organic compounds
(±)-trans-3-Oxo-1,2,3,4,4a,9,10,10a-octahydrophenanthrene-10a-carboxylic acid: catemeric hydrogen bonding in a δ-keto acid
aCarl A. Olson Memorial Laboratories, Department of Chemistry, Rutgers University, Newark, NJ 07102, USA
*Correspondence e-mail: rogerlal@andromeda.rutgers.edu
The title compound, C15H16O3, aggregates as hydrogen-bonded catemers progressing from each carboxyl to the ketone of a screw-related neighbor [O⋯O = 2.6675 (14) Å and O—H⋯O = 170°]. Two parallel centrosymmetrically related single-strand hydrogen-bonding helices proceed through the cell in the b-axis direction. The packing includes three intermolecular C—H⋯O=C close contacts, involving both the ketone and the carboxyl group. The structure is isomorphous with that of the previously described Δ4 α,β-unsaturated ketone.
Related literature
For related literature, see: Allen et al. (1999); Borthwick (1980); Gavezzotti & Filippini (1994); Leiserowitz (1976); Miller et al. (1999); Steiner (1997); Thompson & McPherson (1977); Thompson & Shah (1983).
Experimental
Crystal data
|
Refinement
|
Data collection: APEX2 (Bruker, 2006); cell APEX2; data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.
Supporting information
10.1107/S1600536808026639/fl2217sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808026639/fl2217Isup2.hkl
1-Tetralone was carbomethoxylated and then subjected to Robinson
as described by Thompson & McPherson (1977). The resulting unsaturated keto ester was hydrogenated over a Pd/C catalyst, after which Jones oxidation was employed to correct for overreduction. Mild saponification, modeled on that described by Thompson & Shah (1983), provided (I), which was sublimed and crystallized from diethyl ether to give the crystal used, m.p. 460 K. The solid-state (KBr) infrared spectrum of (I) has C=O absorptions at 1716 & 1685 cm-1. This peak separation is typical of the H-bonding shifts in catemers, due to, respectively, its removal from the acid C=O and its addition to the ketone. In CHCl3 solution, where dimers predominate, these peaks coalesce to a single absorption at 1707 cm-1.All H atoms for (I) were found in electron density difference maps. The O—H was constrained to an idealized position with its distance fixed at 0.84 Å and Uiso(H) = 1.5Ueq(O). The aromatic, methylene & methine Hs were placed in geometrically idealized positions and constrained to ride on their parent C atoms with C—H distances of 0.95, 0.99 & 1.00 Å, respectively, and Uiso(H) = 1.2Ueq(C).
Data collection: APEX2 (Bruker, 2006); cell
APEX2 (Bruker, 2006); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C15H16O3 | F(000) = 520 |
Mr = 244.28 | Dx = 1.330 Mg m−3 |
Monoclinic, P21/n | Melting point: 460 K |
Hall symbol: -P 2yn | Cu Kα radiation, λ = 1.54178 Å |
a = 9.7172 (4) Å | Cell parameters from 4354 reflections |
b = 12.2735 (6) Å | θ = 4.3–67.3° |
c = 10.4867 (5) Å | µ = 0.74 mm−1 |
β = 102.6764 (19)° | T = 100 K |
V = 1220.20 (10) Å3 | Block, colourless |
Z = 4 | 0.41 × 0.38 × 0.36 mm |
Bruker SMART CCD APEXII area-detector diffractometer | 2106 independent reflections |
Radiation source: fine-focus sealed tube | 2019 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.019 |
ϕ and ω scans | θmax = 67.8°, θmin = 5.6° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | h = −11→11 |
Tmin = 0.750, Tmax = 0.775 | k = −14→11 |
7219 measured reflections | l = −12→12 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.039 | H-atom parameters constrained |
wR(F2) = 0.108 | w = 1/[σ2(Fo2) + (0.061P)2 + 0.4428P] where P = (Fo2 + 2Fc2)/3 |
S = 1.05 | (Δ/σ)max < 0.001 |
2106 reflections | Δρmax = 0.25 e Å−3 |
165 parameters | Δρmin = −0.20 e Å−3 |
0 restraints | Extinction correction: SHELXTL (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0050 (8) |
C15H16O3 | V = 1220.20 (10) Å3 |
Mr = 244.28 | Z = 4 |
Monoclinic, P21/n | Cu Kα radiation |
a = 9.7172 (4) Å | µ = 0.74 mm−1 |
b = 12.2735 (6) Å | T = 100 K |
c = 10.4867 (5) Å | 0.41 × 0.38 × 0.36 mm |
