Reinvestigation of benzothiazoline-2-thione and 2-mercaptobenzothiazole tautomers: Conformational stability, barriers to internal rotation and DFT calculations

Tarek A. Mohamed, Ahmed M. Mustafa, Wajdi M. Zoghaib, Mahmoud S. Afifi, Rabei S. Farag, Yehia Badr

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

The Raman (3600-100 cm-1), infrared (4000-400 cm-1), far-infrared (400-200 cm-1), 1H and 13C NMR spectra of solid benzothiazoline-2-thione (BTT) are recorded. Additionally, the 1H NMR spectra were obtained at a temperature range from -90 to +90 °C. In addition, 2-mercaptobenzothiazole (MBT) can either be cis (S-H is eclipsing C{double bond, long}N bond) and/or trans (S-H is eclipsing C{double bond, long}S bond). Therefore, we carried out geometry and frequency calculations for thio-keto and thio-enol conformations using Density Functional Theory (DFT) methods of B3LYP, B3PW91 and SVWN utilizing 6-31 G(d) basis set. Theoretical predictions are consistent with vibrational measurements, which are in favor of the thio-keto (thione) tautomer at ambient temperature (25 °C). From the variable temperature 1H NMR spectra, it is evident that the thione BTT is the only existing tautomer at ambient (25 °C), low- (down to -90 °C) and high- (up to +90 °C) temperatures. Therefore, the thio-keto (BTT) and thio-enol (MBT) equilibrium is unquestionably excluded. B3LYP and B3PW91 calculations are in agreement with vibrational spectra as well as X-ray structural parameters of BTT rather than SVWN at 6-31 G(d) basis set. In addition, we calculated the S-H barriers to internal rotation for cis/trans chalcogen analogues of MBT utilizing B3LYP/MP2 potential surface scans with the 6-31 G(d) basis set. The cis/trans S-H barriers were 4.15/3.61, 3.39/2.90 and 3.71/3.36 kcal/mol for 2-mecaptobenzoxazole (MBO), 2-mercaptobezothiazole (MBT) and 2-mercaptobenzoselenazole (MBSe) analogues, respectively.

Original languageEnglish
Pages (from-to)27-36
Number of pages10
JournalJournal of Molecular Structure: THEOCHEM
Volume868
Issue number1-3
DOIs
Publication statusPublished - Nov 15 2008

Fingerprint

Thiones
tautomers
Density functional theory
density functional theory
nuclear magnetic resonance
analogs
Temperature
Nuclear magnetic resonance
vibrational spectra
ambient temperature
temperature
Chalcogens
Infrared radiation
Vibrational spectra
geometry
predictions
Conformations
benzothiazoline
captax
x rays

Keywords

  • H and C NMR
  • Barriers to internal rotation
  • Benzothiazoline-2-thione
  • DFT calculations
  • Infrared
  • Raman
  • Thio-keto and thio-enol tautomerism

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Biochemistry
  • Condensed Matter Physics

Cite this

Reinvestigation of benzothiazoline-2-thione and 2-mercaptobenzothiazole tautomers : Conformational stability, barriers to internal rotation and DFT calculations. / Mohamed, Tarek A.; Mustafa, Ahmed M.; Zoghaib, Wajdi M.; Afifi, Mahmoud S.; Farag, Rabei S.; Badr, Yehia.

In: Journal of Molecular Structure: THEOCHEM, Vol. 868, No. 1-3, 15.11.2008, p. 27-36.

Research output: Contribution to journalArticle

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abstract = "The Raman (3600-100 cm-1), infrared (4000-400 cm-1), far-infrared (400-200 cm-1), 1H and 13C NMR spectra of solid benzothiazoline-2-thione (BTT) are recorded. Additionally, the 1H NMR spectra were obtained at a temperature range from -90 to +90 °C. In addition, 2-mercaptobenzothiazole (MBT) can either be cis (S-H is eclipsing C{double bond, long}N bond) and/or trans (S-H is eclipsing C{double bond, long}S bond). Therefore, we carried out geometry and frequency calculations for thio-keto and thio-enol conformations using Density Functional Theory (DFT) methods of B3LYP, B3PW91 and SVWN utilizing 6-31 G(d) basis set. Theoretical predictions are consistent with vibrational measurements, which are in favor of the thio-keto (thione) tautomer at ambient temperature (25 °C). From the variable temperature 1H NMR spectra, it is evident that the thione BTT is the only existing tautomer at ambient (25 °C), low- (down to -90 °C) and high- (up to +90 °C) temperatures. Therefore, the thio-keto (BTT) and thio-enol (MBT) equilibrium is unquestionably excluded. B3LYP and B3PW91 calculations are in agreement with vibrational spectra as well as X-ray structural parameters of BTT rather than SVWN at 6-31 G(d) basis set. In addition, we calculated the S-H barriers to internal rotation for cis/trans chalcogen analogues of MBT utilizing B3LYP/MP2 potential surface scans with the 6-31 G(d) basis set. The cis/trans S-H barriers were 4.15/3.61, 3.39/2.90 and 3.71/3.36 kcal/mol for 2-mecaptobenzoxazole (MBO), 2-mercaptobezothiazole (MBT) and 2-mercaptobenzoselenazole (MBSe) analogues, respectively.",
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T1 - Reinvestigation of benzothiazoline-2-thione and 2-mercaptobenzothiazole tautomers

