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

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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

Fingerprint

Nuclear magnetic resonance
nuclear magnetic resonance
infrared spectra
methylidyne
Raman spectra
Infrared radiation
Molecules
Chemical shift
room temperature
Potential energy
Discrete Fourier transforms
Isomers
nitrogen atoms
Gages
chemical equilibrium
solid phases
Raman scattering
molecules
energy distribution
Nitrogen

Keywords

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

ASJC Scopus subject areas

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

Cite this

@article{3e08356397694a12a16ebd56f7981c23,
title = "Vibrational assignments, normal coordinate analysis, B3LYP calculations and conformational analysis of methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1- carbodithioate",
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.",
keywords = "DFT calculations, Infrared, NMR spectra, Raman, Vibrational assignments",
author = "Mohamed, {Tarek A.} and Hassan, {Ali M.} and Soliman, {Usama A.} and Zoghaib, {Wajdi M.} and John Husband and Hassan, {Saber M.}",
year = "2011",
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TY - JOUR

T1 - Vibrational assignments, normal coordinate analysis, B3LYP calculations and conformational analysis of methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1- carbodithioate

AU - Mohamed, Tarek A.

AU - Hassan, Ali M.

AU - Soliman, Usama A.

AU - Zoghaib, Wajdi M.

AU - Husband, John

AU - Hassan, Saber M.

PY - 2011/9

Y1 - 2011/9

N2 - 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.

AB - 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.

KW - DFT calculations

KW - Infrared

KW - NMR spectra

KW - Raman

KW - Vibrational assignments

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U2 - 10.1016/j.saa.2011.05.044

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VL - 79

SP - 1722

EP - 1730

JO - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

JF - Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

SN - 1386-1425

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