J. Phys. Chem. 1991, 95,6912-6915
6912
(A4 Eta = EHF+ EFor the MP2 and QCID methods, the correlation energy can be written as (A-7) where Gbis the contribution to the correlation energy from each doubly excited determinant and is given by
qb= qb(ijllab)
(A-8)
Here a$ is the amplitude of each doubly excited configuration in the multideterminental wave function and (ollab) is the standard electron repulsion integral in the MO basis.** The dipole moment of a molecule is defined as the derivative of the total energy with respect to an external electric field Plot
= aEtot/aF
64-91
For a correlated method, p would then be
(A-10) (A-1 1) = PHF + ~m where PHF is the H F dipole moment and pm is the correlation correction to the HF dipole moment. The correlation corrections to the r and u dipole moments were obtained by numerical differentiation of the energy. Hence (A-12) Pwrr = ~ w n / A F Finally, by substituting (A-7) into (A-12), p, can be written as Pt0t
We can now define pab as a r , u, or r / u contribution to the correlation-corrected &pole moment from each doubly excited determinant in the wave function. Registry NO. ICN, 506-78-5.
Gas-Phase Structures and Conformations of Chlorodlfluoromethanesulfenyl Chloride, CCIF2SCI, and DlchlorofluoromethanesulfenylChloride, CC12FSCI Christoph Renschler," Hans-Georg Mack," Carlos 0. Della V6dova,lb and Heinz Oberhammer**lr Institut fur Physikalische und Theoretische Chemie, Universitiit Tiibingen, D- 7400 Tiibingen, Germany, and the Facultad de Ciencias Exactas, Departamento de Quimica, Quimica Inorganica, Universitad Nacional de La Plata, 1900 La Plata, Argentina (Received: March 18, 1991)
The gas-phase structures of CClF2SCl (1) and CC12FSCl (2) and their conformational composition have been studied by electron diffraction and ab initio calculations (HF/3-21G*). For CClF2SClthe trans conformation (methyl chlorine trans This ratio componds to a freaenergy to sulfenyl chlorine) is predominant (73 (5)%) relative to the gauche structure (27 (9%). difference AG = 1.0 (2) kcal/mol, which is in very good agreement with the ab initio value AE = 1.03 kcal/mol. For 2 the conformation with the methyl fluorine trans to the sulfenyl chlorine is higher in energy than the gauche structure by AG = 0.5 (4)kcal/mol (transxis = 82 (10)%18 (lo)%). The ab initio value (AE = 0.91 kcal/mol) is in reasonable agreement with the experiment. The calculated barriers to internal rotation are 4.58 (1) and 4.85 kcal/mol (2) for fluorine eclipsing the sulfenyl chlorine, and 6.09 (1) and 6.01 kcal/mol(2) for eclipsed chlorine atoms. The skeletal parameters of both compounds are very similar (first value refers to (I), second value to (2)): S-C = 1.813 (15), 1.811 (16) A; S-CI = 2.014 (3), 2.004 (3) A; and ClSC = 99.3 (6), 101.7 (7)O. The SCX angles (X = F or Cl) are strongly distorted from ideal tetrahedral values and differ by almost loo for trans or gauche positions of X.
Introduction
The conformational properties of molecules in general depend on several interactions which involve atoms, bonds, and/or lone pairs. The relative importance of these interactions varies strongly from one type of compounds to another and very little is known about the absolute magnitude of the individual contributions. In cases where one kind of interactions can be considered to be predominant such information can be obtained from known conformation or conformational composition. In chlorodifluoromethanesulfenyl chloride, CClF2SCl (l), and dichlorofluoromethanesulfenylchloride, CClzFSCl (2). two conformations are conceivable depending on the torsional position of the CClF2 and CC12Fgroup around the S-C single bond. The conformations of 1 are characterized by gauche or trans position of the methyl chlorine relative to the sulfenyl chlorine and those of 2 by gauche or trans position of the methyl fluorine relative to the sulfenyl chlorine. If we presume that the relative stability of the two conformers depends mainly on nonbonded interactions between sulfenyl chlorine and the methyl halogens, we can derive information on ( 1 ) (a) TObingen. (b) La Plata.
