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Titolo:
X-RAY-DIFFRACTION AND THEORETICAL-STUDIES OF THE METHYL-ESTER OF (R,R)-TARTARIC ACID MONOAMIDE - SEMIEMPIRICAL AND AB-INITIO CALCULATIONS OF SOME MODEL COMPOUNDS
Autore:
SZARECKA A; HOFFMANN M; RYCHLEWSKI J; RYCHLEWSKA U;
Indirizzi:
ADAM MICKIEWICZ UNIV POZNAN,FAC CHEM,GRUNWALDZKA 6 PL-60780 POZNAN POLAND ADAM MICKIEWICZ UNIV POZNAN,FAC CHEM PL-60780 POZNAN POLAND
Titolo Testata:
Journal of molecular structure
, volume: 374, anno: 1996,
pagine: 363 - 372
SICI:
0022-2860(1996)374:<363:XATOTM>2.0.ZU;2-R
Fonte:
ISI
Lingua:
ENG
Soggetto:
STRUCTURAL CHARACTERISTICS; PARAMETERS; CHEMISTRY;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
31
Recensione:
Indirizzi per estratti:
Citazione:
A. Szarecka et al., "X-RAY-DIFFRACTION AND THEORETICAL-STUDIES OF THE METHYL-ESTER OF (R,R)-TARTARIC ACID MONOAMIDE - SEMIEMPIRICAL AND AB-INITIO CALCULATIONS OF SOME MODEL COMPOUNDS", Journal of molecular structure, 374, 1996, pp. 363-372

Abstract

In its crystal structure, determined by X-ray diffraction, the methylester of(R,R)-tartaric acid monoamide crystallizes with two moleculesper assymetric unit. Each molecule displays subtle conformational differences effected by 180 degrees rotation by the methyl ester group about the C-C bond, whereas the staggered conformation around the central C-C* bond, with a trans arrangement of the ester and amide substituents, and the eclipsed orientation of the amide nitrogen atom with respect to the nearest hydroxyl group, remains the same in both molecules. MNDO and ab initio single-point energies for the two molecules indicate that the lower energy molecule is that with the cr-hydroxyl groupeclipsed by the carbonyl group rather than the methoxy oxygen atom. Conformers observed in the crystal structure differ from those obtainedby full MNDO optimization in the planarity of alpha-hydroxyester and alpha-hydroxyamide residues. Ab initio calculations at the 6-31G level on smaller systems, i.e. (2R,3R)-2,3-butanediol and (2R,3R)-2,3-dihydroxybutanedinitrile, suggest different conformational preferences forthe two model compounds (gauche vs. trans with respect to the carbon chain), and point to the importance of the intramolecular hydrogen bond in stabilizing the gauche orientation of the vicinal OH groups. A similar hydrogen bond may be present in one of two crystallographically independent molecules of the methyl ester of (R,R)-tartaric acid monoamide, but only as a minor component in a complex system of intermolecular hydrogen bonds.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 01/10/20 alle ore 15:03:19