Ab initio quantum mechanical characterization of the ground electronic state of uracil

Journal Article · Thu Feb 09 04:00:00 EST 1978 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100492a021· OSTI ID:5045847

O'Donnell, T J ^[1]; LeBreton, P R; Shipman, L L

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1. Univ. of Illinois, Chicago

The ground electronic state of uracil was characterized by the ab initio molecular fragment floating spherical Gaussian orbital method. Among the properties studied were ionization potentials, permanent diople moment, the electronic charge distributions of the higher occupied and lowest unoccupied molecular orbitals, the populations and bond orders which describe the total ..pi..-electronic charge distribution, and the dipole binding energies of the three hydrogen bonding sites of uracil that are available for base pairing in RNA. A linear relation was found between the calculated orbital energies and the one-electron ionization potentials measured by uv photoelectron spectroscopy. At the x-ray crystallographic geometry, the permanent dipole moment was calculated to have a length of 2.27 D and to form an angle of 27/sup 0/ with the C/sub 4/ ..-->.. N/sub 1/ direction. When the unusually short C-H and N-H bonds in the x-ray structure of uracil were lengthened to 1.10 and 1.00 A, respectively, the calculated dipole moment changed to 3.55 D and formed an angle of 38/sup 0/ with the C/sub 4/ ..-->.. N/sub 1/ direction. The lowest unoccupied molecular orbital is a ..pi..-antibonding molecular orbital while the highest occupied molecular orbital is ..pi.. nonbonding. The lowest unoccupied molecular orbital has a very high virtual electron density at the C/sub 6/ atom and there are nodes between the C/sub 6/ atom and the N/sub 1/ and C/sub 5/ atoms; these two factors combine to make the C/sub 6/ atom highly susceptible to ''focused'' nucleophilic attack. No single resonance structure can adequately represent the total ..pi..-electron charge distribution which has a net bond order of approximately 4.4 ..pi.. bonds. The oxygen atom attached to position 4 of the ring is a better hydrogen bonding site than the oxygen attached to position 2.

• OSTI ID: 5045847
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 82:3; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
AZINES
ELECTRONIC STRUCTURE
ENERGY LEVELS
GROUND STATES
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
MECHANICS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIMIDINES
QUANTUM MECHANICS
URACILS