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  • 1
    Electronic Resource
    Electronic Resource
    The out,out to out,in transition for 1,(n+2)-diazabicyclo[n.3.1]alkanes (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 6580-6591 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00068a015
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  • 2
    Electronic Resource
    Electronic Resource
    The PE spectrum of [1.1.1]propellane: evidence for a non-bonding MO? (1985)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 107 (1985), S. 7172-7174 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00310a068
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  • 3
    Electronic Resource
    Electronic Resource
    Intramolecular vibrations of small water clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 2582-2595 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structures, binding energies, and vibrational frequencies of fully optimized water clusters (H2O)n, n=1– 4, were computed with ab initio molecular orbital theory at the SCF level using different basis sets. The SCF procedure allows satisfactory predictions for these properties compared with experimental results. For quantitative predictions of binding energies and geometrical parameters, a basis set including polarization functions is needed. With respect to intramolecular vibrational frequencies and frequency shifts, however, the split valence basis set 4-31G leads in all cases to the best rationalization of the available experimental data. Analysis of intramolecular force constants, frequencies, and eigenvectors for n=2 to 4 shows that (i) a transition from highly localized (n=2) to highly delocalized (n=4) vibrational modes takes place; (ii) the delocalized O–H vibrations of cyclic (H2O)n clusters (n≥3) can be described as longitudinal/transverse optical phonons; (iii) internal force constants for the hydrogen bonding O–H stretch, k(O–Hb), decrease strongly with size, leading to a decrease in the νbridge O–H frequencies; a similar decrease is found for the intramolecular bending force constant k(aitch-theta); (iv) force constants for the free O–H stretching motions k(O–Hf) stay nearly constant, as do the corresponding vibrational frequencies; (v) intermolecular stretch–stretch couplings increase substantially with n and dominate over intramolecular stretch–stretch couplings for n≥3; similarly, intermolecular bend–libration couplings are very important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454038
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  • 4
    Electronic Resource
    Electronic Resource
    Intermolecular bonding and vibrations of the carbazole⋅B complexes (B=H2O, D2O, NH3) (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1234-1246 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Carbazole⋅B complexes (B=H2O, D2O, NH3) were synthesized and cooled in pulsed supersonic nozzle beams. The intermolecular hydrogen-bond vibrations and dissociation energies were studied by several laser-spectroscopic techniques (fluorescence excitation and emission, resonance-two-photonionization with mass-specific detection). The following results were obtained for both S0 and S1 electronic states: (1) determination of the structural symmetry of the complexes, (2) measurement of the intermolecular stretching (νσ) and bending (νβ) frequencies, (3) determination of stretching force constants, (4) hydrogen-bond dissociation energies D0 for carbazole⋅H2O/D2O, and (5) electronic spectral shifts δν˜ relative to the bare carbazole molecule. The latter are large (500–710 cm−1) and reflect an increase of the hydrogen-bond energy by (approximate)40% upon electronic excitation. Fermi resonance couplings between the intermolecular νσ and an intramolecular b1 vibration of carbazole are observed and partially analyzed. To complement the experimental work, extensive ab initio quantum chemical calculations of the same complexes were performed at the Hartree–Fock level. The calculated complex structures are consistent with the experimental information. Intermolecular potential-energy curves for the stretching vibrational coordinate were calculated for a number of increasingly flexible basis sets (STO-3G, 4-31G, 6-31G, 4-31G*); anharmonic vibrational frequencies were then obtained numerically. Excellent agreement with the experimental intermolecular stretching frequencies was found for all three complexes using the 4-31G* basis set. Good agreement with experiment was also found for the calculated 4-31G* hydrogen-bond dissociation energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451261
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  • 5
    Electronic Resource
    Electronic Resource
    Systematic regularities of molecular SCF energies (1988)
    Springer
    Theoretical chemistry accounts 73 (1988), S. 317-322 
    Details
    ISSN: 1432-2234
    Keywords: Ab initio calculations ; Total molecular energies ; Energy components ; New simple heuristic relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract New formulae for the approximate computation of total molecular energies are developed based on ab initio calculations of n-alkanes. Their application to various kinds of molecules reveals that good expectation values for total molecular energies can be obtained by considering only the one-electron terms h i and the nuclear repulsion energy. It is further shown that very good agreement with SCF total energies is obtained by a relationship which connects the total energy with the sum of inner-shell (core) orbital energies. The results turn out to be better than those obtained using Ruedenberg's approximation, which takes both inner-shell and valence-shell orbital energies into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00527418
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  • 6
    Electronic Resource
    Electronic Resource
    Photoelectron Spectra of Symmetrical 1,4-Dihalonorbornanes (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 2927-2939 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Photoelektronenspektren symmetrischer 1,4-DihalonorbornaneDie He(Iα)-Photoelektronenspektren von 1,4-Dihalonorbornanen (2-4) und 1-Bromnorbornan (5) wurden gemessen. Die Zuordnung basiert auf Ergebnissen eines kürzlich vorgeschlagenen Modells äquivalenter Bindungsorbitale, das auf Halogenatome erweitert wurde und die Spin-Bahn-Kopplung berücksichtigt.
