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Crown ethers formally derived from resorcinol. X-ray crystal structure and NMR investigations of dibenzo-26-crown-8
Journal of
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular Structure 415 (1997) 267-275
Crown ethers formally derived from resorcinol. X-ray crystal structure and NMR investigations of dibenzo-26-crown-8 G.W. Buchanan*, M. Lefort, A. Moghimi ~, C. Bensimon Ottawa-Carleton Chemistry Institute, Department of Chemistry, Carleton University, Ottawa, Ont. K1S 5B6 Canada
Received 12 December 1996; revised 26 February 1997
Abstract The title molecule crystallizes in a pseudo-symmetric conformation with two O - C - C - O units possessmg unusual trans geometries. Solid phase ~3C NMR data are presented as well as LH and 13C NMR chemical shifts and couplings determined in solution. © 1997 Elsevier Science B.V. Keywords: Resorcinol derived crown ether; Conformation
I. Introduction To date, a substantial number of X-ray crystal structures have been published for dibenzo-crown ethers, including those for dibenzo-18-crown-6, 1 [1], and dibenzo-24-crown-8, 2 [2]. Generally, the conformations of C - O - C - C units are transoid in these structures, while O - C - C - O units, where the carbons are not part of the aromatic ring, adopt gauche-type geometries.
Recently [3], we have reported the crystal structure of dibenzo-20-crown-6, 3, in which a pair of O - C C - O units are transoM. Also, all four of the C - O - C - C units in this molecule exhibit unusual geometries, with two such units having gauche conformations and the other two possessing torsion angles near 120 °. In order to explore the scope of such 'abnormal' geometries in other meta substituted dibenzo-crown ether analogues formally derived from resorcinol, we now present the X-ray crystallographic results
1
I
* Corresponding author. Tel.: (613) 520-2600 (3840); fax: (613) 520-3749; e-mail: [email protected] ' Present address: Department of Chemistry, University of Imam Hosein, Tehran, Iran.
for the related dibenzo-26-crown-8 system, 4 (below), as well as NMR data in solution and in the solid phase.
0022-2860/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S0022-2860(97)00088-4
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G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
o_/\ 19
17 ~
20 21
o
/
22 23 24
14
1
1
?\ / \ / o 12
11 10
9
8
/6
5
7
2. Experimental 2.1. Materials Dibenzo-26-crown-8, 4, was prepared according to the following procedure. A 1.0-1 round-bottom flask was charged with resorcinol (Aldrich) (11.0 g, 0.1 mol), distilled water (200 ml) and NaOH (4.0 g, 0.1 mol) and the mixture was stirred for 5 min. To this was added dropwise with stirring, 1,2-bis(2-chloroethoxy)ethane (Aldrich) (9.4 g, 0.05 mol) and the reaction mixture was refluxed for 72 h. After cooling to 40°C, an additional 4.0 g of NaOH was added followed by another 9.4 g of the dichloride. Subsequent to dilution with 15 ml of distilled water, the mixture was refluxed for another 72 h. After cooling, the mixture was acidified to pH 2 by addition of dilute sulphuric acid and extracted with CH2CIE (4 × 100 ml). After washing with 5% NaOH (3 × 150 ml), saturated NaC1 (3 × 150 ml) and water, the extracts were dried over MgSO4. Following solvent removal, the resultant crude solid was recrystallized twice from acetone to yield 4, m.p. 103-105°C, in 2.2% yield. No attempt was made to maximize the yield. 2.2. Spectra All solution NMR spectra were recorded using a
Bruker AMX-400 spectrometer equipped with a 5-mm inverse probe and an Aspect X32 computer. An Aspect 3000 process controller was employed and all standard microprograms used are in the Bruker Software Library. For the IH13C HMQC (heteronuclear multiple quantum coherence) experiment, the free induction decays were acquired over 1024 data points for each of the 512 values of the evolution time, with a digital resolution of ca. 8 Hz per point in F2 and 4 Hz per point in F2. The raw data were zero-filled in FI prior to transformation using the q sine window function for both FI and F2. Proton relaxation delays were set to 1 s. Delays were chosen to emphasize J values of 135-140 Hz. For the COSY experiment, N-type phase cycling was employed with a 45 ° mixing pulse. The free induction decays were acquired over 1024 data points for each of the 256 values of the evolution time, with a digital resolution of 5 Hz. The raw data were zerofilled in F1 prior to transformation using the q sine window function for both FI and F2. Data were symmetrized about the diagonal. The solid phase 13C NMR spectra were obtained at 45.26 MHz using a Bruker CXP-180 spectrometer equipped with a 4.24-T cryomagnet and a Doty Scientific magic angle spinning probe. Samples were contained in 7-mm-diameter zirconia or silicon nitride rotors with Kel-F end caps. IH 90 ° pulse lengths were typically 4.5 #s and spinning rates were 4 - 5 kHz. Dipolar dephased spectra were obtained via interruption of the ~H decoupling for 40 /zs immediately following the cross polarization sequence. Chemical shifts were measured relative to external hexamethylbenzene (HMB) and then corrected to the TMS scale (HMB methyl resonance at 16.9 p.p.m.). 2.3. X-ray crystallographic measurements and structure solution A summary of the crystallographic data is given in Table 4. Diffraction intensities were collected on a Siemens diffractometer using MoK radiation at -100°C. The f~ - 20 scan technique was used to a maximum 20 value of 57 °. The space group was determined by systematic absences. Unit cell parameters were obtained by least squares refinement using the setting angles of 5766 reflections in the range
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G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
3 < 20 < 57. The data were corrected for Lorentz and polarization effects [4]. No absorption correction was made. The structure was solved by direct methods plus Fourier maps and was refined by full matrix least squares analysis, with weights based on counting statistics. Non-H atoms were refined anisotropically. No crystal decay was noted during data collection. All calculations were performed using the NRC VAX Crystal Structure programs [5].
3. Results and discussion
Fig. 1 shows the ORTEP structure for 4 while the crystal packing diagram is illustrated in Fig. 2. Atomic bond lengths and bond angles are collected in Table 1 and Table 2, with selected torsion angles (i.e. those other than angles involving only aromatic carbons) presented in Table 3. Crystallographic data are in
Table 4 while atomic parameters are in Table 5. The 1H and 13C NMR data are collected in Table 6 and Table 7, respectively. Available as supplementary material are anisotropic temperature factors and structure factor tables. 3.1. X - r a y c r y s t a l l o g r a p h i c s t r u c t u r e
From examination of the ORTEP plot it is evident that there are no true elements of symmetry in the crystal structure of 4. However, detailed comparison of the torsion angles for networks related by a centre of symmetry (Table 3) shows that there is a pseudocentre of symmetry, since the average deviation from true symmetry for the 17 torsional networks listed is only 5.4 ° with a standard deviation of 4.4 °. With respect to the conformations of the O - C - C - O networks, 4 exhibits two unusual trans (t) geometries in the 26membered ring--i.e, networks O 3 - C l l - C 1 2 - O 4
C4
C3 C6
C7
C24 07 C8 08 02 C9 06
C10 C11
04
O5
C14
03
C15 C16
Fig. 1. ORTEPplot for 4.
