Equilibrium geometries and relative energies of the lowest singlet and triplet states of o-, m-, and p-benzyne

Journal Article · Wed Jan 03 00:00:00 EST 1979 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00495a009· OSTI ID:6377642

Noell, J O; Newton, M D

The lowest lying singlet and triplet states of each of the three isomers of benzyne have been examined at an ab initio level, using an extended basis (4-31G) of atomic orbitals. Singlet states were treated within the single-pair GVB formalism, which allowed correlation between the symmetric and antisymmetric combinations of the radical orbitals resulting from dehydrogenation of benzene. Limited geometry optimizations were performed for singlet and triplet states of the meta and para isomers. Each of the three isomers was found to have a singlet ground state, though for the para isomer this result is not conclusive. The total energy of the isomers was found to increase in the order ortho < meta < para. The equilibrium structures of the singlet meta and para isomers reflect appreciable diradical character, in sharp contrast to the aryne nature of the ortho isomer. Single-determinant RHF theory was found inadequate for the proper description of the benzynes, resulting in artificially enhanced stabilization of bicyclic structures. Results for the para isomer at the GVB level suggest that the bicyclic structure may correspond to a local minimum, but with energy far above that of the open equilibrium structure. Calculations were also performed for each of the isomers using for the carbon framework the equilibrium structure of the phenyl cation, from which they might be formed by appropriate base-induced deprotonation. The same energy ordering (ortho < meta < para) was found here, though the ortho--meta splitting was considerably reduced.

• Research Organization: Brookhaven National Lab., Upton, NY
• OSTI ID: 6377642
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 101:1
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BENZENE
DEHYDROGENATION
HYDROCARBONS
STRUCTURAL CHEMICAL ANALYSIS
ATOMIC MODELS
COMPARATIVE EVALUATIONS
CONFIGURATION INTERACTION
ELECTRONIC STRUCTURE
ENERGY LEVELS
GROUND STATES
ISOMERS
MOLECULES
AROMATICS
CHEMICAL REACTIONS
MATHEMATICAL MODELS
ORGANIC COMPOUNDS
400301* - Organic Chemistry- Chemical &amp; Physicochemical Properties- (-1987)