Theoretical Study of Intramolecular, CH-X (X = N, O, Cl), Hydrogen Bonds in Thiazole Derivatives
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- 作者：Miguel Castro ; Iné ; s Nicolá ; s-Vá ; zquez ; Jesú ; s I. Zavala ; F. Sá ; nchez-Viesca ; Martha Berros
- 刊名：Journal of Chemical Theory and Computation
- 出版年：2007
- 出版时间：May 2007
- 年：2007
- 卷：3
- 期：3
- 页码：681 - 688
- 全文大小：465K
- 年卷期：v.3,no.3(May 2007)
- ISSN：1549-9626
文摘
CH-X (X = N, O, or Cl) hydrogen bonds formed intramolecularly in 2-methyl-4-(2-chloro-4,5-dimethoxyphenyl)thiazole (Ia), 2-amino-4-(2-chloro-4,5-dimethoxy phenyl)thiazole (Ib),2-amino-4-(2,4,5-trimethoxyphenyl)thiazole (Ic), and 2-methyl-4-(2,4,5-trimethoxyphenyl)thiazole(Id) were studied by means of all-electron calculations performed with the B3LYP/6-311++G(d,p) method. Computed ground states, in the gas phase, show the presence of a single H-bond,CH-Cl, in each Ia and Ib moiety, and two H-bonds, CH-N and CH-O, for each Ic and Idmolecule. H-Cl, H-N, and H-O distances are shorter than the sum of the X and H van derWaals radii. H-bond energies of 
2.0 kcal/mol were estimated for Ia and Ib and 4.0 kcal/molfor Ic and Id. These results agree with those of the theory of atoms in molecules, since bondcritical points were found for these H-X bonds. Finally, the chemical shifts in the 1H NMR werecalculated by the GIAO method; in Ia and Ib they are merely due to the different topologicalpositions of the H atoms. But in Ic and Id the shifts of H-N and H-O have signatures of H-bondformations.
2.0 kcal/mol were estimated for Ia and Ib and 4.0 kcal/molfor Ic and Id. These results agree with those of the theory of atoms in molecules, since bondcritical points were found for these H-X bonds. Finally, the chemical shifts in the 1H NMR werecalculated by the GIAO method; in Ia and Ib they are merely due to the different topologicalpositions of the H atoms. But in Ic and Id the shifts of H-N and H-O have signatures of H-bondformations.