0022-3654/91/2095-6912502.50/0
CI-T
CI-G
F -1
F-G
the relative magnitude of Cb-CI and Cl-F interactions. In this study we report an electron diffraction analysis of the gas-phase structure and of the conformational composition of these two compounds. This investigation is supplemented by IR spectroscopy and by ab initio calculations of the geometric structures and of the torsional potentials for internal rotation. The calculations were performed in the HF/3-21G* approximation using the GAUSSIAN 86 program packagen2 (2) OAUSSIAN 86 Frisch, M. J.; Binkely. J. S.;Schlegel, H. B.; Raghavachari, K.;Melius, C. F.; Martin, R. L.; Stewart, J. J. P.; Bobrowicz, F. W.; Rohlfing, C. M.;Kahn, L. R.; DeFrees, D.F.; Sttgcr, R.; Whitdde, R. A,; FOX,D.J.;Fleuder, E. M.;Pople, J. A. Camegic-Mellon Quantum Chemistry Publishing Unit, Pittsburgh, PA, 1984.
0 1991 American Chemical Society
Gas-Phase Structures of CClF2SCl and CC12FSCI
The Journal of Physical Chemistry, Vol. 95, No. 18, 1991 6913 TABLE 1: Results of Electron Diffraction Analysis and ab Initio Calculations for CCIF$Wi
Geometric Parameters
CI gauche ai
CI trans
ed" c-c12
ai
ed
1.756 1.798 2.010 100.0 103.2
1.748 (12) 1.813 (IS) 2.014 (3) 99.3 (4)
p2 p, p4
ps
1.763 1.791 2.017 99.0
s-c-F1 } S-C-F2
112.3(6)
p6
111.7
1.741 1.820 2.013 100.3 103.8 112,3
s-c-CI2 F 1 -C-F2 FI-C-C12 F2-C-Cl2
103.8 (3) 108.1 (6)b 109.8 (4)
p,
107.6 107.3 109.3
111.8 109.4 109.4 108.9
115.6 108.6 108.9 ,08,4
180
65.7 27 ( 5 )
65.7
s-c
s-CI 1 c-s-CI 1
}
ti(CllSCCl2)
pe
180.0 73 ( 5 )
%
Interatomic Distances and Vibrational Amplitudes for Gauche Conformer b
1
3
2
I
5
RIA
Figure 1. CCIF2SCI. Experimental and calculated radial distribution functions and difference curve. The positions of interatomic distances of the main conformer (Cl trans) are indicated by perpendicular bars.
Infrared Spectra Five fundamental stretching vibrations are expected in the observed frequency range (4000-400 cm-l). The gas-phase 1R spectra give no evidence for the existence of a conformational mixture, or for the kind of conformer present. In the matrix IR spectra the splittings of the C-CI vibrations suggest the presence of two conformations in both molecules. The amount of splitting and the intensity ratios of the bands exclude the possibility of isotopic effects. The band assigned to v(C-Cl) in 1 at 875 cm-l splits in the matrix into two bands at 898 and 883 cm-I. This splitting (Au = 15 cm-') is in excellent agreement with the calculated value (HF/3-21G*) of Au = 15 cm-l (v(C-Cl) = 970 and 955 cm-l). The two bands at 852 and 823 cm-' corresponding to u,(C-CI) and us(C-Cl) in 2 split in the matrix into three bands at 852,820, and 790 cm-I. This observation is in accordance with the ab initio calculations, which predict the symmetric C-CI vibrations of the two conformers to nearly coincide (865 and 869 cm-I). The two asymmetric vibrations are calculated at 907 and 923 cm-I. Since it is not possible to assign the bands to the individual conformers and, furthermore, the absorption coeffcients are not known, it is not possible to determine the ratio of the two conformers from these spectra.
t,:;::
11 S..*F
C-F 1.33 0.050 (3) C-C12 1.751 o.052 S-C 1.81 S-CII 2.01 0.054 (2) FI.**F2 2.16 0.06oC F***CI2 2.54 0.076 (7)
2.63 2.80 2.92 1, F-.*CII 3.18 Cll.**C12 4.49 1,
1;
0.060 ( 5 ) 0.053 ( 5 ) 0.066 (17) 0.120 (6)' 0.079 ( 5 )
1s
/; 1, 1, 1,
O r , distances in A and L, angles in degrees. Error limits are 30 values and include a possible scale error of 0.1% for bond lengths. For atom numbering see Figure 3. bDependent parameter. CNotrefined.
