Stereoisomers of 1,2-diaryl-1,3-propanediols: erythro forms

Racemic erythro-1,2-diphenyl-1,3-propane­diol, C₁₅H₁₆O₂, is a model compound representative of erythro forms of structural elements of the 1,2-diaryl-1,3-propane­diol type in lignins. In the crystal structure, the torsion angle between the bulky phenyl groups is -62.26 (11)°. Strong hydrogen bonds take part in a directed co-operative O-H...O-H...O-H...O-H pattern that is assumed to have a decisive influence on the conformation. This is supported by comparisons with the geometries of related compounds.

S1. Comment

The stereochemistry of lignin models of the 1,2-diaryl-1,3-propanediol type was investigated in a previous paper (Lundquist & Stomberg, 1987). The crystal structure of one of the compounds examined, erythro-1,2-diphenyl-1,3-propanediol (I), is reported in this paper. Previous reports describe the crystal structures of the related compounds erythro-2-(4-methoxyphenyl)-1-phenyl-1,3-propanediol, (II) (Lundquist & Stomberg, 1987), and erythro-1-(4-benzyloxy-3-methoxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol, (III) (Stomberg et al., 1997). The crystal structure of the tetraacetate, (IV), of another related compound, erythro-bis(4-hydroxy-3-methoxyphenyl)-1,3-propanediol, (VI), has also been determined (Stomberg & Lundquist, 1995). Some results from attempts to determine the crystal structure of the diacetate, (V), of erythro-bis(3,4-dimethoxyphenyl)-1,3-propanediol, (VII) (Li et al., 1993; Aoyama et al., 1995), are reported in this paper. The stereochemistry of threo forms of lignin models of the 1,2-diaryl-1,3-propanediol type is discussed in a recent paper (Stomberg et al., 2006).

Syntheses of the compounds discussed above are described in the literature referred to or in references therein. Syntheses of other erythro forms of lignin models of the 1,2-diaryl-1,3-propanediol type have been published by Parkås et al. (2004) [(VIII)], Li et al. (1994) [(IX)], Ahvonen et al. (1983) [(X)], Li et al. (1996) [(XI)] and Kristersson & Lundquist (1980) [(XII)].

A perspective drawing and the atom-numbering of (I) are shown in Fig. 1. Geometric details of (I) are given in Table 1 in which, for comparison, the corresponding geometric data for the related compounds (II) and (III) are also included.

There are strong O—H···O hydrogen bonds (Fig.2) present in the crystal structure of (I); for geometric details and hydrogen-bond notation, see Table 2. On the first-level graph-set, defined by Bernstein et al. (1995) and Grell et al. (1999), R²₂(12) rings, formed by hydrogen bonds a between pairs of molecules related by an inversion centre and C(6) chains formed by hydrogen bonds b were identified. On the second-level graph-set, R⁴₄(8) directed four-membered cooperative O—H···O—H···O—H···O—H rings formed by hydrogen bonds a and b could be recognized.

Disregarding angles between aromatic ring planes, the corresponding geometric details in (I) and the related compounds (II) and (III) are very similar (Table 1 and Fig. 3). Hydrogen bonding may explain the conformational similarities exhibited by these compounds. The overall patterns are different [an R⁴₄(8) ring in (I), a C⁴₄(8) chain in (II) and an R⁶₆(12) ring in (III)], but there are strong hydrogen bonds involved in directed cooperative O—H···O—H···O—H···O—H patterns in the three compounds. The importance of hydrogen bonding for the conformations of compounds (I)–(III) is supported by the conformations adopted by the acetates (IV) and (V). In these compounds, which lack strong hydrogen bonds, the torsion angles between the aromatic groups are close to 180° [-178.8 (4)° in (IV) (Stomberg & Lundquist, 1995) and -172 (2)° in (V) (this work)], implying that the bulky aromatic groups are almost as far apart as possible. This probably governs the conformations adopted by (IV) and (V).

Related literature

For related literature, see: Ahvonen et al. (1983); Aoyama et al. (1995); Bernstein et al. (1995); Grell et al. (1999); Kristersson & Lundquist (1980); Li et al. (1993, 1994, 1996); Lundquist & Stomberg (1987); Parkås et al. (2004); Stomberg & Lundquist (1995); Stomberg et al. (1997, 2006).

S2. Experimental

1,2-Diphenyl-1,3-propanediol, (I), was prepared according to the method of Kristersson & Lundquist (1980). Crystals (m.p. 379–380 K) were obtained from a solution in benzene.

erythro-1,2-Bis(3,4-dimethoxyphenyl)-1,3-propanediol, (VII), and the isomeric threo form were acetylated by treatment with [Which?] anhydride–pyridine (1:1) for 24 h. The diacetate, (V), of compound (VII) was obtained in crystalline form (m.p. 363 K). The crystal structure of (V) was solved, but refinement resulted in residuals too high for publication.

