Modified all-valence INDO/spd method for ground and excited state properties of isolated molecules and molecular complexes

A new semiempirical all-valence method, GRINDOL (Ghost and Rydberg INDO ), based on the INDO approximation, is described. Linderberg–Seamans relation (extended to the d and Rydberg orbitals) for the resonance integrals and a new semitheoretical expression for the core-core repulsion term and energy correction including basis-set superposition error (intermolecular as well as intramolecular) has been applied. The proposed method enables calculation of ground and excited state properties. The ground state results (including intermolecular interactions) as well as the spectral properties are in reasonable agreement with relevant experimental (or ab initio) studies for isolated molecules, molecular complexes, and transition metal compounds. The method contains only one adjustable parameter, all two-center integrals and terms are only basis-set dependent. The one-center integrals are evaluated from the respective atomic terms.     

Unrestricted Hartree-Fock calculations of spin densities with orthogonalized atomic orbitals: Proton and 13C hyperfine splittings in some pi hydrocarbon radicals

The spin density distribution in a few hydrocarbon radicals has been calculated using orthogonalized atomic orbitals in the Unrestricted Hartree-Fock formalism of Amos and Snyder and including certain more important two-electron hybrid and exchange integrals and all the core-resonance integrals. Our calculated spin densities for the cation and anion radicals of alternant hydrocarbons, which are now different due to the breakdown of the pairing theorem, are, in general, of the right relative order so that even the simple McConnell type of relation can account partly for the observed differences in the proton splittings between cations and anions. The proton splittings for position 2 of naphthalene and anthracene radical ions are correctly predicted, thus clearing up the well-known cation-anion anomaly for this position. Comparative calculations have been made to show that the spin density results are worsened with the neglect of the integrals of the type mentioned before. An empirical analysis correlating the observed ¹³C splittings and the spin density results over a non-orthogonal basis set shows that the available ¹³C splittings in alternant hydrocarbon radical ions can be explained with a set of sigma-pi parameters which are consistent with the theory. It is shown that even though the spin densities in cations and anions may be different, these can lead to similar ¹³C splittings.     

Determination of one-centre core integrals from the average energies of atomic configurations

One-center core integrals for valence orbitals are determined from the experimental average energies of neutral atomic configurations from Li through Zn. These values are compared with those estimated from CNDO /1, “INDO /1”, CNDO /2, “INDO /2” and with theoretical values calculated from a pseudo-potential method. The agreement is good between values obtained from neutral atoms and from the psuedo-potential calculation except for the 3d orbitals of the transition elements where the theoretically calculated integrals over single ξ functions are not realistic. These two methods reproduce both term and average configuration energies for the first two rows of atoms; the semiempirical method reliably reproduces them for the third row. The CNDO /1 and INDO /1 methods underestimate atomic energies, while the CNDO /2 and INDO /2 procedures fail rather poorly. The propriety of using core integrals estimated semiempirically in molecular orbital calculations is discussed.     

Electron spin resonance and kinetic study of the photolysis of p-Flouranil (tetrafluoro-p-benzoquinone) in dioxane

The photochemistry of p-fluoranil in dioxane was studied by electron spin resonance (ESR) and the ESR-rotating sector technique. The transient photoradical is identified as the p-tetrafluorobenzosemiquinone neutral radical with a hyperfine splitting of 1.1 gauss for the hydroxy proton and the fluorine hyperfine splittings of 3.8 and 14.1 gauss for the meta and ortho fluorines, respectively. The radicals decayed by self-disproportionation with a second-order rate constant at room temperature of approximately 3.2 × 10⁹M^?1s^?1. The activation energy of the decay process is found to be about 2.4 ± 0.4 kcal/mole.     

Development and parametrization of sindo1 for second-row elements

The semiempirical MO method SINDO 1 is extended to second-row atoms from sodium to chlorine. The basis set has a provision to include d orbitals. To retain rotational invariance in a d orbital set, a number of hybrid integrals has to be included that invalidate the zero differential overlap (ZDO ) assumption even in a symmetrically orthogonalized basis set. The inclusion of d orbitals rendered the set-up of integral calculation of the original INDO method impractical. Instead of one subroutine for each integral, all explicitly calculated integrals (overlap, core, electronic repulsion) are now contained in a single subroutine under unifying aspects. The parametrization scheme includes pseudopotentials and adjusts the total energy under inclusion of zero point energies to experimental heats of formation of ground states. The vibrational frequencies for the calculation of zero point energies are obtained from calculated force constants and G matrix elements by a scaling procedure. The results for geometries, energies, and dipole moments are compared with MNDO data.     

