Ab Initio SCF MO Calculations Research Articles

Ab initio SCF-MO calculations of methyllithium and related systems. Absence of covalent character in the carbon-lithium bonds

SCF calculations are reported for CH/sub 3/Li using several basis sets. The largest basis set used, split shell with d orbitals on carbon (SS + d), gives an optimized geometry of r(C--Li) = 2.021 A, r(C--H) = 1.089 A, and

Bonding studies of compounds of boron and elements of groups 3–5. Part 16.—Ab initio SCFMO calculations and He(I) photoelectron spectra of halogen-bridged dimeric group 3 metal halides and methylmetal halides

He(I) photoelectron spectra are reported for the halogen-bridged dimeric species Al2Cl6, Al2Br6, Ga2Cl6 and (Me2AlX)2(X = Cl, Br, or I). The electronic structures of monomeric and dimeric AlCl3 and Me2AlCl are discussed using the results of all electron ab initio SCFMO calculations in a variety of bases of Gaussian type functions. Assignments of the spectra are made with the aid of these calculations, and by correlation with the corresponding monomers. Values for enthalpies of dimerisation imply a more significant contribution by the Al 3d-orbitals to bonding in the dimer than in the monomer, while Cl 3d-orbitals act only as polarisation functions. For all dimers, calculation and experiment show that the predominantly bridging halogen orbitals ionise at higher ionisation potential (i.p.) than in the respective monomers, in accordance with loss of electron density at the bridging halogen atom. For (AlCl3)2 the lowest i.p.s correspond to ionisation from the terminal chlorine lone pair orbitals, and the highest observed i.p.s. to the Al–Cl bridging orbitals.

The electronic structure of transition metal complexes containing organic ligands

The He(I), He(II) and X-ray photoelectron spectra of iron tricarbonyl trimethylenemethane are reported, and these measurements, together with the bonding in the complex, are discussed with the aid of ab initio SCF MO calculations. The organic ligand is found to bear a net negative charge, and, as was found for other complexes, the position of the low energy photo-electron bands arising from the metal orbitals are inaccurately predicted using Koopmans' theorem.

A pes study on 1,3-thiazole and its monosubstituted halogen derivatives

The photoelectron (HeI) spectra of 1,3-thiazole and its 2F, 2Cl, 2Br, 4Br and 5Br-derivatives are reported. The assignment of the first few bands of the various spectra to the corresponding molecular orbital is based, for thiazole, on the results of an ab initio SCF—MO calculation, while for the various halogen derivatives, on reasonings based on perturbation theory. In particular, the first five outermost molecular orbitals of thiazole probably correspond to π 3 (9.50 eV), π 2 (10.24), σ N (10.48; orbital mainly localized on the nitrogen atom), σ S (12.78; orbital mainly localized on the sulphur atom) and π 1 (13.5).

ChemInform Abstract: STRUCTURE AND ELECTRONIC PROPERTIES OF THE NITROMETHYL ANION, NITROMETHANE AND ACI‐NITROMETHANE

Ab initio SCF MO calculations of the minimal and double-zeta level have been made for nitromethane, its aci tautomers and for planar and pyramidal forms of the nitromethyl anion. Calculations at the double-zeta level suggest that the most stable form of the ion is planar or near planar. Potential energy contours for the ion show that the planar form is expected to protonate on the oxygen (the observed fast reaction) whereas the pyramidal form would protonate on the carbon. This conclusion is not obvious by a comparison of the net atom charges alone. The p.e. spectrum of nitromethane has been re-assigned on the basis of our calculations; the first p.e. band is due to π ionization and the second is a combination of the two oxygen lone-pair ionizations.

Ab initio SCFMO calculations on the structure of the silylmethyl anion and the CH acidity of methylsilane

Ab initio SCFMO calculations have been carried out on the structure and stability of silyl-methyl anion and -ethyl anion. Our results show that SiH 3 and CH 3 as substituents effect the geometry of CH 2 − very little but SiH 3 stabilizes CH 2 − by about 50 kcal mol −1 compared to CH 3, using the neutral RCH 3 molecules as standard.