¹³C NMR spectra [100.6 MHz, solvent CDCl₃, reference (CH₃)₄Si, 300 K, δ, p.p.m.): for (I): 20.8 (CH₃CO), 21.0 (CH₃CO), 49.8 (H—C—CH₂), 55.8–55.9 (4 C, OCH₃), 64.7 (CH₂), 75.4 (H—C—O), [110.2, 110.9 (2 C), 112.1, 119.7, 121.1, 130.1, 130.8, 148.2, 148.6, 148.8, 148.9], (12 C, aromatic C atoms), 169.8 (C═O), 170.7 (C═O); for the diacetate, (V), of threo-1,2-bis(3,4-dimethoxyphenyl)-1,3-propanediol: 20.9 (CH₃CO), 21.2 (CH₃CO), 49.6 (H—C—CH₂), 55.8–55.9 (4 C, OCH₃), 64.7 (CH₂), 76.2 (H—C—O), [110.5, 110.6, 110.9, 112.1, 119.7, 121.2, 130.1, 130.7, 148.1, 148.5 (2 C), 148.7] (12 C, aromatic C atoms), 169.9 (C═O), 170.9(C═O).

S3. Refinement

H atoms were constrained to ideal geometry using an appropriate riding model (C—H = 0.95–1.00 Å) and refined isotropically. For the hydroxyl groups, the O—H distances (0.84 Å) and C—O—H angles (109.5°) were kept fixed, while the torsion angles were refined from starting positions based on the circular Fourier synthesis.

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT and SADABS (Sheldrick, 2003); program(s) used to solve structure: SHELXTL (Bruker, 2003); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A perspective drawing of (I), showing the atom-numbering. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The hydrogen bonds forming chains of molecules in the b axis direction. H atoms not included in the hydrogen-bonding pattern have been omitted for clarity. For labels and symmetry codes, see Table 2.
	Fig. 3. A projection of the overlaid structures of (I) in red/grey, (II) in blue/black and (III) in green/light grey. H atoms have been omitted for clarity.

rac-erythro-1,2-diphenyl-1,3-propanediol

Crystal data

C15H16O2	F(000) = 488
Mr = 228.28	Dx = 1.216 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 5826 reflections
a = 13.9047 (7) Å	θ = 2.5–30.2°
b = 5.4818 (3) Å	µ = 0.08 mm^−1
c = 16.8837 (9) Å	T = 173 K
β = 104.243 (1)°	Needle, colourless
V = 1247.36 (11) Å^3	0.64 × 0.08 × 0.06 mm
Z = 4

Data collection

Siemens SMART CCD area detector diffractometer	3816 independent reflections
Radiation source: fine-focus sealed tube	2877 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.033
ω scans	θmax = 30.6°, θmin = 2.2°
Absorption correction: multi-scan SADABS (Sheldrick, 2003)	h = −19→19
Tmin = 0.846, Tmax = 0.995	k = −7→7
19374 measured reflections	l = −24→24

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.126	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0677P)^2 + 0.2365P] where P = (Fo^2 + 2Fc^2)/3
3816 reflections	(Δ/σ)max = 0.001
172 parameters	Δρmax = 0.39 e Å^−3
0 restraints	Δρmin = −0.16 e Å^−3

Special details

Experimental. Data were collected at 173 K using a Siemens SMART CCD diffractometer equipped with an LT-2 A cooling device. A full sphere of reciprocal space was scanned by 0.3° steps in ω with a crystal-to-detector distance of 3.97 cm, 60 s per frame. The preliminary orientation matrix was obtained from the first 100 frames using SMART (Bruker, 2003). The collected frames were integrated using the preliminary orientation matrix which was updated every 100 frames. Final cell parameters were obtained by refinement of the position of 5826 reflections with I>10σ(I) after integration of all the frames data using SAINT (Bruker, 2003).