Electron Diffraction Analysis
cbkrodiflwnnnethaneslChloride (1). Preliminary values for the geometric parameters and for the ratio of the two possible conformers were derived from the radial distribution curve (Figure 1). In the distance range r > 2.6 A the calculated functions strongly depend on the conformation. In the CI gauche conformer the longest nonbonded distance (F1-411) occurs at 4.1 A (Figure 1, CI-G), for the C1 trans structure the peak at 4.5 A corresponds to the Cll***C12distance (Figure 1, CI-T). Comparison with the experiment (Figure 1, Exp) results in an approximate ratio tramgauche of 3: 1. In the following least-squares refinement the molecular intensities were modified with a diagonal weight matrix and scattering amplituda and phases of Haase3 were used. For the trans conformer C, symmetry was assumed. The ab initio calculations predict considerable differences for geometric parameters of the trans and gauche form, especially for the carbon bond angles. These calculated differences were used as constraints in the (3) Haaw. J. 2.Narurforsch. 1970, ISA, 936.
0
1
2
3
b
5
RIA Figure 2. CCI,FSCI. Experimental and calculated radial distribution functions and difference curve. The positions of interatomic distances of the main conformer (F gauche) are indicated by perpendicular bars.
least-squares analyses. The vibrational amplitudes for the closely spaced C-CI and S-C distances were set equal and that for the F.-F distance was estimated. Vibrational amplitudes for the gauche form were set equal to those of the trans conformer, exchanging the values for the trans distances (Cll4212 and Cl1-Fl) and for gauche distances (CIl-.Fl and Cll--C12). With these assumptions eight geometric parameters, nine vibrational amplitudes, and the conformer ratio were refined simultaneously. The following correlation coefficients had values larger than lo.'II:P2/pp = -0.94, pz/p6 0.80, p3/pS -0.83, pz/l2 = 0.95, p 3 / l l = -0.94, ps/12 = 0.77, and 16/17= 0.74 (for numbering of geometric parameters pi and vibrational amplitudes 1, see Table I). The geometric parameters together with the ab initio results
Renschler et al.
6914 The Journal of Physical Chemistry, Vol. 95, No. 18, 1991
FTs'cL
A E ? 6f,
(1-1
(1-G
Li-l
F-G
Figure 3. Molecular models for the main conformers of CClF#Cl and CCI2FSCI and atom numbering. 0
CdcuhHOns for CCllFSCl
C-F
1.329 (5)
PI
c-c12 } c-c13 ~~.
1.750 (8) 1.811 (16) 2.004 (3) 101.7 (7) 111.3 (26) 101.3 (6) 1 10.8 (30) 111.7 (19)b 110.6 (8)
PZ
62 (7) 82 (IO)
PI0
~
s-c
SCI1 c-SCI 1 S-C-F
s-c-c13 s-c-CI2 CI-c-CI
1
F-c-c12 F-C-C13 a(Cl ISCF) %
P3 P4
Ps P6 P7
Pa P9
1.371 1.768
1.341 1.743
ai 1.383 1.765
1.806 2.016 100.0 110.3 105.6 114.5 110.7 107.3 108.4 58.4
1.817 2.000 103.2 101.7 110.2
1.812 2.012 101.5 100.7 114.2
111.6 110.8
110.6 108.1
180.0 18 (10)
180.0
Interatomic Distances and Vibrational Amplitudes for Gauche Conformer
s-c
S-CI
1.33 0.049 (6) I , S...CI3 0.054 (7) 12 1.81 2.00 0.061 (2) I , C.**CII
90
120
150
180
F trans
ed
~
C-F
60
6 (CLCSCI) Figure 4. CCIF$CI. Potential function for the torsion around the S42 bond, calculated by HF/3-21G*.