Intermediate neglect of differential overlap spectroscopic studies on lanthanide complexes

Summary The Intermediate Nelgect of Differential Overlap model for spectroscopy has been extended to lanthanide complexes by including spin-orbit coupling. The method uses atomic spectroscopy and model Dirac-Fock calculations on the lanthanide atoms and ions to obtain ionization potentials, Slater-Condon factors and basis sets. The spin-orbit interaction strength, (nl), is acquired from atomic spectroscopy, and only one-center terms are formally included. Calculation then proceeds using one open-shell operator for all sevenf-orbitals initially assumed degenerate to generate starting non-relativistic molecular orbitals for the subsequent configuration-interaction and spin-orbit calculation.Calculations are performed on the monoxides La, Ce, Gd, and Lu where there are ample experimental assignments. In general, the results are quite good, suggesting that the calculated energies, oscillator strengths and spin-orbit splittings can be used with success in assigning spectra, even in those cases wherejj-coupling is of intermediate strength.     

Substituent Effects on 31P and 13C Chemical Shifts of Substituted Diphenyl 1-anilino-1-arylmethanephosphonates and Their Anions

Abstract

For a series of 31 novel diphenyl 1-anilino-1-arylmethanephosphonates, substituted in the meta and para position of the anilino and/or the aryl ring, ³¹P chemical shifts show good linear correlation with Taft's [sgrave]° parameters, the ³¹P nucleus appearing better shielded in the case of electron-withdrawing substituents. This inverse relationship is due to a field effect of the substituent dipole which polarizes π-electron clouds in the molecule, resulting in a higher P=O double bond order, and thence better ³¹P shielding. A corresponding shift of π-electron density is likewise observed for the ¹³C resonances of the two diastereotopic phenoxy and the anilino or aryl rings, respectively, where-M ands-I substituents cause a downfield shift of para and meta, and an upfield shift of ortho and ipso carbon resonances.     

Effect of the e2u near degeneracy on the initialization of indo spin density calculations in symmetrically ortho disubstituted benzenes

Erroneous results in earlier INDO spin density calculations for hydroaromatic radicals containing ortho disubstituted benzene rings are shown to be due to the wrong order of the e_2u near degenerate π molecular orbitals of the benzene ring after the extended Hückel initialization. Agreement with experiment is obtained by interchanging these orbitals.     

Molecular orbital calculations on transition metal complexes : XIX. π-cyclopentadienyl-π-cyclopropenylnickel

INDO SCF molecular orbital calculations for π-cyclopentadienyl-π-cyclopropenylnickel indicate a formally d¹⁰ configuration for the metal. Calculations of the ionisation energies show that electron loss should take place first from the occupied closely grouped set of dominantly d-orbitals, and then from a mainly π-cyclopentadienyl e orbital, this being the highest occupied ligand level. This latter level shows however only a slight mixing with the metal d-orbitals, resulting in a small ligand→metal electron donation; the dominant interaction is that between the higher lying π-cyclopropenyl e level and the metal 3d_xz and 3d_yz orbitals which leads to a substantial metal→ligand charge donation. The behaviour of the π-cyclopropenyl ligand is discussed using the calculated charge distributions.     

Full configuration interaction for the benzyl radical

The electronic structure of the benzyl radical in its ground state has been computed using a model Hamiltonian due to Pariser–Parr with full configuration interaction as well as with different truncated configurational sets built on SCF open-shell orbitals. The correlation energy corresponding to this model was found to be equal to –0.929722 eV. With the singly excited configurations only 18% of this energy is taken into account. By extending the basis to include the doubly excited configurations one can account for 94% of the correlation energy. An analysis of the accuracy of the proton hyperfine splitting calculation caused by inaccurate computation of the wave function is given. If only singly and even doubly excited configurations are taken into account one cannot hope to obtain splittings with an accuracy of more than 0.5 g. Inclusion of triply excited configurations lowers this error by one order. In addition, the use of the simple McConnell relation may lead to an error in splitting calculations of no less than 1.5 g.     