C19
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
270
O - C - C - O networks and two trans cases. For the C - O - C - C networks in 3, all four such geometries are 'abnormal', with major deviations from the expected transoid geometry. Thus it appears that as the distance between the aromatic rings increases in these resorcinol derivatives, the incidence of normal geometries in the O - C - C - O and C - O - C - C networks increases. In order to compare the observed conformation in the crystal with theoretical predictions in the gas phase, we have carried out semi-empirical RHF/ MNDO calculations [8] using the Spartan program [9]. The results are presented below for torsion angles not involving three contiguous aromatic carbons.
I
Network
r, -S
Fig. 2. Crystal packing diagram for 4.
and O 7 - C 2 3 - C 2 4 - O 8 . The remaining four such units adopt the more common [6,7] gauche (g) type geometries, with angles ranging from 65.2 (2) ° to 73.5 (2) °. Hence this sequence of O - C - C - O units is t - g - g . For the C - O - C - C networks not involving contiguous aromatic carbons, 4 possesses eight such networks with the expected [6,7] transoid structures, and four networks with nearly orthogonal geometries. The latter are C 8 - O 2 - C 9 - C 1 0 , C 2 0 - O 6 - C 2 1 - C 2 2 , C l l - O 3 - C 1 0 - C 9 and C 2 3 - O 7 - C 2 2 - C 2 1 , with dihedral angles ranging from 83.9(3) to 97.3(3) ° . It is of interest to compare the structure of 4 with that recently reported for dibenzo-20-crown-6 ether, 3 [3]. In this material there are two normal gauche
C24-O8-C2-C1 C24-O8-C2-C3 C2-O8 -C24-C23 C 7 - O 1- C 6 - C 1 C7-O1-C6-C5 C6-O1-C7-C8 C9-O2-C8-C7 C 8 - O 2 - C 9 - C 10 C23-O7-C22-C21 C22-O7-C23-C24 O 1- C 7 - C 8 - O 2 O2-C9-C 10-03 O3-C11-C12-O4
4( ° )
-174.2 4.6 162.5 - 166.3 15.5 -171.6 172.6 -83.9 97.3 167.2 -65.2 -68.9 177.5
Minimum energy conformation (°) 128 -37 - 173 168 -20 102 170 -175 157 158 85 -68 66
Clearly there are some major deviations between the minimum energy conformation in the gas phase and that observed in the crystal. For the O - C - C - O networks, the calculated minimum energy conformation of the O 3 - C 1 1 - C 1 2 - O 4 network is the normal gauche geometry, while the torsion angle for this network in the crystal is 177.5 °. For the C - O - C - C networks, there are four cases in which the difference between observed and calculated torsion angles exceeds 45 ° . In general, the calculated geometry tends to be much closer to that expected by analogy with 'normal' cases [6,7], i.e. transoid C - O - C - C units and gauche O - C - C - O geometries. Of course, crystal packing phenomena could be playing a role here in determining the preferred conformation of 4 in the solid. The energy difference between the observed conformation in the crystal and the
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G. W. Buchanan et aL/Journal of Molecular Structure 415 (1997) 267-275
Table 1 Atomic bond distances (A) O1-C6 O2-C9 O4-C 12 O5-C19 O7-C22 O8-C24 C2-C3 C5-C6 C11-C12 C14-C15 CI7-C18 C23-C24
1.368 1.422 1.425 1.428 1.419 1.437 1.378 1.391 1.501 1.383 1.376 1.482
(2) (2) (2) (2) (2) (2) (2) (3) (3) (2) (3) (3)
O1-C7 O3-C10 O4-C13 O6-C20 O7-C23 C1-C2 C3-C4 C7-C8 C13-C14 C15-C16 C 19-C20
theoretical isolated global minimum is, however, rather small, i.e. 3.5 kJ mol -l. 3.2. NMR results
The solution 13C NMR spectrum exhibits seven resonances at ambient temperature, which is consistent with a rapid interconversion (on the NMR timescale) between all conformations. Lowering the temperature to 200 K results in no spectral changes other than minor temperature dependent chemical shifts.
