Molecular orbitals carbenium ions

In line with Higashimura s view34 that carbenium ions are not strictly sp2 hybridized and that they retain some sp3 character, a more nucleophilic G would be expected to induce more sp3 character to the growing cation. Pronounced sp3 character of the carbenium ion would prevent orbital overlap, i.e., the formation of transition state leading to transfer, and thus to increase in molecular weight. 

What are the geometries of carbon radicals, and how do they differ from those of carbenium ions or carbanions And what types of bonding are found at the carbon atoms of these three species First we will discuss geometry (Section 1.1.1). and then use molecular orbital (MO) theory to provide a description of the bonding (Section 1.1.2). 

In this section we will discuss various reactive intermediates that contain silicon. In particular, the silicon analogues of the classic organic reactive intermediates such as carbenes (silylenes), carbenium (silicenium) ions and carbanions (silyl anions) have attracted the interest of experimentalists and theoreticians. In light of the elusive nature of these species it is not surprising that much of what we know about their properties comes from theory, in particular ab initio molecular orbital calculations. 

Additionally, this cyclopropane is set in conjugation with the C5-C6 insaturation in such a way that the bisected geometry derived from its spyrocyclic disposition maximizes the overlap between the n and cyclopropane 3d molecular orbitals. The setting is ideal for the constitution of a non-classical carbenium ion (8) if a proton is trapped by the C5-C6 double bond, Fig (5) route A. The nucleophilic attack of water from the medium would yield the rupture of the cyclopropane unit, and water elimination from the tertiary alcohol in the resulting diol (9) would furnish a conjugated dienone (10). Aromatization to the observed product, pterosin B (11), would occur by acid-induced glycolysis. Conversely,... 

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