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The rotational and centrifugal constants of cyclobutanes, [C.sub.4][H.sub.8] which was measured accurately by employing femtosecond rotational Raman coherence, detected by degenerate four-wave mixing is presented. The vibrational levels of cyclobutane exhibit tunneling splitting due to the ring-puckering interconversion between the symmetry-equivalent minima via a planar barrier.

An investigation is conducted of the relative importance of hydrogen bonding versus pie stacking interactions in DNA where the hydrogen-bonded complexes of the nucleobase mimic 2-pyridone (2PY) with seven different fluorinated benzenes. Ab initio studies are performed on the individual hydrogen bonds occurring between nucleobases and fluronated isomers.

A study conducted on modified DNA oligomers and polymerase reactions have demonstrated that canonical nucleobases can exhibit stable and even selective pairing with shape-complementary fluorobenzene nucleotides. Hydrogen bonds are believed to be absent because of the fluorination of the pairing edges and the local DNA stability is attributed pie-stacking and shape complementarity.

The mixed dimers 2-pyridone.uracil(2PY.U), 2-pyridone.thymine(2PY.T), and 2-pyridone.5-florouracil(2PY.5-FU) are investigated, in which 2PY acts as the UV chromophore, avoiding the photophysical drawbacks of U, T, and 5-FU as shown by theoretical investigations, 2-pyridone forms only two H-bonds, which restricts the number of isomers to only three. The results revealed that the comparison of the spectra of 2PY.U, 2PY.T, and 2PY.5-FU allows determining the effects of methylation and fluorination on the ground- and excited-state binding energies, vibrational frequencies, and intermolecular forces.

We characterized the entrance channel, reaction threshold, and mechanism of an excited-state H atom transfer reaction along a unidirectionally hydrogen-bonded 'wire' -O--H *** N[H.sub.3] *** N[H.sub.3] *** N[H.sub.3] *** N. Excitation of supersonically cooled 7-hydroxyquinoline * [(N[H.sub.3]).sub.3] to its vibrationless [S.sub.1] state produces no reaction, whereas excitation of ammonia-wire vibrations induces H atom transfer with a reaction threshold ≅ 200 wave numbers. Further translocation steps along the wire produce the [S.sub.1] state 7-ketoquinoline * [(N[H.sub.3]).sub.3] tautomer. Ab initio calculations show that proton and electron movement along the wire are closely coupled. The rate-controlling [S.sub.1] state barriers arise from crossings of a π [π.sup.*] with a Rydberg-type π [σ.sup.*] state., Proton and H atom transfer mechanisms and dynamics are of fundamental importance for acid-base chemistry (1-13). The transport of protons displays a number of unusual properties, in part because the [...]

The 2-aminopuridine.2-pyridone complex (2AP.2PY) is linked by antiparallel N-H...O=C and N-H...N hydrogen bonds, providing a model for the Watson-Crick hydrogen bond configuration of the adenine-thymine and adenine-uracil nucleobase pairs. The hydrogen bond vibrations and the three in-plane vibrations v3 (opening), v5 (shear), and v6 (stretch) were observed in the S(sub 0) and S(sub 1) states.

The proton translocation along ammonia wires is investigated in 7-hydroxyquinoline.(NH3)(sub n) clusters, both experimentally by laser spectroscopy and theoretically by Hartree-Fock and density functional theory (DFT) calculations. It was seen that the step with the highest barrier involves a complex proton transfer mechanism, involving structural reorganization and large-scale diffusive motions of the cluster.

The combination of femtosecond time-resolved rotational coherence spectroscopy with high-level ab initio theory were used to obtain accurate structural information for the nonpolar antiaromatic molecule 1,3,5,7-cyclooctatetraene ([C.sub.8][H.sub.8], COT) and its perdeuterated isotopomer COT-[d.sub.8] ([C.sub.8][D.sub.8]). The effect of decreased [pi]-electron delocalization due to the twisting of adjacent C=C double bonds in COT relative to butadiene was observed for the C-C bonds but not for the C=C bonds.

The correlation of the calculated TD-B3LYP [S.sub.0] relates to [S.sub.1] vertical and adiabatic excitation energies are investigated for a series of 19 hydrogen-bonded complexes and clusters involving 7-hydroxyquinoline. The TD-B3LYP-computed adiabatic excitation energies are close to the experimentation excitation energies in absolute terms.

The development of a one-pot procedure for the synthesis of substituted 2,6-dicyanoanilines starting from readily available ynones and malononitrile is reported. The synthesis provides a new one-pot pathway for regioselective formation of polysubstituted benzenes.

The intermolecular binding energies [D.sub.e] of the ten doubly hydrogen bonded [uracil.sub.2] isomers are investigated by the correlated resolution of identity MP2 (RMIP2) method. All structures are optimized at the RIMP2/aug-cc-pVTZ level.

The five singly and doubly hydrogen bonded dimers of formamide are calculated at the correlated level by using resolution of identity Moller-Plesset second-order perturbation theory (RIMP2) and the coupled cluster with singles, doubles, and perturbative triples [CCSD(T)] method. A comparison with the N...O hydrogen bond distances in crystalline formamide has shown that a reversal of H-bond lengths occurs with respect to the gas-phase dimer, where the slightly longer gas-phase FA4 hydrogen bond becomes shorter and the shorter gas-phase FA1 H-bond becomes longer in the crystal.

The sugar-edge, Watson-Crick and wobble hydrogen-bonding sites of uracil and 1-,3-, and 5-methyluracilusing 2-pyridone as a probe chromophore are probed. The Watson-Crick wobble isomers are thereby determined to be several kcal/mol less strongly bound than the sugar-edge isomers.

The structure, rotational constants, vibrational frequencies, and binding and dissociation energies of (2-pyridone)(sub 2) are calculated at the correlated level using second order Moller-Plesset perturbation theory with medium to very large basis sets. It is implied that (2PY)(sub 2) is the most strongly bound doubly hydrogen-bonded dimer so far.

Author(s): Samuel Leutwyler (corresponding author) Chemical concepts have a long history of success in rationalizing the huge variety of phenomena observed at and above the molecular level. There are, for [...]

Aug-cc-pVXZ basis sets were used for calculating the binding energies of five different H-bonded (FA2) dimers at the MP2 level of theory. The complete basis set (CBS) extrapolation curve with an unusual shape was a result of the application of only half of the necessary counterpoise (CP) correction to the aug-cc-pVDZ binding energy.

Spectroscopic and ab initio computations were used to investigate the hydrogen-bonded 6-hydroxyquinoline*H2O complex. Geometry optimization at the self-consistent field (SCF) 6-31G(d,p) level resulted in translinear hydrogen bonding arrangements with Cs symmetry as minimum-energy structures for both the cis and trans rotamers. Small variations in the structural parameters were observed in the cis- and trans-6-hydroxyquinoline*H2O and 2-naphthol*H2O, computed at the same level of theory.

A study relating to research on the excited-state proton transfer reaction of 1-naphthol to water and other solvents was conducted to further elucidate how complexation with water affects vibrational and vibrational-electronic coupling in this significant prototype molecule. Among other results of the study, it was found that in the resonant two-photon ionization absorption spectrum, intermolecular modes are very weak compared to other similar complexes.