A CNDO/INDO molecular orbital formalism for the elements H to Br. theory

A CNDO and INDO formalism is presented that can be used for any atom combination up to bromine under inclusion of the first transition metal series. The semiempirical parameters were chosen to reproduce results ofab initio calculations on metalorganic compounds. The calculational results are invariant to rotations of the coordinate system but not to a general transformation into other basis functions. The one-center Coulomb-expressions were selected in order to include intraatomic correlation contributions. Within the CNDO model this could be achieved by the scaled monopole termF ₀, while in the INDO framework the one-center Coulomb integrals are given as a sum of the monopole-contributionF ₀ and higher multipole contributions expressed as a linear combination of Slater-Condon parameters. The invariance problem in the case of local rotations within the INDO approximation was solved by considering the combination of one-center Coulomb and exchange integrals as a function ofl but independent ofm. The two-center electron-electron interaction terms were calculated via the Dewar-Sabelli, Ohno-Klopman relation. Penetration effects were treated according to Fischer and Kollmar. For the resonance integralH _v ^AB parameters are used which carry information related to the directed nature of the chemical bond by using optimized Klondyke functions. The core-core repulsion is constructed as a superposition of a soft potential function, describing polarization effects of the atomic cores, and a hard repulsion function, avoiding the collapse of the atomic cores with decreasing distance.     

Unrestricted Hartree-Fock spin density calculations with orthogonalized atomic orbitals on aza and nitroaromatic radical anions

The spin density distributions in some aza and nitroaromatic radical anions have been calculated using Löwdin's orthogonalized basis set of atomic orbitals in the Unrestricted Hartree-Fock method of Amos and Snyder. The present calculations lead to a satisfactory account of proton splittings in these radicals. Least squares analyses correlating the observed ¹⁴N splittings and the spin density results over completely localized nonorthogonal basis have been separately carried out for aza and nitroaromatic radical anions and the sigma-pi parameters thus obtained are discussed and compared with earlier estimates for these quantities. Unlike the earlier results, the present estimate of Q _NN ^N for aza and nitroaromatic radicals are not very much different from each other.     

The inclusion of a correlation function in the calculation of the ZFS of benzene

We calculated the one-center atomic integral of the spin—spin interaction with respect to Slater orbitals where we have included a two-electron correlation function that we used previously to calculate the hyperfine splitting of the 2³P state of He. The ZFS of the benzene molecule was calculated from this value of the one-center integral and by using the Mulliken approximation combined with a previously introduced approximation for extimating the other integrals. The calculation was performed for two different non-hexagonal configurations I and II, the results are D₁ = 0.132 cm^?1 and D_II = 0.143 cm^?1. The experimental value is D = 0.158 cm^?1.     

An analysis of the through-bond interaction using the localized molecular orbitals—II : Long-range proton hyperfine coupling in bridgehead alkyl radicals: bicyclo[1.1.1]pent-1-yl,bicyclo[2.1.1]hex-1-yl and bicyclo[2.2.1]hept-1-yl radicals

The INDO calculations were performed on three bridgehead alkyl radicals; bicyclo[1.1.1]pent-1-yl, bicyclo[2.1.1]hex-l-yl and bicyclo[2.2.1]hept-1-yl radicals. We have transformed the canonical molecular orbitals obtained by the INDO method into the localized molecular orbitals. With the use of the obtained localized molecular orbitals, the variation in the hyperfine coupling constant at the bridgehead proton in these radicals was pursued in terms of the through-bond (and/or the through-space) interaction according to the method by which we selectively can pick up a particular interaction between the specified localized molecular orbitals in a radical. As a result of this analysis, it was found that the hyperfine coupling constants in these radicals can be expressed by the summation of several terms; through-virtuals, through-space, through-bond, and some other coupling terms.     

Very-low-pressure pyrolysis of N-methyl aniline and N,N-dimethyl aniline. Enthalpy of formation of the anilino and N-methyl anilino radicals

The kinetics of the thermal unimolecular decompositions of N-methyl aniline and N,N-dimethyl aniline into anilino and N-methyl anilino radicals, respectively, have been studied under very low-pressure conditions. The enthalpies of formation of both radicals, ΔH°_f,298°K(Ph?H,g) = 55.1 and ΔH°_f,298°K(Ph?Me,g) = 53.2 kcal/mol, which have been derived from the experimental data, lead to BDE(PhNH-H) = 86.4 ± 2, BDE[PhN(Me)-H] = 84.9 ± 2 kcal/mol and to a value of 16.4 kcal/mol for the stabilization energy of the PhNH radical (relative to MeNH). These results are discussed in connection with earlier work. At high temperatures, the anilino radical loses HNC and forms the very stable cyclopentadienyl radical, a decomposition comparable to that of the phenoxy radical.     

