THE LOWEST SINGLET AND TRIPLET-STATES OF O-BENZYNE - SPIN-COUPLED INTERPRETATION OF THE ELECTRONIC-STRUCTURE AT CAS SCF EQUILIBRIUM GEOMETRIES

TY - JOUR

T1 - THE LOWEST SINGLET AND TRIPLET-STATES OF O-BENZYNE - SPIN-COUPLED INTERPRETATION OF THE ELECTRONIC-STRUCTURE AT CAS SCF EQUILIBRIUM GEOMETRIES

AU - KARADAKOV, P B

AU - GERRATT, J

AU - RAOS, G

AU - COOPER, D L

AU - RAIMONDI, M

PY - 1993

Y1 - 1993

N2 - The electronic structure of the ($) over tilde X (1)A(1), and ($) over tilde a(3)B(2) states of o-benzyne is analyzed by means of spin-coupled (SC) wave functions involving eight active orbitals: two at the dehydro centers, in the plane of the ring, and six pi: orbitals, inherited from benzene. The equilibrium geometries of the two states, at which all calculations have been carried out result from separate full geometry optimizations employing '8 in 8' complete active space self-consistent field (CAS SCF) wave functions incorporating an analogous core-valence partitioning. The diradical character of the ground state of o-benzyne, as approximated by the singlet SC wave function, is reflected in the value of the overlap (0.46) between the two in-plane sp(2)-like SC orbitals at the dehydro centers, which are just 1.274 Angstrom apart, and in the nonnegligible extent of triplet coupling between the spins of the electrons in these orbitals - ca. 6.4% of the total spin function for the valence electrons (expressed in the Serber spin basis) is made up of spin eigenfunctions, in which these electrons enter as a triplet pair. The geometry of the ground state is found to have an aryne-like character, which is further confirmed by the pattern of alternation of the overlaps between neighboring pi valence orbitals, and by the domination of the total spin function for the valence electrons (expressed in the Rumer spin basis) by the spin-coupling patterns corresponding to an arynic structure.

AB - The electronic structure of the ($) over tilde X (1)A(1), and ($) over tilde a(3)B(2) states of o-benzyne is analyzed by means of spin-coupled (SC) wave functions involving eight active orbitals: two at the dehydro centers, in the plane of the ring, and six pi: orbitals, inherited from benzene. The equilibrium geometries of the two states, at which all calculations have been carried out result from separate full geometry optimizations employing '8 in 8' complete active space self-consistent field (CAS SCF) wave functions incorporating an analogous core-valence partitioning. The diradical character of the ground state of o-benzyne, as approximated by the singlet SC wave function, is reflected in the value of the overlap (0.46) between the two in-plane sp(2)-like SC orbitals at the dehydro centers, which are just 1.274 Angstrom apart, and in the nonnegligible extent of triplet coupling between the spins of the electrons in these orbitals - ca. 6.4% of the total spin function for the valence electrons (expressed in the Serber spin basis) is made up of spin eigenfunctions, in which these electrons enter as a triplet pair. The geometry of the ground state is found to have an aryne-like character, which is further confirmed by the pattern of alternation of the overlaps between neighboring pi valence orbitals, and by the domination of the total spin function for the valence electrons (expressed in the Rumer spin basis) by the spin-coupling patterns corresponding to an arynic structure.

KW - MOLECULES

KW - BOND

KW - ENERGIES

KW - BENZENE

M3 - Article

SN - 0021-2148

VL - 33

SP - 253

EP - 264

JO - Israel Journal of Chemistry

JF - Israel Journal of Chemistry

IS - 3

ER -