C.O. Della Védova

Separation of keto–enol tautomers in β-ketoesters: a gas chromatography–mass spectrometric study

Abstract The gas chromatographic behaviour for some β-ketoesters was studied. Additionally, the feasibility of the gas chromatographic separation of the corresponding tautomer forms was examined. In this work mass spectrometric detection allowed identification of both keto and enol forms and an estimation of their relative amounts for methylacetoacetate, α-chloromethylacetoacetate, ethylacetoacetate and α-chloroethylacetoacetate. This finding demonstrates slow tautomerisation kinetics permitting the chemical identity maintenance of the tautomers.

TGA-DTA, infrared and x-ray powder diffraction studies on strontium nitroprusside and its hydrates

Abstract Dehydration data for the tetra-, di- and monohydrate of strontium nitroprusside and the vibrational behaviour of the water molecules in normal and deuterated samples agree with crystal data previously reported (for the di- and tetrahydrate as single crystals) and in this paper (monohydrate as a powder). Four distinct types of water molecules are present in the three hydrates with one type (oxygen bonded to Sr 2+ ) in common. Other types are a non hydrogen-bonded molecule (dihydrate), a molecule bonded by a single hydrogen atom to the nitrogen atom of a cyanide group and a set of two molecules similarly bonded to the oxygen atom of the previous type (tetrahydrate). The spatial orientation of the NO groups of the nitroprusside ions in the tetrahydrate is confirmed by the observed dichroism of the corresponding stretching band.

N-Sulfinylimine compounds, R–NSO: a chemistry family with strong temperament

Abstract In this review, an update on the structural properties and theoretical studies of N -sulfinylimine compounds (R–NSO) is reported. They were deduced using several experimental techniques: gas–electron diffraction (GED), X-ray diffraction, 17 O NMR, ultraviolet-visible absorption spectroscopy (UV–Vis), FTIR (including matrix studies of molecular randomisation) and Raman (including pre-resonant Raman spectra). Data are compared with those obtained by theoretical calculations. With these tools, excited state geometry using the time-dependent theory was calculated for these kinds of compounds. The existence of pre-resonant Raman effect was reported recently for R–NSO compounds. The configuration of R–NSO compounds was checked for this series confirming the existence of only one syn configuration. This finding is corroborated by theoretical calculations. The method of preparation is also summarised.

S-ethyl thiochloroformate, ClC(O)SCH2CH3: Unusual conformational properties?

Abstract The conformational equilibrium of S-ethyl thiochloroformate, ClC(O)SCH2CH3, was determined by vibrational spectroscopy (FTIR and FTRaman spectra), ab initio and density functional theory calculations (HF/3-21G*, HF/6-31G* and B3PW91/6-31G*). The evaluation of experimental and theoretical results suggests the existence of two conformers syn, gauche (CO double bond syn with respect to the S–C single bond and C–S single bond gauche with respect to the C–C single bond, respectively) and syn, anti, being the former most stable one. The existence of this rotational isomerism is rather unexpected for this thioester compound, owing to the known conformational equilibrium reported for some thioesters that depends on the ClCSC torsion angle. Photolysis products of the compound irradiated in adequate inert gas matrices were identified as CO, SCO, C2H5SCl and C2H5Cl.

Tautomers and conformers of malonamide, NH2-C(O)-CH2-C(O)-NH2: vibrational analysis, NMR spectra and ab initio calculations

The conformational and tautomeric compositions of malonamide, NH2-C(O)-CH2-C(O)-NH2 were determined by vibrational spectroscopy and theoretical calculations (HF/6-31G*, B3PW91/6-31G*). Solid state Fourier transform infrared and Raman spectra were analysed. They reveal the existence of a diketo tautomer. Theoretical calculations predict a diketo structure belonging to the C1 symmetry group. No enol form is present in the molecule in the solid. 13C-NMR studies show only signals of a diketo tautomer.

