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NMR of partially oriented iodobenzene; A determination of the rα structure and of bond-contributions to the degree of order
Journal ofMolecular Structure, 216 (1990) 325-332 Elsevier Science Publishers B.V.. Amsterdam - Printed
325 in The Netherlands
NMR OF PARTIALLY ORIENTED IODOBENZENE; A DETERMINATION OF THE r, STRUCTURE AND OF BONDCONTRIBUTIONS TO THE DEGREE OF ORDER
R. UGOLINI
and P. DIEHL
Department of Physics, University of Base& Klingelbergstrasse 82, CH-4056 Base1 (Switzerland) (Received
17 May 1989)
ABSTRACT The r, structure of iodobenzene corrected for correlated deformation has been derived from direct couplings measured in six different liquid crystal solvents. A comparison with other halogen substituted benzenes confirms a linear relation between the ipso angle and the substituent electronegativity. A study of the bond interaction parameters shows that the halogen substituent contributes significantly to the order parameters, particularly in liquid crystal solvents containing cyclohexane rings.
INTRODUCTION
NMR spectroscopy of oriented molecules has been used during the past twenty years for the determination of accurate molecular structures. The biggest disadvantage of this method has been the impossibility of studying the free molecule, because the orientation had to be achieved by dissolution in liquid crystals. The interaction between the solute and the anisotropic solvent which orients the solute causes a molecular deformation which in a correlated way varies with the orientation of molecular axis with respect to the liquid crystal director. This correlated deformation contributes to the measured direct coupling constants, i.e. it causes solvent effects on the structure. In order to correct for the solvent effects an approach has been used [ 1,2] in which it is assumed that the solute-solvent interaction can be described by its anisotropy AA and its asymmetry q. The asymmetry turned out to be small so that it can safely be neglected. A computer program MASTER [ 31 has been developed which, on the basis of the measured direct couplings as well as information on the molecular force field, is able to derive solvent independent (corrected for harmonic vibration and for correlated deformation) molecular structures as well as bond interaction parameters AA. In the present study the spectra of iodobenzene have been analyzed, a compound for which only very scarce structural information can be found in the 0022.2860/90/$03.50
0 1990 Elsevier Science Publishers
B.V.
326
literature [ 4,5]. The results are compared with recent data for chlorobenzene [31. EXPERIMENTAL
Commercially available iodobenzene (6 mol% ) was studied in six different nematic liquid crystals (Table 1) at identical reduced temperatures on a Bruker AC-250 Fourier transform NMR spectrometer. The resulting direct couplings obtained with the program LEQUOR [6] are summarized in Table 2 and the numbering of nuclei is shown in Fig. 1.Indirect couplings were taken from the literature [ 71. The corrections for harmonic vibrations and for correlated deformation were performed with the program MASTER [ 31. The force field had to be derived from that for bromobenzene [8] with corresponding adaptations for the carbon-halogen bond length of 2.08 A [4,9] and for the halogen mass. The resulting solvent independent structure is shown in Table 3. DISCUSSION
