Theoretical investigations into the blue-shifting hydrogen bond in benzene complexes. |
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Authors: | Vladimír Spirko Pavel Hobza |
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Affiliation: | Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Centre for Biomolecules and Complex Molecular Systems, 166 10 Prague 6, Czech Republic. |
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Abstract: | The benzene...X complexes (X=benzene, antracene, ovalene) were optimised at the MP2/6-31G** level with the C2v symmetry of the complex and planarity of the proton acceptor being preserved. The resulting stabilisation energies amount to 1.2, 2.3 and 2.9 kcal mol(-1), and the C-H bond of the proton donor is contracted by 0.0035, 0.0052 and 0.0055 A, respectively. The contraction is connected with a blue-shift of the C-H stretch vibration frequency. A two-dimensional anharmonic vibration treatment based on a MP2/6-31G** potential energy surface yields the following blue shifts for the complexes studied: 28, 42 and 43 cm(-1). The dominant attraction in the complexes is London dispersion, while the attractive contribution from electrostatic quadrupole-quadrupole interactions is considerably smaller. |
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Keywords: | ab initio calculations electron transfer electrostatic interations hydrogen bonds hyperconjugation |
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