The Rotational Spectrum of Monothioformic Acid. III. Dipole Moment and Relative Intensity Measurements<sup>1,2</sup>

Hocking, W. H.; Winnewisser, G.

doi:10.1515/zna-1976-0820

Cited by 47 publications

(28 citation statements)

References 10 publications

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“…The importance of the above-mentioned intramolecular interactions in s-cis conformations reflects also in the large changes produced by the HC(=X)OH --+ HC(=X)SH " Ref. (11). " This work. '…”

Section: Molecular Geometries and Energiesmentioning

confidence: 93%

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s-cis and s-trans Conformers of formic, thioformic and dithioformic acids. An ab initio study

Fausto¹,

Carvalho²,

Teixeira‐Dias³

et al. 1989

J. Chem. Soc., Faraday Trans. 2

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Ab initio SCF-MO calculations have been carried out for formic, thioformic and dithioformic acids using the 6-31G* basis set. Fully optimized geometries, atomic charges, relative stabilities and harmonic force fields for s-cis and s-trans conformers of these molecules have been determined and the effects of oxygen-by-sulphur substitution analysed. A realistic description of the molecular charge distribution can be reached by introducing a quantum-mechanical correction to the Mulliken atomic charges, derived from the 'charge'-'charge flux'-'overlap' (CCFO) model. Unlike reported theoretical results, the present ab initio calculations yield relative stabilities of the thioformic acid conformers in agreement with experiment [s-cis (thiol) > s-trans(thio1) > s-cis(thione) > s-trans(thione)]. The success of these ab initio calculations should be partially ascribed to the inclusion of polarization functions on all non-hydrogen atoms. Dithiocompounds constitute an ideal res-'*lance Raman (RR) probe for monitoring catalytic events within an enzyme's active site.'-3 The catalylic hydrolysis of substrates containing the RC(=O)O fragment by cysteine proteases (e.g. papain) proceeds through the formation of a thiolacyl enzyme, RC(=O)S-Enz. Using a thion-substituted substrate, it is possible to generate an enzyme-substrate intermediate that contains the chromophore-C(=S)S-, thus differing from the 'natural' intermediate by a single atom substitution Interpretation of the RR spectra of dithioenzyme-substrate intermediates has relied heavily on joint Raman and crystallographic studies on suitable model c o m p~u n d s .~-~ While our understanding of some of these probes has reached a sophisticated level, it is apparent that the assessment of changes in molecular properties produced by oxygenby-sulphur substitutions in molecules containing the-C(=X)Y-, (X,Y = 0 or S) fragment has a major interest to further oiir understanding of the active site data. We have recently initiated a systematic approach to the study of thione-and thiolsubstituted carboxylic acids and esters using ab initio quantum-mechanical calcu'lations.7-' The results obtained for HCSSH using the 3-21G basis set8 were compared with previous data on HCOOH, HC(=O)SH and HC(=S)OH,'* and revealed a remarkable similarity between molecular properties of dithioformic and thiolformic acids. This trend was also observed along the series of the corresponding methyl esters, HCSSCH3 resembling more HC(=O)SCH, than the compounds possessing an oxygen ester at om. 7*9 The importance of rnesomerism in determining the properties of this kind of molecule (fig. 1) is well known, in particular, for their ground conformational state (the s-cis form). We have proposed' that the main effect resulting from C(=O)O-+ C(=O)S or C(=S)O-C (=S)$ substitutions is originated in the poorer conjugating properties of the sulphur 3p orbitals as compared with those of the oxygen 2p orbitals.

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Section: Molecular Geometries and Energiesmentioning

confidence: 93%

“…The experimental values for these modes presented in table 13 have been derived in ref. (11) from the HCOSH microwave spectrum.…”

Section: Th Ioformic Acidmentioning

confidence: 99%

s-cis and s-trans Conformers of formic, thioformic and dithioformic acids. An ab initio study

Fausto¹,

Carvalho²,

Teixeira‐Dias³

et al. 1989

J. Chem. Soc., Faraday Trans. 2

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“…A systematic search for a-type Q-branch transitions and 6-type P-branch transitions was then undertaken. The bootstrap procedure described previously 36 was employed for this purpose. For the important In -20o fr-type transition the assignment was further confirmed through the Stark effect.…”

