Vibrational assignments, normal coordinate analysis, B3LYP calculations and conformational analysis of methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1- carbodithioate

Tarek A. Mohamed, Ali M. Hassan, Usama A. Soliman, Wajdi M. Zoghaib, John Husband, Saber M. Hassan

Research output: Contribution to journalArticle

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Abstract

The Raman and infrared spectra of solid methyl-5-amino-4-cyano-3- (methylthio)-1H-pyrazole-1-carbodithioate (MAMPC, C 7H 8N 4S 3) were measured in the spectral range of 3700-100 cm -1 and 4000-200 cm -1 with a resolution of 4 and 0.5 cm -1, respectively. Room temperature 13C NMR and 1H NMR spectra from room temperature down to -60 °C were also recorded. As a result of internal rotation around C-N and/or C-S bonds, eighteen rotational isomers are suggested for the MAMPC molecule (Cs symmetry). DFT/B3LYP and MP2 calculations were carried out up to 6-311++G(d,p) basis sets to include polarization and diffusion functions. The results favor conformer 1 in the solid (experimentally) and gaseous (theoretically) phases. For conformer 1, the two -CH 3 groups are directed towards the nitrogen atoms (pyrazole ring) and CS, while the -NH 2 group retains sp 2 hybridization and C-CN bond is quasi linear. To support NMR spectral assignments, chemical shifts (δ) were predicted at the B3LYP/6-311+G(2d,p) level using the method of Gauge-Invariant Atomic Orbital (GIAO) method. Moreover, the solvent effect was included via the Polarizable Continuum Model (PCM). Additionally, both infrared and Raman spectra were predicted using B3LYP/6-31G(d) calculations. The recorded vibrational, 1H and 13C NMR spectral data favors conformer 1 in both the solid phase and in solution. Aided by normal coordinate analysis and potential energy distributions, confident vibrational assignments for observed bands have been proposed. Moreover, the CH 3 barriers to internal rotations were investigated. The results are discussed herein are compared with similar molecules whenever appropriate.

Original languageEnglish
Pages (from-to)1722-1730
Number of pages9
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume79
Issue number5
DOIs
Publication statusPublished - Sep 2011

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Keywords

  • DFT calculations
  • Infrared
  • NMR spectra
  • Raman
  • Vibrational assignments

ASJC Scopus subject areas

  • Instrumentation
  • Atomic and Molecular Physics, and Optics
  • Analytical Chemistry
  • Spectroscopy

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