than the conjugation energy of benzene [47].…”

Properties and Reactions of Thiazole

“…Dipole moments were calculated for a large number of thiazole derivatives; the corresponding results are reported in Table 1 In Table 1 The introduction of a methyl substituent into the empirical calculations may be performed according to two main different models: the pseudoheteroatomic model and the hyperconjugated model (161)(162)(163)(164)(165)(166). Both approximations have been used in a-electron methods (HMO, w, PPP).…”

“…Proton abstraction by 162 gives the dilithio intermediate (166) and regenerates 2-methylthiazole for further reaction. During the final hydrolysis, 166 affords the dimer (167) that could be isolated by molecular distillation (433).…”

Partitioning of molecular systems and subsystem replacement by single-centered perturbations: II. Applications of the pseudo substituent technique within hückel molecular orbital theory

“…The Coulomb parameters for the pyrrole and pyridine type nitrogen atoms are chosen to reproduce the charge density and bond orders of the A systems in HartreeFock calculations by Clementi and coworkers [3]. Parameters for hyperconjugation of the methyl group, kCHa and kC-CHa, are those suggested by Muller et al [4]. The value of kN-CHa was scaled relative to kc-cH3 after noting that kc-N is less than kc-c by ten to twenty percent, depending on the set of empirical parameters used.…”