Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101015943/fr1348sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270101015943/fr1348Isup2.hkl |
CCDC reference: 179275
For related literature, see: Borthwick (1980); Brunskill et al. (1999); Lalancette et al. (1998, 1999); Leiserowitz (1976); Steiner (1997); Steiner & Desiraju (1998).
Compound (I) was prepared by Rh-catalyzed hydrogenation of 3-hydroxycinnamic acid, followed by Jones oxidation. Crystals suitable for X-ray were produced from a cyclohexane–Et2O solution (m.p. 315 K).
All H atoms were found in electron-density difference maps but were placed in calculated positions (0.97 Å for the methylene and 0.98 Å for the methine H atoms) and allowed to refine as riding models on their respective C atoms. Their displacement parameters were fixed at 120% of those of their respective C atoms. The positional parameters of the carboxyl H atoms were allowed to refine, but their displacement parameters were fixed at 150% of those of their respective O atoms.
Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: XPin SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXL97.
C9H14O3 | F(000) = 368 |
Mr = 170.20 | Dx = 1.213 Mg m−3 |
Triclinic, P1 | Melting point: 315 K |
a = 5.429 (3) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 12.005 (7) Å | Cell parameters from 31 reflections |
c = 14.570 (8) Å | θ = 4.0–10.1° |
α = 87.05 (2)° | µ = 0.09 mm−1 |
β = 88.96 (2)° | T = 260 K |
γ = 79.39 (2)° | Parallelepiped, colourless |
V = 932.1 (9) Å3 | 0.46 × 0.16 × 0.07 mm |
Z = 4 |
Siemens P4 diffractometer | 2085 reflections with I > 2σ(I) |
Radiation source: normal-focus sealed tube | Rint = 0.000 |
Graphite monochromator | θmax = 25.0°, θmin = 2.3° |
2θ/θ scans | h = −6→6 |
Absorption correction: numerical (Sheldrick, 1997) | k = −14→14 |
Tmin = 0.97, Tmax = 0.99 | l = 0→17 |
3303 measured reflections | 3 standard reflections every 97 reflections |
3303 independent reflections | intensity decay: variation <1.2% |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.063 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.175 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | w = 1/[σ2(Fo2) + (0.0751P)2 + 0.3643P] where P = (Fo2 + 2Fc2)/3 |
3303 reflections | (Δ/σ)max < 0.001 |
223 parameters | Δρmax = 0.42 e Å−3 |
0 restraints | Δρmin = −0.18 e Å−3 |
C9H14O3 | γ = 79.39 (2)° |
Mr = 170.20 | V = 932.1 (9) Å3 |
Triclinic, P1 | Z = 4 |
a = 5.429 (3) Å | Mo Kα radiation |
b = 12.005 (7) Å | µ = 0.09 mm−1 |
c = 14.570 (8) Å | T = 260 K |
α = 87.05 (2)° | 0.46 × 0.16 × 0.07 mm |
β = 88.96 (2)° |