1.426 1.421 1.370 1.422 1.415 1.386 1.373 1.487 1.384 1.383 1.494
(2) (2) (2) (2) (2) (2) (3) (3) (2) (2) (3)
O2-C8 O3-C11 O5-C15 O6-C21 O8-C2 C1-C6 C4-C5 C9-C10 C13-C18 C16-C17 C21 -C22
1.412 1.415 1.371 1.427 1.370 1.372 1.378 1.500 1.387 1.381 1.494
Regarding assignment of the solution spectra, the aromatic IH resonances show characteristic patterns and assignment is straightforward. The aromatic protons give rise to the expected A2XY type spectrum, while the aliphatics show AA'BB' and A4 patterns, respectively. The data are summarized in Table 6. First order analysis yielded the aromatic proton shifts and couplings while iterative computer analysis was employed to analyse the AA'BB' spectrum. Assignment of the more deshielded half of the AA'BB' multiplet to protons at sites 7, 12, 19 and 24 was made on the basis of the observed n.O.e
Table 2 Atomic bond angles (°) C6-01-C7 C10-03-C11 04-C13-CI4 C15-05-C19 C14-C13-C18 C13-C14-C15 C2-C1-C6 05-C15-C16 C14-C15-C16 C15-C16-C17 C2-C3-C4 C3-C4-C5 C4-C5-C6 Ol-C6-C1 CI-C6-C5 06-C20-C19 06-C21 -C22 07-C22-C21 07-C23-C24 0 4 - C 1 2 - C 11
118.6 (1) 114.0 (1) 115.3 (2) 117.9 (1) 120.4 (2) 120.1 (2) 119.9 (2) 124.8 (2) 120.1 (2) 118.7 (2) 119.1 (2) 121.7 (2) 118.6 (2) 115.4 (1) 120.4 (2) 109.3 (1) 113.3 (1) 112.6 (2) 107.4 (1) 106.0 (1)
(2) (2) (2) (2) (2) (2) (3) (3) (3) (3) (2)
C8-02-C9 C12-04-C13 04-C13-C18 C20-06-C21 C22-07-C23 C2-08-C24 05-C15-C14 08-C2-C 1 08-C2-C3 C1-C2-C3 C16-C17-C18 C13-C18-C17 05-C19-C20 01-C6-C5 01-C7-C8 02-C8-C7 02-C9-C10 03-C10-C9 03-C11-C12 08-C24-C23
113.6 (1) 118.1 (1) 124.3 (2) 112.8 (1) 113.8 (1) 118.3 (1) 115.1 (1) 115.2 (1) 124.6 (2) 120.2 (2) 122.4 (2) 118.3 (2) 107.7 (1) 124.1 (2) 107.9 (2) 110.1 (2) 113.6 (1) 112.3 (1) 107.0 (2) 106.0 (1)
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G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
Table 3 Selected torsion angles (o) for pseudosymmetry related networks O 1-C7-C8-O2 C7-C8-O2-C9 C8-O2-C9-C I0 O 2 - C 9 - C 10-03 C9-C 10-O3-C 11 C10-O3-C11-C12 O3-C11-C12-O4 C 11-C 12-O4-C 13 C12-O4-C13-C14 O4-C13-C14-C15 C13-C14-C15-O5 C14-C15-O5-C19 C15-O5-C19-C20 C19-O5-C15-C16 O5-C15-C16-C17 C24-O8-C2-C3 O8-C2-C3-C4
-65.2 (2) 172.6 (3) -83.9 (3) -68.9 (2) 95.0 (3) 178.2 (3) 177.5 (4) 176.6 (3) -174.2 (3) 179.5 (4) -179.1 (3) -177.0 (3) 179.0 (3) 3.3 (2) 179.6 (3) 4.6 (2) -177.0 (4)
O5-C 19-C20-O6 C 19-C20-O6-C21 C20-O6-C21 -C22 O6-C21 -C22-O7 C21 -C22-O7-C23 C22-O7-C23-C24 O7-C23-C24-O8 C23-C24-O8-C2 C24-O8-C2-C1 O8-C2-C1-C6 C2-C1-C6-O1 C1-C6-OI-C7 C6-OI-C7-C8 C7-O1-C6-C5 OI-C6-C5-C4 C 12-O4-C 13-C 18 O4-C13-C18-C17
-73.5 (2) 168.9 (3) -86.8 (2) -67.2 (3) 97.3 (3) 167.2 (3) 172.1 (4) 162.5 (3) -174.2 (3) 176.5 (3) -176.9 (3) -166.3 (3) -171.6 (3) 15.5 (2) 178.4 (4) 5.9 (2) 179.9 (4)
Table 4 Crystallographic data for 4 Formula fw Crystal system Space group a (,~) b (,~) c (A) fl V (,~3) Z (molecules per unit cell) Dc (g cm -3) Crystal dimensions (mm 3) Radiation (h, ,~) Octants measured Max 20 (°) Temperature (°C) No. of measured reflections No. of unique reflections No. of observed reflections with l,et > 2.5 oc l.et Rf Rw GoF Final - D map Deepest hole (e ,~-3) Highest peak (e ,~ 3) No. of atoms No. of parameters
C 24H320 8 448.51 Monoclinic P 2 l/n 11.3982 (2) 16.1245 (1) 12.8961 (3) 102.545 ( 1) 2313,59 (7) 4 1.288 0.20 x 0.20 x 0.20 MoKo~, 0.70930 h (-15 to 14), k (0 to 21), / (0 to 17) 57.0 -100 16108 5892 3099 0.041 0.041 1.64 ~).150 0.220 64 418
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 2 6 7 - 2 7 5
273
Table 5 Atomic parameters x, y, z and Biso. ESDs (estimated standard deviations) refer to last digit printed
x O1 02 03 04 05 06 07 08 C1 C2 C3 C4 C5 C6 C7 C8 C9 CI0 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24
0.20283 -0.02759 -0.14775 0.10344 (I.40796 (I.66361 0.75101 0.51221 0.36305 0.48427 0.56695 (/.52717 0.40680 0.32462 0.15741 0.02471 -0.15257 -0.17948 -0.03224 -0.01521 0.14031 0.25187 0.29755 0.23242 0.12182 0.07382 0.46292 0.58209 0.77201 0.76347 0.63074 0.63446
y (10) (101 (101 (11 ) (10) (10) (101 (10) (141 (15) (151 (161 (16) (141 (151 (16) (15) (151 (16) (15) (15) (151 (141 (151 (16) (151 (15) (151 (161 (151 (15) (161
0.15911 0.10775 0.27195 0.40170 0.59049 0.60752 0.48668 0.33989 0.24385 0.26362 0.20885 0.13569 0.11566 0.17091 0.07838 0.08475 0.12525 0.21218 0.30688 0.37000 0.46427 0.49757 0.56159 0.59202 0.55729 0.49415 0.65378 0.67333 0.61359 0.57414 0.45884 0.36799
z (7) (7) (7) (8) (7) (7) (7) (7) (10) (101 (111 (121 (11 ) (101 (121 (13) (111 (12) (111 (111 (101 (I 11 (101 (11) (12) (11) (10) (111 (11) (111 (111 (121
0.94052 0.95827 0.96998 1.07568 1.20504 1.28893 1.14811 1.08348 1.01511 1.03794 1.01322 0.96320 0.93718 0.96415 0.90950 0.87283 0.92723 0.88772 0.97813 1.06573 1.14720 1.14598 1.21431 1.28483 1.28520 1.21736 1.27685 1.25223 1,25112 1.14495 1.11687 1.10024
Biso
(10) (9) (101 (10) (9) (9) (10) (11) (131 (13) (151 (171 (16) (141 (15) (16) (14) (151 (15) (15) (131 (141 (12) (13) (15) (14) (141 (141 (15) (15) (15) (17)
4.63 4.30 4.76 5.13 4.19 4.08 4.22 5.17 3.53 3.61 4.27 4.96 4.63 3.52 4.60 5.17 4.18 4.52 4.61 4.30 3.64 3.89 3.45 3.96 4.57 4.07 3.92 4.21 4.38 4.28 4.20 5.07
(6) (6) (6) (6) (6) (6) (6) (6) (8) (8) (9) (101 (9) (8) (9) (101 (8) (9) (9) (9) (8) (8) (8) (8) (9) (8) (8) (9) (9) (9) (9) (10)
Biso is the mean of the principal axes of the thermal ellipsoid.