The electronic structure of transition metal complexes containing organic ligands

The He(I) and He(II) photoelectron spectrum of iron tricarbonyl cyclobutadiene are reported and interpreted with the aid of ab initio SCF MO calculations. The bonding in the complex is calculated to be similar to that in iron tricarbonyl butadiene [1], and as in the case of this molecule the assignment of the photoelectron spectrum is assisted by the relative intensities of the He(I) and He(II) spectra. The application of Koopmans' theorem to the interpretation of the bands arising from the metal MO's is again found to be inaccurate.

Cyanogen azide: Ionisation potentials and ab initio SCF Mo calculation

The Ne(I) and He(I) photoelectron(PE) spectra of cyanogen azide, NCN 3, have been recorded at high resolution. Their interpretation is achieved by comparison with the PE spectrum of HN 3 and an ab initio LCGO SCF MO calculation. Deviations from Koopmans' theorem of quite different magnitudes are found dependent on the type of ionisation process.

A b i n i t i o and semiempirical SCF–MO computations for N+4; comparison of spin unrestricted and spin restricted methods

Various basis sets (all but one minimal) were used in spin unrestricted ab initio SCF–MO computations on N+4. Computed values of the N+4 dissociation energy, D (N2−N+2), ranged from 49–72 kcal/mole for linear N+4 at a fixed internuclear separation R of 2.00 Å. Smaller dissociation energies were obtained by a spin restricted ab initio method in which the α- and β-spin eigenvector matrices were forced to be the same. All dissociation energies are larger than the experimental bond energy, but the smallest value was obtained with the extended basis set by the spin restricted ab initio method. There De(N2−N+2) was found to be 32.7 kcal/mole at Re=1.90 Å. Minimal basis set semiempirical computations were found to give results similar to those obtained by ab initio computations.

Ab initio SCF-MO calculations on carbanions. Methyl, ethyl, vinyl, and ethynyl anions

Ab initio SCF-MO calculations on carbanions. Methyl, ethyl, vinyl, and ethynyl anions

ChemInform Abstract: IONIZATION POTENTIALS OF CYCLOALKENES

Chemischer InformationsdienstVolume 6, Issue 3 Physical Organic Chemistry ChemInform Abstract: IONIZATION POTENTIALS OF CYCLOALKENES DAVID C. CLARY, DAVID C. CLARYSearch for more papers by this authorAKIN A. LEWIS, AKIN A. LEWISSearch for more papers by this authorDEREK MORLAND, DEREK MORLANDSearch for more papers by this authorJOHN N. MURRELL, JOHN N. MURRELLSearch for more papers by this authorEDGAR HEILBRONNER, EDGAR HEILBRONNERSearch for more papers by this author DAVID C. CLARY, DAVID C. CLARYSearch for more papers by this authorAKIN A. LEWIS, AKIN A. LEWISSearch for more papers by this authorDEREK MORLAND, DEREK MORLANDSearch for more papers by this authorJOHN N. MURRELL, JOHN N. MURRELLSearch for more papers by this authorEDGAR HEILBRONNER, EDGAR HEILBRONNERSearch for more papers by this author First published: January 21, 1975 https://doi.org/10.1002/chin.197503056AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume6, Issue3January 21, 1975 RelatedInformation

Structure and electronic properties of the nitromethyl anion, nitromethane and aci-nitromethane

Ab initio SCF MO calculations of the minimal and double-zeta level have been made for nitromethane, its aci tautomers and for planar and pyramidal forms of the nitromethyl anion. Calculations at the double-zeta level suggest that the most stable form of the ion is planar or near planar. Potential energy contours for the ion show that the planar form is expected to protonate on the oxygen (the observed fast reaction) whereas the pyramidal form would protonate on the carbon. This conclusion is not obvious by a comparison of the net atom charges alone. The p.e. spectrum of nitromethane has been re-assigned on the basis of our calculations; the first p.e. band is due to π ionization and the second is a combination of the two oxygen lone-pair ionizations.