Iodobenzene r,-structure: comparisons with chlorobenzene Table 3 compares the NMR r, structure of iodobenzene with that of chlorobenzene determined recently by the same method [ 31 and with a theoretical structure from the literature [ 51. For iodo- as well as chlorobenzene it is observed that r(1,7) >r(3,9) >r(2,8) in iodobenzene the ortho-CH bond is longer than the para-CH bond by about
1.2%. TABLE 1 Temperature T (K) at which the ‘H spectra of iodobenzene were recorded in six different liquid crystals and the reduced temperature T *= T/TN1 Solvent
T
T*
ZLI 1167 ZLI 1132 65% ZLI 1167/35% EBBA 55% ZLI 1132/45% EBBA Phase 4 EBBA
306 298 294 296 296 299
0.881 0.881 0.884 0.880 0.882 0.880
2
-2.32 - 1.71
- 1.97
12.88+
26.41+ -3.77 26.16+ -5.42 - 28.72 + - 3.74
-0.28 -5.43
-7197.30+ -29.56+
-16.50+ - 17.40+
-0.20 -0.19
-211.49+ -625.76+
112.17+ -0.22 328.72 •l--0.44
-0.35 - 1.80
- 1.20 -0.20
114.57+ - 169.05+
-75.1 + - 12.7 90.10+ -0.28
3834.61+ 12.76+
-1.65 - 1.91
-761.10+ - 1093.00+
402.77+ -1.11 493.75 + - 1.33
59.97 + - 2.86 137.87+ -2.62
- 39.73 + - 0.50 71.36+ -0.79
- 1.61 - 1.86
-2.88 -2.86
-0.91 -0.05
- 135.03 + - 1.34 - 386.64 + - 0.95
- 1126.51+ -747.10+
59.78+ 116.92+
-349.44+ -49.97+
- 2538.06 + -0.05
397.15+ - 1.39 69.4 + - 13.1 175.66 + - 0.38
- 77.99 + - 0.69 513.08+ - 1.04
22.72 + -0.08 -39.88+ -0.49
-0.16 -0.37
- 185.29
9.69
1352.67+ 184.28+
- 179.83
220.77
*z-
*3
*l-*3
and dipolar couplings ZLI 1132
shift differences
ZLI 1167
Experimental
TABLE
- 2.40 - 11.1 -2.23 -2.83 -5.49 -0.96 -2.40 -8.92 -2.24
56.04+ 108.9 + -911.85+ -641.56+ -111.63+ -314.78+ 59.37+ -116.98+ -656.74+
22.19+
24.27-k - 7.64 20.16+ - 7.73
-7.64 -7.74
-22.08-l-
-539.52 + -0.25 -6235.01+ -0.45
105.84 + - 5.68 -146.76+ -0.18 - 183.27+ -0.37
- 879.98 + - 2.79
-0.95 -0.04
-301.95+ -40.45+
-1.49 - 1.10
-2.89
-0.19
-22.88+
-2.23
17.85 + - 2.18 16.24+ -2.89
-21.55+
-5386.28+
77.79 + - 2.45 -126.85+ -0.14 -158.88+ -0.14 -471.80+ -0.15
-574.86+ -852.23+
40.86 + - 0.88 - 102.81+ - 1.44
-4.81 -2.77 -0.19 -0.22
-493.19+ 78.44+ -93.26+ -116.12+
-0.39 -1.15
-0.28 -0.35
-0.20
- 1.24
-5.24+ - 13.21+
- 5.48
-5.65+ -1.60 29.04+ - 1.36 29.02 + - 1.46
-111.10+ -0.17 -314.68+ -0.16 - 3820.90 + - 0.40
-90.72+
- 167.74 + - 0.88 127.25+ - 1.16
-65.74+ -397.48+
-83.08+ 66.16+
- 390.48 + - 0.82 -64.93 + - 1.28
127.77 + -0.36 -212.76+ - 1.11
-9.87+ -0.03 65.64 + - 0.33
- 1368.60+ -0.04 - 178.73 + -0.34
- 42.88 - 120.78
EBBA
-16.77+ -5.53 16.43 + -4.53 20.85 + - 5.45
-340.81+ -0.47 -3916.9 + -56.2
-5.95 -6.59
-76.88+ -417.61+
- 193.39 + -0.27 40.06 + - 0.70
- 408.88 + - 4.75 -74.94+ -2.76
-561.49+ - 1.05 - 102.45 + - 2.61 - 307.27 + -0.34
-0.03 -0.71
-23.77+ 40.01+
79.06 + - 4.49 -531.43+ -5.51
-0.03 -0.89
-0.27
- 190.67+
- 1405.62 + - 0.07
- 50.70 - 119.16
Phase 4
79.00 + - 1.53 -881.75+ -1.51
-39.28+ 41.19+
- 263.03 + -0.33
- 1905.82 + - 0.03
- 112.83 - 147.80
1132/EBBA
dissolved in six liquid crystals
- 2204.53 + - 0.06
- 130.86 - 162.24
1167/EBBA
(Hz) of iodobenzene
328 I
H3
Fig. 1. Numbering
of the nuclei and definition
of the coordinate
axes.