between the resonance centred at 4.073 p.p.m, and the aromatic resonance at 6.480 p.p.m, arising from aromatic protons 3, 5, 16 and 18. It is of interest to compare the aliphatic vicinal coupling constants for 4 to those found previously [ 10] for dibenzo-18-crown6, which possesses only gauche O - C - C - O units in the crystal structure. Both materials have been examined in CDC13 solution. The presence of the trans O - C - C - O units in crystalline 4, for example, would lead to the expectation of larger vicinal couplings in the XH spectrum of 4. In reality there is only a small increase observed. The 3j values for dibenzo-18-crown-6 are 5.7 and 3.3 Hz, while those for 4 are 6.0 and 3.9 Hz. It is to be noted that the vicinal couplings involving the aliphatic protons of
4 are within 0.1 Hz of those observed in the corresponding dibenzo-20-crown-6 case [3]. Hence conformational averaging in solution appears to render the vicinal couplings more nearly equal than would be expected based on crystal geometries alone. From the IJ HMQC experiment, protonated aromatic carbons are identified and consideration of relative intensities and substituent induced chemical shifts [11] leads to the assignments shown in Table 7. Quaternary carbons 2, 6, 13 and 15 are the most deshielded, as expected from the early data on aromatic ethers [ 11 ]. The known shielding effect of ortho oxygen atoms is clearly evident here, giving rise to the resonance at 102.0 p.p.m, for C1, 14. The resonance at 107.1 p.p.m, is twice the intensity of that at 102.0,
274
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
Table 6 IH NMR data for 4 (0.01 M in CDC10 Proton
0 (_+0.001 )
2j (Hz)
1, 14 3, 5, 16, 18 4, 17 7, 12, 19, 24
6.540 6.480 7.117 4.073
-11.0
8, 11, 20, 23
3.846
-11.0
9, 10, 21, 22
3.719
consistent with the assignment of the 107.1 peak to C3, 5, 16, 18. The remaining CH resonance at 129.8 p.p.m. arises from C4, 17. In the aliphatic region, the more shielded methylene carbon resonance at 67.4 p.p.m, is attributed to C7, 12, 19, 24 based on results of the ~J HMQC spectrum. The carbon at 71.0 p.p.m, must arise from C9, 10, 21, 22 since it is correlated to the ~H singlet at 3.719 p.p.m, in the JJ HETCOR experiment. In the solid phase, the 13C spectral multiplicity will reflect the asymmetric unit in the crystal if no unusual crystal packing effects or nonequivalent molecules in the unit cell are present [12]. The crystal packing diagram is presented in Fig. 2. From this diagram it can be seen that there are four identical molecules in the unit cell. Although there are no true symmetry elements in the crystal structure, examination of the torsion angle data in Table 3 indicate that there is a pseudo-centre of symmetry. On this basis, the asymmetric unit in the crystalline structure of 4 is effectively one half of the molecule. Accordingly one anticipates, in the solid phase J3C NMR spectrum, the observation of two quaternary carbon resonances for the oxygenated aromatic carbons C2, 6, 13, 15 near 160 p.p.m. The 13C data in Table 7 are consistent Table 7 13C NMR chemical shifts for 4 (0c from TMS -+ 0.1) Carbon
c3c (0.1 M in CDC13)
0c (solid)
2, 6, 13, 15
160.0
l, 3, 4, 7, 8, 9,
102.0 107.1 129.8 67.4 69.7 71.0
160.1 159.6 100.4 104.6 130.0 63.6-65.2 68.8-70.8 68.8-70.8
14 5, 16, 18 17 12, 19, 24 11, 20, 23 10, 21, 22
3j (Hz)
8,2 8.2 6.0 3.9 6.0 3.9
4j (Hz) 2.4 2.4
with this interpretation. Also the observation of a single 13C resonance in the solid near 100 p.p.m, for C1, 14 supports this argument as does the line at 130.0 p.p.m, assigned to C4, 17. For the aromatic carbons C3, 5, 16 and 18, there is only a broadened singlet observed in the solid state t3C spectrum at 104.6 p.p.m., indicating that the chemical shift differences between the two nonequivalent sites in the solid state are too small to be resolved. In the case of the aliphatic carbon resonances, the most highly shielded carbons in the range of 63.6-65.2 p.p.m, are assigned to C7, 12, 19, 24 due to the fact that these carbons have nearly planar gauche-q/steric interactions with the aromatic C5, 18, 16 and 3 sites, respectively, and hence are anticipated [12] to be shielded relative to the other aliphatics. The remainder of the aliphatic carbons give rise to a multiplet in the range of 68.8-70.8 p.p.m. In general, the solid state 13C chemical shifts are within ca. 2 p.p.m, of those observed in solution for 4, in spite of the fact that the shifts are not conformationally averaged in the solid. In conclusion, it appears from the NMR work that the crystallographically observed conformation is compatible with a major conformation present in solution. This agreement also suggests that the X-ray structure is closer to the global minimum than the structure calculated by the semi-empirical methods. Crystalline complexes of 4 are under study to determine the optimum complexation geometry.
4. Supplementary material available Tables of anisotropic temperature factors and structure factors have been deposited with the British
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
L i b r a r y D o c u m e n t S u p p l y C e n t r e a n d are a v a i l a b l e as P u b l i c a t i o n No. S U P 2 6 5 8 1 (34 pp. o f table).
References [1] D. Bright, M.R. Truter, J. Chem. Soc. (B) (1970) 1544. [2] I.R. Hanson, D.L. Hughes, M.R. Tinter, J. Chem. Soc. Perkin Trans. 2 (1976) 972. [3] G.W. Buchanan, A. Moghimi, C. Bensimon, Can. J. Chem. 73 (1995) 100. [4] D.F. Grant, E.J. Gabe, J. Appl. CrystaUogr. 11 (1978) 114.
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[5] E.J. Gabe, F.L. Lee, Y. Lepage, J. Appl. Crystallogr. 22 (1989) 384. [6] A.C. Coxon, D.A. Laidler, R.B. Pettman, J.F. Stoddart, J. Am. Chem. Soc. 100 (1978) 8260. [7] M.J. Bovill, D.J. Chadwick, I.O. Sutherland. J. Chem. Soc. Perkin Trans. 2 (1980) 1529. [8] M.J.S. Dewar, W.J. Thiel, J. Am. Chem. Soc. 99 (1977) 4899. [9] W.J. Hehre, W.W. Huang, Chemistry With Computation. An Introduction to Spartan, Wavefunction Inc., Irvine, CA, 1995. [10] D. Live, S.I. Chart, J. Am. Chem. Soc. 98 (1976) 3769. [11] J.B. Stothers, Carbon-13 NMR Spectroscopy, Academic Press, New York, NY, 1972. [12] K. Seidman, G.E. Maciel, J. Am. Chem. Soc. 99 (1977) 659.