An ab initio molecular orbital study of the S N2 reaction of H − with HF

Ab initio SCF MO calculations have been performed for the reactants, products and reaction complex in the title reaction. The influence of diffuse and polarization basis functions in determining the presence of a reaction barrier was investigated. No barrier to the forward or reverse reactions was found.

The He I photoelectron spectra of mixed boron trihalides and the microwave spectrum of BClF2

Although the mixed boron halides BXnX′3 – n cannot be isolated pure, but exist in essentially statistical equilibrium with BX3 and BX′3, it is shown that their He I photoelectron (p.e.) spectra, as well as their microwave spectra, can be measured; the p.e. spectra of BC1F2 and BC12F, and the microwave spectrum, structure, and quadrupole interaction data for BC1F2 are described and are supported by ab initio SCF MO calculations.

The electronic structure of transition metal complexes containing organic ligands

All electron ab initio SCF MO calculations of Cr(C6H6)2 and C6H6Cr(CO)3 are described. In both complexes the benzene ligand bears a net negative charge and in the carbonyl complex the -CO ligands accept more electron density than in unsubstituted carbonyls. The He(I) and He(II) p.e. spectra of both complexes are reported and interpreted with the aid of these calculations. For ionization from mainly ligand MO's, Koopmans' theorem allows a satisfactory interpretation of the measured I.P.'s and the change in intensity between He(I) and He(II) spectra may be correlated with the atomic orbital character of the M.O.'s. However, for ionization from these MO's having substantial metal character the relaxation energy is dependent upon their degree of localization and direct calculation of the energy of the ion states is necessary to interpret this region of the p.e. spectra.

Theoretical investigation of the symmetric trisubstituted borazines

The bonding in borazine and four symmetric tri-substituted derivatives, B-trifluoroborazine, N-trifluoroborazine, B-trimethylborazine and N-trimethylborazine, is discussed by means of all electron ab initio SCFMO calculations. B-trifluoroborazine is predicted to be 12·9 eV more stable than the N-trifluoro derivative and B-trimethylborazine 2·8 eV more stable than the N-trimethyl derivative. The calculated wavefunctions are used to interpret the low energy photoelectron spectra of these molecules. The calculated sequence for the three highest filled orbitals is πσπ in all derivatives except B-trifluoroborazine, where the sequence ππσ is realised.

Photoelectron studies of boron compouds. Part 5.—Higher boron hydrides B4H10, B5H9and B10H14

The He I and He II photoelectron (p.e.) spectra of the title compounds are reported. Ab initio SCF-MO calculations have been carried out on diborane, pentaborane(9) and tetraborane(10) using a double zeta basis of Slater-type orbitals. Assignment of the spectra is made with the aid of these calculations and by correlation with the spectrum of diborane. The p.e. spectrum of pentaborane (9) shows marked differences from one previously reported.

Ab initio SCF-MO calculations of thiomethyl anion. Polarization in stabilization of carbanions

Ab initio SCF-MO calculations of thiomethyl anion. Polarization in stabilization of carbanions

The electronic structure of transition metal complexes containing organic ligands

The He(I), He(II) and X-ray photoelectron spectra of iron tricarbonyl butadiene are reported and these measurements, together with the bonding in the complex, are discussed with the aid of ab initio SCF MO calculations. The latter yield a substantial negative charge on the butadiene ligand, and the low energy photoelectron spectra can only be satisfactorily interpreted when deviations from Koopmans' theorem are taken into account by performing RHF calculations on the various low-lying ionic states of the molecule.

The structure and stability of silyl-substituted carbonium ions

Ab-initio SCFMO calculations on silyl-substituted alkanes, alkyl-radicals and carbonium ions show that the carbonium ion is destabilized by an α-silyl group but stabilized by a β-silyl group in comparison with the carbon analogues. In contrast, replacement of α or β-methyl by silyl has little effect on the stability of the radicals or alkanes. These results are consistent with observations on the rates of S N1 solvolysis of trimethylsilylalkyl halides, and indicate that the relative rates are largely determined by the relative stabilities of the carbonium ions. A non-classical bridged structure for SiH 3CH 2CH + 2 has been found to have an energy approximately 0.5 eV (50kJ/mole) lower than that of a classical open structure.