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DFT calculations were used to access information about structure, energy and electronic properties of series of phenyl- and phenoxymethyl-(thio)semicarbazone derivatives with demonstrated activity against the larvae of Aedes aegypti in stage L4. The way as the thiosemicarbazone derivatives can interact with solvents like DMSO and water were analyzed from the comparison between calculated and experimental 1 H NMR chemical shifts. The evidences of thiosemicarbazone derivatives making H-bond interaction to solvent have provide us insights on how they can interact with a potential A . aegypti ’ s biological target, the Sterol Carrier Protein-2. [ABSTRACT FROM AUTHOR]

Abstract: B3LYP and MP2 theoretical calculations with 6-31++G(d,p) basis set have been performed to interpret the infrared spectrum of maleimide. The anharmonicity effect has been included to correct the calculated harmonic frequency values. As expected, this has allowed a better agreement with the experimental ones, especially B3LYP values. The more pronounced changes have been verified to the Xsp sp="0.25" />=C or N) stretching modes. The calculated IR intensities compare favorably well with their corresponding relative experimental values in vapor phase. The large discrepancy is found to the symmetric Cing mode of the heterocyclic ring. It appears to be a strong band at 897cm−1, in contrast to B3LYP and MP2 calculated values. The calculated intensities due to the out-of-plane and in-plane bending and stretching modes for the Xtors (X=C or N) have been adequately interpreted in terms of hydrogen atomic charges and Xfluxes extracted from the modified charge–charge flux-overlap model (CCFOM) for infrared intensities. [Copyright &y& Elsevier]

Abstract: MP2/6-31++G(d,p) and B3LYP/6-31++G(d,p) theoretical calculations have been employed to investigate the hydrogen bonding formation involving the vic-, cis- and trans-C2H2F2 isomers and hydrogen fluoride. Our calculations have revealed for each isomer the preferential existence of two possible hydrogen-bonded complexes: a non-cyclic complex and a cyclic complex. For all the three isomers the binding energies for the non-cyclic and cyclic hydrogen complexes are essentially equal using both the MP2 and B3LYP calculations, being that the cyclic structure is slightly more stable. For instance, the binding energies including BSSE and ZPE corrections for the non-cyclic and cyclic structures of cis-C2H2F···HF are 8.7 and 9.0kJmol−1, respectively, using B3LYP calculations. The cyclic complex formation reduces the polarity, in contrast to what occurs with the non-cyclic complex. This result is more accentuated in vic-C2H2F2···HF. In this latter, Δμ(cyclic) is −3.07D, whereas Δμ(non-cyclic) is +1.92D using B3LYP calculations. Their corresponding MP2 values are +0.44D and −1.89D, respectively. As expected, the complexation produces an Hing frequency downward shift, whereas its IR intensity is enhanced. On the other hand, the vibrational modes of the vic-, cis- and trans-C2H2F2 isomers are little affected by complexation. The new vibrational modes due to hydrogen bonding formation show several interesting features, in particular the HF bending modes which are pure rotations in the free molecule. [Copyright &y& Elsevier]

Abstract: MP2/6-31++G(d,p) ab initio calculations have been performed to estimate the effect of the H-bond on the vibrational properties of HF due to its complexation with aromatic azines (C n N6-n H n , with n =5, 4 or 3). Our calculations have revealed that the greater is the number of nitrogen atoms in the aromatic ring, the smaller will be the HF stretching frequency downward shift and the increase of the H–F stretching intensity due to complexation. For example, the H–F frequency downward shift is 899cm−1 in pyridine-HF, whereas its corresponding value is 597cm−1 in 1,3,5-triazine-HF. Their infrared intensity ratios between the complexes and their corresponding monomers are 18.7 and 14.3cm−1, respectively. We have found a relationship between the HF stretching frequency downward shift and the number and position of the nitrogen atoms in the aromatic ring. As expected, the HF stretching intensity is enormously increased upon complexation and its value can be predicted by using the ∂P z /∂z H element of the hydrogen polar tensor, where z is the Cartesian axis along the H–F chemical bond. [Copyright &y& Elsevier]

Abstract: Ab initio molecular orbital calculations have been performed at the MP2/6-31++G** theoretical level in order to obtain molecular properties of hydrogen-bonded complexes involving pyrazine and the HX linear acids with, X=F, NC, Cl, CN, and CCH. Both the 1:1 and 1:2 adducts have been investigated, i.e., Pyz⋯HX and XH⋯Pyz⋯HX. The H-bond strength for these complexes can be interpreted in terms of the H–X stretching frequency downward displacement. This latter shows a good linear correlation with the intermolecular charge transfer and follows the order: X=F>X=NC>X=Cl>X=CN>X=CCH. As expected, the H–X stretching intensity is much enhanced upon H-bond formation. Here these effects on the HX infrared spectra are much more pronounced than those previously found in complexes with unsaturated hydrocarbons as proton acceptors. On the other hand, no important change has been verified in pyrazine, except the inhibition of the lone-pair trans effect from the lone-pair of nitrogen to the σ* antibonding orbital of the CC chemical bond in pyrazine. The new vibrational modes arising from complexation show several interesting features, specially the bending modes of the proton-donor molecule and the intermolecular stretching mode. [Copyright &y& Elsevier]