Orbitals, molecular ethyl cation

Figure 6.12 Stabilization of the ethyl carbocation, CH3CH2+, through hyperconjugation. Interaction of neighboring C H

For an earlier study, see Apeloig, Y., Schleyer, P. v. R., Pople, J. A. (1977). Molecular orbital theory of the electronic structure of molecules. 35. p -Substituent effects on the stabilities of ethyl and vinyl cations. Comparison with isoelectronic methyl boranes. The relative importance of hyperconjugative and inductive effects. Journal of the American Chemical Society, 99,5901-5909. 

FIGURE 7.9 In the ethyl carhocation, CH3CH2", there is a stabilizing interaction between the carhocation p orbital and adjacent C-H methyl substituent, as indicated by this molecular orbital. The more substituents there are, the greater the stabilization of the cation. Only the C-H bonds that are roughly parallel to the neighboring p orbital are oriented properly to take part in hyperconjugation. 

Carbocations can also be stabilized by a heteroatom that bears a lone pair of electrons able to donate into the empty p orbital (Figure 5.24). Thus, in mass spectrometry, the fragmentation generally occurs such that the cation formed can be stabilized by the heteroatom. The mass spectrum of 2-methyl-2-butanol (Figure 5.25) illustrates. The molecular ion (M would be 88) is not seen as there are good routes to stable cations. The peaks at m/z 73 and 59 represent the loss of methyl and ethyl radicals to give cations stabilized by lone pair... 

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