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.09514 (6)	0.22146 (15)	0.99146 (4)	0.02768 (19)
H1	0.0640	0.2644	1.0260	0.041 (4)*
O2	0.01966 (6)	−0.36389 (14)	0.90674 (5)	0.02613 (18)
H2	0.0540	−0.4865	0.9255	0.049 (5)*
C1	0.23566 (8)	0.0369 (2)	1.08856 (6)	0.0240 (2)
C2	0.29633 (9)	0.2395 (2)	1.09326 (7)	0.0328 (3)
H2A	0.2826	0.3581	1.0509	0.042 (4)*
C3	0.37738 (10)	0.2700 (3)	1.15979 (9)	0.0426 (3)
H3	0.4187	0.4093	1.1626	0.062 (5)*
C4	0.39794 (10)	0.0994 (3)	1.22151 (8)	0.0442 (3)
H4	0.4535	0.1209	1.2667	0.056 (5)*
C5	0.33819 (11)	−0.1017 (3)	1.21778 (8)	0.0433 (3)
H5	0.3522	−0.2193	1.2604	0.066 (5)*
C6	0.25709 (9)	−0.1330 (2)	1.15145 (7)	0.0332 (3)
H6	0.2159	−0.2723	1.1491	0.048 (4)*
C7	0.14662 (7)	−0.00193 (19)	1.01723 (6)	0.0228 (2)
H7	0.0998	−0.1139	1.0358	0.023 (3)*
C8	0.17352 (7)	−0.12065 (19)	0.94247 (6)	0.0231 (2)
H8	0.2095	−0.2757	0.9620	0.031 (3)*
C9	0.07975 (8)	−0.1914 (2)	0.87751 (6)	0.0256 (2)
H9A	0.0401	−0.0427	0.8591	0.028 (3)*
H9B	0.0993	−0.2614	0.8297	0.029 (3)*
C10	0.24266 (8)	0.0328 (2)	0.90658 (6)	0.0254 (2)
C11	0.34348 (9)	−0.0232 (3)	0.92319 (8)	0.0362 (3)
H11	0.3681	−0.1615	0.9558	0.043 (4)*
C12	0.40842 (10)	0.1204 (3)	0.89269 (9)	0.0473 (4)
H12	0.4769	0.0803	0.9046	0.056 (5)*
C13	0.37331 (11)	0.3218 (3)	0.84504 (9)	0.0468 (4)
H13	0.4179	0.4214	0.8248	0.060 (5)*
C14	0.27383 (11)	0.3782 (2)	0.82691 (8)	0.0390 (3)
H14	0.2496	0.5155	0.7937	0.055 (5)*
C15	0.20896 (9)	0.2345 (2)	0.85717 (7)	0.0291 (2)
H15	0.1403	0.2742	0.8440	0.036 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0285 (4)	0.0305 (4)	0.0266 (4)	0.0101 (3)	0.0116 (3)	0.0053 (3)
O2	0.0272 (4)	0.0241 (4)	0.0285 (4)	0.0002 (3)	0.0097 (3)	0.0014 (3)
C1	0.0253 (5)	0.0257 (5)	0.0217 (4)	0.0037 (4)	0.0073 (4)	0.0003 (4)
C2	0.0317 (6)	0.0305 (6)	0.0349 (6)	−0.0017 (5)	0.0055 (5)	0.0027 (5)
C3	0.0316 (6)	0.0444 (8)	0.0488 (7)	−0.0058 (6)	0.0043 (5)	−0.0090 (6)
C4	0.0350 (6)	0.0560 (9)	0.0350 (6)	0.0112 (6)	−0.0038 (5)	−0.0091 (6)
C5	0.0515 (8)	0.0473 (8)	0.0263 (6)	0.0132 (6)	0.0005 (5)	0.0051 (5)
C6	0.0422 (6)	0.0304 (6)	0.0260 (5)	0.0033 (5)	0.0066 (5)	0.0039 (4)
C7	0.0237 (5)	0.0229 (5)	0.0226 (4)	0.0014 (4)	0.0073 (4)	0.0035 (4)
C8	0.0242 (5)	0.0220 (5)	0.0236 (5)	0.0031 (4)	0.0065 (4)	0.0023 (4)
C9	0.0291 (5)	0.0254 (5)	0.0227 (5)	−0.0011 (4)	0.0069 (4)	0.0025 (4)
C10	0.0258 (5)	0.0280 (5)	0.0241 (5)	−0.0007 (4)	0.0097 (4)	−0.0035 (4)
C11	0.0275 (5)	0.0448 (7)	0.0368 (6)	0.0018 (5)	0.0088 (5)	−0.0038 (5)
C12	0.0278 (6)	0.0696 (10)	0.0477 (8)	−0.0082 (6)	0.0151 (5)	−0.0121 (7)
C13	0.0476 (8)	0.0564 (9)	0.0442 (7)	−0.0227 (7)	0.0261 (6)	−0.0110 (7)
C14	0.0543 (8)	0.0342 (6)	0.0359 (6)	−0.0094 (6)	0.0250 (6)	−0.0020 (5)
C15	0.0343 (6)	0.0281 (6)	0.0293 (5)	0.0004 (4)	0.0162 (4)	−0.0008 (4)

Geometric parameters (Å, º)

