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  • Assignment of electronic transitions  (2)
  • Theoretical, Physical and Computational Chemistry  (2)
  • 1
    ISSN: 0020-7608
    Keywords: hybridization displacement charge ; transferability of properties ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular electrostatic potential (MEP) maps and MEP-derived charges for certain molecules were studied by the ab initio approach using the 6-31G basis set. These results were used to obtain the parameters (K and ζ) for fluorine, sulfur, and chlorine required for the hybridization displacement charge (HDC) calculations employing the MNDO and AMI methods. The HDC combined with Löwdin charges, distributed continuously in three-dimension spherically and symmetrically, were shown to reproduce ab initio MEP features of molecules fairly well. This method of computing the MEP was applied to two molecules of pharmacological importance, namely, dimaprit and mustard gas. It is shown by studying the cis and trans forms of two amino acids that transferability of the MEP is appreciably less acceptable than that of charges in going from one conformation to the other.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 149-156, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 61 (1982), S. 559-579 
    ISSN: 1432-2234
    Keywords: Assignment of electronic transitions ; Excited state geometry optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Adiabatic excitation energies, excited state geometries, excited state charges, bond orders and dipole moments have been obtained for HCN, CO2,H2CO, HFCO, F2CO, ethylene, trans-butadiene, furan, pyrrole and uracil using the SINDO1 semi-empirical method with configuration interaction. Our results generally agree with those ofab initio calculations and experiment satisfactorily. Geometry optimization is found to mix configurations differing in their allowedness in vertical excitation from the ground state, which in turn helps in the assignment of spectral transitions. TheV excited singlet state of trans-butadiene and various excited states of furan, pyrrole and uracil have been found to be appreciably non-planar. The single and double CC bonds are found to exchange positions due to the lowest triplet and singlet transitions of furan and pyrrole. The first triplet and first singlet transitions of uracil have been found to be of π-π* and π-σ* types respectively in agreement with recent experimental findings.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 61 (1982), S. 559-579 
    ISSN: 1432-2234
    Keywords: Assignment of electronic transitions ; Excited state geometry optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Adiabatic excitation energies, excited state geometries, excited state charges, bond orders and dipole moments have been obtained for HCN, CO2,H2CO, HFCO, F2CO, ethylene, trans-butadiene, furan, pyrrole and uracil using the SINDO1 semi-empirical method with configuration interaction. Our results generally agree with those ofab initio calculations and experiment satisfactorily. Geometry optimization is found to mix configurations differing in their allowedness in vertical excitation from the ground state, which in turn helps in the assignment of spectral transitions. TheV excited singlet state of trans-butadiene and various excited states of furan, pyrrole and uracil have been found to be appreciably non-planar. The single and double CC bonds are found to exchange positions due to the lowest triplet and singlet transitions of furan and pyrrole. The first triplet and first singlet transitions of uracil have been found to be of π-π* and π-σ* types respectively in agreement with recent experimental findings.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0020-7608
    Keywords: hydrogen bonding ; DNA ; base analogs ; stacking interaction ; reaction field ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a recent experimental study, it was reported that replacement of thymine in the adenine-thymine base pair of DNA by its molecular analogs which cannot form proper hydrogen bonds with adenine (A) does not cause disruption of DNA structure and synthesis. AM1 and ab initio molecular orbital calculations and electric field mapping were carried out in order to examine the possibility of pairing of A with each one of two analogs of thymine in the gas phase. Self-consistent reaction field calculations were also carried out on the individual molecules and their pairs using the polarized continuum model in order to examine their stability in aqueous media. Our results are broadly in agreement with the conclusions drawn in the above-mentioned experimental work.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 351-355, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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