Siemens P4 diffractometer | 2085 reflections with I > 2σ(I) |
Absorption correction: numerical (Sheldrick, 1997) | Rint = 0.000 |
Tmin = 0.97, Tmax = 0.99 | 3 standard reflections every 97 reflections |
3303 measured reflections | intensity decay: variation <1.2% |
3303 independent reflections |
R[F2 > 2σ(F2)] = 0.063 | 0 restraints |
wR(F2) = 0.175 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | Δρmax = 0.42 e Å−3 |
3303 reflections | Δρmin = −0.18 e Å−3 |
223 parameters |
Experimental. Crystal mounted on glass fiber with epoxy resin. |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.3531 (5) | 0.1644 (2) | 0.46678 (16) | 0.0671 (7) | |
O2 | 0.0112 (5) | 0.4559 (2) | 0.89251 (15) | 0.0656 (7) | |
O3 | 0.3059 (5) | 0.4071 (2) | 0.99924 (16) | 0.0616 (7) | |
C1 | 0.4486 (5) | 0.2449 (2) | 0.69517 (19) | 0.0401 (7) | |
C2 | 0.3881 (6) | 0.2785 (3) | 0.59365 (19) | 0.0443 (7) | |
C3 | 0.4816 (6) | 0.1858 (3) | 0.5291 (2) | 0.0425 (7) | |
C4 | 0.7478 (6) | 0.1255 (3) | 0.5426 (2) | 0.0506 (8) | |
C5 | 0.8117 (6) | 0.0956 (3) | 0.6444 (2) | 0.0561 (9) | |
C6 | 0.7285 (6) | 0.1968 (3) | 0.7045 (2) | 0.0523 (8) | |
C7 | 0.3519 (6) | 0.3463 (3) | 0.7546 (2) | 0.0504 (8) | |
C8 | 0.3822 (7) | 0.3192 (3) | 0.8576 (2) | 0.0582 (9) | |
C9 | 0.2166 (7) | 0.4022 (3) | 0.9179 (2) | 0.0481 (8) | |
O1' | −0.0001 (5) | 0.8195 (2) | 1.01843 (17) | 0.0805 (8) | |
O2' | 0.1602 (4) | 0.58615 (17) | 0.54830 (13) | 0.0456 (6) | |
O3' | −0.1838 (4) | 0.52836 (19) | 0.60580 (14) | 0.0497 (6) | |
C1' | 0.1728 (6) | 0.7993 (2) | 0.78151 (18) | 0.0390 (7) | |
C2' | 0.1517 (6) | 0.7407 (3) | 0.87663 (19) | 0.0465 (8) | |
C3' | 0.1433 (6) | 0.8200 (3) | 0.9545 (2) | 0.0469 (8) | |
C4' | 0.3325 (6) | 0.8971 (3) | 0.9504 (2) | 0.0508 (8) | |
C5' | 0.3486 (7) | 0.9555 (3) | 0.8554 (2) | 0.0562 (9) | |
C6' | 0.3813 (6) | 0.8693 (3) | 0.7807 (2) | 0.0489 (8) | |
C7' | 0.2047 (6) | 0.7162 (3) | 0.7034 (2) | 0.0471 (8) | |
C8' | −0.0158 (5) | 0.6570 (2) | 0.69202 (18) | 0.0398 (7) | |
C9' | −0.0015 (5) | 0.5877 (2) | 0.60849 (19) | 0.0356 (7) | |
H3 | 0.205 (8) | 0.466 (3) | 1.036 (3) | 0.092* | |
H1 | 0.3572 | 0.1842 | 0.7140 | 0.048* | |
H2A | 0.2079 | 0.3004 | 0.5873 | 0.053* | |
H2B | 0.4618 | 0.3442 | 0.5757 | 0.053* | |
H4A | 0.8602 | 0.1733 | 0.5169 | 0.061* | |
H4B | 0.7749 | 0.0563 | 0.5093 | 0.061* | |
H5A | 0.7302 | 0.0336 | 0.6661 | 0.067* | |
H5B | 0.9912 | 0.0701 | 0.6502 | 0.067* | |
H6A | 0.7651 | 0.1732 | 0.7682 | 0.063* | |
H6B | 0.8233 | 0.2557 | 0.6871 | 0.063* | |
H7A | 0.4410 | 0.4073 | 0.7371 | 0.060* | |
H7B | 0.1758 | 0.3734 | 0.7418 | 0.060* | |
H8A | 0.3459 | 0.2440 | 0.8714 | 0.070* | |
