Pyramidal carbocation

In these ions, a single carbon atom hovers over a four- or five-sided polygon, in effect forming a pyramid.

The apparent coordination number of five, or even six, associated with the carbon atom at the top of the pyramid is a rarity as compared to the usual maximum of four.

While calculating the optimal geometry of the mono-cation which arises from the extraction of chloride from 3-chlorotricyclo[2.1.0.02,5]pentane, the three bridges were expected to orient in space with angles of roughly 120°.

Towards the basic polygon, three orbitals are available: The approximation for the base of the pyramid is a closed ring of carbon atoms, all of them sp2 hybridised.

The exact results depend on the ring size; overall conclusions can be formulated as: To obtain bonding interactions between atoms or parts of molecules, two conditions should be met: The orbitals at the apical carbon and the basic polygon are able to combine with respect to their symmetries.

Filling the atomic and molecular orbitals in pyramidal structures of different base size leads to the next table.

In the case of the three-sided pyramid, clearly no ion results; a known neutral species arises: tetrahedrane.

[3] As described above, independent from its synthetic route, pyramidal ion 5a reacts with methanol or benzoate giving rise to products governed by reagent and the reaction medium as is clear by the substitution patterns.

This charge concentration has several effects: In chemistry, the prefix "homo-" denotes a homolog, a likewise compound containing one, or as in this case two, extra CH2-groups.

The stability of this ion at first may seem strange, as enlargement of the ring in general will diminish the bonding overlap between the orbitals at the center of the pyramidal structure.

Stiffening the configuration by a bridge between the homo-atoms, converting the base of the pyramid, to a norbornadiene, creates an even more stable structure.

Dissolution of this compound in fluorosulfonic acid gives rise to the dication (structure III in table 4).

Rapid equilibriums between degenerated classical or non-classical carbocations are discarded as the position of the signals does not match the expected values for those kind of structures.