MOLECULAR STRUCTURE ELSEVIER
Journal of Molecular Structure 415 (1997) 267-275
Crown ethers formally derived from resorcinol. X-ray crystal structure and NMR investigations of dibenzo-26-crown-8 G.W. Buchanan*, M. Lefort, A. Moghimi ~, C. Bensimon Ottawa-Carleton Chemistry Institute, Department of Chemistry, Carleton University, Ottawa, Ont. K1S 5B6 Canada
Received 12 December 1996; revised 26 February 1997
Abstract The title molecule crystallizes in a pseudo-symmetric conformation with two O - C - C - O units possessmg unusual trans geometries. Solid phase ~3C NMR data are presented as well as LH and 13C NMR chemical shifts and couplings determined in solution. © 1997 Elsevier Science B.V. Keywords: Resorcinol derived crown ether; Conformation
I. Introduction To date, a substantial number of X-ray crystal structures have been published for dibenzo-crown ethers, including those for dibenzo-18-crown-6, 1 [1], and dibenzo-24-crown-8, 2 [2]. Generally, the conformations of C - O - C - C units are transoid in these structures, while O - C - C - O units, where the carbons are not part of the aromatic ring, adopt gauche-type geometries.
Recently [3], we have reported the crystal structure of dibenzo-20-crown-6, 3, in which a pair of O - C C - O units are transoM. Also, all four of the C - O - C - C units in this molecule exhibit unusual geometries, with two such units having gauche conformations and the other two possessing torsion angles near 120 °. In order to explore the scope of such 'abnormal' geometries in other meta substituted dibenzo-crown ether analogues formally derived from resorcinol, we now present the X-ray crystallographic results
1
I
* Corresponding author. Tel.: (613) 520-2600 (3840); fax: (613) 520-3749; e-mail: [email protected] ' Present address: Department of Chemistry, University of Imam Hosein, Tehran, Iran.
for the related dibenzo-26-crown-8 system, 4 (below), as well as NMR data in solution and in the solid phase.
0022-2860/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S0022-2860(97)00088-4
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o_/\ 19
17 ~
20 21
o
/
22 23 24
14
1
1
?\ / \ / o 12
11 10
9
8
/6
5
7
2. Experimental 2.1. Materials Dibenzo-26-crown-8, 4, was prepared according to the following procedure. A 1.0-1 round-bottom flask was charged with resorcinol (Aldrich) (11.0 g, 0.1 mol), distilled water (200 ml) and NaOH (4.0 g, 0.1 mol) and the mixture was stirred for 5 min. To this was added dropwise with stirring, 1,2-bis(2-chloroethoxy)ethane (Aldrich) (9.4 g, 0.05 mol) and the reaction mixture was refluxed for 72 h. After cooling to 40°C, an additional 4.0 g of NaOH was added followed by another 9.4 g of the dichloride. Subsequent to dilution with 15 ml of distilled water, the mixture was refluxed for another 72 h. After cooling, the mixture was acidified to pH 2 by addition of dilute sulphuric acid and extracted with CH2CIE (4 × 100 ml). After washing with 5% NaOH (3 × 150 ml), saturated NaC1 (3 × 150 ml) and water, the extracts were dried over MgSO4. Following solvent removal, the resultant crude solid was recrystallized twice from acetone to yield 4, m.p. 103-105°C, in 2.2% yield. No attempt was made to maximize the yield. 2.2. Spectra All solution NMR spectra were recorded using a
Bruker AMX-400 spectrometer equipped with a 5-mm inverse probe and an Aspect X32 computer. An Aspect 3000 process controller was employed and all standard microprograms used are in the Bruker Software Library. For the IH13C HMQC (heteronuclear multiple quantum coherence) experiment, the free induction decays were acquired over 1024 data points for each of the 512 values of the evolution time, with a digital resolution of ca. 8 Hz per point in F2 and 4 Hz per point in F2. The raw data were zero-filled in FI prior to transformation using the q sine window function for both FI and F2. Proton relaxation delays were set to 1 s. Delays were chosen to emphasize J values of 135-140 Hz. For the COSY experiment, N-type phase cycling was employed with a 45 ° mixing pulse. The free induction decays were acquired over 1024 data points for each of the 256 values of the evolution time, with a digital resolution of 5 Hz. The raw data were zerofilled in F1 prior to transformation using the q sine window function for both FI and F2. Data were symmetrized about the diagonal. The solid phase 13C NMR spectra were obtained at 45.26 MHz using a Bruker CXP-180 spectrometer equipped with a 4.24-T cryomagnet and a Doty Scientific magic angle spinning probe. Samples were contained in 7-mm-diameter zirconia or silicon nitride rotors with Kel-F end caps. IH 90 ° pulse lengths were typically 4.5 #s and spinning rates were 4 - 5 kHz. Dipolar dephased spectra were obtained via interruption of the ~H decoupling for 40 /zs immediately following the cross polarization sequence. Chemical shifts were measured relative to external hexamethylbenzene (HMB) and then corrected to the TMS scale (HMB methyl resonance at 16.9 p.p.m.). 2.3. X-ray crystallographic measurements and structure solution A summary of the crystallographic data is given in Table 4. Diffraction intensities were collected on a Siemens diffractometer using MoK radiation at -100°C. The f~ - 20 scan technique was used to a maximum 20 value of 57 °. The space group was determined by systematic absences. Unit cell parameters were obtained by least squares refinement using the setting angles of 5766 reflections in the range
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3 < 20 < 57. The data were corrected for Lorentz and polarization effects [4]. No absorption correction was made. The structure was solved by direct methods plus Fourier maps and was refined by full matrix least squares analysis, with weights based on counting statistics. Non-H atoms were refined anisotropically. No crystal decay was noted during data collection. All calculations were performed using the NRC VAX Crystal Structure programs [5].
