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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.

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.

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.