TABLE 3 Distance ratios and bond angles (deg) (r, structure) of iodobenzene compared with its calculated (modified spd-CNDO/Z) geometry and with the r, structure of chlorobenzene Iodobenzene Experiment
r(1,7)lr(7,8) r(2,8)lr(7,8) r(W)lr(7,8) r(6,7)lr(7,8) r(8,9)lr(7,8) L L L L L L L
(1,796) (2,8,7) (3,998) (7,6,11) (6,738) (7,899) (8,9,10)
0.7750 0.7660 0.7719 0.9932 0.9944
(18) (20) (10) (15) (13)
120.61 (8) 119.38 (3) 119.58 (8) 121.13 (13) 119.42 (8) 119.59 (10) 120.85 (17)
Chlorobenzene Mod. spdCNDO/Z [5] 0.806 0.807 0.807 0.994 1.000 122.2 119.7 119.9 124.4 117.1 120.6 120.2
[ 31
Experiment
0.7763 0.7737 0.7747 0.9959 0.9989
(7) (7) (4) (8) (5)
120.07 (7) 119.38 (2) 119.89 (5) 121.56 (13) 119.04 (7) 120.06 (5) 120.23 (9)
In both molecules the following relation for the CC bonds is valid t-(7,8) >r(8,9) >r(6,7) The ipso angle (C7,C&11) is generally considerably enlarged [lo].
It in-
329 124
123
!!I
122
z a 8 &
121
120
119
I
I
I
2.0
2.5
3.0
ELECTRONEGATIVITY
I
3.5
I
4.0
(PAULING)
Fig. 2. Linear relationship between the ipso angle (C,,C,,C,,) (deg.) and the electronegativity of the halogen. The direct couplings of fluorobenzene were taken from ref. 11 and corrected for correlated deformation.
creases almost linearly with the substituent electronegativity as shown in Fig. 2. The widening of the angle is accompanied by an expansion of r (7,ll) so that generally r(7,ll)
>r(8,10)
To our knowledge there exists only one early experimental structure determination for iodobenzene [4] based on hexagonal symmetry of the benzene ring. An earlier NMR determination [ 121 did not consider correlated deformation. The results of the theoretical calculations [5] do not agree with our experimental structure. Bond interaction contributions to the degree of order For planar molecules the components of the interaction tensor are given by A,,=C,
AA,(2/3-sin2
A,, = In WJ2/,
0,)
-cos2 0,)
A, = I,, A&/3 where AA, is the asymmetry of the interaction tensor of bond n and 0, is the
330
TABLE 4 Anisotropies AA (IO-** J) of the different bonds (CH, CC, CI) in iodobenzene, with CH anisotropies AA and direct couplings DCH(Hz) of methane, measured in the same sample ZLI 1167 MACH A&c MCI &(CH,) A&,(CH,)
ZLI 1132
1167/EBBA
1132/EBBA
Phase 4
EBBA
12.4 (11) 10.6 (12) 53.5 (11)
11.8 (11) 9.9 (11) 48.4 (11)
8.2 (10) 7.6 (10) 41.2 (10)
6.7 (8) 6.7 (9) 35.5 (8)
-0.8 (8) 8.5 (8) 22.5 (8)
-1.8 (6) 7.1 (7) 24.0 (6)
-5.32 (3) 2.59 (1)
-5.28 (5) 2.58 (3)
0.76 (5) -0.37 (3)
2.12 (5) - 1.03 (2)
9.50 (7) -4.63 (3)
11.34 (1) -5.53 (1)
__
60
Axx
55
55-
50
50-
45
45-
40
40 -
35
35 -
30
30 -
-0.5Ayy
25 20 r 15 10 5 0 -5
:ti
-5 -10 -15
-6
AA
-4
-2
0
2
of methane
4
-6
AA
-4
-2
0
of methane
2
4
-20L---6 -4
AA
7
-2
0
2
4
of methane
Fig. 3. Interaction contributions of the various bonds of iodobenzene parallel to the coordinate axes as a function of the methane CH bond interaction anisotropy. The symbols refer to contributions in iodobenzene as follows: CH bond ( + ), CC bond (0 ), CI bond ( * ), the sum of all bonds (m ) and for comparison the contribution of the C-Cl bond in chlorobenzene (A ) [ 31.