3. Results and discussion
Fig. 1 shows the ORTEP structure for 4 while the crystal packing diagram is illustrated in Fig. 2. Atomic bond lengths and bond angles are collected in Table 1 and Table 2, with selected torsion angles (i.e. those other than angles involving only aromatic carbons) presented in Table 3. Crystallographic data are in
Table 4 while atomic parameters are in Table 5. The 1H and 13C NMR data are collected in Table 6 and Table 7, respectively. Available as supplementary material are anisotropic temperature factors and structure factor tables. 3.1. X - r a y c r y s t a l l o g r a p h i c s t r u c t u r e
From examination of the ORTEP plot it is evident that there are no true elements of symmetry in the crystal structure of 4. However, detailed comparison of the torsion angles for networks related by a centre of symmetry (Table 3) shows that there is a pseudocentre of symmetry, since the average deviation from true symmetry for the 17 torsional networks listed is only 5.4 ° with a standard deviation of 4.4 °. With respect to the conformations of the O - C - C - O networks, 4 exhibits two unusual trans (t) geometries in the 26membered ring--i.e, networks O 3 - C l l - C 1 2 - O 4
C4
C3 C6
C7
C24 07 C8 08 02 C9 06
C10 C11
04
O5
C14
03
C15 C16
Fig. 1. ORTEPplot for 4.
C19
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
270
O - C - C - O networks and two trans cases. For the C - O - C - C networks in 3, all four such geometries are 'abnormal', with major deviations from the expected transoid geometry. Thus it appears that as the distance between the aromatic rings increases in these resorcinol derivatives, the incidence of normal geometries in the O - C - C - O and C - O - C - C networks increases. In order to compare the observed conformation in the crystal with theoretical predictions in the gas phase, we have carried out semi-empirical RHF/ MNDO calculations [8] using the Spartan program [9]. The results are presented below for torsion angles not involving three contiguous aromatic carbons.
I
Network
r, -S
Fig. 2. Crystal packing diagram for 4.
and O 7 - C 2 3 - C 2 4 - O 8 . The remaining four such units adopt the more common [6,7] gauche (g) type geometries, with angles ranging from 65.2 (2) ° to 73.5 (2) °. Hence this sequence of O - C - C - O units is t - g - g . For the C - O - C - C networks not involving contiguous aromatic carbons, 4 possesses eight such networks with the expected [6,7] transoid structures, and four networks with nearly orthogonal geometries. The latter are C 8 - O 2 - C 9 - C 1 0 , C 2 0 - O 6 - C 2 1 - C 2 2 , C l l - O 3 - C 1 0 - C 9 and C 2 3 - O 7 - C 2 2 - C 2 1 , with dihedral angles ranging from 83.9(3) to 97.3(3) ° . It is of interest to compare the structure of 4 with that recently reported for dibenzo-20-crown-6 ether, 3 [3]. In this material there are two normal gauche
C24-O8-C2-C1 C24-O8-C2-C3 C2-O8 -C24-C23 C 7 - O 1- C 6 - C 1 C7-O1-C6-C5 C6-O1-C7-C8 C9-O2-C8-C7 C 8 - O 2 - C 9 - C 10 C23-O7-C22-C21 C22-O7-C23-C24 O 1- C 7 - C 8 - O 2 O2-C9-C 10-03 O3-C11-C12-O4
4( ° )
-174.2 4.6 162.5 - 166.3 15.5 -171.6 172.6 -83.9 97.3 167.2 -65.2 -68.9 177.5
Minimum energy conformation (°) 128 -37 - 173 168 -20 102 170 -175 157 158 85 -68 66
Clearly there are some major deviations between the minimum energy conformation in the gas phase and that observed in the crystal. For the O - C - C - O networks, the calculated minimum energy conformation of the O 3 - C 1 1 - C 1 2 - O 4 network is the normal gauche geometry, while the torsion angle for this network in the crystal is 177.5 °. For the C - O - C - C networks, there are four cases in which the difference between observed and calculated torsion angles exceeds 45 ° . In general, the calculated geometry tends to be much closer to that expected by analogy with 'normal' cases [6,7], i.e. transoid C - O - C - C units and gauche O - C - C - O geometries. Of course, crystal packing phenomena could be playing a role here in determining the preferred conformation of 4 in the solid. The energy difference between the observed conformation in the crystal and the
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Table 1 Atomic bond distances (A) O1-C6 O2-C9 O4-C 12 O5-C19 O7-C22 O8-C24 C2-C3 C5-C6 C11-C12 C14-C15 CI7-C18 C23-C24
1.368 1.422 1.425 1.428 1.419 1.437 1.378 1.391 1.501 1.383 1.376 1.482
(2) (2) (2) (2) (2) (2) (2) (3) (3) (2) (3) (3)
O1-C7 O3-C10 O4-C13 O6-C20 O7-C23 C1-C2 C3-C4 C7-C8 C13-C14 C15-C16 C 19-C20
theoretical isolated global minimum is, however, rather small, i.e. 3.5 kJ mol -l. 3.2. NMR results
The solution 13C NMR spectrum exhibits seven resonances at ambient temperature, which is consistent with a rapid interconversion (on the NMR timescale) between all conformations. Lowering the temperature to 200 K results in no spectral changes other than minor temperature dependent chemical shifts.
