Hyperconjugation neutral

Cations are by no means the only species where the effects of hyperconjugative delocalization reveal themselves in such a striking manner. Similar effects exist in neutral systems or in anions. For instance, the normal propyl anion should tend to be eclipsed (E) since in this manner the molecule would optimize the 4-electron interactions between the ethyl group t orbital and the p orbital which carries the electron pair. In the bisected conformation, where ttchs and ttchs have both been raised in energy, the four-electron, destabilizing (see Section 1.7, rule 2) p ->7r interaction is stronger than in the eclipsed conformation. At the same time the two-electron, stabilizing p ->ir interaction is weaker than in the eclipsed conformation. Both effects favor the eclipsed conformation. 

Simple linear equations could also be developed for the other three systems of Figure 4, PA of aldehydes and ketones(4e), and their hydride ion affinities, both of the neutral (4f) and protonated forms (4g), However, in addition to effective polarizability and electronegativity, hyperconjugation had also to be used as a parameter, as p-orbitals carrying a partial positive charge are involved in the reactions 4e to 4g (26),... 

In addition to the stabilization of /1-carbocations, the /1-effect of silicon can also be observed in the ground states of neutral molecules. Lambert and Singer58 studied compounds of the type 42 where hyperconjugation should be enhanced by increasing the electron-accepting properties of the substituent X (MeO < Me < H < CN). o-tt overlap in this system gives the resonance structure 43 shown in equation 19. 

This also proves an earlier conclusion on hyperconjugation in an 0CH20 fragment of the 1,3-dioxolane cation radical this conclusion was based on mass spectrometry (To-dres, Kukovitskii et al. 1981). As calculated, the carbon-hydrogen bonds corresponding to 0CH20 in the radical cation are weaker than those in the neutral molecule. For this reason, this site exhibits a maximal probability that deprotonation will result in the formation of the 2-yl radical (Belevskii et al. 1998). In experiments, photoirradiation of 1,3-dioxolane solutions in sulfur hexafluoride at 77 K really leads to formation of the cation radical of 1,3-dioxolane and the l,3-dioxolan-2-yl radical as a result of deprotonation. Consecutive ring... 

Adcock, W. Abeywickrema, A. N. Substituent effects in the bicyclo[2.2.2]octane ring system. A carbon-13 and fluorine-19 nuclear magnetic resonance study of 4-substituted bicyclo[2.2.2]oct-l-yl fluorides, / Org. Chem 1982,47,2957-2966. Laube, T Ha, T. K. Detection of hyperconjugative effects in expaimentaUy dete-mined structures of neutral molecules, J. Am. Chem. Soc. 1988,110, 5511-5517. Rozeboom, M. D. Houk, K. N. Stereospecific alkyl group effects on amine lone-pair ionization potentials Photoelectron spectra of alkylpiperidines, / Am Chem Soc. 1982,104,1189-1191. 

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