Selective Ortho Chlorination of Phenols with n,n-Dichloro-t-Butylamine in Various Solvents

Chlorination of phenol with N,N-dichlororo-t-butylamine (DCB) in appropriate solvents affording o- and p-chlorophenols exhibits high ortho/para ratio up to >10. Solvents associate with phenolic OH group and interfere with the hydrogen bonding between phenol and DCB tend to decrease both rate of reaction and ortho/para ratio; e.g., <1.1 in acetonitrile. The reaction shows autocatalysis exerted by a product, t-butylamine, which would accelerate the reaction by abstracting a proton from the benzene site on which C1 of DCB attacks. Anhydrous sodium phenoxide is little chlorinated. These facts imply a transition state in which phenol and DCB is hydrogen-bonded for the ortho chlorination. This type of chlorination is applicable to the ortho chlorination of other phenols.     

Rotational invariance of INDO theories including d-orbitals into the basis set

It is proved that in general the INDO approximation to the full Roothaan theory does not lead to expressions which are invariant under a rotation of local atomic axes. However, when only s- and p-functions are used in the atomic basis set, the equations obtained are invariant due to the special properties of the p-functions. When d-orbitals are included into the basis set, rotational invariance is lost but can be restored if a supplementary approximation is introduced.     

A CNDO/INDO crystal orbital model for transition metal polymers of the 3d series—basis equations

The crystal orbital formalism in the tight-binding approximation is combined with a recently developed CNDO/INDO model for transition metal species of the 3d series in order to allow band structure calculations on the Hartree-Fock (HF) SCF level for one-dimensional (1D) chains with organometallic unit cells. The band structure approach based on the CNDO and INDO approximation can be used for any atom combination up to bromine under the inclusion of the 3d series. The matrix elements for the tight-binding Hamiltonian are derived for an improved CNDO and INDO framework. The total energy of the 1D chain is partitioned into one-center contributions and into two-center increments of the intracell and intercell type. Semiempirical band structure calculations on simple model systems are compared with available ab initio data of high quality.     

The very low-pressure pyrolysis of phenyl ethyl ether,phenyl allyl ether,and benzyl methyl ether and the enthalpy of formation of the phenoxy radical

A value of the enthalpy of formation of the phenoxy radical in the gas phase, ΔH°_,298K (?O·, g) = 11.4 ± 2.0 kcal/mol, has been obtained from the kinetic study of the unimolecular decompositions of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl ether

1 Trivial names for ethoxy benzene, 2-propenoxy (allyloxy) benzene, and α-methoxytoluene, respectively

at very low pressures. Bond fission, producing phenoxy or benzyl radicals, respectively, is the only mode of decomposition in each case. The present value leads to a bond dissociation energy BDE(?O—H) = 86.5 ± 2 kcal/mol,

2 1 kcal = 4.18674 kJ (absolute)

in good agreement with recent estimates made on the basis of competitive oxidation steps in the liquid phase. A comparison with bond dissociation energies of aliphatic alcohols, BDE(RO—H) = 104 kcal/mol, reveals that the stabilization energy of the phenoxy radical (17.5 kcal/mol) is considerably greater than the one observed for the isoelectronic benzyl radical (13.2 kcal/mol). Decomposition of phenoxy radicals into cyclopentadienyl radicals and CO has been observed at temperatures above 1000°K, and a mechanism for this reaction is proposed.     

Calculation of the exchange splitting of N and O 1s binding energies in NO

The splitting of the N and O 1s binding energies in NO due to ionization to either triplet or singlet states of the inner-hole-state ions is calculated from exchange integrals over the molecular orbitals from ground-state LCAO SCF MO wavefunctions in a double- basis. Calculated splittings (in eV) of 1.26 (N_1s ) and 0.77 (O_1s ) are in reasonable agreement with experimental values of 1.5 and 0.7, respectively, suggesting that such a ground state only model will be useful for core energy splittings in paramagnetic molecules.The Radiation Laboratory of the University of Notre Dame is operated under contract with the U.S. Atomic Energy Commision. This is A.E.C. Document No. COO-38-763.