TABLE 11: R d b of Electron Diffraction Analysis and ab Initio Geometric Parameters F gauche ed" ai
30
2.93 2.96 0.090
Cll***C13 4.48 0.084 (6)
1.1
erSee footnotes in Table I.
and the vibrational amplitudes are collected in Table I. WcblorofluorometbanesuHenylCbloride (2). The calculated radial distribution functions for the two conformers, F trans and F gauche, and the experimental curve are shown in Figure 2. The peak at ca. 4.1 A in the trans form corresponds to the CIl--F distance and the peak at ca. 4.5 A in the gauche form to the C11.413 distance. The difference between the two curves near 2.5 A is mainly due to different SCF and SCCl angles in the trans and gauche conformations. The experimental radial distribution function demonstrates that the gauche form is predominant and comparison with the calculated curves results in an approximate ratio gauchetrans of 5:l. The least-squares refinement was camed out analogous to that for 1. The geometric parameters for the gauche form were refined assuming equal C-CI bond lengths and equal FCCl bond angles (Le., FCCl2 = FCCI3). Both assumptions are well justified by the ab initio calculations (see Table 11). The differences between geometric parameters of the trans and gauche conformers were again fixed to the calculated values and constraints for vibrational amplitudes are evident from Table 11. With these assumptions ten geometric parameters, seven vibrational amplitudes, and the conformer ratio were refined simultaneously. Several large correlations (larger than 10.71) between refined parameters occur for this compound and consequently standard deviations for some parameters are high: p2/p3= 4.95, p2/& = 0.71, pn/& = 4 . 7 6 , Pb/PS = 4.75, Pb/P9 e 4 - 8 8 ?Pb/PlO 4.75, PdPlO = 0.94, P2/12 3 0.94, pa/l2.= 4.95, ~7112= 0.72, palls 4.88, plo/ls 4.90
(for numbering of geometric parameters p f and vibrational amsee Table 11). The results of the electron diffraction plitudes Ik
analysis and of the ab initio calculations are presented in Table 11.
Discussion The geometries of both molecules are reasonably well reproduced by the ab initio calculations, considering the small basis sets. Larger discrepancies exist for the C-F bonds which arc predicted too long and for the SCCl angles, where in all cases the calculated values are larger by about 4 O relative to the experimental angles. For the carbon bond angles a remarkably strong distortion from the ideal tetrahedral values is obacmed. The SCX angles (X = F or Cl) differ by almost loo depending on the position of X,i.e., trans or gauche to C11. The skeletal parameters (S-C,S-C1, and CSCl) of both compounds are very similar to those of CF3SCl (S-C = 1.842 (6) A, S-CI = 2.015 (3) A, and CSCl = 98.9 (4)0).4 The most interesting result of this investigation is the conformational composition for these compounds. In CClFgCl the conformationwith the methyl chlorine trans to the sulfenyl chlorine is energetically favored over the CI gauche form. The experimental ratio (27 (5)% CI gauche) correspondsto a free-mergy diffence of AG = 1.0 (2) kcal/mol, if the multiplicity of the gauche form is taken into account. The difference between AG and AE (emrgy difference between minima of the potential curve) is much smaller than the experimental error limits of AG. According to the ab initio calculations the entropy difference is a.0.1 cal/(mol*K) and the difference in zero-point vibrational energies is 25 cal/mol. In CC12FSCI the F gauche conformation (82 (lo)%) is favored over the F trans form (18 (lo)%) corresponding to AE AG = 0.5 (4) kcal/mol. The ab inito calculations reproduce the energy difference for both compounds within the experimental error limits or close to it, i.e. AE = 1.03 kcal/mol for 1 and AE = 0.91 kcal/mol for 2. If we presume that the relative stability of the two conformers depends only on nonbonded interactions between the sulfenyl chlorine and the methyl halogens, which arc in gauche position to C11, we can estimate the relative magnitude of (CI-.Cl),wk and (CI--F),* interactions. In CClF$CI the low-energy conformer has two (CI--F),& contacts and the high-energy conformer one (Cl-*F),d and one (Cl***Cl),, contact. Thus, the ( C l - c l ) ~interaction energy is higher than the (C1-F)interaction by the energy difference between the two conformers, i.e., 1.O (2) kcal/mol. In CC12FSCl the energy difference between the two forms (0.5 (4) kcal/mol) again corresponds to the difference in interaction energies between (CI..-CI),,h and (CI...F),d contacts. This simple model assumes that all other interactions in the two conformers are equal and thus do not effect the energy difference. Since the nonbonded CI-CI and CI-F distances are slightly different in the two compounds, we cannot expect to obtain exactly the same energy difference in both cases. According to the electron diffraction experiment, the AG values differ more strongly (1 .O (2) vs 0.5
-
(4) Oberhammer, H.;Gomblcr, W.;Willner, H.J . Mol. Struct. 1%1,70, 213.
