- Email: [email protected]
The crystal and molecular structures of trans-1,4-dichlorocyclohexane
Journal
of
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular
Structure 445
( 1998) 269-275
The crystal and molecular structures of trans- 1,4-dichlorocyclohexane’ Per Olav Kvernberg, Department
of Chemistry, Received
Bj@rn Pedersen*,
University
ofOslo,
19 September
Christian R@mming
Box 1033 Blindem,
1997; accepted
N-0315
20 October
Oslo, Norway
1997
Abstract A new phase transition in the title compound is observed at 260 K by DSC and NMR. Furthermore, the phase stable between 260 K and 280 K is found to be triclinic and not monoclinic as believed earlier. The structure is determined from single crystal X-ray data, and the molecules are found to be in the ee chair conformation. In the phase stable below 260 K the ‘“C CPMAS NMR spectrum shows that the molecules are in the aa chair conformation. 0 1998 Elsevier Science B.V. Keywords: Phase transition;
NMR spectroscopy;
Crystal structure; X-ray diffraction
1. Introduction In connection with Otto Bastianseris 70th birthday in 1988 Bjarn Pedersen published an NMR study of trans-1,Cdichlorocyclohexane (DCC)-a classical compound in the Hassel-Bastiansen tradition [ 11. We have continued the study of this compound, and we will in this paper show that the phase relations in solid DCC is somewhat more complex than found by Hassel er al. DCC has been found to exist in two chair conformations: au and ee. Hassel and Lunde [2] reported a transition point in solid DCC at 12-13°C. They suggested that the modification stable below this temperature has a crystal structure corresponding to that of the other tram- 1,4-dihalogenocyclohexanes showed by them from single crystal X-ray data to be monoclinic with the molecules in the ee conformation. Dahl, Hassel and Ramming [3] have studied * Corresponding author. Tel: +47 22 85 56 90; fax: +47 22 85 47 71; e-mail: [email protected]. ’Dedicated to the memory of Professor Otto Bastiansen.
the phase stable above 12°C using single crystal Xray methods and ‘H-NMR. Due to extraordinarily strong thermal damping the number of independent X-ray reflections was found to be very limited. They concluded that the structure is disordered, and that the molecules are in the ee conformation. Infrared investigations by Ellestad and Klaboe [4] indicated that the phase stable above 12°C consists of a mixture of ee and au conformers. They also found that by applying pressure crystals of the au conformer formed at room temperature, and that crystals of the au conformer formed when an amorphous solid, obtained by shock freezing at 90 K, was annealed at temperatures below 10°C. In the vapour of DCC the ee and au conformers exist in nearly equal amounts [5]. Roughly equal amounts of both conformers are observed when DCC is dissolved in non-polar solvents. In polar solvents, however, the equilibrium is shifted in favour of the ee conformer with its larger electric quadrupole moments (both conformers have zero electric dipole moment) [ 61.
0022-2860/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved PII SOO22-2860(97)00430-4
210
P.O. Kvernberg et al./Journcd of Moleculur Structure 445 (1998) 269-275
2. Experimental
50.3 MHz on a Bruker DMX Avance spectrometer equipped with a 4.8 T magnet. Some preliminary spectra were also recorded at 75 MHz on a Bruker MSL spectrometer in Uppsala. The 13CCPMAS spectrum given in Fig. 1 was observed of a sample kept at about 2.50 K for several days before placing it in the NMR probe at 253 K. The spectrum did not change when cooling the sample to 243 K. However, when the sample was heated to 263 K the spectrum slowly changed to the spectrum shown in Fig. 2. In Fig. 3 the relative amount of the low temperature phase as a function of time is shown. Assuming first order kinetics the half-life is about 1 h. This slow rate may explain why this phase transition has not been detected earlier. The existence of this phase transition is not in conflict with the many observations made by Ellestad and Klaboe [4] in their careful IR study. We are now attempting to grow single crystals of this new phase stable below 260 K for a crystal structure determination. At about 280 K we observed a small discontinuity in the position of the two peaks as a function of temperature as shown in Fig. 4. This supported the accepted view that the phase transition is not due to a conformational change, but due to a change from an
2.1. The sample The sample of DCC was a commercial sample from TCI. Well developed crystals formed by sublimation when the sample was kept in a refrigerator at about 4”C, and they were used without further purification. 2.2. DSC analysis The analysis was performed on a Mettler TA3000 system. Two endothermic peaks were detected in the temperature region from 110 K to 320 K obtained by scanning at a rate of 1 K min-‘. We found a large, narrow peak at 300 K (AH = 5.8 kJ mol-‘) and one smaller and broader peak at 273 K (AH = 1.l kJ mol-‘). In one scan at a slower rate only the high temperature peak was observed. Scanning from high to low temperature shifted the peaks 20 K to lower temperature. 2.3. C CPMAS NMR The 13C CPMAS
NMR spectra were recorded
at
I”“I”“I~“‘I”“l”“I”‘~I”““““”
65
60
‘1
55
50
45
Fig. 1. ’'C-CPMASspectrum of polycrystalline tram-1,4-dichlorocyclohexane IO s recycle time, I .5 ms contact time, 12 kHz rotation rate.
