Groups bridging nonbonding

In each case, it is the carbon atom that has the negative formal charge that makes it the "electron-rich" end of the structure. Moreover, there are antibonding orbitals in both CO and CN that can accept electron density transferred from the nonbonding d orbitals on the metal (as described in Section 16.10). Because of the nature of these ligands, it is not uncommon for them to function also as bridging groups in which they are bonded to two metal atoms or ions simultaneously. 

A similar situation prevails in the aromatic derivatives Villa and Vlllb (74-76). In these dimeric species, the phenyl groups are oriented perpendicularly to the Al-Al axis so that the ir-orbitals on the ring (or the p orbital on the bridging carbon atom) is permitted by symmetry to interact with the vacant nonbonding orbitals on the metal atoms. Again,... 

Cyclization of C-(cycloalkenyl)nitrones has been extensively investigated.13-15 For example, the cy-clohexenylnitrone (30) (an equilibrated 2 1 ( )/(Z) isomer mixture) afforded (31) in 56% yield (Scheme 7).13 Presumably the (Z)-nitrone cyclized exclusively based on the strained transition state required for cyclization of the ( )-nitrone. None of the isomeric bridged [4.2.1] product (32) was formed this is attributed to unfavorable nonbonded interaction between the carbonyl group and a ring methylene group in the required transition state. 

The stereochemical outcome of the reaction above is explained in terms of a structurally rigid 1,3-bridged six-membered chairlike transition state (Scheme 3.2i). Transition state B would be disfavored relative to transition state A because the phenyl group of benzoin is engaged in nonbonded interactions with the methyl and the hydrogen of the crotylsilane. 

Consider the interaction of methyl, CH3, with a surface, in on-top and bridging sites, 110.78 Let s assume low coverage. The important methyl orbital is obviously its nonbonding or radical orbital n, a hybrid pointing away from the CH3 group. It will have the greatest overlap with any surface orbitals. The position of the n orbital in energy is probably just below the bottom of the metal d band. How to analyze the interactions of metal and methyl ... 

---