Some Miscellaneous
Neighboring Group Effects

1.  Homoconjugation:  through space effects.

The LUMO of the 7-norbornenyl cation.  Note how this orbital sticks out over the C=C π system:


Show the HOMO; note the interaction of the C7-p orbital with the π orbital of the double bond.
Show the LUMO. Still centered on the cationic carbon, but also some π participation.
Compare the ESP map on the two faces.

2.  The cyclopropylcarbinyl cation:  parallel vs. perpendicular orientations and cyclopropyl conjugation.

Below are the electrostatic potential maps (identically indexed) for the parallel (left) and perpendicular (right) arrangement of a cyclopropylmethyl cation.  Note the greater localization of positive charge in the perpendicular arrangement:

Cyclopropylcarbinyl: "parallel" conformation: Cyclopropylcarbinyl: "perpendicular" conformation:
Show the HOMO; note the interaction with the p center in the parallel form, and the absence of participation in the perpendicular.
Show the LUMO. Both strongly centered on the carbocation, but some visible hyperconjugation in the parallel form.
Compare the ESP maps; the perpendicular form has the more localized (and less stable) charge.

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Last updated: 05/08/2014
Comments to K. Gable