angle between the direction of bond n and the molecular z axis [ 21. For iodobenzene, assuming hexagonal symmetry the resulting axial components are 4, = “IS A&X + A&c - ‘/s A&X A,, = - “13 A&H - 2 A&c - ‘13 A&I A,, = ‘/3 A&H + A&c
+2/3 MCI
Resulting AA values for the various bonds in the different solvents are sum-
331 TABLE 5 Contributions of each type of bond to the interaction tensor principal components ( 10ez2 J) of iodobenzene, dissolved in six liquid crystals ZLI 1167 16.6 10.6 - 17.8 -20.7 -21.2 - 17.8 4.1 10.6 35.7
ZLI 1132
-
15.8 9.9 16.1 19.7 19.8 16.1 3.9 9.9 32.3
1167/EBBA
-
10.9 7.6 13.7 13.6 15.2 13.7 2.7 7.6 27.5
1132/EBBA 8.9
6.7 -11.8 - 11.1 - 13.4 - 11.8 2.2 6.7 23.7
Phase 4
EBBA
-1.1 8.5 -7.5 1.4 - 17.0 -7.5 -0.3 8.5 15.0
-2.4 7.1 -8.5 3.0 - 14.2 -8.0 -0.6 7.1 16.0
marked in Table 4 together with the observed direct couplings DCH and the interaction parameters AA cn of methane in the same solvent. These additional parameters may be used as indicators for the strength of the solute-solvent interactions [ 131. Figure 3 shows the contributions of each type of bond to the components of the molecular interaction tensor (Table 5 ) of iodobenzene and also the contribution of the C-Cl bond of chlorobenzene for comparison. On the whole small differences (below 5 x 1O-22 J ) are observed between iodo- and chlorobenzene for the interaction parameters Ucn and AAcc. The halogen contribution however is considerably larger for the C-I than for the C-Cl bond. The difference increases from EBBA to ZLI 1167 for which in A”” it reaches 15 x 1O-22 J. CONCLUSIONS
NMR of oriented molecules may be used to study small differences in molecular structures if corrections for harmonic vibrations as well as for correlated deformation are performed. As a by-product of the structural analysis, bond contributions to the orientation energy may be derived and can be compared between similar molecules.
REFERENCES 1 2 3 4 5 6
J. Lounila and P. Diehl, J. Magn. Reson., 56 (1984) 254. J. Lounila and P. Diehl, Mol. Phys., 52 (1984) 827. R. Wasser, M. Kellerhals and P. Diehl, Magn. Reson. Chem., 27 (1989) 335. K. Johansson, H. Oldenberg and H. Selen, Ark. Fys., 29 (1965) 531. P. Scharfenberg, Chem. Phys. Lett., 65(2) (1979) 304. P. Diehl, H.P. Kellerhals and W. Niederberger, Mol. Phys., 4 (1971) 352.
332 7 8 9 10 11 12 13
L. Ernst, V. Wray, V.A. Chertkov and N.M. Sergeyev, J. Magn. Reson., 25 (1977) 123. T. Uno, A. Kuwae and K. Machida, Spectrochim. Acta, Part A, 33 (1977) 607. M.D. Harmony, V.W. Laurie, R.L. Kuczkowski, R.H. Schwedemann, D.A. Ramsay,F.J. Lovas, W.J. Lafferty and A.G. Maki, J. Phys. Chem. Ref. Data, 8 (1979) 619. A. Domenicano, A. Vaciago and C.A. Coulson, Acta Crystallogr., Sect. B, 31 (1975) 1630. J. Lounila and T. Vliin&nen, Mol. Phys., 49 (1983) 859. J. Jokisaari, T. VPSinanenand J. Lounila, Mol. Phys., 45 (1982) 141. J. Jokisaari, Y. Hiltunen and T. Vtiniinen, Mol. Phys., 51 (1984) 779.