40
35
30
at 253 K. Recording conditions:
25
mm
16 scans, 66 ms aqusition time,
211
P.O. Kvernberg et al./Journal of Molecular Structure 445 (1998) 269-275
I
”
“I’.
Fig. 2. ’'C-MAS spectrum polarisation.
1
60
65
of polycrystalline
1.
55
“‘I”“(‘,
”
45
50
trans- I ,4-dichlorocyclohexane
I
”
”
I
”
”
at 263 K. Recording
I
”
”
30
35
40
1 ”
25
conditions
as in Fig.
ordered phase to a disordered (plastic) phase. In the ‘H-study published earlier no discontinuities in the line width or the spin lattice relaxation time curves as a function of temperature were observed [ 11.
Crystals were formed by sublimation at 277 K. A needle-formed single crystal was mounted on the
J
/
25
50 Time/minutes
Fig. 3. The mole fraction of the low temperature as a function of time at 263 K.
I, but without cross-
C-l
2.4. X-ray crystallography
0
1
.-.
60
0.00
”
ppm
75
100
phase (the aa solid)
59
? +?====
36 4 260
270
Fig. 4. The chemical temperature.
290 300 280 Temperature/K shifts
310
320
of the ee solid as a function
of
272
P.O. Kvernherg
et ul./Journc~l
of Molecular Structure
goniometer head in a cold carbon dioxide atmosphere and put into the cold nitrogen stream at 140 K on a NICOLET P3F diffractometer. We believe this sudden cooling preserved the crystal structure of the ee solid stable between 280 K and 260 K. (If the crystal was cooled slowly it changed from a single crystal to a powder. This observation supported the existence of a low temperature phase transition.) Unit cell dimensions were determined by a least squares fit to the refined diffractometer settings of 25 general reflections with 20” < 28 < 39”. Details of the experimental conditions for intensity measurements are given in Table 1. The intensities were corrected for Lorentz and polarisation effects; no corrections for absorption and extinction were applied. The structure was determined and refined using the SHELXTL program package [7]. The non-hydrogen atoms were refined with anisotropic thermal parameters; hydrogen positions were found from a difference Fourier map and refined with isotropic thermal parameters. Final figures of merit are included in Table 1. Table
Positional and equivalent isotropic thermal parameters for the atoms are listed in Table 2. Structure factors, lists of thermal parameters, and a complete list of bond lengths, bond angles and torsion angles may be obtained from C. Ramming upon request.