1.426 1.421 1.370 1.422 1.415 1.386 1.373 1.487 1.384 1.383 1.494
(2) (2) (2) (2) (2) (2) (3) (3) (2) (2) (3)
O2-C8 O3-C11 O5-C15 O6-C21 O8-C2 C1-C6 C4-C5 C9-C10 C13-C18 C16-C17 C21 -C22
1.412 1.415 1.371 1.427 1.370 1.372 1.378 1.500 1.387 1.381 1.494
Regarding assignment of the solution spectra, the aromatic IH resonances show characteristic patterns and assignment is straightforward. The aromatic protons give rise to the expected A2XY type spectrum, while the aliphatics show AA'BB' and A4 patterns, respectively. The data are summarized in Table 6. First order analysis yielded the aromatic proton shifts and couplings while iterative computer analysis was employed to analyse the AA'BB' spectrum. Assignment of the more deshielded half of the AA'BB' multiplet to protons at sites 7, 12, 19 and 24 was made on the basis of the observed n.O.e
Table 2 Atomic bond angles (°) C6-01-C7 C10-03-C11 04-C13-CI4 C15-05-C19 C14-C13-C18 C13-C14-C15 C2-C1-C6 05-C15-C16 C14-C15-C16 C15-C16-C17 C2-C3-C4 C3-C4-C5 C4-C5-C6 Ol-C6-C1 CI-C6-C5 06-C20-C19 06-C21 -C22 07-C22-C21 07-C23-C24 0 4 - C 1 2 - C 11
118.6 (1) 114.0 (1) 115.3 (2) 117.9 (1) 120.4 (2) 120.1 (2) 119.9 (2) 124.8 (2) 120.1 (2) 118.7 (2) 119.1 (2) 121.7 (2) 118.6 (2) 115.4 (1) 120.4 (2) 109.3 (1) 113.3 (1) 112.6 (2) 107.4 (1) 106.0 (1)
(2) (2) (2) (2) (2) (2) (3) (3) (3) (3) (2)
C8-02-C9 C12-04-C13 04-C13-C18 C20-06-C21 C22-07-C23 C2-08-C24 05-C15-C14 08-C2-C 1 08-C2-C3 C1-C2-C3 C16-C17-C18 C13-C18-C17 05-C19-C20 01-C6-C5 01-C7-C8 02-C8-C7 02-C9-C10 03-C10-C9 03-C11-C12 08-C24-C23
113.6 (1) 118.1 (1) 124.3 (2) 112.8 (1) 113.8 (1) 118.3 (1) 115.1 (1) 115.2 (1) 124.6 (2) 120.2 (2) 122.4 (2) 118.3 (2) 107.7 (1) 124.1 (2) 107.9 (2) 110.1 (2) 113.6 (1) 112.3 (1) 107.0 (2) 106.0 (1)
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Table 3 Selected torsion angles (o) for pseudosymmetry related networks O 1-C7-C8-O2 C7-C8-O2-C9 C8-O2-C9-C I0 O 2 - C 9 - C 10-03 C9-C 10-O3-C 11 C10-O3-C11-C12 O3-C11-C12-O4 C 11-C 12-O4-C 13 C12-O4-C13-C14 O4-C13-C14-C15 C13-C14-C15-O5 C14-C15-O5-C19 C15-O5-C19-C20 C19-O5-C15-C16 O5-C15-C16-C17 C24-O8-C2-C3 O8-C2-C3-C4
-65.2 (2) 172.6 (3) -83.9 (3) -68.9 (2) 95.0 (3) 178.2 (3) 177.5 (4) 176.6 (3) -174.2 (3) 179.5 (4) -179.1 (3) -177.0 (3) 179.0 (3) 3.3 (2) 179.6 (3) 4.6 (2) -177.0 (4)
O5-C 19-C20-O6 C 19-C20-O6-C21 C20-O6-C21 -C22 O6-C21 -C22-O7 C21 -C22-O7-C23 C22-O7-C23-C24 O7-C23-C24-O8 C23-C24-O8-C2 C24-O8-C2-C1 O8-C2-C1-C6 C2-C1-C6-O1 C1-C6-OI-C7 C6-OI-C7-C8 C7-O1-C6-C5 OI-C6-C5-C4 C 12-O4-C 13-C 18 O4-C13-C18-C17
-73.5 (2) 168.9 (3) -86.8 (2) -67.2 (3) 97.3 (3) 167.2 (3) 172.1 (4) 162.5 (3) -174.2 (3) 176.5 (3) -176.9 (3) -166.3 (3) -171.6 (3) 15.5 (2) 178.4 (4) 5.9 (2) 179.9 (4)
Table 4 Crystallographic data for 4 Formula fw Crystal system Space group a (,~) b (,~) c (A) fl V (,~3) Z (molecules per unit cell) Dc (g cm -3) Crystal dimensions (mm 3) Radiation (h, ,~) Octants measured Max 20 (°) Temperature (°C) No. of measured reflections No. of unique reflections No. of observed reflections with l,et > 2.5 oc l.et Rf Rw GoF Final - D map Deepest hole (e ,~-3) Highest peak (e ,~ 3) No. of atoms No. of parameters
C 24H320 8 448.51 Monoclinic P 2 l/n 11.3982 (2) 16.1245 (1) 12.8961 (3) 102.545 ( 1) 2313,59 (7) 4 1.288 0.20 x 0.20 x 0.20 MoKo~, 0.70930 h (-15 to 14), k (0 to 21), / (0 to 17) 57.0 -100 16108 5892 3099 0.041 0.041 1.64 ~).150 0.220 64 418
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 2 6 7 - 2 7 5
273
Table 5 Atomic parameters x, y, z and Biso. ESDs (estimated standard deviations) refer to last digit printed
x O1 02 03 04 05 06 07 08 C1 C2 C3 C4 C5 C6 C7 C8 C9 CI0 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24
0.20283 -0.02759 -0.14775 0.10344 (I.40796 (I.66361 0.75101 0.51221 0.36305 0.48427 0.56695 (/.52717 0.40680 0.32462 0.15741 0.02471 -0.15257 -0.17948 -0.03224 -0.01521 0.14031 0.25187 0.29755 0.23242 0.12182 0.07382 0.46292 0.58209 0.77201 0.76347 0.63074 0.63446
y (10) (101 (101 (11 ) (10) (10) (101 (10) (141 (15) (151 (161 (16) (141 (151 (16) (15) (151 (16) (15) (15) (151 (141 (151 (16) (151 (15) (151 (161 (151 (15) (161
0.15911 0.10775 0.27195 0.40170 0.59049 0.60752 0.48668 0.33989 0.24385 0.26362 0.20885 0.13569 0.11566 0.17091 0.07838 0.08475 0.12525 0.21218 0.30688 0.37000 0.46427 0.49757 0.56159 0.59202 0.55729 0.49415 0.65378 0.67333 0.61359 0.57414 0.45884 0.36799
z (7) (7) (7) (8) (7) (7) (7) (7) (10) (101 (111 (121 (11 ) (101 (121 (13) (111 (12) (111 (111 (101 (I 11 (101 (11) (12) (11) (10) (111 (11) (111 (111 (121
0.94052 0.95827 0.96998 1.07568 1.20504 1.28893 1.14811 1.08348 1.01511 1.03794 1.01322 0.96320 0.93718 0.96415 0.90950 0.87283 0.92723 0.88772 0.97813 1.06573 1.14720 1.14598 1.21431 1.28483 1.28520 1.21736 1.27685 1.25223 1,25112 1.14495 1.11687 1.10024
Biso
(10) (9) (101 (10) (9) (9) (10) (11) (131 (13) (151 (171 (16) (141 (15) (16) (14) (151 (15) (15) (131 (141 (12) (13) (15) (14) (141 (141 (15) (15) (15) (17)
4.63 4.30 4.76 5.13 4.19 4.08 4.22 5.17 3.53 3.61 4.27 4.96 4.63 3.52 4.60 5.17 4.18 4.52 4.61 4.30 3.64 3.89 3.45 3.96 4.57 4.07 3.92 4.21 4.38 4.28 4.20 5.07
(6) (6) (6) (6) (6) (6) (6) (6) (8) (8) (9) (101 (9) (8) (9) (101 (8) (9) (9) (9) (8) (8) (8) (8) (9) (8) (8) (9) (9) (9) (9) (10)
Biso is the mean of the principal axes of the thermal ellipsoid.
