D orbitals conjugation

Another important and influential paper was by Bernard and coworkers28 (containing in its title the phrase the irrelevance of d orbital conjugation ) and was a rather more elaborate study closely related to the above, since it concerned a non-empirical MO investigation of the reactions described in equation 1. 

The effect of the sulfone dipole on the ESR spectrum of the dibenzothiophene 5,5-dioxide anion has been examined, modified Hiickel calculations which ignored d-orbital conjugation predicting spin distributions which agreed with experimental data. Proton hyperfine splitting constants have also been obtained for the sulfone. Correlation with MO calculations shows that the sulfone group contributes a vacant symmetric orbital to the conjugated system. ... 

The decrease in effective conjugation discussed above is much more important than any possible participation of phosphorus Sd z orbitals. Such weak d-orbital conjugation is not expected to lower the energy of the 7T2 MO to any significant degree. Fig. 15 roughly summarizes the orbital schemes of the two heterosystems. 

The structural features and the spectroscopic characteristics of the thiirene dioxide system (22) are of special theoretical interest since, on the basis of analogy with cyclopropenone (23), it is a possible nonbenzenoid aromatic system with all the physical and chemical implications involved. Aromatic and/or conjugative effects, if any, require transmission through the d-orbitals of the sulfur atom. 

In view of the limited capacity of the sulfur atom in the sulfoxide and sulfone functional groups to transmit conjugative effects due to the insulating effect of the LUMO sulfur d-orbitals , the application of the UV technique even in the case of the cyclic vinyl sulfones (e.g. thiete dioxides 6b) cannot be expected to find extensive use. UV spectra of substituted thiete dioxides in which an extended conjugated system (e.g. 194) exists in the molecule, did provide useful information for structure elucidation . However, the extent... 

Among many examples of -orbital interaction, only the following two are selected to illustrate the feature of HO—LU conjugation. One is the cyclooctadiene-transition metal complex ">. The figure indicates the symmetry-favourable mode of interaction in a nickel complex. The electron configuration of nickel is (3d)8 (4s)2. The HO and LU of nickel can be provided from the partly occupied 3d shell from which symmetry-allowed occupied and unoccupied d orbitals for interaction with cyclo-octadiene orbitals are picked up. 

A pjr-djr effect was found also in the silicon derivative in the series p-CICgEEMMes (M = C, Si, Ge, Sn)74. In this case the hyperconjugation minimizes the difference in orbital energy 712-713, where 713 is the phenyl orbital affected by the conjugation, which is stabilizing for the chlorine 3p orbitals, destabilizing for the M empty d orbitals. 

In addition, it should be useful to mention that silicon as a spiro atom is able to conjugate its mutually orthogonal aromatic constituents, and thus, secures a release of an unpaired electron in a cation-radical. Scheme 3.61 shows such a phenomenon, revealed by Hirao et al. (2007). Obviously, vacant d orbitals of silicon provide the cation-radical with the possibility of delocalizing spin density. 

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