The alkane s-bond basicity scale revisited
Por:
Esteves P.M., Alberto G.G.P., Ramírez-Solís A., Mota C.J.A.
Publicada:
1 ene 1999
Resumen:
The energy of the n-butonium and isobutonium cations was calculated. At the MP4/6-311++-G**//MP2(fu)/6-31G** level, the C-carbonium ions were more stable than the H-carbonium ions. The results are in agreement with gas- phase data of n-butane and isobutane protonation but disagree with results in liquid superacid, where protonation of the tertiary C - H of isobutane is preferred over C - C protonation. Additional calculations, including the superacid moiety, revealed that the activation energy for C - C protonation is higher than the energy for attack at the tertiary C - H. This suggests that the s bond reactivity in the liquid superacid system is controlled by the activation energy for proton transfer, rather than by the intrinsic basisity of the bond. The higher stability of the C-carbonium relative to the H-carbonium ions was ascribed to a better charge distribution among the atoms and groups of the three center bond.
Filiaciones:
Instituto de Química, Depto. de Quim. Orgânica, Univ. Federal do Rio de Janeiro, Cd. Universitária CT Bloco A, 21949-900, Rio de Janeiro, Brazil
Facultad de Ciencias, Univ. Auton. del Estado de Morelos, Cuernavaca, Morelos 62210, Mexico
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