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  • 1
    ISSN: 1572-8854
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electric-field maps of certain anions and cations of adenine and guanine have been studied. The results are compared with those of neutral adenine and guanine. In all cases, the geometries were fully optimized using the MNDO molecular orbital method and the fields were computed using Mulliken charges. Reactivities and hydrogen-bonding pattern predicted by electric fields, including those of cations, are in satisfactory agreement with experiment. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular orbital geometry optimization study of the potential surface of guanine, guanine—O2, and guanine—O2—water reaction products in the ground state has been carried out. The origin of the asymmetric double-well potential surface of guanine suggested earlier on the basis of experimental observations has been explained. The most stable binding of O2 with guanine (G) is found to occur at the C4C5 double bond of the latter molecule. In the case of G—O2—water reaction product (HOO—G—OH), the groups —OOH and —OH bind at C4 and C8, respectively. The possiblity of a polymeric reaction product of the type R1—(G—O—O—G)n—R2 (R1, R2 = H, OH) has also been suggested. These results are broadly supported by experimental observations. The mechanism of spectral oscillations observed in UV-irradiated guanine solutions has been discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrostatic potential and electric field maps of some suosan series of sweeteners have been studied. Geometries optimized using the MNDO molecular orbital method and charge distributions obtained by the Mulliken population analysis were employed in the calculations. Sweetness potencies of the molecules were compared with electrostatic potentials and electric field strengths near the terminal COOH group. The observed sweetness potencies of the compounds and calculated electric fields near the carbonyl oxygen of the COOH group are found to be strongly correlated. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 225-229 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Changes of electronic charge distribution following the lowest singlet n-π* transitions of benzaldehyde, benzamide, benzoic acid, the phthalaldehydes, pyridine, and the diazines have been examined using the CNDO-S/CI method. A Singlet n-π* transition is found as a general rule to direct electronic charges to the para position of the atom in the ring that carries the lone pair or to which the substituent carrying the lone pair is attached.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: VE-PPP, CNDO/2, and CNDO/s-CI methods have been used to investigate the electronic spectrum and structure of benzaldehyde. Electronic charge distributions and bond orders in the ground and lowest excited singlet π* ← π and π* ← n states of the molecule have been studied. The molecule has been shown to be nonplanar in the lowest π* ← n excited singlet state, in agreement with the conclusions drawn from the study of vibrational spectra. Dipole moments in both excited states have been shown to be larger than the ground-state value. Thus, the ambiguity in the experimental result for the π* ← π n excited singlet state dipole moment has been resolved. It has been shown that the n orbital is mainly localized on the CHO group. Furthermore, charge distributions, dipole moments, and molecular geometries are shown to be very different in the excited singlet π* ← π and π* ← n states.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
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  • 9
    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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  • 10
    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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