H8B | 0.5558 | 0.3174 | 0.8734 | 0.070* | |
H3' | −0.173 (7) | 0.491 (3) | 0.552 (3) | 0.075* | |
H1' | 0.0150 | 0.8526 | 0.7707 | 0.047* | |
H2'A | 0.0010 | 0.7080 | 0.8790 | 0.056* | |
H2'B | 0.2938 | 0.6792 | 0.8852 | 0.056* | |
H4'A | 0.4958 | 0.8533 | 0.9665 | 0.061* | |
H4'B | 0.2875 | 0.9544 | 0.9954 | 0.061* | |
H5'A | 0.1970 | 1.0111 | 0.8441 | 0.067* | |
H5'B | 0.4892 | 0.9950 | 0.8533 | 0.067* | |
H6'A | 0.5410 | 0.8184 | 0.7890 | 0.059* | |
H6'B | 0.3852 | 0.9090 | 0.7212 | 0.059* | |
H7'A | 0.2314 | 0.7574 | 0.6462 | 0.056* | |
H7'B | 0.3538 | 0.6591 | 0.7149 | 0.056* | |
H8'A | −0.0281 | 0.6076 | 0.7461 | 0.048* | |
H8'B | −0.1681 | 0.7138 | 0.6890 | 0.048* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0621 (16) | 0.0818 (17) | 0.0584 (15) | −0.0127 (14) | −0.0055 (13) | −0.0124 (13) |
O2 | 0.0818 (19) | 0.0675 (15) | 0.0400 (13) | 0.0074 (14) | −0.0035 (13) | −0.0068 (11) |
O3 | 0.0621 (16) | 0.0698 (16) | 0.0518 (14) | −0.0060 (13) | 0.0020 (12) | −0.0155 (12) |
C1 | 0.0385 (17) | 0.0409 (16) | 0.0409 (16) | −0.0084 (14) | 0.0059 (13) | −0.0009 (13) |
C2 | 0.0367 (17) | 0.0475 (17) | 0.0462 (17) | −0.0024 (14) | 0.0031 (14) | −0.0003 (14) |
C3 | 0.0425 (18) | 0.0483 (18) | 0.0375 (16) | −0.0116 (15) | 0.0034 (14) | 0.0010 (14) |
C4 | 0.0459 (19) | 0.0544 (19) | 0.0482 (18) | 0.0004 (16) | 0.0074 (15) | −0.0102 (15) |
C5 | 0.047 (2) | 0.062 (2) | 0.055 (2) | 0.0033 (17) | 0.0037 (16) | 0.0002 (16) |
C6 | 0.0461 (19) | 0.065 (2) | 0.0435 (18) | −0.0049 (16) | −0.0025 (15) | −0.0018 (16) |
C7 | 0.053 (2) | 0.0495 (18) | 0.0472 (18) | −0.0070 (16) | 0.0067 (16) | −0.0038 (15) |
C8 | 0.061 (2) | 0.062 (2) | 0.0473 (19) | −0.0011 (18) | 0.0032 (17) | −0.0014 (16) |
C9 | 0.058 (2) | 0.0447 (18) | 0.0400 (18) | −0.0090 (17) | 0.0054 (16) | 0.0059 (14) |
O1' | 0.096 (2) | 0.096 (2) | 0.0601 (16) | −0.0412 (17) | 0.0226 (16) | −0.0191 (14) |
O2' | 0.0462 (13) | 0.0553 (13) | 0.0403 (11) | −0.0188 (10) | 0.0058 (10) | −0.0187 (10) |
O3' | 0.0529 (14) | 0.0635 (14) | 0.0407 (12) | −0.0277 (12) | 0.0053 (10) | −0.0189 (10) |
C1' | 0.0425 (17) | 0.0415 (16) | 0.0342 (15) | −0.0091 (14) | 0.0024 (13) | −0.0085 (12) |
C2' | 0.056 (2) | 0.0513 (18) | 0.0386 (16) | −0.0257 (16) | 0.0008 (14) | −0.0074 (14) |
C3' | 0.055 (2) | 0.0553 (19) | 0.0329 (15) | −0.0163 (16) | 0.0039 (15) | −0.0060 (14) |
C4' | 0.056 (2) | 0.056 (2) | 0.0449 (18) | −0.0196 (17) | −0.0037 (16) | −0.0178 (15) |
C5' | 0.062 (2) | 0.062 (2) | 0.052 (2) | −0.0288 (18) | −0.0005 (17) | −0.0138 (16) |
C6' | 0.054 (2) | 0.0565 (19) | 0.0432 (17) | −0.0264 (16) | 0.0082 (15) | −0.0116 (15) |