325 in The Netherlands
NMR OF PARTIALLY ORIENTED IODOBENZENE; A DETERMINATION OF THE r, STRUCTURE AND OF BONDCONTRIBUTIONS TO THE DEGREE OF ORDER
R. UGOLINI
and P. DIEHL
Department of Physics, University of Base& Klingelbergstrasse 82, CH-4056 Base1 (Switzerland) (Received
17 May 1989)
ABSTRACT The r, structure of iodobenzene corrected for correlated deformation has been derived from direct couplings measured in six different liquid crystal solvents. A comparison with other halogen substituted benzenes confirms a linear relation between the ipso angle and the substituent electronegativity. A study of the bond interaction parameters shows that the halogen substituent contributes significantly to the order parameters, particularly in liquid crystal solvents containing cyclohexane rings.
INTRODUCTION
NMR spectroscopy of oriented molecules has been used during the past twenty years for the determination of accurate molecular structures. The biggest disadvantage of this method has been the impossibility of studying the free molecule, because the orientation had to be achieved by dissolution in liquid crystals. The interaction between the solute and the anisotropic solvent which orients the solute causes a molecular deformation which in a correlated way varies with the orientation of molecular axis with respect to the liquid crystal director. This correlated deformation contributes to the measured direct coupling constants, i.e. it causes solvent effects on the structure. In order to correct for the solvent effects an approach has been used [ 1,2] in which it is assumed that the solute-solvent interaction can be described by its anisotropy AA and its asymmetry q. The asymmetry turned out to be small so that it can safely be neglected. A computer program MASTER [ 31 has been developed which, on the basis of the measured direct couplings as well as information on the molecular force field, is able to derive solvent independent (corrected for harmonic vibration and for correlated deformation) molecular structures as well as bond interaction parameters AA. In the present study the spectra of iodobenzene have been analyzed, a compound for which only very scarce structural information can be found in the 0022.2860/90/$03.50
0 1990 Elsevier Science Publishers
B.V.
326
literature [ 4,5]. The results are compared with recent data for chlorobenzene [31. EXPERIMENTAL
Commercially available iodobenzene (6 mol% ) was studied in six different nematic liquid crystals (Table 1) at identical reduced temperatures on a Bruker AC-250 Fourier transform NMR spectrometer. The resulting direct couplings obtained with the program LEQUOR [6] are summarized in Table 2 and the numbering of nuclei is shown in Fig. 1.Indirect couplings were taken from the literature [ 71. The corrections for harmonic vibrations and for correlated deformation were performed with the program MASTER [ 31. The force field had to be derived from that for bromobenzene [8] with corresponding adaptations for the carbon-halogen bond length of 2.08 A [4,9] and for the halogen mass. The resulting solvent independent structure is shown in Table 3. DISCUSSION
