Energy donor-acceptor interaction parameter

Energy parameters and charge-transfer spectra of complexes of Br2 with several substituted pyridines have now been compared with the force constants k(Br—Br) and k(N- Br2) and with the properties of the donors. The complexes with orr/to-substituted pyridines show systematic deviations from the relations found to be valid for the other donors. The n.m.r. spectrum of the pyridine-Br2 complex in a nematic phase has been obtained and analysed. The results indicate that the donor-acceptor interaction is similar to that found in the solid state for other halogen-pyridine complexes. The equilibrium constant for the formation of the 1 1 complex of Br2 with hexamethyl-phosphortriamide (HMPA) has been determined by n.m.r. spectroscopy. Solid adducts of Br2 with poly-HMPA could also be prepared. 

Separations in GLC are the resultant of selective solute-stationary-phase interactions and differences in the vapor pressure of solutes. The main forces that are responsible for solute interaction with a stationary phase are dispersion, induction, orientation and donor-acceptor interactions (25-27), the sum of which serves as a measure of the polarity of the stationary toward the solute. Selectivity, on the other hand, may be viewed in terms of the magnitude of the individual energies of interaction. In GLC, the selectivity of a column governs band spacing or the degree to which peak maxima are separated. The following parameters influence selectivity ... 

We can also verify that the usual ECAO-MO description (3.2) and (3.4) leads to predicted hybridizations that are generally consistent with the donor-acceptor estimates (3.8). Suppose that each H atom is associated with a valence spin-orbital of hybridized form (3.6). According to Eq. (3.2), the optimal electronic energy of bond formation is obtained by choosing the hybridization parameter k to maximize the magnitude of the interaction element... 

In order to estimate and compare the magnitude of the M-B interactions in these isoelectronic complexes, a whole set of structural and spectroscopic parameters determined experimentally and/or computed theoretically were considered. This includes the M - B distance the ratio r between the M -B distance and the sum of covalent radii (to take into account the different sizes of the metals involved), the pyramidaliza-tion of the boron environment XB, the rlB NMR chemical shift <5 11B, the difference AqB between the charge at boron in the metal boratrane and the free ligand TPB, the difference A M between the charge at the metal in the metal boratrane and that in the related borane-free complex [M(i-Pr2PPh)3], and the NBO delocalization energy A NBo associated with the main donor-acceptor M-B interaction found at the second order in the NBO analysis (Table 2). Only the conclusions of this detailed analysis will be recalled here ... 

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