Artículo
Contreras, R.H.; Biekofsky, R.R.; Esteban, A.L.; Diez, E.; Fabian, J.S. "Carbonyl 17O chemical shift in the proximity of a methyl group in amides: An experimental and theoretical study" (1996) Magnetic Resonance in Chemistry. 34(6):447-452
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Abstract:
The effect of a cis-N-methyl group on the carbonyl 17O chemical shift, cis-MSCS, was investigated both from theoretical and experimental points of view in ten amide derivatives. Experimentally, it was observed that the cis-MSCS in N-methylformamide (2) corresponds to a shielding effect of 12.0 ppm with respect to formamide (1). LORG calculations at both the 6-31G* and 6-311G** levels reproduced fairly well this trend, i.e. 10.2 and 11.4 ppm, respectively, provided that as the N-methyl group conformation was such that a C - H bond eclipsed the C - N bond (2a). This is the preferential conformation at the 6-31G*/MP2 level. For other methyl group conformations the LORG calculations did not reproduce that experimental trend. For instance, for an N-methyl C - H bond eclipsing the N - H bond (2b), deshielding cis-MSCSs of 3.7 ppm (6-31G*) and 3.6 ppm (6-311G**) were predicted. Analyses of LORG bond-bond contributions suggested that the interaction that defines 2a as the preferential conformation is an attractive interaction between the in-plane N-methyl C - H bond and the carbonyl oxygen lone pairs. Experimental trends observed for the 17O chemical shifts measured in the remaining compounds can be rationalized on the same grounds.
Registro:
| Documento: | Artículo |
| Título: | Carbonyl 17O chemical shift in the proximity of a methyl group in amides: An experimental and theoretical study |
| Autor: | Contreras, R.H.; Biekofsky, R.R.; Esteban, A.L.; Diez, E.; Fabian, J.S. |
| Filiación: | Departtamento de Física, Fac. de Ciencias Exactas y Naturales, Universidad de Buenos Aires, (1428) Buenos Aires, Argentina Depto. de Quim. Física, Universidad de Alicante, 03080-Alicante, Spain Facultad de Ciencias C2-103, Univ. Autónoma de Madrid, 28049-Madrid, Spain |
| Palabras clave: | 17O NMR chemical shifts; Ab initio LORG study; Amides |
| Año: | 1996 |
| Volumen: | 34 |
| Número: | 6 |
| Página de inicio: | 447 |
| Página de fin: | 452 |
| DOI: | http://dx.doi.org/10.1002/(SICI)1097-458X(199606)34:6<447::AID-OMR903>3.0.CO;2-W |
| Título revista: | Magnetic Resonance in Chemistry |
| Título revista abreviado: | Magn. Reson. Chem. |
| ISSN: | 07491581 |
| CODEN: | MRCHE |
| Registro: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_07491581_v34_n6_p447_Contreras |
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Citas:
---------- APA ----------
Contreras, R.H., Biekofsky, R.R., Esteban, A.L., Diez, E. & Fabian, J.S. (1996) . Carbonyl 17O chemical shift in the proximity of a methyl group in amides: An experimental and theoretical study. Magnetic Resonance in Chemistry, 34(6), 447-452.http://dx.doi.org/10.1002/(SICI)1097-458X(199606)34:6<447::AID-OMR903>3.0.CO;2-W
---------- CHICAGO ----------
Contreras, R.H., Biekofsky, R.R., Esteban, A.L., Diez, E., Fabian, J.S. "Carbonyl 17O chemical shift in the proximity of a methyl group in amides: An experimental and theoretical study" . Magnetic Resonance in Chemistry 34, no. 6 (1996) : 447-452.http://dx.doi.org/10.1002/(SICI)1097-458X(199606)34:6<447::AID-OMR903>3.0.CO;2-W
---------- MLA ----------
Contreras, R.H., Biekofsky, R.R., Esteban, A.L., Diez, E., Fabian, J.S. "Carbonyl 17O chemical shift in the proximity of a methyl group in amides: An experimental and theoretical study" . Magnetic Resonance in Chemistry, vol. 34, no. 6, 1996, pp. 447-452.http://dx.doi.org/10.1002/(SICI)1097-458X(199606)34:6<447::AID-OMR903>3.0.CO;2-W
---------- VANCOUVER ----------
Contreras, R.H., Biekofsky, R.R., Esteban, A.L., Diez, E., Fabian, J.S. Carbonyl 17O chemical shift in the proximity of a methyl group in amides: An experimental and theoretical study. Magn. Reson. Chem. 1996;34(6):447-452.http://dx.doi.org/10.1002/(SICI)1097-458X(199606)34:6<447::AID-OMR903>3.0.CO;2-W
