7c-Interaction

The observation of an intense absorption at 43,300 cm-1 (e = 10,900) in the electronic spectra of phenylpentamethyldisilane 212 and a red shift of this Laband of 6000 cm-1 relative to benzene has been suggested to be due to interaction between the Si-Si bond and the aromatic ring.188 Support for this interpretation was provided by the electronic spectra of the stereochemically constrained disilanes 213 and 214. The disilane 214, which can achieve a conformation allowing overlap between the Si-Si bond and the Jt system, displays an intense absorption at 42,900 cm-1 (e = 11,000) similar to 212. However, disilane 213, in which the constraints of the five-membered ring place the Si-Si bond close to the nodal plane of the benzene ring, did not display this absorption. 

The [2.2]naphthalcnophane 92 served in a project by Haenel et al. as a model for investigations of transannular 7c-interactions in strongly distorted aromatic... 

Note The 7C interactions undoubtedly enhance the stability of the unsaturated compounds over the saturated analogues [95]. 

Another prominent ligand-binding site that exploits cation—7C interactions is the SH2 domain, a ubiquitous regulatory unit that binds phosphotyrosine. The cationic side chain of an arginine from the protein makes contact with the 7U face of the phosphotyrosine. 

Umezawa, Y. Nishio. M. Thymine-methyl/7c interaction implicated in the sequence-dependent deformability of DNA. Nucleic Acids Res. 2002, 30, 2183-2192. 

Other forces, like 7C-interactions, are also of value. Benzene, or fused rings, contribute to stronger lateral interactions, and, by these means, the aliphatic chains can be shortened, or even eliminated in some cases. For such "in situ" chemical reactions, the drawbacks are that the syntheses are more difficult, and that the aromatic rings are more reactive than the inert aliphatic chains. 

The 7c-interaction only slightly influences the metal-alkyl bond because the carbon and Py orbitals form bonds with hydrogen (sp carbon atoms). In the case of alkenyl. 

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