The rotational barrier around the C-S bond in chlorocarbonylsulphenyl
chloride (CIC(O)SCI)is investigated using the INDO, PCILO and GAUSSIAN-70techniques. The results confirm the existence of planar cis and trans conformers with a higher stability of the latter, as suggested by previous vibrational results. The origin of the rotational barrier is due to an increase of electronic delocalization as demonstrated by INDO and PCILO calculations. The optimized geometrical parameters obtained by means of the ab-initio method with an STO-3G basis set are reported for the different conformers.
Valence force constants have been calculated and the values
obtained compare fairly well with the results from a previous
normaI coordinate calculation. The experimental electronic spectrum, maximum molar absortivities, oscillator strengths and atentative assignrnent of its electronic bands, are reported

Alicia H. Jubert

Carlos O. Della Vedova

Pedro J. Aymonino

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CROATICA CHEMICA ACTA CCACAA 60 (2) 207-213 (1987)CCA-1718YU ISSN 0011-1643UDC 541Original Scientific PaperTheoretical Calculation of the Rotational Barrier, Valence ForceConstants and Experimental Electronic Spectrum ofChlorocarbonylsulphenyl Chloride (CIC(O)SCI)Alicia H. Jubert/", Carlos O. Della Vedova* and Pedro J. Aymonino*Departamento de Quimica, Programa QUINOR,Facultad de Ciencias, Exactas,Universidad Nacional de La Plata, 47 y 115, (1900) La Plata, Republica ArgentinaReceived January 8, 1986The rotational barrier around the C-S bond in chlorocarbo-nylsulphenyl chloride (CIC(O)SCI)is investigated using the INDO,PCILO and GAUSSIAN-70 techniques. The results confirm theexistence of planar cis and trans conformers with a higher sta-bility of the latter, as suggested by previous vibrational results.The origin of the rotational barrier is due to an increase of elec-tronic delocalization as demonstrated by INDO and PCILO cal-culations.The optimized geometrical parameters obtained by means ofthe ab-initio method with an STO-3G basis set are reported forthe different conformers.Valence force constants have been calculated and the valuesobtained compare fairly well with the results from a previousnormaI coordinate calculation.The experimental electronic spectrum, maximum molar ab-sortivities, oscillator strengths and atentative assignrnent of itselectronic bands, are reported.INTRODUCTIONThe IR and Raman spectra of gaseous and liquid chlorocarbonylsulphenylchloride (ClC(O)SCl) 1, as well as its electron diffraction study" suggest theexistence of a stable trans planar conformer as the most stable one. Previousexperimental and theoretical studies performed on its homolog FC(O}SC13showthat it exists as a conformational mixture, as indicated by the existence of twoCO stretching bands with a temperature dependence of their relative intensities.In order to explain the different behaviour and properties of the com-pounds, a theoretical treatment was performed by means of semiempiricaland ab-initio quantum chemistry techniques. The barrier to rotation aboutthe C-S bond was calculated using INDO, PCILO and ab-initio methods.v"Valence force constants were estimated from the INDO data by a simplemethod derived from a point charge model for the chemical bond." The* Member of the Research Career of CIC, Provincia de Buenos Aires, Repu-blica Argentina. To whom correspondence should be addressed.