Iodobenzene r,-structure: comparisons with chlorobenzene Table 3 compares the NMR r, structure of iodobenzene with that of chlorobenzene determined recently by the same method [ 31 and with a theoretical structure from the literature [ 51. For iodo- as well as chlorobenzene it is observed that r(1,7) >r(3,9) >r(2,8) in iodobenzene the ortho-CH bond is longer than the para-CH bond by about
1.2%. TABLE 1 Temperature T (K) at which the ‘H spectra of iodobenzene were recorded in six different liquid crystals and the reduced temperature T *= T/TN1 Solvent
T
T*
ZLI 1167 ZLI 1132 65% ZLI 1167/35% EBBA 55% ZLI 1132/45% EBBA Phase 4 EBBA
306 298 294 296 296 299
0.881 0.881 0.884 0.880 0.882 0.880
2
-2.32 - 1.71
- 1.97
12.88+
26.41+ -3.77 26.16+ -5.42 - 28.72 + - 3.74
-0.28 -5.43
-7197.30+ -29.56+
-16.50+ - 17.40+
-0.20 -0.19
-211.49+ -625.76+
112.17+ -0.22 328.72 •l--0.44
-0.35 - 1.80
- 1.20 -0.20
114.57+ - 169.05+
-75.1 + - 12.7 90.10+ -0.28
3834.61+ 12.76+
-1.65 - 1.91
-761.10+ - 1093.00+
402.77+ -1.11 493.75 + - 1.33
59.97 + - 2.86 137.87+ -2.62
- 39.73 + - 0.50 71.36+ -0.79
- 1.61 - 1.86
-2.88 -2.86
-0.91 -0.05
- 135.03 + - 1.34 - 386.64 + - 0.95
- 1126.51+ -747.10+
59.78+ 116.92+
-349.44+ -49.97+
- 2538.06 + -0.05
397.15+ - 1.39 69.4 + - 13.1 175.66 + - 0.38
- 77.99 + - 0.69 513.08+ - 1.04
22.72 + -0.08 -39.88+ -0.49
-0.16 -0.37
- 185.29
9.69
1352.67+ 184.28+
- 179.83
220.77
*z-
*3
*l-*3
and dipolar couplings ZLI 1132
shift differences
ZLI 1167
Experimental
TABLE
- 2.40 - 11.1 -2.23 -2.83 -5.49 -0.96 -2.40 -8.92 -2.24
56.04+ 108.9 + -911.85+ -641.56+ -111.63+ -314.78+ 59.37+ -116.98+ -656.74+
22.19+
24.27-k - 7.64 20.16+ - 7.73
-7.64 -7.74
-22.08-l-
-539.52 + -0.25 -6235.01+ -0.45
105.84 + - 5.68 -146.76+ -0.18 - 183.27+ -0.37
- 879.98 + - 2.79
-0.95 -0.04
-301.95+ -40.45+
-1.49 - 1.10
-2.89
-0.19
-22.88+
-2.23
17.85 + - 2.18 16.24+ -2.89
-21.55+
-5386.28+
77.79 + - 2.45 -126.85+ -0.14 -158.88+ -0.14 -471.80+ -0.15
-574.86+ -852.23+
40.86 + - 0.88 - 102.81+ - 1.44
-4.81 -2.77 -0.19 -0.22
-493.19+ 78.44+ -93.26+ -116.12+
-0.39 -1.15
-0.28 -0.35
-0.20
- 1.24
-5.24+ - 13.21+
- 5.48
-5.65+ -1.60 29.04+ - 1.36 29.02 + - 1.46
-111.10+ -0.17 -314.68+ -0.16 - 3820.90 + - 0.40
-90.72+
- 167.74 + - 0.88 127.25+ - 1.16
-65.74+ -397.48+
-83.08+ 66.16+
- 390.48 + - 0.82 -64.93 + - 1.28
127.77 + -0.36 -212.76+ - 1.11
-9.87+ -0.03 65.64 + - 0.33
- 1368.60+ -0.04 - 178.73 + -0.34
- 42.88 - 120.78
EBBA
-16.77+ -5.53 16.43 + -4.53 20.85 + - 5.45
-340.81+ -0.47 -3916.9 + -56.2
-5.95 -6.59
-76.88+ -417.61+
- 193.39 + -0.27 40.06 + - 0.70
- 408.88 + - 4.75 -74.94+ -2.76
-561.49+ - 1.05 - 102.45 + - 2.61 - 307.27 + -0.34
-0.03 -0.71
-23.77+ 40.01+
79.06 + - 4.49 -531.43+ -5.51
-0.03 -0.89
-0.27
- 190.67+
- 1405.62 + - 0.07
- 50.70 - 119.16
Phase 4
79.00 + - 1.53 -881.75+ -1.51
-39.28+ 41.19+
- 263.03 + -0.33
- 1905.82 + - 0.03
- 112.83 - 147.80
1132/EBBA
dissolved in six liquid crystals
- 2204.53 + - 0.06
- 130.86 - 162.24
1167/EBBA
(Hz) of iodobenzene
328 I
H3
Fig. 1. Numbering
of the nuclei and definition
of the coordinate
axes.