3. Results 3.1. Phase relations We interpret the observations in terms of the following model: at temperatures below 260 K the spectrum in Fig. 1 shows that an aa solid is the stable phase. Above 260 K the stable phase is an ee solid. The phase transition at 280 K is the phase transition observed by Hassel and Lunde [2]. In this phase transition the packing and motion change, but both phases are built with ee conformers. The exact temperature where the phase transition takes place is uncertain. Ellestad and Klabo found 15°C in their DTA analysis. In our DSC analysis the peak maximum is at 17.4”C (scan rate 1 K min?) and 12.3”C (scan rate
I
Crystal data and structure refinement for diclorcyclohexane Empirical formula
Ch H IO Clz
Formula weight
153.04
Temperature
138(2) K
Wavelength
0.71073
Crystal system
Triclinic
Space group
P-l
A
Unit cell dimensions: a =5408(l)
A
cx=
h = 5.792(l)
A
p = 92.28(2)”
c=
I 1.685(2)
A
104.91(l)”
y = 91.78(2)”
Volume, Z
353.1(l)AX,
Density (calculated)
I .439 g/cm’
Absorption coefficient
0.81 mm-’
2
F(000)
160
Crystal size
0.35 x 0.35 x 0.2 mm
0 range for data collection Limiting indices
I .80-32.62” -7~h~8.-8~k~8,-17=~/~17
Reflections collected
2594
Independent reflections
2594
Refinement method
Full matrix least squares on F’
Data/restraints/parameters
2582/O/l 13
Goodness-of-fit on F*
I .074
Final R indices [I > 20(0]
Rl = 0.046. wK2 = 0.126
R indices (all data)
RI = 0.062, wR2 = 0.157
Largest diff. peak and hole
0.528 and -0.5 12 e.A-’
445 (1998) 269-275
P.O. Kvernherg Table 2 Atomic coordinates ( x 10”) and equivalent orthogonalised U,, tensor x
CK1) W2) C(11)
cc13 C(13) C(21) C(22) C(23) H(11) H(l2A) H(12B) H( I3A) H(l3B) H(21) H(22A) H(22B) H(23A) H(23B)
6468( I ) 11250(l) 9005(3) 8421(3) 9464(4) 13897(3) 13596(3) 14181(3) 10340(43) 8093(46) 6887(45) 8097(57) 9969(50) 15292(45) 13464(44) 12147(47) I2644(38) 14476(48)
et al./Journal
isotropic
of Molecular
displacement
v 2618(l) 2934( 1) 1590(3) 1883(3) -984(3) 3814(3) 2745(3) 65 17(3) 2637(4 1) 3544(45) 926(43) -2018(57) -1155(47) 3203(42) 1003(43) 3242(44) 7 148(36) 7064(45)
0.1 K mini’). This is a first order transition and the transition temperature will depend on the purity of the sample and how slowly the measurements are made.
3.2. Structure of the ee solid stable between 260 K and 280 K The structure of the phase stable below 12°C suggested by Hassel and Lunde [2] (inferred from mixed crystal experiments with dibromo- and dichlorocyclohexane [3]), has not been verified. The crystal structure found is triclinic, space group P-l with two
Fig. 5. Thermal ellipsoid plot of the two crystallographic independent 263 K and 285 K. Both molecules have a centre of symmetry.
Structure
parameters
273
445 (1998) 269-275
(A’ x 10’); CJ(eq) is defined as one third of the trace of the
z
Weq)
8577( 1) 6530( 1) 9340( I ) 10627(2) 8720( 1) 5817(l) 4489(2) 6122(2) 9293(21) 11036(22) 10668(2 I ) 8727(27) 79 13(23) 6193(21) 4339(2 I ) 4183(22) 5837(18) 6982(23)
36(l) 34(I)
231) 28(l) 28(l) 25(l) 27(l) 28(l) 27(5) 33(6) 30(6) 51(8) 39(7) 28(5) 30(6) 33(6) 17(5) 37(6)
molecules per unit cell situated at 2 non-equivalent centres of symmetry. The geometries of the 2 independent molecules are within the accuracy of the determination identical, both molecules having the chlorine atom in equatorial positions as shown in Fig. 5. The mean bond lengths and angles are as follows: Cl-Cl = 1,807(2) A, Cl-C2 = 1.516(2) A, C2-C3 = 1.527(2) A, C2-Cl-Cl = 109.8(2)“, C2Cl-Cl” = 111.7(l)“, and Cl-C2-C3 = 110.0(2):, The C-H bond lengths range from 0.93 to 1.00 A with an average of 0.97 A. The individual bond lengths and angles are given in Table 3. The crystal packing shown in Fig. 5 is governed by normal van der Waals’ Cl-H and H-H contacts.