Section: Rotational Spectrum and Assignmentmentioning

confidence: 99%

“…Very recently, the results of a thorough investigation of the rotational spectrum of monothioformic acid have been reported [35][36][37][38] . Two planar rotamers of the thiol form, HC(:0)SH, were identified.…”

Section: Introductionmentioning

confidence: 99%

The Other Rotamer of Formic Acid, cis-HCOOH¹

Hocking

1976

Zeitschrift Für Naturforschung A

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237

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The rotational spectrum of the planar eis rotamer of formic acid, cis-HCOOH, has been detected for the first time. Twenty transitions belonging to the IRK , "JQi, QQ2 > r Po» r Pi r P2 brandies of the parent isotopic species in its ground state have been assigned and measured. The rotational constants and quartic centrifugal distortion constants have been determined using Watson's reduced Hamiltonian. Stark effect measurements have yielded the molecular electric dipole moment: /na= 2.65(1) D, ^6 = 2.71(1) D and ,« = 3.79(1) D. The energy difference between the ground vibrational states of eis-and iraras-HCOOH has been determined by microwave relative intensity measurements. The eis rotamer is found to lie at higher energy than the trans rotamer by 1365 + 30 cm -1 . A one dimensional potential energy curve has been calculated for the OH torsional vibration of formic acid.

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“…Thus the theoretical results suggest that the stabilization achieved by an intramolecular HB is not sufficient to sacrifice the most stable Z configuration of the carboxylic groups. The difference between E and Z rotamers in formic acid was attributed to intramolecular hydrogen bonding by Hocking 32 and empirically corrected by Császár,20 who measured the energy difference to be 17.2(3) kJ mol À1 .…”

Section: Resultsmentioning

confidence: 99%

Conformational steering in dicarboxy acids: the native structure of succinic acid

Jahn

Méndez

Nair

et al. 2015

Phys. Chem. Chem. Phys.

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The torsional freedom of the carbon backbone and hydroxyl groups of succinic acid, an important platform chemical fi nding numerous industrial applications as well as being the focus of considerable research in atmospheric science, is elucidated. The question of the potential presence of numerous conformers is answered by an unambiguous identifi cation of the structural and molecular properties using microwave and millimeter wave spectroscopy. The precise spectroscopic data provides evidence that the anomalous tendency of "folding the methylene unit" is favoured. Succinic acid, a dicarboxylic acid molecule, has been investigated spectroscopically with computational support to elucidate the complex aspects of its conformational composition. Due to the torsional freedom of the carbon backbone and hydroxy groups, a large number of potentially plausible conformers can be generated with an indication that the gauche conformer is favored over the trans form. The microwave and millimeter wave spectra have been analyzed and accurate spectroscopic constants have been derived that correlate best with those of the lowest energy gauche conformer. For an unambiguous conformational identification measurements were extended to the monosubstituted isotopologues, precisely determining the structural properties. Besides bond distances and angles, particularly the dihedral angle has been determined to be 67.76(11)1, confirming the anomalous tendency of the methylene units to favor gauche conformers when a short aliphatic segment is placed between two carbonyl groups.

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The Rotational Spectrum of Monothioformic Acid. III. Dipole Moment and Relative Intensity Measurements^1,2

Cited by 47 publications

References 10 publications

s-cis and s-trans Conformers of formic, thioformic and dithioformic acids. An ab initio study

s-cis and s-trans Conformers of formic, thioformic and dithioformic acids. An ab initio study

The Other Rotamer of Formic Acid, cis-HCOOH¹

Conformational steering in dicarboxy acids: the native structure of succinic acid

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The Rotational Spectrum of Monothioformic Acid. III. Dipole Moment and Relative Intensity Measurements1,2

Cited by 47 publications

References 10 publications

s-cis and s-trans Conformers of formic, thioformic and dithioformic acids. An ab initio study

s-cis and s-trans Conformers of formic, thioformic and dithioformic acids. An ab initio study

The Other Rotamer of Formic Acid, cis-HCOOH1

Conformational steering in dicarboxy acids: the native structure of succinic acid

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The Rotational Spectrum of Monothioformic Acid. III. Dipole Moment and Relative Intensity Measurements^1,2

The Other Rotamer of Formic Acid, cis-HCOOH¹