T2 - Conformational stability, barriers to internal rotation and DFT calculations

AU - Mohamed, Tarek A.

AU - Mustafa, Ahmed M.

AU - Zoghaib, Wajdi M.

AU - Afifi, Mahmoud S.

AU - Farag, Rabei S.

AU - Badr, Yehia

PY - 2008/11/15

Y1 - 2008/11/15

N2 - The Raman (3600-100 cm-1), infrared (4000-400 cm-1), far-infrared (400-200 cm-1), 1H and 13C NMR spectra of solid benzothiazoline-2-thione (BTT) are recorded. Additionally, the 1H NMR spectra were obtained at a temperature range from -90 to +90 °C. In addition, 2-mercaptobenzothiazole (MBT) can either be cis (S-H is eclipsing C{double bond, long}N bond) and/or trans (S-H is eclipsing C{double bond, long}S bond). Therefore, we carried out geometry and frequency calculations for thio-keto and thio-enol conformations using Density Functional Theory (DFT) methods of B3LYP, B3PW91 and SVWN utilizing 6-31 G(d) basis set. Theoretical predictions are consistent with vibrational measurements, which are in favor of the thio-keto (thione) tautomer at ambient temperature (25 °C). From the variable temperature 1H NMR spectra, it is evident that the thione BTT is the only existing tautomer at ambient (25 °C), low- (down to -90 °C) and high- (up to +90 °C) temperatures. Therefore, the thio-keto (BTT) and thio-enol (MBT) equilibrium is unquestionably excluded. B3LYP and B3PW91 calculations are in agreement with vibrational spectra as well as X-ray structural parameters of BTT rather than SVWN at 6-31 G(d) basis set. In addition, we calculated the S-H barriers to internal rotation for cis/trans chalcogen analogues of MBT utilizing B3LYP/MP2 potential surface scans with the 6-31 G(d) basis set. The cis/trans S-H barriers were 4.15/3.61, 3.39/2.90 and 3.71/3.36 kcal/mol for 2-mecaptobenzoxazole (MBO), 2-mercaptobezothiazole (MBT) and 2-mercaptobenzoselenazole (MBSe) analogues, respectively.

AB - The Raman (3600-100 cm-1), infrared (4000-400 cm-1), far-infrared (400-200 cm-1), 1H and 13C NMR spectra of solid benzothiazoline-2-thione (BTT) are recorded. Additionally, the 1H NMR spectra were obtained at a temperature range from -90 to +90 °C. In addition, 2-mercaptobenzothiazole (MBT) can either be cis (S-H is eclipsing C{double bond, long}N bond) and/or trans (S-H is eclipsing C{double bond, long}S bond). Therefore, we carried out geometry and frequency calculations for thio-keto and thio-enol conformations using Density Functional Theory (DFT) methods of B3LYP, B3PW91 and SVWN utilizing 6-31 G(d) basis set. Theoretical predictions are consistent with vibrational measurements, which are in favor of the thio-keto (thione) tautomer at ambient temperature (25 °C). From the variable temperature 1H NMR spectra, it is evident that the thione BTT is the only existing tautomer at ambient (25 °C), low- (down to -90 °C) and high- (up to +90 °C) temperatures. Therefore, the thio-keto (BTT) and thio-enol (MBT) equilibrium is unquestionably excluded. B3LYP and B3PW91 calculations are in agreement with vibrational spectra as well as X-ray structural parameters of BTT rather than SVWN at 6-31 G(d) basis set. In addition, we calculated the S-H barriers to internal rotation for cis/trans chalcogen analogues of MBT utilizing B3LYP/MP2 potential surface scans with the 6-31 G(d) basis set. The cis/trans S-H barriers were 4.15/3.61, 3.39/2.90 and 3.71/3.36 kcal/mol for 2-mecaptobenzoxazole (MBO), 2-mercaptobezothiazole (MBT) and 2-mercaptobenzoselenazole (MBSe) analogues, respectively.

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KW - Barriers to internal rotation

KW - Benzothiazoline-2-thione

KW - DFT calculations

KW - Infrared

KW - Raman

KW - Thio-keto and thio-enol tautomerism

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