molecules of trans-
I ,4-dichlorocyclohexane
in the phase stable between
214
P.O. Kvernberg
et al.Nournul of Molecular
Srrumre
445 (1998) 269-275
Table 3 Bond lengths (A) and angles (“)
I .805(2)
Cl(I)-C(II) U(2)-C(21) C(ll)-C(13) C(1 I)-C(12) C(ll)-H(II) C(l2)-C(13)#1 C(l2)-H(12A) C(l2)-H(12B) C(13)-C(12)#I C(13)-H(l3A) C(13)-H(l3B) C(21)-C(23) C(21)-C(22) C(21)-H(21) C(22)-C(23)#2 Symmetry
C(22)-H(22A) C(22)-H(22B) C(23)-C(22)#2 C(23)-H(23A) C(23)-H(23B) C(13)-C(ll)-C(12) C(13)-C(II)-Cl(I) C(12)-C( I I)-Cl( I) C(ll)-C(l2)-C(l3)#1 C(I I)-C(l3)-C(12)#1 C(23)-C(21 )-C(22) C(23)-C(21)-Cl(2) C(22)-C(21 )-Cl(2) C(21)-C(22)-C(23)#2 C(2 1)-C(23)-C(22)#2
I .809(2) I .5 13(2) I .5 17(2) 0.94(2) I .527(3) 0.98(2) 0.99(2) I .527(3) 0.94(3) 0.97(3) 1.515(2) 1.515(2) 0.98(2) 1.527(2) transformations
used to generate equivalent
atoms: #I =x+2,
3.3. The structure of the phase stable below 260 K The 250 K 13C CPMAS NMR spectrum shown in Fig. 1 contains 3 peaks. The observed chemical shifts [661.5 (C-l); 28.8 and 27.3(C-2)] are very similar to the shifts observed for the aa conformer in solution [659.9 (C-l); 28.2(C-2)] except for a splitting of the
Fig. 6. Packing of rrans-1,4-dichlorocyclohexane
-y,
-z+2;#2=
0.98(2) 0.93(3) 1.527(2) 1.00(2) 0.98(3) 1 I 1.77( 14) 109.54( I 2) 109.52( 12) 110.12(14) 109.88(14) 111.58(14) 109.65( 1 I) 109.80( 12) 110.22(14) 109.55( 13) -x+3,
-4’+
1, -_z+
I.
C-2 peak probably due to a reduction of molecular symmetry [l]. The observed chemical shifts in the solid state therefore show that the low temperature phase consists of aa conformers. The room temperature 13C CPMAS NMR spectrum is very similar to the spectrum shown in Fig. 2 except for small changes in the positions of the peaks (i.e. the
in the phase stable between 263 K and 285 K.
P.O. Kvernberg et al./Journal of Molecular Structure 445 (1998) 269-275
chemical shift). We were unable to find a small peak at 627.1 observed in a spectrum published earlier [ 11. This peak was interpreted as the C-2 peak from the au conformer present in the high temperature phase. No sign of an au conformer can be observed in the higher quality spectra recorded either on our new spectrometer or in spectra recorded on the Bruker MSL spectrometer in Uppsala. We are continuing our studies of molecular motion in the high temperature phase, and will return to this point in a forthcoming paper.
Acknowledgements We would like to thank Mrs Kari Bjerkelund for assistance in recording the DSC curves. We would also thank Dr Jorgen Tegenfeldt, Institute of
275
Chemistry at the University of Uppsala, for the opportunity of recording the first low temperature 13C CPMAS NMR spectra of DCC in his laboratory. We gratefully acknowledge the support from the Norwegian Research Council for the purchase of the DMX spectrometer and a scolarship to C. Ramming.
References [l] B. Pedersen, Acta Chem. Stand. A42 (1988) 421. [2] 0. Hassel, K. Lunde, Acta Chem. Stand 6 (I 952) 126. [3] T. Dahl, 0. Hassel, C. Remming, Acta Chem. Stand. 18 (1964) 2280. [4] O.H. Ellestad, P. Klaboe, .I. Mol. Struct. 26 (1975) 25. [5] V.A. Atkinson, 0. Hassel, Acta Chem. Stand. I3 (1959)1737. [6] R.J. Abraham, Z. Rossetti, L. Tetrahedron Lett. 0 (1972) 4965. [l] G.M. Sheldrick, SHELXTL, Version 5, Siemens Analytical Xray Instruments, Madison, WI.
