A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium CH+3, methanium CH+5 and vinyl C2H+3 cations. Occasionally, carbocations that bear more than one positively charged carbon atom are also encountered.
The sp2 lone pair of molecule A is oriented such that it forms sufficient orbital overlap with the empty p orbital of the carbonation to allow the formation of a π bond, sequestering the carbonation in a contributing resonance structure. The lone pair of molecule B is rotated 90° with respect to the empty p orbital of the carbonation, demonstrated by the Newman projection (bottom right). Without proper orbital overlap, the nitrogen lone pair cannot donate into the carbocation's empty p orbital. Thus, the carbocation in molecule B is not resonance-stabilized.
Image: Aromatic cations
Image: Pyramidal ion 4 sided with numbers
Image: Pyramidal dikation, hexamethyl
George Andrew Olah was a Hungarian-American chemist. His research involved the generation and reactivity of carbocations via superacids. For this research, Olah was awarded a Nobel Prize in Chemistry in 1994 "for his contribution to carbocation chemistry." He was also awarded the Priestley Medal, the highest honor granted by the American Chemical Society and F.A. Cotton Medal for Excellence in Chemical Research of the American Chemical Society in 1996.
Olah in 2009
Olah in 2010
