Interaction diagram nonbonding

Photolysis of benzaldehyde and trimethylethylene yields a mixture of cis and trans oxetanes with the two orientations shown in Eq. 42. Orientation 7 predominates and biradical intermediates generated after formation of a bond involving the lone nonbonding electron of an n, n excited benzaldehyde have been postulated. 66> Fig. 5 is the interaction diagram, the molecular parameters being based on HMO calculations, and spectroscopic experiments. 55,56,109) The orbital interaction E(n) F(n) is obviously dominant since the energy gap between F n ) and E n ) is over 4 eV. Therefore, a biradical mechanism should be postulated. The dominant orbital interaction is largest for attack of the... 

MO s of the component system can be easily developed. The final simplified interaction diagram is shown in Scheme 1. Clearly, we now have an additional interaction, as compared to the 1,2-difluoroethylene case, which stabilizes the cis isomer. Hence, the sigma nonbonded interaction of bonds is expected to favor a cis structure when the two bonds are coupled through another sigma bond. 

We first consider pi nonbonded interactions in difluoromethane and employ the dissection shown below. The appropriate interaction diagram for the pi system only is shown in Fig. 13. From this diagram it is obvious that only the symmetric... 

The sigma lone pair nonbonded interaction in F2C=CH2 can be treated in a similar fashion. The appropriate interaction diagram is shown in Fig. 15 and our conclusions are identical to the ones reached in the case of F2CH2, i.e. nonbonded attraction between the fluorine 2px lone pairs favors angle shrinkage in CF2=CH2. The results of calculations shown above are, once again, in agreement with these predictions. 

Consider the molecule 1-fluoropropane dissected in the manner shown below. First, we consider the sigma nonbonded interaction between methyl and fluorine and we construct the group MO s of the CH3—F fragment as shown by the interaction diagram of Fig. 19. 

The appropriate interaction diagrams are similar to that of Fig. 28. Reasoning as before, we conclude that pi nonbonded interactions favor the staggered conformation. Sigma nonbonded interactions, on the other hand, favor the eclipsed conformation. We expect pi nonbonded attractive interactions to dominate sigma interactions and the resulting order of stability is predicted to be > Cee. 

Figure 9.3. Interaction diagram which yields the nature of bonding in the axial bonds of a trigonal bipyramid. The HOMO is nonbonding. If enough stabilization results from the bonding combination, a stable intermediate may be formed. There are no known examples where this is the case when C is the central atom.

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