of
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular
Structure 445
( 1998) 269-275
The crystal and molecular structures of trans- 1,4-dichlorocyclohexane’ Per Olav Kvernberg, Department
of Chemistry, Received
Bj@rn Pedersen*,
University
ofOslo,
19 September
Christian R@mming
Box 1033 Blindem,
1997; accepted
N-0315
20 October
Oslo, Norway
1997
Abstract A new phase transition in the title compound is observed at 260 K by DSC and NMR. Furthermore, the phase stable between 260 K and 280 K is found to be triclinic and not monoclinic as believed earlier. The structure is determined from single crystal X-ray data, and the molecules are found to be in the ee chair conformation. In the phase stable below 260 K the ‘“C CPMAS NMR spectrum shows that the molecules are in the aa chair conformation. 0 1998 Elsevier Science B.V. Keywords: Phase transition;
NMR spectroscopy;
Crystal structure; X-ray diffraction
1. Introduction In connection with Otto Bastianseris 70th birthday in 1988 Bjarn Pedersen published an NMR study of trans-1,Cdichlorocyclohexane (DCC)-a classical compound in the Hassel-Bastiansen tradition [ 11. We have continued the study of this compound, and we will in this paper show that the phase relations in solid DCC is somewhat more complex than found by Hassel er al. DCC has been found to exist in two chair conformations: au and ee. Hassel and Lunde [2] reported a transition point in solid DCC at 12-13°C. They suggested that the modification stable below this temperature has a crystal structure corresponding to that of the other tram- 1,4-dihalogenocyclohexanes showed by them from single crystal X-ray data to be monoclinic with the molecules in the ee conformation. Dahl, Hassel and Ramming [3] have studied * Corresponding author. Tel: +47 22 85 56 90; fax: +47 22 85 47 71; e-mail: [email protected]. ’Dedicated to the memory of Professor Otto Bastiansen.
the phase stable above 12°C using single crystal Xray methods and ‘H-NMR. Due to extraordinarily strong thermal damping the number of independent X-ray reflections was found to be very limited. They concluded that the structure is disordered, and that the molecules are in the ee conformation. Infrared investigations by Ellestad and Klaboe [4] indicated that the phase stable above 12°C consists of a mixture of ee and au conformers. They also found that by applying pressure crystals of the au conformer formed at room temperature, and that crystals of the au conformer formed when an amorphous solid, obtained by shock freezing at 90 K, was annealed at temperatures below 10°C. In the vapour of DCC the ee and au conformers exist in nearly equal amounts [5]. Roughly equal amounts of both conformers are observed when DCC is dissolved in non-polar solvents. In polar solvents, however, the equilibrium is shifted in favour of the ee conformer with its larger electric quadrupole moments (both conformers have zero electric dipole moment) [ 61.
0022-2860/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved PII SOO22-2860(97)00430-4
210
P.O. Kvernberg et al./Journcd of Moleculur Structure 445 (1998) 269-275
2. Experimental
50.3 MHz on a Bruker DMX Avance spectrometer equipped with a 4.8 T magnet. Some preliminary spectra were also recorded at 75 MHz on a Bruker MSL spectrometer in Uppsala. The 13CCPMAS spectrum given in Fig. 1 was observed of a sample kept at about 2.50 K for several days before placing it in the NMR probe at 253 K. The spectrum did not change when cooling the sample to 243 K. However, when the sample was heated to 263 K the spectrum slowly changed to the spectrum shown in Fig. 2. In Fig. 3 the relative amount of the low temperature phase as a function of time is shown. Assuming first order kinetics the half-life is about 1 h. This slow rate may explain why this phase transition has not been detected earlier. The existence of this phase transition is not in conflict with the many observations made by Ellestad and Klaboe [4] in their careful IR study. We are now attempting to grow single crystals of this new phase stable below 260 K for a crystal structure determination. At about 280 K we observed a small discontinuity in the position of the two peaks as a function of temperature as shown in Fig. 4. This supported the accepted view that the phase transition is not due to a conformational change, but due to a change from an
2.1. The sample The sample of DCC was a commercial sample from TCI. Well developed crystals formed by sublimation when the sample was kept in a refrigerator at about 4”C, and they were used without further purification. 2.2. DSC analysis The analysis was performed on a Mettler TA3000 system. Two endothermic peaks were detected in the temperature region from 110 K to 320 K obtained by scanning at a rate of 1 K min-‘. We found a large, narrow peak at 300 K (AH = 5.8 kJ mol-‘) and one smaller and broader peak at 273 K (AH = 1.l kJ mol-‘). In one scan at a slower rate only the high temperature peak was observed. Scanning from high to low temperature shifted the peaks 20 K to lower temperature. 2.3. C CPMAS NMR The 13C CPMAS
NMR spectra were recorded
at
I”“I”“I~“‘I”“l”“I”‘~I”““““”
65
60
‘1
55
50
45
Fig. 1. ’'C-CPMASspectrum of polycrystalline tram-1,4-dichlorocyclohexane IO s recycle time, I .5 ms contact time, 12 kHz rotation rate.