* Member of the Research Career of CONICET,Republica Argentina.208 A. H. JUBERT ET AL.present results are compared with numerical values obtained previously bya normal coordinate analysis.'The experimental electronic spectrum of CIC(O)SCl is reported andthe bands tentatively assigned.EXPERIMENTALThe sample of CIC(O)SCI was prepared as published.' Electronic spectra wererun with a Shimadzu UV-300 Spectrophotometer. Gas phase speetra were measuredin a 10 cm quarz gas eell.COMPUTATIONAL PROCEDUREMolecular wave functions of the different conformers were calculated usingthe INDO method employing the original parametrization given by Pople et aL,4.The PCILO method was also used", as well as the GAUSSIAN-70 package withan STO-3G basis set."The plan ar trans conformation (regarding the halogen atom s) was suggested tobe the most stable one by analogy with FC(O)SCP as well as by the observedband envelopes in the IR spectrum in the gas phase, the polarization of some bandsin the Raman spectrum in the liquid phase' and by eleetron diffraction measure-ments,"The molecular parameters were taken trom" (in A or angular degrees) c=o:1.183; C-Cl: 1.749; C-S: 1.791; S-Cl: 2.01; sco. 126.9; SCCl: 106.0; CSCl: 100.6.The geometries conformations of the three principal conformers are depicted inFigure 1. The geometric parameters of the eonformers were optimized by mini-mizing the total energy with respect to the geometry variables defining the struc-ture. This was .done by interpolation between energies calculated for a numberof specific geometries around the minimum (loeal) energy. With the optimizedstructural parameters, density and overlap matrices, total and bond energies forthe three eonformers were determined.ooCltrans ciso\!}-----{ S ClClqaucbeFigure 1. Geometries of the conformers of chlorocarbonylsulphenyl chloride.CIC(O)SCl 209RESULTS AND DISCUSSIONThe conformational energies involved in the rotation of the S-Cl grouparound the C-S bond were calculated for different values of the azimuthalangle e formed by the C-S bond and the ClC(O)S(xz) plane. The resultsobtained by the INDO method confirm that for CSCl = 104° the cis and thetrans conformers have the lowest energy and that the trans configurationis 145.9 kJ/mol more stable than the cis one, while the height of the rotationalbarrier is 10.9 kJ/mol. The PCILO and GAUSSIAN-70 methods predict thatthe trans conformer is 1.9 and 13.4 kJ/mol more stable than the cis oneand that the corresponding heights of the rotational barrier are 36.4 and 35.2kJ/mol, repectively. The experirnental" and the optimized geometrical para-mete rs obtained by means of the ab-initio technique are summarized inTable I for the different conformers.TABLE IExperimental and Optimized Bond Angles and Bond Lengths jar the DifferentConformers of ClC(O)SCl, Obtained by Means of the Ab-initio Technique(GAUSSIAN-70 with STO-3G Basis Sets'Experimen tal il' TRANS GAUCHE CISC-Cl 1.749 1.33 1.83 1.82C-S 1.791 1.80 1.83 1.81S-Cl 2.01 2.08 2.09 2.07C=O 1.183 1.21 1.21 1.20ClCS 106.0 109.4 114.9 115.3CSCl 100.6 100.4 97.6 104.5OCS 126.9 128.5 125.3 122.8* In A or angular degrees for bond lengths or angles, respecti vely.il' From ref. 2.We studied the orbital symmetries of the frontier orbitals and theirassociated eigenvalues for CIC(O)SCI in order to correlate the results obtainedfrom different methods. It was found that they may be correlated withoutany inversion of the order of their eigenvalues. The HOMO is localized onthe S-Cl bond and it has (J symmetry. The results indicate, at least quali-tatively, that the existence of the trans conformer is favoured over the cisand gauche configuration. The INDO calculation shows from the molecularorbital analysis that the lone pairs of the sulphur and chlorine atoms aremore localized in the gauche form than in the planar configuration. Thus,it can be postulated that the origin of the barrier is in the decrease of thedelocalization for the gauche conformer. Consequently, the major relativestability of the planar conformers should be explained by their highestdelocalization. Also, the