The Journal of Physical Chemistry, Vol. 95, No. 18, 1991 6915
Gas-Phase Structures of CCIF,SCI and CC1,FSCl
I
0
0
30
60
90
120
Figure 5. CC12FSCI.Potential function for the torsion around the S-C bond, calculated by HF/3-21G*.
1
I
0
5
10
20
15
25
30
5
10
20
15
25
30
35
Sk'
180 6(FCSCII 150
35
sh-' Figure 6. CCIF$CI. Experimental (dots) and calculated (full line) molecular scattering intensities and differences.
(4) kcal/mol) than the calculated energy differences (1.03 vs 0.91 kcal/mol), but experimental and calculated values agree with each other within the experimental error limits. The electron diffraction experiment does not give reliable information for the barriers to internal rotation for both compounds. Therefore, the potential functions for internal rotation were calculated (see Figures 4 and 5) and the following barriers were obtained: 4.58 (1) and 4.85 kcal/mol(2) for fluorine eclipsing the sulfenyl chlorine and 6.09 (1) and 6.01 kcal/mol (2) for eclipsed chlorine atoms. These rather high barriers are in close agreement with the experimental value for CF3SCI (5.8 (16) kcal/mol) .*
Experimental Section
Figure 7. CCI2FSCI. Experimental (dots) and calculated (full line) molecular scattering intensities and differences.
spectroscopy. Infrared spectra between 4000 and 400 cm-' were recorded with a FT Bruker IFS 856 spectrometer with resolution of 1 cm-'. Low-temperature matrix spectra in N2 were taken in a cryogenic system using the continuous deposition technique. The following wavenumbers were observed: CCIF2SCI (gas phase): 1130 (u,(C-F)), 1111 (v,(C-F)), 875 (v(C-CI)), 546 (v(S-CI)), 460 (v(C-S)) cm-'; CCIF#CI (N2 matrix): 1120, 1099,898,883, 546, 460 cm-'. CC12FSCl (gas-phase): 1069 (v(C-F)), 852 (vJC-Cl)), 823 (v,(C-CI)), 546 (v(S-Cl)), 462 (v(C-S)) cm-'; CC1,FSCl (N2 matrix): 1057,852,820,790,546 and 458 cm-'. The electron diffraction intensities were recorded at two camera distances with the Balzers Gasdiffractograph KD-G2.6 The electron wavelength was calibrated by ZnO diffraction patterns. The sample reservoirs were kept at -26 OC (1) and 0 OC (2) and the inlet system and nozzle were maintained at room temperature. The camera pressure never exceeded l(Tsmhr. Two photographic plates for each compound and camera distance were analyzed with the usual procedures.' The averaged molecular intensities in the s range 2-18 A-' and 8-35 A-' in steps of hs = 0.2 A-l are presented in Figures 6 and 7. Acknowledgment. We acknowledge financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. C.O.D.V. thanks Prof. Dr. mult. A. Haas (RuhrUniversitiit Bochum, Germany) for his stimulating contribution and thanks the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Argentina, Facultad de Ciencias Exactas (UNLP) and Fundacion Antorchas, for financial support. Re&@ NO. 1, 993-38-4; 2, 2712-93-8; N2, 7727-37-9.
The compounds 1 and 2 were synthesized according to ref 5. The purity of the samples was checked by IR and I9F NMR
Supplementary Material Available: Tables of the total intensities for CClF2SCI and CClzFSCl (4 pages). Ordering information is given on any current masthead page.
(5) H m ,A.; Niemann, U. Adu. Inorg. Chem. Rcrdlochem. 1976,18,143, and references cited therein.
(6) Oberhammer, H. Molecular Structures by Dsffrection Meilrods; The Chemical Society: London, 1976; Vol. 4, p 24.