C7' | 0.0501 (19) | 0.0562 (18) | 0.0407 (17) | −0.0210 (16) | 0.0064 (15) | −0.0199 (14) |
C8' | 0.0387 (17) | 0.0470 (16) | 0.0350 (15) | −0.0096 (14) | 0.0003 (13) | −0.0101 (13) |
C9' | 0.0339 (16) | 0.0372 (15) | 0.0360 (15) | −0.0058 (13) | −0.0049 (13) | −0.0057 (12) |
O1—C3 | 1.221 (4) | C2—H2A | 0.9700 |
O2—C9 | 1.234 (4) | C2—H2B | 0.9700 |
O3—C9 | 1.297 (4) | C4—H4A | 0.9700 |
C1—C6 | 1.529 (4) | C4—H4B | 0.9700 |
C1—C7 | 1.538 (4) | C5—H5A | 0.9700 |
C1—C2 | 1.538 (4) | C5—H5B | 0.9700 |
C2—C3 | 1.503 (4) | C6—H6A | 0.9700 |
C3—C4 | 1.504 (4) | C6—H6B | 0.9700 |
C4—C5 | 1.539 (4) | C7—H7A | 0.9700 |
C5—C6 | 1.530 (4) | C7—H7B | 0.9700 |
C7—C8 | 1.524 (4) | C8—H8A | 0.9700 |
C8—C9 | 1.518 (4) | C8—H8B | 0.9700 |
O1'—C3' | 1.203 (4) | O3'—H3' | 0.91 (4) |
O2'—C9' | 1.228 (3) | C1'—H1' | 0.9800 |
O3'—C9' | 1.324 (3) | C2'—H2'A | 0.9700 |
C1'—C6' | 1.528 (4) | C2'—H2'B | 0.9700 |
C1'—C2' | 1.534 (4) | C4'—H4'A | 0.9700 |
C1'—C7' | 1.538 (4) | C4'—H4'B | 0.9700 |
C2'—C3' | 1.513 (4) | C5'—H5'A | 0.9700 |
C3'—C4' | 1.503 (4) | C5'—H5'B | 0.9700 |
C4'—C5' | 1.527 (4) | C6'—H6'A | 0.9700 |
C5'—C6' | 1.525 (4) | C6'—H6'B | 0.9700 |
C7'—C8' | 1.517 (4) | C7'—H7'A | 0.9700 |
C8'—C9' | 1.501 (4) | C7'—H7'B | 0.9700 |
O3—H3 | 0.98 (4) | C8'—H8'A | 0.9700 |
C1—H1 | 0.9800 | C8'—H8'B | 0.9700 |
C6—C1—C7 | 114.7 (3) | C1—C6—H6A | 109.2 |
C6—C1—C2 | 109.4 (2) | C5—C6—H6A | 109.2 |
C7—C1—C2 | 109.7 (2) | C1—C6—H6B | 109.2 |
C3—C2—C1 | 113.9 (2) | C5—C6—H6B | 109.2 |
O1—C3—C2 | 122.0 (3) | H6A—C6—H6B | 107.9 |
O1—C3—C4 | 121.9 (3) | C8—C7—H7A | 108.7 |
C2—C3—C4 | 116.0 (3) | C1—C7—H7A | 108.7 |
C3—C4—C5 | 112.7 (3) | C8—C7—H7B | 108.7 |
C6—C5—C4 | 112.0 (3) | C1—C7—H7B | 108.7 |
C1—C6—C5 | 112.0 (3) | H7A—C7—H7B | 107.6 |
C8—C7—C1 | 114.0 (3) | C9—C8—H8A | 108.6 |
C9—C8—C7 | 114.8 (3) | C7—C8—H8A | 108.6 |
O2—C9—O3 | 123.5 (3) | C9—C8—H8B | 108.6 |
O2—C9—C8 | 122.6 (3) | C7—C8—H8B | 108.6 |
O3—C9—C8 | 113.8 (3) | H8A—C8—H8B | 107.5 |
C6'—C1'—C2' | 110.3 (2) | C9'—O3'—H3' | 110 (2) |
C6'—C1'—C7' | 112.0 (2) | C6'—C1'—H1' | 107.1 |
C2'—C1'—C7' | 113.0 (2) | C2'—C1'—H1' | 107.1 |
C3'—C2'—C1' | 113.3 (2) | C7'—C1'—H1' | 107.1 |
O1'—C3'—C4' | 121.1 (3) | C3'—C2'—H2'A | 108.9 |
O1'—C3'—C2' | 122.5 (3) | C1'—C2'—H2'A | 108.9 |
C4'—C3'—C2' | 116.4 (3) | C3'—C2'—H2'B | 108.9 |
C3'—C4'—C5' | 112.4 (3) | C1'—C2'—H2'B | 108.9 |
C6'—C5'—C4' | 110.9 (3) | H2'A—C2'—H2'B | 107.7 |
C5'—C6'—C1' | 113.1 (3) | C3'—C4'—H4'A | 109.1 |
C8'—C7'—C1' | 114.4 (2) | C5'—C4'—H4'A | 109.1 |
C9'—C8'—C7' | 114.7 (2) | C3'—C4'—H4'B | 109.1 |
O2'—C9'—O3' | 123.0 (2) | C5'—C4'—H4'B | 109.1 |
O2'—C9'—C8' | 124.2 (3) | H4'A—C4'—H4'B | 107.9 |