O1—C7	1.4312 (12)	C7—H7	1.0000
O1—H1	0.8400	C8—C10	1.5120 (14)
O2—C9	1.4277 (13)	C8—C9	1.5329 (14)
O2—H2	0.8400	C8—H8	1.0000
C1—C6	1.3886 (15)	C9—H9A	0.9900
C1—C2	1.3851 (16)	C9—H9B	0.9900
C1—C7	1.5148 (14)	C10—C11	1.3945 (16)
C2—C3	1.3917 (17)	C10—C15	1.3950 (16)
C2—H2A	0.9500	C11—C12	1.3892 (19)
C3—C4	1.377 (2)	C11—H11	0.9500
C3—H3	0.9500	C12—C13	1.382 (2)
C4—C5	1.373 (2)	C12—H12	0.9500
C4—H4	0.9500	C13—C14	1.376 (2)
C5—C6	1.3905 (17)	C13—H13	0.9500
C5—H5	0.9500	C14—C15	1.3863 (16)
C6—H6	0.9500	C14—H14	0.9500
C7—C8	1.5456 (14)	C15—H15	0.9500
C7—O1—H1	109.5	C9—C8—C7	110.90 (8)
C9—O2—H2	109.5	C10—C8—H8	106.8
C6—C1—C2	118.74 (11)	C9—C8—H8	106.8
C6—C1—C7	119.56 (10)	C7—C8—H8	106.8
C2—C1—C7	121.69 (10)	O2—C9—C8	112.79 (8)
C3—C2—C1	120.22 (12)	O2—C9—H9A	109.0
C3—C2—H2A	119.9	C8—C9—H9A	109.0
C1—C2—H2A	119.9	O2—C9—H9B	109.0
C4—C3—C2	120.37 (13)	C8—C9—H9B	109.0
C4—C3—H3	119.8	H9A—C9—H9B	107.8
C2—C3—H3	119.8	C11—C10—C15	117.91 (11)
C3—C4—C5	120.01 (12)	C11—C10—C8	120.24 (10)
C3—C4—H4	120.0	C15—C10—C8	121.84 (9)
C5—C4—H4	120.0	C12—C11—C10	120.90 (13)
C4—C5—C6	119.85 (12)	C12—C11—H11	119.6
C4—C5—H5	120.1	C10—C11—H11	119.6
C6—C5—H5	120.1	C13—C12—C11	119.99 (13)
C5—C6—C1	120.81 (12)	C13—C12—H12	120.0
C5—C6—H6	119.6	C11—C12—H12	120.0
C1—C6—H6	119.6	C12—C13—C14	120.03 (12)
O1—C7—C1	111.80 (8)	C12—C13—H13	120.0
O1—C7—C8	108.39 (8)	C14—C13—H13	120.0
C1—C7—C8	113.19 (8)	C13—C14—C15	120.00 (13)
O1—C7—H7	107.8	C13—C14—H14	120.0
C1—C7—H7	107.8	C15—C14—H14	120.0
C8—C7—H7	107.8	C14—C15—C10	121.16 (11)
C10—C8—C9	111.52 (8)	C14—C15—H15	119.4
C10—C8—C7	113.49 (9)	C10—C15—H15	119.4
C6—C1—C2—C3	0.33 (17)	C1—C7—C8—C9	171.29 (9)
C7—C1—C2—C3	179.80 (11)	C10—C8—C9—O2	171.76 (8)
C1—C2—C3—C4	−0.1 (2)	C7—C8—C9—O2	−60.71 (11)
C2—C3—C4—C5	−0.2 (2)	C9—C8—C10—C11	−132.16 (11)
C3—C4—C5—C6	0.2 (2)	C7—C8—C10—C11	101.72 (12)
C4—C5—C6—C1	0.11 (19)	C9—C8—C10—C15	48.63 (13)
C2—C1—C6—C5	−0.36 (17)	C7—C8—C10—C15	−77.49 (12)
C7—C1—C6—C5	−179.84 (11)	C15—C10—C11—C12	1.20 (18)
C6—C1—C7—O1	140.20 (10)	C8—C10—C11—C12	−178.04 (11)
C2—C1—C7—O1	−39.27 (13)	C10—C11—C12—C13	−0.1 (2)
C6—C1—C7—C8	−97.06 (12)	C11—C12—C13—C14	−0.9 (2)
C2—C1—C7—C8	83.48 (12)	C12—C13—C14—C15	0.7 (2)
O1—C7—C8—C10	62.36 (11)	C13—C14—C15—C10	0.43 (18)
C1—C7—C8—C10	−62.26 (11)	C11—C10—C15—C14	−1.37 (17)
O1—C7—C8—C9	−64.09 (11)	C8—C10—C15—C14	177.86 (10)