Acta Crystallographica Section B

Structural Science

Volume 55, Part 3 (June 1999)

Acta Cryst. (1999). B55, 441-447 [doi:10.1107/S0108768198014013]

3(5),4-Dimethyl- and 3,4,5-trimethylpyrazole at 200 K. X-ray crystallography and quantum-chemical analysis

L. Infantes, C. Foces-Foces and J. Elguero

Abstract: The crystal and molecular structures of 3(5),4-dimethylpyrazole, C₅H₈N₂, (I), and of 3,4,5-trimethylpyrazole, C₆H₁₀N₂, (II), have been determined at 200 K. In (I) the 4,5-dimethylpyrazole tautomer is present in the solid state and the six independent molecules in the asymmetric unit form trimers via NHN hydrogen bonds related by a pseudo centre of symmetry. The asymmetric unit of (II) contains one and a half molecules: these exhibit NH proton disorder and are hydrogen bonded to each other via their respective NH groups to form chains. Ab initio calculations at HF and B3LYP/6-31G** levels indicate that the 3,4-dimethylpyrazole tautomer is more stable than the 4,5-dimethylpyrazole tautomer by only approximately 0.5 kcal mol^-1 (1 kcal mol^-1 = 4.184 kJ mol^-1).

Online 1 June 1999


	Structure factor file (CIF format) (246.5 kbytes) Contains datablock Ib

	Structure factor file (CIF format) (73.2 kbytes) Contains datablock II

Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.