40
35
30
at 253 K. Recording conditions:
25
mm
16 scans, 66 ms aqusition time,
211
P.O. Kvernberg et al./Journal of Molecular Structure 445 (1998) 269-275
I
”
“I’.
Fig. 2. ’'C-MAS spectrum polarisation.
1
60
65
of polycrystalline
1.
55
“‘I”“(‘,
”
45
50
trans- I ,4-dichlorocyclohexane
I
”
”
I
”
”
at 263 K. Recording
I
”
”
30
35
40
1 ”
25
conditions
as in Fig.
ordered phase to a disordered (plastic) phase. In the ‘H-study published earlier no discontinuities in the line width or the spin lattice relaxation time curves as a function of temperature were observed [ 11.
Crystals were formed by sublimation at 277 K. A needle-formed single crystal was mounted on the
J
/
25
50 Time/minutes
Fig. 3. The mole fraction of the low temperature as a function of time at 263 K.
I, but without cross-
C-l
2.4. X-ray crystallography
0
1
.-.
60
0.00
”
ppm
75
100
phase (the aa solid)
59
? +?====
36 4 260
270
Fig. 4. The chemical temperature.
290 300 280 Temperature/K shifts
310
320
of the ee solid as a function
of
272
P.O. Kvernherg
et ul./Journc~l
of Molecular Structure
goniometer head in a cold carbon dioxide atmosphere and put into the cold nitrogen stream at 140 K on a NICOLET P3F diffractometer. We believe this sudden cooling preserved the crystal structure of the ee solid stable between 280 K and 260 K. (If the crystal was cooled slowly it changed from a single crystal to a powder. This observation supported the existence of a low temperature phase transition.) Unit cell dimensions were determined by a least squares fit to the refined diffractometer settings of 25 general reflections with 20” < 28 < 39”. Details of the experimental conditions for intensity measurements are given in Table 1. The intensities were corrected for Lorentz and polarisation effects; no corrections for absorption and extinction were applied. The structure was determined and refined using the SHELXTL program package [7]. The non-hydrogen atoms were refined with anisotropic thermal parameters; hydrogen positions were found from a difference Fourier map and refined with isotropic thermal parameters. Final figures of merit are included in Table 1. Table
Positional and equivalent isotropic thermal parameters for the atoms are listed in Table 2. Structure factors, lists of thermal parameters, and a complete list of bond lengths, bond angles and torsion angles may be obtained from C. Ramming upon request.
