Tracy P. Hamilton

Infrared absorption of cis‐ and trans‐alkali‐metal peroxynitrites (MOONO, M=Li, Na, and K) in solid argon

Potassium nitrate (KNO3) isolated in solid argon at 13 K was irradiated with emission from an ArF excimer laser at 193 nm. Recombination of the photofragments led to formation of both cis‐ and trans‐potassium peroxynitrites (KOONO). The cyclic conformer, cis‐KOONO, absorbs at 1444.5, 952.3, 831.6, and 749.1 cm−1, whereas trans‐KOONO absorbs at 1528.4, 987.4, and 602.2 cm−1. The assignments are based on observed 18O‐ and 15N‐isotopic shifts and comparison with similar compounds, cis–cis and trans–perp HOONO. Ab initio calculations using density functional theory at a Becke3LYP level predicted similar line positions and isotopic shifts for both conformers. Photoconversion among these three isomers was achieved at various wavelengths and periods of irradiation; cis‐KOONO was photolyzed readily at 308 nm, whereas trans‐KOONO increased slightly in intensity initially and was eventually transformed to KNO3 on prolonged irradiation. Similar results were obtained for LiNO3 and NaNO3; cis‐LiOONO and cis‐NaOONO absorb at (1423.4, 1422.0), 966.2, 874.2, 792.3 cm−1 and (1437.4, 1434.6), 961.4, 840.7, (770.9, 768.7) cm−1, respectively, whereas trans‐LiOONO and trans‐NaOONO absorb at (1581.6, 1580.4), (998.3, 995.6), 600.4 cm−1 and (1549.3, 1540.6), (996.3, 994.1), (609.4, 607.4) cm−1, respectively; the numbers in parentheses are due to line splitting.

Ab initio predictions of the lowest electronic states, structures vibrational frequencies of phenylphosphinidene

Abstract The singlet-triplet energy splitting of phenylphosphinidene is predicted to be −21 kcal/mol at the Davidson corrected TC-CISD/6-31G∗ / /CISD/6-31G∗ level of theory. The ΔEs-t of phenylphosphinidene is the same as that of phenylnitrene, which also has a triplet ground state. The open-shell singlet and closed shell singlet states reverse their order when the group 15 elements is changed from N to P. Comparisons between NR and PR (R H, methyl and phenyl) show that the phenyl group strongly stabilizes the S0 state of phenylnitrene whereas there is no significant change in ΔEs-t for phenylphosphinidene. Methyl substitution leaves Δs-t unchanged for both nitrene and phosphinidene.

Ab initio studies of peroxynitrite anion-water complexes

Quantum mechanical methods have been applied to thecis-ONOO−-H2O,cis-ONOO−-(H2O)2 andtrans- ONOO−-H2O complexes. Equilibrium geometries, binding energies, net atomic charges and vibrational frequencies are presented for several different arrangements. The MØller-Plessett second-order perturbation (MP2) method predicted shorter hydrogen bonds than the SCF method, but the computed Hartree-Fock (HF) binding energies are similar to counterpoise corrected MP2 values. The geometry changes of ONOO− and water after solvation are examined. The ONOO− and H2O bond length changes follow typical hydrogen bond structural trends, whereas bond angles in ONOO− are unaffected when the hydrogen bond is formed, similar to the conclusions from NO2−-(H2O)n HF/6-31G studies and Monte Carlo simulations. Thecis-ONOO−-(H2O)n frequencies are compared with the solution Raman spectrum and with calculations on isolated ONOO−.

A theoretical study of B2Li6

Abstract Structures and energetics of B 2 Li 6 are predicted at HF, MP2 and B3LYP/6-31G(d) including energy evaluations at G2MP2, CBS-Q, and B3LYP/6-311G(2d). Six minima are identified on the singlet surface. The cohesive (B 2 Li 6 →B 2 +Li 6 ) and Li 2 elimination energies indicate significant stability for the global minimum 3a , which is a B 2 unit with two bridging Li ligands and a bridging tetrahedral Li 4 unit. Sandwich structure 3d , containing two triangular Li 3 units and relating to a C 2 Li 6 isomer is 6.9 kcal/mol less stable. Diborane[6]-like structure 3g is not a minimum.

Structural studies on conformationally defined 6-s-trans UAB retinoids

The calculated structures of ten conformationally defined 6-s-trans retinoids are reported here. These compounds are precursors and intermediates in the synthesis of biologically active derivatives of retinoic acid. Of particular interest are the ring geometries in these compounds because of their importance in the interaction of the derivatives with the binding site of the receptors. The ring conformation in these compounds depends primarily on two specific sites of steric interaction.

HP−4: the monoconjugate base from tetraphosphabicyclobutane. Evidence for an exo ground state conformation in the gas phase

Abstract Ab initio theoretical studies reconsider recent experimental findings concerning the ground state conformation of the HP − 4 anion. Basis sets as large as triple zeta plus double polarization plus f functions plus diffuse functions (TZ2Pf + diffuse) were used in connection with methods that explicitly include the effects of electron correlation. At the highest level of theory, the exo structure is predicted to lie about two kcal/mol below the endo structure, in apparent disagreement with experiment. The Li + HP − 4 system has also been examined to approximate more closely the system synthesized in the laboratory. The energetics are significantly shifted by the appendage of the LI + cation, and the agreement between theory and experiment deteriorates further.