VIBRATIONAL STUDIES OF FLUOROFORMYLIMINOSULFUR DIFLUORIDE : FC(O)NSF2

Abstract The Raman spectrum of liquid fluoroformyliminosulfur difluoride. FC(O)NSF2, and its IR spectrum of the vapor phase were obtained. The observed features and the polarized Raman spectra are consistent with the existence of only one conformer possessing Cs symmetry both in the vapor and liquid phases. Assignment of 13 of the 15 fundamental vibrations are reported. The UV-visible spectrum was recorded and its bands assigned. The preresonance Raman effect was not detected. A theoretical ab initio vibrational spectrum was also obtained using a 6-31G∗ basis set. Symmetry force constants arising from experimental data were determined for the A′ species.

Conformational and bond properties of chlorosulfonyl isocyanate, CISO2NCO

Abstract The Raman and IR spectra of chlorosulfonyl isocyanate in the liquid phase are reinvestigated, and the IR spectra of the vapour phase are recorded. A complete assignment of the observed bands is proposed. Subsequently a normal coordinate analysis is performed. Vibrational data confirm that CISO 2 NCO exists only in one single conformation in both phases. The presence of depolarized bands in the Raman spectra of the liquid phase is consistent with either C 1 symmetry and a very low rotational barrier between the two equivalent optic isomers or with a C S symmetry. This interpretation allows the rationalization of data obtained from several spectroscopic techniques. An unusual force constant-bond length relationship is found for the S-Cl moiety.

Spectroscopic and conformational comparative study of trimethyl chalcogenphosphates

Abstract Geometrical, conformational and spectroscopical properties of three chalcogenphosphates were studied comparatively. Rotational isomerism and conformational flexibility were evaluated for trimethyl phosphate, O , O , O -trimethyl thiophosphate and O , O , O -trimethyl selenophosphate by studying the vibrational and NMR spectroscopy. Semi empirical and ab initio calculations have been carried out. Experimental and theoretical results show similar conformational behavior, founding equivalent symmetries for conformations of minimal energies, but a decrease in the conformational flexibility is observed when going from O, to S and to Se species. This result would represent a new factor to explain the higher ability of interaction of O-organophosphorus compounds in some biological active sites, in esterases for example, with respect to the analogous S-organophosphorus compounds and Se-organophosphorus compounds.

A solid state study of the configuration and conformation of OSN–R (R=C6H5 and C6H3(CH3–CH2)2-2,6)

Abstract The X-ray crystal structures for N-sulfinyl-benzenamine (OSN–C 6 H 5 ) and N-sulfinyl-2,6-diethyl benzenamine (OSN–C 6 H 3 (CH 3 –CH 2 ) 2 -2,6) are reported. For OSN–C 6 H 5 a planar structure with syn configuration of the OSN–R group was determined. For OSN–C 6 H 3 (CH 3 –CH 2 ) 2 -2,6 this configuration was maintained, however, the spacial requirements of the substituents in the ortho position affect the planarity of the molecule. The OSN group is rotated by 55.3° from the planar structure. Ab initio calculations predict the most stable structures for both compounds.

Vibrational and conformational study of FSO2NCO: FT-IR, preresonance Raman effect, force field and theoretical calculations

Abstract Starting with ClSO 2 NCO and SbF 3 , fluorosulphuryl isocyanate, FSO 2 NCO, was prepared. FT-IR data for the vapour and Raman spectra for the liquid were obtained. The observed features and the pre-resonance Raman data are consistent with the existence of only one conformer possessing C 1 symmetry both in the vapour and liquid phase. For all but the torsional mode of this rotamer, experimental wavenumbers are reported. Symmetry force constants were calculated using a torsional frequency taken from ClSO 2 NCO. The experimental studies were augmented by ab initio calculations at various levels of sophistication (HF/3-21G*, HF/6-31G*, MP2/6-31G*). The predicted conformational properties for FSO 2 NCO are in good agreement with the experimental data.