3. Results 3.1. Phase relations We interpret the observations in terms of the following model: at temperatures below 260 K the spectrum in Fig. 1 shows that an aa solid is the stable phase. Above 260 K the stable phase is an ee solid. The phase transition at 280 K is the phase transition observed by Hassel and Lunde [2]. In this phase transition the packing and motion change, but both phases are built with ee conformers. The exact temperature where the phase transition takes place is uncertain. Ellestad and Klabo found 15°C in their DTA analysis. In our DSC analysis the peak maximum is at 17.4”C (scan rate 1 K min?) and 12.3”C (scan rate
I
Crystal data and structure refinement for diclorcyclohexane Empirical formula
Ch H IO Clz
Formula weight
153.04
Temperature
138(2) K
Wavelength
0.71073
Crystal system
Triclinic
Space group
P-l
A
Unit cell dimensions: a =5408(l)
A
cx=
h = 5.792(l)
A
p = 92.28(2)”
c=
I 1.685(2)
A
104.91(l)”
y = 91.78(2)”
Volume, Z
353.1(l)AX,
Density (calculated)
I .439 g/cm’
Absorption coefficient
0.81 mm-’
2
F(000)
160
Crystal size
0.35 x 0.35 x 0.2 mm
0 range for data collection Limiting indices
I .80-32.62” -7~h~8.-8~k~8,-17=~/~17
Reflections collected
2594
Independent reflections
2594
Refinement method
Full matrix least squares on F’
Data/restraints/parameters
2582/O/l 13
Goodness-of-fit on F*
I .074
Final R indices [I > 20(0]
Rl = 0.046. wK2 = 0.126
R indices (all data)
RI = 0.062, wR2 = 0.157
Largest diff. peak and hole
0.528 and -0.5 12 e.A-’
445 (1998) 269-275
P.O. Kvernherg Table 2 Atomic coordinates ( x 10”) and equivalent orthogonalised U,, tensor x
CK1) W2) C(11)
cc13 C(13) C(21) C(22) C(23) H(11) H(l2A) H(12B) H( I3A) H(l3B) H(21) H(22A) H(22B) H(23A) H(23B)
6468( I ) 11250(l) 9005(3) 8421(3) 9464(4) 13897(3) 13596(3) 14181(3) 10340(43) 8093(46) 6887(45) 8097(57) 9969(50) 15292(45) 13464(44) 12147(47) I2644(38) 14476(48)
et al./Journal
isotropic
of Molecular
displacement
v 2618(l) 2934( 1) 1590(3) 1883(3) -984(3) 3814(3) 2745(3) 65 17(3) 2637(4 1) 3544(45) 926(43) -2018(57) -1155(47) 3203(42) 1003(43) 3242(44) 7 148(36) 7064(45)
0.1 K mini’). This is a first order transition and the transition temperature will depend on the purity of the sample and how slowly the measurements are made.
3.2. Structure of the ee solid stable between 260 K and 280 K The structure of the phase stable below 12°C suggested by Hassel and Lunde [2] (inferred from mixed crystal experiments with dibromo- and dichlorocyclohexane [3]), has not been verified. The crystal structure found is triclinic, space group P-l with two
Fig. 5. Thermal ellipsoid plot of the two crystallographic independent 263 K and 285 K. Both molecules have a centre of symmetry.
Structure
parameters
273
445 (1998) 269-275
(A’ x 10’); CJ(eq) is defined as one third of the trace of the
z
Weq)
8577( 1) 6530( 1) 9340( I ) 10627(2) 8720( 1) 5817(l) 4489(2) 6122(2) 9293(21) 11036(22) 10668(2 I ) 8727(27) 79 13(23) 6193(21) 4339(2 I ) 4183(22) 5837(18) 6982(23)
36(l) 34(I)
231) 28(l) 28(l) 25(l) 27(l) 28(l) 27(5) 33(6) 30(6) 51(8) 39(7) 28(5) 30(6) 33(6) 17(5) 37(6)
molecules per unit cell situated at 2 non-equivalent centres of symmetry. The geometries of the 2 independent molecules are within the accuracy of the determination identical, both molecules having the chlorine atom in equatorial positions as shown in Fig. 5. The mean bond lengths and angles are as follows: Cl-Cl = 1,807(2) A, Cl-C2 = 1.516(2) A, C2-C3 = 1.527(2) A, C2-Cl-Cl = 109.8(2)“, C2Cl-Cl” = 111.7(l)“, and Cl-C2-C3 = 110.0(2):, The C-H bond lengths range from 0.93 to 1.00 A with an average of 0.97 A. The individual bond lengths and angles are given in Table 3. The crystal packing shown in Fig. 5 is governed by normal van der Waals’ Cl-H and H-H contacts.