changes in charge density caused by a trans-gaucherotation show that in the gauche form the carbonyl oxygen and carbonatoms lose negative and positive charges, respectively, while the C-S bondindex in the planar configuration is higher than in the gauche configuration,showing an increase of delocalization.If we divide the total energy variation obtained by means of the PCILOmethod in to its components: the zeroth order energy (~Eo) and the corre-sponding corrections of the second and third order (~(E2 + E3)), the termr210 A. H. JUBERT ET AL.of higher weight could be determined and the rotational barrier originderived. f.. ED and f.. (E2 +E3) could be considered as measures of the energyvariation due to the repulsion between non-bond ed atoms and the electronicdelocalization, respectively. Figure 2 depicts the results of this analysis forthe trans conformer. As can be seen, the second and third order energy cor-rections are the major contributors to the total energy and the origin of therotational barrier is in the variation of the electronic delocalization.20"- ,\\\\\\\\\\\\\\\\\\\\\\\\\,[ !.kJ.lmol301045 90 145Figure 2. Decomposition of the variation of the total energy obtained by thePCrLO method for trans ClC(O)SCl:tJ. ET (--) total energy variation, tJ. ED (_._):zeroth order energy, tJ. (E2 + E3) (- - - -): the second and third order correctionsto the energy.The valence force constants were estimated from the expression:?where ZA: charge of atom A as used in the INDO approximation, qB: netcharge on atom B, QA: gross charge on atom A, R: bond distance, BAB: bondindex calculated from the Wiberg bond index." For single bonds BAB:;:: WAB,for double bonds BAB = WABC"+ 2-'/' WAB" and for the triple bonds BAB == WABC"+ (2/3) 21/2 WAB". The factor (ZA - 2)/ZA' the so called atomic dipolecontribution, occurs only when atom A possesses lone pairs, as in P, N,halogens, etc. Our results are listed in Table II together with those obtainedpreviously with a normal coordinate analysis.' The comparison of internal forceconstants shows that the values obtained are reasonable. As an additionalCIC(O)SCl 211TABLE IIINDO and Stepwise CoupHng Force Constants for CLC(O)SCL*fe-s fCl-S fc!_c ReferenceINDOBecher- Ma ttes13.6012.603.103.182.903.212.523.17this work[1]* Units are mdyn A-l.check of the computational results, the S-Cl force constant for the SChmolecule was also obtained using the same procedure. The value comparedfairly well with the result obtained by means of normal coordinate analysis[3.32 mdyn A-l against 2.77 mdyn kl].9TABLE IIIExperimentaL ELectronic Spectrum of ChLorocarbonyLsuLphenyL ChLoride: TransitionEnergies, Maximum MoLar Absortivities (E) OsciHator Strengths (f) and TentativeAssignmentsTransitionenergy (nm) fexp assignation22030043001200.1510.00362n* ~ nn*~nThe experimental electronic spectrum of CIC(O)SCI is reported in Figure 3and its bands at 220 and 300 nm are assigned to the 1t* ~ 1t and 1t* ~ ntransition, respectively. Tentatively, we can correlate the 1t* ~ n transitionA241.81.20.6200 300 400 AhmlFigure 3. Electronic spectrum of chlorocarbonylsulphenyl chloride. Optical path10 cm. Pressure 30 torr.:212 A. H. JUBERT ET AL.with the excitation of asingle electro n from the HOMO, localized on thesulphur lone pair, to the LUMO + 1 localized on the C=O bond.In Table III the maximum molar absortivities and the oscillator strengthsof the electronic bands of ClC(O)SCl are reported, as well as tentative as-signments.CONCLUSIONSIt has been found that tmns ClC(O)SCl is 1.9 or 13.4 kJ/mol more stablethan the cis conformer and the height of the rotational barrier is 36.4 or 35.2kJ/mol, as calculated by the PCILO and ab-initio methods, respectively. TheINDO method also predicts that