Molecular orbital resolution

A particularly useful property of the PX monomer is its enthalpy of formation. Conventional means of obtaining this value, such as through its heat of combustion, are, of course, excluded by its reactivity. An experimental attempt was made to obtain this measure of chemical reactivity with the help of ion cyclotron resonance a value of 209 17 kJ/mol (50 4 kcal/mol) was obtained (10). Unfortunately, the technique suffers from lack of resolution in addition to experimental imprecision. It is perhaps better to rely on molecular orbital calculations for the formation enthalpy. Using a semiempirical molecular orbital technique, which is tuned to give good values for heat of formation on experimentally accessible compounds, the heat of formation of /5-xylylene has been computed to be 234.8 kj/mol (56.1 kcal/mol) (11). 

Unlike the stable molecule N2O, the sulfur analogue N2S decomposes above 160 K. In the vapour phase N2S has been detected by high-resolution mass spectrometry. The IR spectrum is dominated by a very strong band at 2040 cm [v(NN)]. The first ionization potential has been determined by photoelectron spectroscopy to be 10.6 eV. " These data indicate that N2S resembles diazomethane, CH2N2, rather than N2O. It decomposes to give N2 and diatomic sulfur, S2, and, hence, elemental sulfur, rather than monoatomic sulfur. Ab initio molecular orbital calculations of bond lengths and bond energies for linear N2S indicate that the resonance structure N =N -S is dominant. 

Hartree-Fock wave functions, 269 High resolution electron energy loss spectroscopy, HREELS, 43, 69 Highest occupied molecular orbital, HOMO, 269... 

We shall introduce the technique of projection operators to determine the appropriate expansion coefficients for symmetry-adapted molecular orbitals. Projection by operators is a generalization of the resolution of an ordinary 3-vector into x, y and z components. The result of applying symmetry projection operators to a function is the expression of this function as a sum of components each of which transforms according to an irreducible representation of the appropriate symmetry group. 

The resolution of tris(catecholato)chromate(III) has been achieved by crystallization with L-[Co(en)3]3+ the diastereomeric salt isolated contained the L-[Cr(cat)3]3 ion.793 Comparison of the properties of this anion with the chromium(III) enterobactin complex suggested that the natural product stereospeeifically forms the L-cis complex with chromium(III) (190). The tris(catecholate) complex K3[Cr(Cat)3]-5H20 crystallizes in space group C2/c with a = 20.796, 6 = 15.847 and c = 12.273 A and jS = 91.84° the chelate rings are planar.794 Electrochemical and spectroscopic studies of this complex have also been undertaken.795 Recent molecular orbital calculations796 on quinone complexes are consistent with the ligand-centred redox chemistry generally proposed for these systems.788... 

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