molecules of trans-
I ,4-dichlorocyclohexane
in the phase stable between
214
P.O. Kvernberg
et al.Nournul of Molecular
Srrumre
445 (1998) 269-275
Table 3 Bond lengths (A) and angles (“)
I .805(2)
Cl(I)-C(II) U(2)-C(21) C(ll)-C(13) C(1 I)-C(12) C(ll)-H(II) C(l2)-C(13)#1 C(l2)-H(12A) C(l2)-H(12B) C(13)-C(12)#I C(13)-H(l3A) C(13)-H(l3B) C(21)-C(23) C(21)-C(22) C(21)-H(21) C(22)-C(23)#2 Symmetry
C(22)-H(22A) C(22)-H(22B) C(23)-C(22)#2 C(23)-H(23A) C(23)-H(23B) C(13)-C(ll)-C(12) C(13)-C(II)-Cl(I) C(12)-C( I I)-Cl( I) C(ll)-C(l2)-C(l3)#1 C(I I)-C(l3)-C(12)#1 C(23)-C(21 )-C(22) C(23)-C(21)-Cl(2) C(22)-C(21 )-Cl(2) C(21)-C(22)-C(23)#2 C(2 1)-C(23)-C(22)#2
I .809(2) I .5 13(2) I .5 17(2) 0.94(2) I .527(3) 0.98(2) 0.99(2) I .527(3) 0.94(3) 0.97(3) 1.515(2) 1.515(2) 0.98(2) 1.527(2) transformations
used to generate equivalent
atoms: #I =x+2,
3.3. The structure of the phase stable below 260 K The 250 K 13C CPMAS NMR spectrum shown in Fig. 1 contains 3 peaks. The observed chemical shifts [661.5 (C-l); 28.8 and 27.3(C-2)] are very similar to the shifts observed for the aa conformer in solution [659.9 (C-l); 28.2(C-2)] except for a splitting of the
Fig. 6. Packing of rrans-1,4-dichlorocyclohexane
-y,
-z+2;#2=
0.98(2) 0.93(3) 1.527(2) 1.00(2) 0.98(3) 1 I 1.77( 14) 109.54( I 2) 109.52( 12) 110.12(14) 109.88(14) 111.58(14) 109.65( 1 I) 109.80( 12) 110.22(14) 109.55( 13) -x+3,
-4’+
1, -_z+
I.
C-2 peak probably due to a reduction of molecular symmetry [l]. The observed chemical shifts in the solid state therefore show that the low temperature phase consists of aa conformers. The room temperature 13C CPMAS NMR spectrum is very similar to the spectrum shown in Fig. 2 except for small changes in the positions of the peaks (i.e. the
in the phase stable between 263 K and 285 K.
P.O. Kvernberg et al./Journal of Molecular Structure 445 (1998) 269-275
chemical shift). We were unable to find a small peak at 627.1 observed in a spectrum published earlier [ 11. This peak was interpreted as the C-2 peak from the au conformer present in the high temperature phase. No sign of an au conformer can be observed in the higher quality spectra recorded either on our new spectrometer or in spectra recorded on the Bruker MSL spectrometer in Uppsala. We are continuing our studies of molecular motion in the high temperature phase, and will return to this point in a forthcoming paper.
Acknowledgements We would like to thank Mrs Kari Bjerkelund for assistance in recording the DSC curves. We would also thank Dr Jorgen Tegenfeldt, Institute of
275
Chemistry at the University of Uppsala, for the opportunity of recording the first low temperature 13C CPMAS NMR spectra of DCC in his laboratory. We gratefully acknowledge the support from the Norwegian Research Council for the purchase of the DMX spectrometer and a scolarship to C. Ramming.
References [l] B. Pedersen, Acta Chem. Stand. A42 (1988) 421. [2] 0. Hassel, K. Lunde, Acta Chem. Stand 6 (I 952) 126. [3] T. Dahl, 0. Hassel, C. Remming, Acta Chem. Stand. 18 (1964) 2280. [4] O.H. Ellestad, P. Klaboe, .I. Mol. Struct. 26 (1975) 25. [5] V.A. Atkinson, 0. Hassel, Acta Chem. Stand. I3 (1959)1737. [6] R.J. Abraham, Z. Rossetti, L. Tetrahedron Lett. 0 (1972) 4965. [l] G.M. Sheldrick, SHELXTL, Version 5, Siemens Analytical Xray Instruments, Madison, WI.