    Notes: The He(Iα) photoelectron spectra of 1,4-dihalonorbornanes (2-4) and of 1-bromonorbornane (5) have been recorded. Their assignment is based on results derived from recently proposed equivalent bond orbital treatment which has now been adapted to include halogen atoms and to account for spin-orbit coupling.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851180729
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  • 7
    Electronic Resource
    Electronic Resource
    Photoelectron-Spectroscopic Characterization of 3,4-Dimethyl-2,4-hexadienes (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 640-653 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The He(Ia) photoelectron (PE) spectra of the (E,E)-, (E,Z)- and (Z,Z)-isomers of the title compound have been recorded to obtain information about their conformation in the gas phase. For a valid correlation with the PE data of other dienes it is necessary to take the potentials V(ϕ) for internal rotation and the corresponding conformer population densities P (ϕ) into account, as well as the rather complicated way wy in which the π-1 ionization energy gap ΔI(ϕ) depends on the direct π-orbital interaction and the long-range ‘through-space’ interaction between the semi-localized methyl-group orbitals and the π-orbitals. These factors being taken into account, the mean twist angles, ϕ, compatible with the PE-spectroscopic results are ϕ (E,E) ≍ O° ± 30°, ϕ (E,Z) ≍ 80° or 110° within ± 15°, and ϕ (Z,Z) ≍ 85° to 105°. These results are in rough agreement with electron diffraction data by Traetteberg [15], other spectroscopic results and, for the (E, E)- and (Z,Z)-isomers, internal rotation potentials V(ϕ) previously calculated by Roth [17]. On the other hand the potential V (ϕ) proposed for the (E,Z)-isomer does not seem to be compatible with our findings.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670303
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  • 8
    Electronic Resource
    Electronic Resource
    Interactions between Oxygen Lone-Pair Orbitals and Double-Bond π-Orbitals in β,γ-Unsaturated, Bicyclic Ketones; a PE-Spectroscopic Investigation (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 1540-1550 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The HE(Iα) photoelectron (PE) spectra of 2,3,5,6-tetramethylidene-2-bicyclo[2.2.1]heptanone (12), 5,6-dimethylidene-2-bicyclo[2.2.1]heptanone (14), 5,6-dimethylidene-2-bicyclo[2.2.2]octanone (16), and 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone (17) have been recorded, Comparison with the PE data of other β,γ-unsaturated ketones and parent alkenes, and with the result of ab initio STO-3G calculations, confirm the existence of significant interactions between the oxygen lone-pair orbital no and the double-bond π orbital(s). It is argued that the major contributions to the basis energy shifts and to the cross term between the no and π orbitals are due to a ‘through-bond’ mechanism.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700612
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  • 9
    Electronic Resource
    Electronic Resource
    The Persistence of Ribbon Orbitals in Polycyclic AlkanesPart II of ‘The Equivalent Bond Orbital Model Revisited’. Part I. cf. [1]. (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1681-1690 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equivalent bond orbital (EBO) calculations by a procedure based on recalibrated, localized bond orbitals derived from an ab initio model, suggest that the two frontier ‘ribbon’ orbitals ϕHOMO, ϕHOMO-1 of polycyclic hydrocarbons consisting of all-trans-connected six-membered rings are well separated in energy from the remaining manifold of σ-orbitals. Assuming the validity of Koopmans' theorem, a PE-spectroscopic investigation of perhydroanthracenes, 2-methylperhydrophenalene and perhydroperylene have shown that this is indeed the case. According to the theoretical treatment these ribbon orbitals are evenly delocalized over the whole of the molecular frame and they conserve the characteristic phase relationship postulated by Hoffmann et al. [16] for cyclohexane moieties. Their behaviour under the successive introduction of centres of unsaturation, i.e., of double bonds is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670703
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  • 10
    Electronic Resource
    Electronic Resource
    ‘Lone Pair’ and ‘CI Bond’ Ionization Energies of exo- and endo-2-Norbornyl Iodides (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1691-1697 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A PE-spectroscopic study of exo- and endo-2-norbornyl iodides suggests that the relative ability of the 2-norbornyl group to stabilize an electron deficiency on a substituent X (e.g. I) in exo- or endo-position depends on the location of the positive charge. There is no difference if the positive hole is strongly localized on on the substituent X (e.g. the 5p-1 state of the title compounds). On the other hand, our results indicate that teh positive hole semi-localized in an exo-C—X bond is better stabilized by the 2-norbornyl group than a semi-localized, positive hole in an endo-C—X bond.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670704
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