TABLE 3 Distance ratios and bond angles (deg) (r, structure) of iodobenzene compared with its calculated (modified spd-CNDO/Z) geometry and with the r, structure of chlorobenzene Iodobenzene Experiment
r(1,7)lr(7,8) r(2,8)lr(7,8) r(W)lr(7,8) r(6,7)lr(7,8) r(8,9)lr(7,8) L L L L L L L
(1,796) (2,8,7) (3,998) (7,6,11) (6,738) (7,899) (8,9,10)
0.7750 0.7660 0.7719 0.9932 0.9944
(18) (20) (10) (15) (13)
120.61 (8) 119.38 (3) 119.58 (8) 121.13 (13) 119.42 (8) 119.59 (10) 120.85 (17)
Chlorobenzene Mod. spdCNDO/Z [5] 0.806 0.807 0.807 0.994 1.000 122.2 119.7 119.9 124.4 117.1 120.6 120.2
[ 31
Experiment
0.7763 0.7737 0.7747 0.9959 0.9989
(7) (7) (4) (8) (5)
120.07 (7) 119.38 (2) 119.89 (5) 121.56 (13) 119.04 (7) 120.06 (5) 120.23 (9)
In both molecules the following relation for the CC bonds is valid t-(7,8) >r(8,9) >r(6,7) The ipso angle (C7,C&11) is generally considerably enlarged [lo].
It in-
329 124
123
!!I
122
z a 8 &
121
120
119
I
I
I
2.0
2.5
3.0
ELECTRONEGATIVITY
I
3.5
I
4.0
(PAULING)
Fig. 2. Linear relationship between the ipso angle (C,,C,,C,,) (deg.) and the electronegativity of the halogen. The direct couplings of fluorobenzene were taken from ref. 11 and corrected for correlated deformation.
creases almost linearly with the substituent electronegativity as shown in Fig. 2. The widening of the angle is accompanied by an expansion of r (7,ll) so that generally r(7,ll)
>r(8,10)
To our knowledge there exists only one early experimental structure determination for iodobenzene [4] based on hexagonal symmetry of the benzene ring. An earlier NMR determination [ 121 did not consider correlated deformation. The results of the theoretical calculations [5] do not agree with our experimental structure. Bond interaction contributions to the degree of order For planar molecules the components of the interaction tensor are given by A,,=C,
AA,(2/3-sin2
A,, = In WJ2/,
0,)
-cos2 0,)
A, = I,, A&/3 where AA, is the asymmetry of the interaction tensor of bond n and 0, is the
330
TABLE 4 Anisotropies AA (IO-** J) of the different bonds (CH, CC, CI) in iodobenzene, with CH anisotropies AA and direct couplings DCH(Hz) of methane, measured in the same sample ZLI 1167 MACH A&c MCI &(CH,) A&,(CH,)
ZLI 1132
1167/EBBA
1132/EBBA
Phase 4
EBBA
12.4 (11) 10.6 (12) 53.5 (11)
11.8 (11) 9.9 (11) 48.4 (11)
8.2 (10) 7.6 (10) 41.2 (10)
6.7 (8) 6.7 (9) 35.5 (8)
-0.8 (8) 8.5 (8) 22.5 (8)
-1.8 (6) 7.1 (7) 24.0 (6)
-5.32 (3) 2.59 (1)
-5.28 (5) 2.58 (3)
0.76 (5) -0.37 (3)
2.12 (5) - 1.03 (2)
9.50 (7) -4.63 (3)
11.34 (1) -5.53 (1)
__
60
Axx
55
55-
50
50-
45
45-
40
40 -
35
35 -
30
30 -
-0.5Ayy
25 20 r 15 10 5 0 -5
:ti
-5 -10 -15
-6
AA
-4
-2
0
2
of methane
4
-6
AA
-4
-2
0
of methane
2
4
-20L---6 -4
AA
7
-2
0
2
4
of methane
Fig. 3. Interaction contributions of the various bonds of iodobenzene parallel to the coordinate axes as a function of the methane CH bond interaction anisotropy. The symbols refer to contributions in iodobenzene as follows: CH bond ( + ), CC bond (0 ), CI bond ( * ), the sum of all bonds (m ) and for comparison the contribution of the C-Cl bond in chlorobenzene (A ) [ 31.