O3'—C9'—C8' | 112.9 (2) | C6'—C5'—H5'A | 109.5 |
C9—O3—H3 | 113 (2) | C4'—C5'—H5'A | 109.5 |
C6—C1—H1 | 107.6 | C6'—C5'—H5'B | 109.5 |
C7—C1—H1 | 107.6 | C4'—C5'—H5'B | 109.5 |
C2—C1—H1 | 107.6 | H5'A—C5'—H5'B | 108.0 |
C3—C2—H2A | 108.8 | C5'—C6'—H6'A | 109.0 |
C1—C2—H2A | 108.8 | C1'—C6'—H6'A | 109.0 |
C3—C2—H2B | 108.8 | C5'—C6'—H6'B | 109.0 |
C1—C2—H2B | 108.8 | C1'—C6'—H6'B | 109.0 |
H2A—C2—H2B | 107.7 | H6'A—C6'—H6'B | 107.8 |
C3—C4—H4A | 109.1 | C8'—C7'—H7'A | 108.7 |
C5—C4—H4A | 109.1 | C1'—C7'—H7'A | 108.7 |
C3—C4—H4B | 109.1 | C8'—C7'—H7'B | 108.7 |
C5—C4—H4B | 109.1 | C1'—C7'—H7'B | 108.7 |
H4A—C4—H4B | 107.8 | H7'A—C7'—H7'B | 107.6 |
C6—C5—H5A | 109.2 | C9'—C8'—H8'A | 108.6 |
C4—C5—H5A | 109.2 | C7'—C8'—H8'A | 108.6 |
C6—C5—H5B | 109.2 | C9'—C8'—H8'B | 108.6 |
C4—C5—H5B | 109.2 | C7'—C8'—H8'B | 108.6 |
H5A—C5—H5B | 107.9 | H8'A—C8'—H8'B | 107.6 |
C6—C1—C2—C3 | 51.8 (3) | C6'—C1'—C2'—C3' | 48.7 (4) |
C7—C1—C2—C3 | 178.4 (3) | C7'—C1'—C2'—C3' | 174.9 (3) |
C1—C2—C3—O1 | 136.4 (3) | C1'—C2'—C3'—O1' | 136.5 (3) |
C1—C2—C3—C4 | −46.9 (4) | C1'—C2'—C3'—C4' | −46.0 (4) |
O1—C3—C4—C5 | −139.1 (3) | O1'—C3'—C4'—C5' | −135.9 (3) |
C2—C3—C4—C5 | 44.2 (4) | C2'—C3'—C4'—C5' | 46.6 (4) |
C3—C4—C5—C6 | −48.3 (4) | C3'—C4'—C5'—C6' | −50.6 (4) |
C7—C1—C6—C5 | 179.4 (3) | C4'—C5'—C6'—C1' | 56.8 (4) |
C2—C1—C6—C5 | −56.9 (3) | C2'—C1'—C6'—C5' | −55.4 (4) |
C4—C5—C6—C1 | 56.2 (4) | C7'—C1'—C6'—C5' | 177.9 (3) |
C6—C1—C7—C8 | −61.5 (4) | C6'—C1'—C7'—C8' | −171.5 (3) |
C2—C1—C7—C8 | 175.0 (3) | C2'—C1'—C7'—C8' | 63.3 (4) |
C1—C7—C8—C9 | −160.7 (3) | C1'—C7'—C8'—C9' | 172.3 (2) |
C7—C8—C9—O2 | 28.7 (5) | C7'—C8'—C9'—O2' | −6.8 (4) |
C7—C8—C9—O3 | −154.2 (3) | C7'—C8'—C9'—O3' | 173.6 (3) |
Experimental details
Crystal data | |
Chemical formula | C9H14O3 |
Mr | 170.20 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 260 |
a, b, c (Å) | 5.429 (3), 12.005 (7), 14.570 (8) |
α, β, γ (°) | 87.05 (2), 88.96 (2), 79.39 (2) |
V (Å3) | 932.1 (9) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.46 × 0.16 × 0.07 |
Data collection | |
Diffractometer | Siemens P4 diffractometer |
Absorption correction | Numerical (Sheldrick, 1997) |
Tmin, Tmax | 0.97, 0.99 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3303, 3303, 2085 |
Rint | 0.000 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.063, 0.175, 1.04 |
No. of reflections | 3303 |
No. of parameters | 223 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.42, −0.18 |
Computer programs: XSCANS (Siemens, 1996), XSCANS, SHELXS97 (Sheldrick, 1997a), SHELXL97 (Sheldrick, 1997a), XPin SHELXTL (Sheldrick, 1997b), SHELXL97.
