Through-space orbital interactions

The spectroscopic and chemical properties of l,4-diazabicyclo[2.2.2]octane (DAB-CO) are consistent with a strong interaction of the in-phase combination of the non-bonded electron pairs of the nitrogen atoms with the symmetric combination of the C—C a bonds, one consequence of which is that the in-phase combination is the HOMO. The two lowest IPs are 7.6 and 9.7 eV [89]. Compare these to the IPs of trimethyl amine (8.44 eV) and ammonia (10.5 eV) [90]. The relative importance of intramolecular orbital interactions through space and through bonds has been reviewed by Hoffmann [6]. 

Chau, D. D., Paddon-Row, M. N., Patney, H. K. Orbital interactions. XII. Product studies and competition kinetic measurements of the Birch reduction of a series of hexahydrodimethanonaphthalenes and their interpretation in terms of orbital interactions through space and through bonds. Ai/sf. J. Chem. 1983, 36, 2423-2446. 

Orbital Interactions Through Space and Through Bonds... 

ORBITAL INTERACTIONS THROUGH SPACE AND THROUGH BONDS... 

This unusual enhancement is attributed to relative rotamer populations in the two solvents. Extensive intramolecular hydrogen-bonding is observed in chloroform but intermolecular bonding to the solvent in DMSO. Consequently only in chloroform does the hydroxy-group hydrogen-bond to the cyclobutene and in DMSO reaction is facilitated by orbital interaction through space between the and orbitals. In view of the relation between rate and the difference in energy between HOMO and LUMO orbitals these results are not unexpected. 

Orbital Interactions through Space and through Bonds... 

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