between the resonance centred at 4.073 p.p.m, and the aromatic resonance at 6.480 p.p.m, arising from aromatic protons 3, 5, 16 and 18. It is of interest to compare the aliphatic vicinal coupling constants for 4 to those found previously [ 10] for dibenzo-18-crown6, which possesses only gauche O - C - C - O units in the crystal structure. Both materials have been examined in CDC13 solution. The presence of the trans O - C - C - O units in crystalline 4, for example, would lead to the expectation of larger vicinal couplings in the XH spectrum of 4. In reality there is only a small increase observed. The 3j values for dibenzo-18-crown-6 are 5.7 and 3.3 Hz, while those for 4 are 6.0 and 3.9 Hz. It is to be noted that the vicinal couplings involving the aliphatic protons of
4 are within 0.1 Hz of those observed in the corresponding dibenzo-20-crown-6 case [3]. Hence conformational averaging in solution appears to render the vicinal couplings more nearly equal than would be expected based on crystal geometries alone. From the IJ HMQC experiment, protonated aromatic carbons are identified and consideration of relative intensities and substituent induced chemical shifts [11] leads to the assignments shown in Table 7. Quaternary carbons 2, 6, 13 and 15 are the most deshielded, as expected from the early data on aromatic ethers [ 11 ]. The known shielding effect of ortho oxygen atoms is clearly evident here, giving rise to the resonance at 102.0 p.p.m, for C1, 14. The resonance at 107.1 p.p.m, is twice the intensity of that at 102.0,
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G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
Table 6 IH NMR data for 4 (0.01 M in CDC10 Proton
0 (_+0.001 )
2j (Hz)
1, 14 3, 5, 16, 18 4, 17 7, 12, 19, 24
6.540 6.480 7.117 4.073
-11.0
8, 11, 20, 23
3.846
-11.0
9, 10, 21, 22
3.719
consistent with the assignment of the 107.1 peak to C3, 5, 16, 18. The remaining CH resonance at 129.8 p.p.m. arises from C4, 17. In the aliphatic region, the more shielded methylene carbon resonance at 67.4 p.p.m, is attributed to C7, 12, 19, 24 based on results of the ~J HMQC spectrum. The carbon at 71.0 p.p.m, must arise from C9, 10, 21, 22 since it is correlated to the ~H singlet at 3.719 p.p.m, in the JJ HETCOR experiment. In the solid phase, the 13C spectral multiplicity will reflect the asymmetric unit in the crystal if no unusual crystal packing effects or nonequivalent molecules in the unit cell are present [12]. The crystal packing diagram is presented in Fig. 2. From this diagram it can be seen that there are four identical molecules in the unit cell. Although there are no true symmetry elements in the crystal structure, examination of the torsion angle data in Table 3 indicate that there is a pseudo-centre of symmetry. On this basis, the asymmetric unit in the crystalline structure of 4 is effectively one half of the molecule. Accordingly one anticipates, in the solid phase J3C NMR spectrum, the observation of two quaternary carbon resonances for the oxygenated aromatic carbons C2, 6, 13, 15 near 160 p.p.m. The 13C data in Table 7 are consistent Table 7 13C NMR chemical shifts for 4 (0c from TMS -+ 0.1) Carbon
c3c (0.1 M in CDC13)
0c (solid)
2, 6, 13, 15
160.0
l, 3, 4, 7, 8, 9,
102.0 107.1 129.8 67.4 69.7 71.0
160.1 159.6 100.4 104.6 130.0 63.6-65.2 68.8-70.8 68.8-70.8
14 5, 16, 18 17 12, 19, 24 11, 20, 23 10, 21, 22
3j (Hz)
8,2 8.2 6.0 3.9 6.0 3.9
4j (Hz) 2.4 2.4
with this interpretation. Also the observation of a single 13C resonance in the solid near 100 p.p.m, for C1, 14 supports this argument as does the line at 130.0 p.p.m, assigned to C4, 17. For the aromatic carbons C3, 5, 16 and 18, there is only a broadened singlet observed in the solid state t3C spectrum at 104.6 p.p.m., indicating that the chemical shift differences between the two nonequivalent sites in the solid state are too small to be resolved. In the case of the aliphatic carbon resonances, the most highly shielded carbons in the range of 63.6-65.2 p.p.m, are assigned to C7, 12, 19, 24 due to the fact that these carbons have nearly planar gauche-q/steric interactions with the aromatic C5, 18, 16 and 3 sites, respectively, and hence are anticipated [12] to be shielded relative to the other aliphatics. The remainder of the aliphatic carbons give rise to a multiplet in the range of 68.8-70.8 p.p.m. In general, the solid state 13C chemical shifts are within ca. 2 p.p.m, of those observed in solution for 4, in spite of the fact that the shifts are not conformationally averaged in the solid. In conclusion, it appears from the NMR work that the crystallographically observed conformation is compatible with a major conformation present in solution. This agreement also suggests that the X-ray structure is closer to the global minimum than the structure calculated by the semi-empirical methods. Crystalline complexes of 4 are under study to determine the optimum complexation geometry.
4. Supplementary material available Tables of anisotropic temperature factors and structure factors have been deposited with the British
G.W. Buchanan et al./Journal of Molecular Structure 415 (1997) 267-275
L i b r a r y D o c u m e n t S u p p l y C e n t r e a n d are a v a i l a b l e as P u b l i c a t i o n No. S U P 2 6 5 8 1 (34 pp. o f table).
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[5] E.J. Gabe, F.L. Lee, Y. Lepage, J. Appl. Crystallogr. 22 (1989) 384. [6] A.C. Coxon, D.A. Laidler, R.B. Pettman, J.F. Stoddart, J. Am. Chem. Soc. 100 (1978) 8260. [7] M.J. Bovill, D.J. Chadwick, I.O. Sutherland. J. Chem. Soc. Perkin Trans. 2 (1980) 1529. [8] M.J.S. Dewar, W.J. Thiel, J. Am. Chem. Soc. 99 (1977) 4899. [9] W.J. Hehre, W.W. Huang, Chemistry With Computation. An Introduction to Spartan, Wavefunction Inc., Irvine, CA, 1995. [10] D. Live, S.I. Chart, J. Am. Chem. Soc. 98 (1976) 3769. [11] J.B. Stothers, Carbon-13 NMR Spectroscopy, Academic Press, New York, NY, 1972. [12] K. Seidman, G.E. Maciel, J. Am. Chem. Soc. 99 (1977) 659.