O2—C9 | 1.234 (4) | O2'—C9' | 1.228 (3) |
O3—C9 | 1.297 (4) | O3'—C9' | 1.324 (3) |
O2—C9—C8 | 122.6 (3) | O2'—C9'—C8' | 124.2 (3) |
O3—C9—C8 | 113.8 (3) | O3'—C9'—C8' | 112.9 (2) |
C2—C1—C7—C8 | 175.0 (3) | C2'—C1'—C7'—C8' | 63.3 (4) |
C1—C7—C8—C9 | −160.7 (3) | C1'—C7'—C8'—C9' | 172.3 (2) |
C7—C8—C9—O2 | 28.7 (5) | C7'—C8'—C9'—O2' | −6.8 (4) |
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The crystal structures of keto carboxylic acids display five known hydrogen-bonding modes. Two of these lack ketone involvement, reflecting the common pairing and much rarer chain modes known for simple acids (Leiserowitz, 1976). Acid-to-ketone chains (catemers) constitute a sizable minority of cases, while intramolecular hydrogen bonds and acid-to-ketone dimers are rarely observed. We have previously provided and cited examples of many of these, along with discussions of the factors that appear to govern the choice of mode (Lalancette et al., 1998, 1999; Brunskill et al., 1999).
We report here the crystal structure of the title compound, (I). The category of ε-keto acids to which (I) belongs includes catemers of the helical, translational and glide types, as well as dimers and hydrated patterns. Fig. 1 presents a view of the asymmetric unit of (I) with its numbering. The two molecules in this unit, (Ic) and (It), differ in the conformations of their side chains, as illustrated in the Scheme. Although the chain extends away from the ring equatorially in a standard staggered-anti fashion in both molecules, C7 has two options for the onward direction the chain can take, differing by a rotation of 111.7 (5)° about C1—C7. For both these conformations, the staggered-anti arrangement of the chain extends into the ring, but in one case [(Ic), `cisoid' carbonyls], this extension includes C2 and C3 (the ketone carbon), while in the other [(It), `transoid' carbonyls], it includes C6 and C5. Except for a 35.5 (6)° difference in rotational conformations for the carboxyl groups relative to their chains [torsion angle O2—C9—C8—C7 = 28.7 (5)° for (Ic) and -6.8 (4)° for (1 t)], the distinction between (Ic) and (It) would disappear in the absence of the ketone function. The ketone O atom is sufficiently remote from the side chain that, without packing forces, enthalpy differences between (Ic) and (It) are negligible; remarkably, of these isoenthalpic conformers, the crystal packing arrangement chooses both.
Although averaging of the C—O bond lengths and C—C—O angles by disorder is common in dimeric carboxyls (Leiserowitz, 1976), neither (Ic) nor (It) displays significant carboxyl disorder. In (Ic), the C—O bond lengths are 1.234 (4)/1.297 (4) Å, with angles of 122.6 (3)/113.8 (3)°; the corresponding values for (It) are 1.228 (3)/1.324 (3) Å, with angles of 124.2 (3)/112.9 (2)°. Typical values cited for highly ordered dimeric carboxyls are 1.21/1.31 Å and 123/112° (Borthwick, 1980).
Fig. 2 illustrates the packing of the cell. Each of the two conformers pairs centrosymmetrically with its own enantiomer. Dimers of the cisoid type, (Ic), are centered on the b edges of the chosen cell, while dimers of the (It) type are centered on the bc faces. The O···O distance and O—H···O angle are 2.698 (4) Å and 167 (4)° for (Ic), and 2.681 (3) Å and 177 (4)° for (It).
In the packing, a 2.64 Å intermolecular C—H···O close contact was found for the ketone function of the transoid species (It) to H8A of a neighboring molecule of type (Ic). This lies within the 2.7 Å range we usually employ for non-bonded C—H···O packing interactions (Steiner, 1997). Using compiled data for a large number of C—H···O contacts, Steiner & Desiraju (1998) have found significant statistical directionality even as far out as 3.0 Å, and conclude that these are legitimately viewed as `weak hydrogen bonds', with a greater contribution to packing forces than simple van der Waals attractions.
The solid-state (KBr) IR spectrum of (I) has a broadened stretching absorption at 1709 cm-1 for both C═O functions in both species, typical for acids having and ketones lacking hydrogen bonding; a shoulder appears at ca 1730 cm-1. In CHCl3 solution, this broad peak appears at 1708 cm-1, with a typical carboxyl-dilution shoulder at ca 1740 cm-1.