A theoretical investigation on the isomerism and the NMR properties of thiosemicarbazones |
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Authors: | N W S V Nuwan De Silva Titus V Albu |
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Institution: | (1) Department of Chemistry, Tennessee Technological University, Cookeville, Tennessee 38505, USA |
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Abstract: | Hybrid density functional theory calculations at the mPW1PW91/6-31+G(d,p) level of theory have been used to investigate the
optimized structures and other molecular properties of five different series of thiosemicarbazones. The investigated compounds
were obtained from acenaphthenequinone, isatin and its derivatives, and alloxan. The focus of the study is the isomerism and
the NMR characterization of these thiosemicarbazones. It was found that only one isomer is expected for thiosemicarbazones
and methylthiosemicarbazones, while for dimethylthiosemicarbazones, two isomers are possible. All investigated thiosemicarbazones
exhibit a hydrazinic proton that is highly deshielded and resonates far downfield in the proton NMR spectra. This proton is
a part of a characteristic sixmembered ring, and its NMR properties are a result of its strong, intermolecular hydrogen bond.
The relationships between the calculated 1H and 13C NMR chemical shifts and various geometric parameters are reported.
![MediaObjects/11532_2006_Article_12_Fig1_HTML.jpg](/content/eu25057g0n836321/MediaObjects/11532_2006_Article_12_Fig1_HTML.jpg) |
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Keywords: | Thiosemicarbazones isomerism NMR chemical shifts hybrid density functional theory |
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