Strong intramolecular hydrogen bonds and steric effects involving C═S groups: An NMR and computational study |
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| Authors: | Rita S Elias Bahjat A Saeed Fadhil S Kamounah Fritz Duus Poul Erik Hansen |
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| Institution: | 1. Department of Pharmaceutical Chemistry, College of Pharmacy, University of Basrah, Basrah, Iraq;2. Department of Chemistry, College of Education for Pure Sciences, University of Basrah, Basrah, Iraq;3. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark;4. Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark |
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| Abstract: | A number of 5-acyl rhodanines and thiorhodanines with bulky acyl groups (pivaloyl and adamantoyl), not previously available, have been synthesized. The compounds are shown to exist in the enol form. Structures have been calculated using both the MP2 approach and the B3LYP-GD3BJ functional and the 6-311++G(d,p) basis set. Hydrogen bond energies are estimated by subtracting energies of a structure with the OH group turned 180° from those of the intramolecularly hydrogen-bonded one. Properties such as OH chemical shifts, two-bond isotope effects on 13C chemical shifts, electron densities at the bond critical point from atoms in molecules analysis, and the hydrogen bond energies show that the sterically hindered compounds have stronger hydrogen bonds than methyl or isopropyl derivatives. The combination of oxygen and sulfur derivatives enables a detailed analysis of hydrogen bond energies. |
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| Keywords: | adamantyl derivatives intramolecular hydrogen bonding isotope effects steric effects thiorhodanines |
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