title: Isoelectronic homologues and isomers: tropolone, 5-azatropolone, 1-H-azepine-4,5-dione, saddle points, and ions.
abstract: Computational studies of 12 64-electron homologues and isomers of tropolone in the S(0) electronic ground state are reported. Three minimum-energy structures, tropolone (Tp), 5-azatropolone (5Azt), and 5-H-5-azatropolonium (5AztH(+)), have an internal H-bond and planar C(s)) geometry, and three, tropolonate (TpO(-)), 5-azatropolonate (5AzO(-)), and 1-H-azepine-4,5-dione (45Di), lack the H-bond and have twisted C(2) geometry. All 6 substances have an equal double-minimum potential energy surface and a saddle point with planar C(2)(v) geometry. The energy for the gas-phase isomerization reaction 45Di --> 5Azt is near +4 kJ mol(-1) at the MP4(SDQ)/6-311++G(df,pd)//MP2/6-311++G(df,pd) (energy//geometry) theoretical level and around -20 kJ mol(-1) at lower theoretical levels. The dipole moments computed for 45Di and 5Azt are 9.6 and 2.1 D, respectively, and this large difference contributes to MO-computed free energies of solvation that strongly favor--as experimentally observed--45Di over 5Azt in chloroform solvent. The MO-computed energy for the gas-phase protonation reaction 45Di + H(+) --> 5AztH(+) is -956.4 kJ mol(-1), leading to 926.8 kJ mol(-1) as the estimated proton affinity for 45Di at 298 K and 1 atm. The intramolecular dynamical properties predicted for 5Azt and 5AztH(+) parallel those observed for tropolone. They are therefore expected to exhibit spectral tunneling doublets. Once they are synthesized, they should contribute importantly to the understanding of multidimensional intramolecular H transfer and dynamical coupling processes.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, USA.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Redington
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D001381:Azepines / Q000737:chemistry*; D003198:Computer Simulation; D005740:Gases; D007477:Ions; D007536:Isomerism; D015394:Molecular Structure; D011789:Quantum Theory; D013057:Spectrum Analysis; D013816:Thermodynamics; D014334:Tropolone / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: C521896:1-H-azepine-4,5-dione; C521895:5-azatropolone; D001372:Aza Compounds; D001381:Azepines; D005740:Gases; D007477:Ions; D014334:Tropolone