angle between the direction of bond n and the molecular z axis [ 21. For iodobenzene, assuming hexagonal symmetry the resulting axial components are 4, = “IS A&X + A&c - ‘/s A&X A,, = - “13 A&H - 2 A&c - ‘13 A&I A,, = ‘/3 A&H + A&c
+2/3 MCI
Resulting AA values for the various bonds in the different solvents are sum-
331 TABLE 5 Contributions of each type of bond to the interaction tensor principal components ( 10ez2 J) of iodobenzene, dissolved in six liquid crystals ZLI 1167 16.6 10.6 - 17.8 -20.7 -21.2 - 17.8 4.1 10.6 35.7
ZLI 1132
-
15.8 9.9 16.1 19.7 19.8 16.1 3.9 9.9 32.3
1167/EBBA
-
10.9 7.6 13.7 13.6 15.2 13.7 2.7 7.6 27.5
1132/EBBA 8.9
6.7 -11.8 - 11.1 - 13.4 - 11.8 2.2 6.7 23.7
Phase 4
EBBA
-1.1 8.5 -7.5 1.4 - 17.0 -7.5 -0.3 8.5 15.0
-2.4 7.1 -8.5 3.0 - 14.2 -8.0 -0.6 7.1 16.0
marked in Table 4 together with the observed direct couplings DCH and the interaction parameters AA cn of methane in the same solvent. These additional parameters may be used as indicators for the strength of the solute-solvent interactions [ 131. Figure 3 shows the contributions of each type of bond to the components of the molecular interaction tensor (Table 5 ) of iodobenzene and also the contribution of the C-Cl bond of chlorobenzene for comparison. On the whole small differences (below 5 x 1O-22 J ) are observed between iodo- and chlorobenzene for the interaction parameters Ucn and AAcc. The halogen contribution however is considerably larger for the C-I than for the C-Cl bond. The difference increases from EBBA to ZLI 1167 for which in A”” it reaches 15 x 1O-22 J. CONCLUSIONS
NMR of oriented molecules may be used to study small differences in molecular structures if corrections for harmonic vibrations as well as for correlated deformation are performed. As a by-product of the structural analysis, bond contributions to the orientation energy may be derived and can be compared between similar molecules.
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L. Ernst, V. Wray, V.A. Chertkov and N.M. Sergeyev, J. Magn. Reson., 25 (1977) 123. T. Uno, A. Kuwae and K. Machida, Spectrochim. Acta, Part A, 33 (1977) 607. M.D. Harmony, V.W. Laurie, R.L. Kuczkowski, R.H. Schwedemann, D.A. Ramsay,F.J. Lovas, W.J. Lafferty and A.G. Maki, J. Phys. Chem. Ref. Data, 8 (1979) 619. A. Domenicano, A. Vaciago and C.A. Coulson, Acta Crystallogr., Sect. B, 31 (1975) 1630. J. Lounila and T. Vliin&nen, Mol. Phys., 49 (1983) 859. J. Jokisaari, T. VPSinanenand J. Lounila, Mol. Phys., 45 (1982) 141. J. Jokisaari, Y. Hiltunen and T. Vtiniinen, Mol. Phys., 51 (1984) 779.