title: Theoretical Study of Intramolecular, CH [Formula: see text] X (X = N, O, Cl), Hydrogen Bonds in Thiazole Derivatives.
abstract: CH [Formula: see text] 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 [Formula: see text] Cl, in each Ia and Ib moiety, and two H-bonds, CH [Formula: see text] N and CH [Formula: see text] O, for each Ic and Id molecule. H [Formula: see text] Cl, H [Formula: see text] N, and H [Formula: see text] O distances are shorter than the sum of the X and H van der Waals radii. H-bond energies of ≅2.0 kcal/mol were estimated for Ia and Ib and ≅4.0 kcal/mol for Ic and Id. These results agree with those of the theory of atoms in molecules, since bond critical points were found for these H [Formula: see text] X bonds. Finally, the chemical shifts in the (1)H NMR were calculated by the GIAO method; in Ia and Ib they are merely due to the different topological positions of the H atoms. But in Ic and Id the shifts of H [Formula: see text] N and H [Formula: see text] O have signatures of H-bond formations.
authors.affiliation: Departamento de Física y Química Teórica and Departamento de Química Orgánica, DEPg., Facultad de Química, Universidad Nacional Autónoma de México, México D.F., C.P. 04510, México, and Departamento de Ciencias Químicas, Facultad de Estudios Superiores Cuautitlán, Campo 1, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, C. P. 54740, Edo. de México, México.
authors.forename: Miguel
authors.initials: M
authors.lastname: Castro
authors.affiliation: Departamento de Física y Química Teórica and Departamento de Química Orgánica, DEPg., Facultad de Química, Universidad Nacional Autónoma de México, México D.F., C.P. 04510, México, and Departamento de Ciencias Químicas, Facultad de Estudios Superiores Cuautitlán, Campo 1, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, C. P. 54740, Edo. de México, México.
authors.forename: Inés
authors.initials: I
authors.lastname: Nicolás-Vázquez
authors.affiliation: Departamento de Física y Química Teórica and Departamento de Química Orgánica, DEPg., Facultad de Química, Universidad Nacional Autónoma de México, México D.F., C.P. 04510, México, and Departamento de Ciencias Químicas, Facultad de Estudios Superiores Cuautitlán, Campo 1, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, C. P. 54740, Edo. de México, México.
authors.forename: Jesús I
authors.initials: JI
authors.lastname: Zavala
authors.affiliation: Departamento de Física y Química Teórica and Departamento de Química Orgánica, DEPg., Facultad de Química, Universidad Nacional Autónoma de México, México D.F., C.P. 04510, México, and Departamento de Ciencias Químicas, Facultad de Estudios Superiores Cuautitlán, Campo 1, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, C. P. 54740, Edo. de México, México.
authors.forename: F
authors.initials: F
authors.lastname: Sánchez-Viesca
authors.affiliation: Departamento de Física y Química Teórica and Departamento de Química Orgánica, DEPg., Facultad de Química, Universidad Nacional Autónoma de México, México D.F., C.P. 04510, México, and Departamento de Ciencias Químicas, Facultad de Estudios Superiores Cuautitlán, Campo 1, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, C. P. 54740, Edo. de México, México.
authors.forename: Martha
authors.initials: M
authors.lastname: Berros