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  • 1
    Electronic Resource
    Electronic Resource
    Electronic States of Phenylene and Naphthylene Bicyclobutanes. Linear Dichroism in Stretched Polyethylene (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 676-686 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Excited singlet states of bicyclobutylene-benzene (2), 1,2:4,5-bis (bicyclo-butylene)benzene (3), 2,3-bicyclobutylene-naphthalene (4), and 1,8-bicyclobutylene-naphthalene (5) are investigated by means of linear dichroic absorption spectroscopy of molecules oriented in stretched polyethylene films and by semiempirical model calculations. The results indicate a strong hyperconjugative impact of the bicyclobutylene group on the aromatic chromophores in these compounds. Valence isomerization to aromatic products is predicted as the preferred photochemical pathway.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660231
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  • 2
    Electronic Resource
    Electronic Resource
    On Excited States of Alkyl Bridged [14] Annulenes (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 2999-3013 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The linear dichroic absorption spectrum of 1,3,6,8-trans-15, 16-hexamethyl-dihydropyrene has been measured in stretched polyethylene at 77K, and CNDO-CI calculations with inclusion of singly and doubly excited configurations have been carried out on a series of alkyl bridged [14] annulenes with pyrene- and anthracene-shaped perimeters. Transitions to e3g → e4u type 1B states are well described, and the results indicate that additional low-energy excited states originate from e3g→ e5g and e2u → e4u type configurations interacting strongly with doubly excited configurations of the e3g, e3g → e4u, e4u type. The second excited singlet state responsible for the weak transition observed between the 1L bands may be assigned to one of these additional states, but it is probably of complex nature, similar to the ‘phantom’ state in linear polyenes.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610825
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic and Molecular Structure of Simple 3,3′-Bicyclopropenyls. Photoelectron Spectroscopy and Model Calculations (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 968-982 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic and molecular structure of 3,3′-bicyclopropenyl (1) and its alkyl derivatives 3,3′-dirnethyl-3,3′-bicyclopropenyl (2), dispiro [2.0.2.3]nona-1,5-diene (3), dispiro[2.0.2.4]deca-1,5-diene (4), dispiro [2.0.2.5]undeca-1, 5-diene (5), and dispiro [2.0.2.6]dodeca-1, 5-diene (6) are studied by means of photoelectron spectroscopy and model calculations. Through-bond' effects in model compound 1 are analyzed in detail, illustrating a general difficulty with NDO models. Low-energy photoelectron bands of 2-6 can be assigned to ejection of electrons from cyclo-propenyl π- and Walsh-orbitals. Strong ‘through-bond’ coupling leads to splitting of the π-bands in the range 1.0-1.5 eV, while the strongly conformation-dependent splitting of the Walsh-bands allows conclusions concerning the preferred torsional angles. The preference of a gauche-conformation is predicted for 2 in the gas phase.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650329
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  • 4
    Electronic Resource
    Electronic Resource
    The Electronic Structure of Phenylene and Naphthylene Bicyclobutanes. Photoelectron spectroscopy and model calculations (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 1312-1321 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photoelectron (PE.) spectra of 1,2,3-methenoindane (2), 1,2,3-metheno-2,3-dihydro-1H-cyclopenta [b]naphthalene (3) and 1,2,3-metheno-2,3-dihydro-1H-phenalene (4) are investigated. The PE. spectrum of 1,3-methano-2,3-dihydrophenalene (7) is reported and compared with that of 4. The experimental results are analyzed in terms of empirical correlation diagrams and the results of semiempirical MINDO/3 and CNDO/S calculations. The analysis indicates that the strong impact of the bicyclobutylene group on the spectroscopic properties of the aromatic π-systems in 2, 3 and 4 is due to hyperconjugative interactions involving bicyclobutane Walsh orbitals.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640508
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  • 5
    Electronic Resource
    Electronic Resource
    Conjugative, Exciton and Charge-Resonance Interactions in D2d-9,9′-Spirobifluorene and D2d-Tetrabenzotricyclo [5.5.0.02,8]dodeca-3,5,9,11-tetraene. Photoelectron and Polarized Absorption Spectra (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 1441-1455 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photoelectron spectroscopy, polarized electronic absorption spectroscopy in stretched polymer sheets, and semiempirical theoretical methods have been applied to investigate the valence electronic structures of the two title compounds 1 and 2, considering fluorene (3) as a reference compound. The results are analyzed in terms of ‘through space’ and ‘through bond’ conjugative effects and exciton and charge-resonance interactions. Spiro-conjugation in 1 is found to play a similar role as ‘through bond’ interaction via the cyclobutane ring in 2. In contrast to the results of a recent investigation, exciton coupling is found to be relatively insignificant, while charge-resonance effects are important. The transition close to 41 000 cm-1 in the absorption spectra of 1 and 2 has no obvious counterpart in the spectrum of 3; it is assigned to a 1E- state with large charge-resonance character, involving promotion of an electron from the HOMO of one half-chromophore to the LUMO of the other.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660513
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  • 6
    Electronic Resource
    Electronic Resource
    Structure-reactivity correlations for aza-arenes. Proton affinities, pKa values, hydrogen-deuterium exchange rates and radical-induced 13C shifts (1995)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 496-505 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular reactivity parameters based on the concept of an effective electronic potential and defined as a simple function of the molecular charge distribution were applied in a study of various aspects of the chemical reactivity of azabenzenes and azanaphthalenes. Excellent linear correlations were obtained for proton affinities, pKa values, H-D exchange rate exponents and 13C shifts induced by the paramagnetic shift reagent TEMPO. In the last case, the predictions for quinazoline prompted a reinvestigation of the 13C NMR spectrum of this compound, resulting in a reassignment of the spectrum relative to the assignment assumed by Grant and co-workers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610080709
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  • 7
    Electronic Resource
    Electronic Resource
    The Electronic Structure of Azuleno[1,2,3-cd]phenalene and Azuleno[5,6,7-cd]phenalene, a Comparison (1976)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 59 (1976), S. 1459-1468 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photoelectron (PE.) spectra of azuleno[l, 2, 3-cd]phenalene (1) and azuleno- [5,6,7-cd]phenalene(2) have been recorded. The first five bands of both compounds could be assigned to transitions corresponding to removal of electrons from 4a2, 6b1, 5b1, 3a2 and 4bl orbitals. This assignment is based mainly on a comparison between the observed ionization potentials and orbital energies calculated in a HMO and a PPP model.The UV./VIS. polarized absorption spectrum of 1 in the region 10000-45000 cm-1 has been measured by means of the stretched film technique. The measurements were performed in polyethylene sheets at 77°K. Several bands could be assigned to π* ← π transitions calculated by a PPP-CI method.A comparison between the electronic structures of 1 and2 is made by means of a simple HMO diagram.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19760590507
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    Paper (German National Licenses)
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