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Boletín de la Sociedad Chilena de Química

versão impressa ISSN 0366-1644

Resumo

WEISS-LOPEZ, BORIS E et al. CONFORMATIONAL DYNAMICS OF SUBSTITUTED N-ACETYL-N-PHENYLBENZYLAMINES. 1H-DNMR AND AM1-MO STUDY. Bol. Soc. Chil. Quím. [online]. 2001, vol.46, n.3, pp.261-269. ISSN 0366-1644.  http://dx.doi.org/10.4067/S0366-16442001000300005.

Activation parameters for the rotation around the methylene-nitrogen single bond found in a series of four 2,2´-disubstituted N-acetyl-N-phenylbenzylamines, dissolved in DMSO-d6, were measured employing the temperature dependence of the 1H-NMR spectrum lineshape between 340 and 400 K. The results are : (I) 2 ­ [N-acetyl -N- (2-acetamidophenyl) aminomethyl]phenylacetate DG¹=79.9±2.0 kJ/mol (370K), DH¹=96.2±6.0 kJ/mol and DS¹=+45±20 J/Kmol; (II) 2 - [N ­ acetyl ­ N - (2-acetyloxybenzyl)amino]benzylacetate DG¹=82.0±2.0 kJ/mol (370K), DH¹=79.1±6.0 kcal/mol and DS¹=-8±20 J/Kmol; (III) 2 - [N ­ Acetyl ­ N ­ (2-nitrobenzyl)amino]benzylacetate DG¹=80.8±2.0 kJ/mol (380K), DH¹=60.7±6.0 kcal/mol and DS¹=-53±20 J/Kmol; (IV) 2-[N­Acetyl­N-(2-acetyloxybenzyl)amino]phenylacetate DG¹=77.0±2.0 kJ/mol (370K), DH¹=65.3±6.0 kJ/mol and DS¹=-32±20 J/Kmol. Substitution at positions 2 and 2´ with bulky groups appears to be essential to freeze the gauche structure at room temperature and consequently, the main contribution to the barrier arises from the steric hindrance between these two groups. Structure I shows an anomalous behavior, possibly due to the formation of a hydrogen bond between the NH at position 2´ and the solvent. This interaction increases DHp and freezes the rotation around the aryl-nitrogen bond, increasing DS¹

Palavras-chave : Conformational Dynamics; 1H-NMR; N-AcetyPhenylbenzylamines; AM1-MO.

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