the trans conformer is the most stable,although its results are far apart from those obtained by the other twomethods.The origin of the rotational barrier is due to electronic delocalization,as demonstrated by INDO and PCILO calculations.The ab-initio technique yielded a geometry which agreed with experi-mental results'' and can be considered as reliable since as we go from the cisto trans conformer the CSCl and ClCS angles decrease as expected due tothe repulsion between the lone pairs of both Cl atoms.The values found for the semiempirical valence force constants comparefavourably with the. results from a previous normal coordinate calculation.The bands found in the electronic spectrum of ClC(O)SCl are possibly dueto 1t* ~ 1t and 1t* ~ n transitions.Acknowledgements. - Thanks are due to CONICET (Programa QUINOR),SUBCYT and CIC Provincia de Buenos Aires, Argentina, for financial support.REFERENCE S1. C. O. De 11aVe d ova, E. H. Cu t i n, E. L. V are t t i, and P. J. A y m o-n i n o, Can. J. Spectrosc. 29 (1984) 69.2. Qua n g S h e n and K. Ha gen, J. MoL Struct. 128 (1985) 41.3. C. O. De 11aVe d ova, E. L. Va r e t t i, and P. J. A y m on i n o, Can. J.Spectrosc. 28 (1983) 107.4. J. A. P oP 1e, D. F. S a n t r s, and G. A. Se gal, J. Chem. Phys. 43 (1965)5129; J. A. P o p 1e and G. A. Se gal, J. Chem. Phys. 44 (1966) 3289; J. A.P o p 1e, D. F. S a n t r y, and G. A. Se gal, J. Chem. Phys. 43 (1965) 5136;J. A. P o p 1e and D. L. B e ver i d g e, Approximate molecular orbital theory,New York, McGraw Hill, 1970.5. S. D i ner, J. P. Ma 1rie u, and P. Cl ave r i s, Theoret. Chim. Acta 13(1969) 1; S. Diner, J. P. Malrieu, F. Jordan, and M. Gilbert,Theoret. Chim. Acta 15 (1969) 100; F. Jordan, M. Gilbert, J. P. Malrieu,and V. P i n c i n e l l i, Theoret. Chim. Acta 15 (1969) 211.6. W. J. He h r e, W. A. Lat han, R. D i t c h f i e 1d, M. D. New t o n, andJ. A. P o P1e, GAUSSIAN 70 Program QCPE No 236; R. Di t c h f i e 1d, N.. J.He h r e, and J. A. P o p 1e, J. Chem. Phys. 54 (1971) 724.7. W. K o s m u s, Z. Naturjorsch. 33a (1978) 1956.8. K. B. W i b e r g, Tetrahedron 24 (1968) 1083.9. D. B i e 1efe 1d t and H. Will ner, Spectrochim. Acta 36A (1980) 989.CIC(O)SCl 213SAŽETAKTeorijski račun rotacijske barijere i valentnih konstanti sila te eksperimentalnielektronski spektar klorokarbonilsulfanil klorida (CIC(O)SCI)ALicia H. Jubert, Carlos O. DeLLa Vedova i Pedro J. AymoninoBarijera za rotaciju oko veze C-S u klorokarbonilsulfanil-kloridu (CIC(O)SCI)istraživana je s pomoću INDO, PCILO i GAUSSIAN-70 računa. Rezultati potvrđujupostojanje planarnih cis- i trans-konformera te veću stabilnost trans-konformera,u skladu s prijašnjim rezultatima vibracijske analize. INDO i PCILO računi poka-zuju da rotacijska barijera nastaje uslijed pojačane delokalizacije elektrona.Optimizrrani geometrijski parametri na temelju računa ab initio s baznimskupom STO-3G navedeni su za različite konformere.Izračunane valentne konstante sila slične su rezultatima prijašnje analizenormalnih koordinata.Također su prikazani eksperimentalni elektronski spektar, maksimalne molarneapsorbancije, oscilatorske jakosti, kao i tentativna asignacija elektronskih vrpci.Uz maksimalne molarne apsorbancije i oscilatorske jakosti, prikazan je ieksperimentalni elektronski spektar te tentativna asignacija elektronskih vrpci.

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Theoretical Calculation of the Rotational Barrier, Valence Force Constants and Experimental Electronic Spectrum of Chlorocarbonylsulphenyl Chloride (ClC(O)SCl)

Theoretical Calculation of the Rotational Barrier, Valence Force Constants and Experimental Electronic Spectrum of Chlorocarbonylsulphenyl Chloride (ClC(O)SCl)

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