β = 102.6764 (19)° |
Bruker SMART CCD APEXII area-detector diffractometer | 2106 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2001) | 2019 reflections with I > 2σ(I) |
Tmin = 0.750, Tmax = 0.775 | Rint = 0.019 |
7219 measured reflections |
R[F2 > 2σ(F2)] = 0.039 | 0 restraints |
wR(F2) = 0.108 | H-atom parameters constrained |
S = 1.05 | Δρmax = 0.25 e Å−3 |
2106 reflections | Δρmin = −0.20 e Å−3 |
165 parameters |
Experimental. crystal mounted on cryoloop using Paratone-N |
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 | 0.16954 (13) | 0.53956 (9) | 0.02162 (9) | 0.0406 (3) | |
C1 | −0.01276 (13) | 0.72351 (11) | 0.19416 (12) | 0.0252 (3) | |
H1A | −0.0968 | 0.6757 | 0.1741 | 0.030* | |
H1B | −0.0461 | 0.7999 | 0.1845 | 0.030* | |
O2 | 0.29511 (10) | 0.78231 (9) | 0.34146 (10) | 0.0350 (3) | |
C2 | 0.07805 (14) | 0.70150 (11) | 0.09446 (12) | 0.0265 (3) | |
H2A | 0.0172 | 0.7036 | 0.0054 | 0.032* | |
H2B | 0.1490 | 0.7603 | 0.1005 | 0.032* | |
O3 | 0.14561 (11) | 0.87586 (8) | 0.43269 (10) | 0.0356 (3) | |
H3 | 0.2108 | 0.9222 | 0.4436 | 0.053* | |
C3 | 0.15250 (14) | 0.59394 (11) | 0.11443 (13) | 0.0267 (3) | |
C4B | 0.19751 (13) | 0.56160 (11) | 0.49180 (12) | 0.0238 (3) | |
C4 | 0.21490 (14) | 0.55868 (12) | 0.25238 (13) | 0.0278 (3) | |
H4A | 0.3090 | 0.5927 | 0.2809 | 0.033* | |
H4B | 0.2286 | 0.4787 | 0.2534 | 0.033* | |
C4A | 0.12567 (13) | 0.58788 (11) | 0.35068 (12) | 0.0230 (3) | |
H4AA | 0.0417 | 0.5387 | 0.3295 | 0.028* | |
C5 | 0.31064 (14) | 0.48895 (11) | 0.52183 (13) | 0.0268 (3) | |
H5A | 0.3480 | 0.4589 | 0.4531 | 0.032* | |
C6 | 0.36977 (14) | 0.45965 (12) | 0.65045 (14) | 0.0305 (3) | |
H6A | 0.4460 | 0.4095 | 0.6689 | 0.037* | |
C7 | 0.31676 (15) | 0.50411 (12) | 0.75139 (13) | 0.0322 (4) | |
H7A | 0.3559 | 0.4841 | 0.8394 | 0.039* | |
C8A | 0.14555 (14) | 0.60769 (11) | 0.59434 (13) | 0.0255 (3) | |
C8 | 0.20659 (15) | 0.57772 (12) | 0.72309 (13) | 0.0297 (3) | |
H8A | 0.1715 | 0.6087 | 0.7927 | 0.036* | |
C9 | 0.02840 (15) | 0.69172 (11) | 0.57102 (13) | 0.0287 (3) | |
H9A | 0.0670 | 0.7615 | 0.6108 | 0.034* | |
H9B | −0.0455 | 0.6678 | 0.6165 | 0.034* | |
C10A | 0.06525 (13) | 0.70445 (10) | 0.33777 (12) | 0.0226 (3) | |
C10 | −0.04018 (14) | 0.71177 (11) | 0.42685 (13) | 0.0266 (3) | |
H10A | −0.0841 | 0.7849 | 0.4177 | 0.032* | |
H10B | −0.1159 | 0.6574 | 0.3980 | 0.032* | |
C11 | 0.18214 (14) | 0.78966 (11) | 0.37191 (12) | 0.0250 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0641 (7) | 0.0364 (6) | 0.0228 (5) | 0.0208 (5) | 0.0127 (5) | 0.0039 (4) |
C1 | 0.0259 (6) | 0.0238 (7) | 0.0242 (7) | 0.0037 (5) | 0.0017 (5) | 0.0005 (5) |
O2 | 0.0286 (5) | 0.0341 (6) | 0.0421 (6) | −0.0062 (4) | 0.0075 (4) | −0.0009 (4) |
C2 | 0.0313 (7) | 0.0254 (7) | 0.0211 (6) | 0.0038 (5) | 0.0021 (5) | 0.0029 (5) |
O3 | 0.0500 (6) | 0.0266 (6) | 0.0339 (6) | −0.0128 (4) | 0.0173 (5) | −0.0087 (4) |
C3 | 0.0303 (7) | 0.0273 (7) | 0.0229 (7) | 0.0029 (5) | 0.0063 (5) | 0.0024 (5) |
C4B | 0.0268 (6) | 0.0220 (7) | 0.0219 (6) | −0.0057 (5) | 0.0039 (5) | 0.0016 (5) |
C4 | 0.0330 (7) | 0.0274 (7) | 0.0219 (7) | 0.0085 (5) | 0.0037 (5) | 0.0019 (5) |
C4A | 0.0255 (6) | 0.0220 (7) | 0.0207 (6) | −0.0008 (5) | 0.0036 (5) | 0.0008 (5) |
C5 | 0.0271 (7) | 0.0282 (8) | 0.0242 (7) | −0.0036 (5) | 0.0038 (5) | 0.0034 (5) |
C6 | 0.0268 (7) | 0.0317 (8) | 0.0301 (7) | −0.0049 (6) | −0.0002 (5) | 0.0086 (6) |
C7 | 0.0332 (7) | 0.0381 (8) | 0.0221 (7) | −0.0130 (6) | −0.0007 (5) | 0.0071 (6) |
C8A | 0.0288 (7) | 0.0238 (7) | 0.0240 (7) | −0.0089 (5) | 0.0056 (5) | 0.0004 (5) |
C8 | 0.0352 (7) | 0.0316 (8) | 0.0224 (7) | −0.0125 (6) | 0.0068 (5) | −0.0009 (5) |
C9 | 0.0362 (7) | 0.0259 (7) | 0.0267 (7) | −0.0042 (6) | 0.0129 (6) | −0.0015 (5) |
C10A | 0.0244 (6) | 0.0214 (7) | 0.0214 (6) | −0.0005 (5) | 0.0035 (5) | 0.0000 (5) |
C10 | 0.0268 (6) | 0.0250 (7) | 0.0288 (7) | −0.0013 (5) | 0.0078 (5) | −0.0015 (5) |
C11 | 0.0309 (7) | 0.0243 (7) | 0.0185 (6) | −0.0023 (5) | 0.0025 (5) | 0.0030 (5) |
O1—C3 | 1.2210 (17) | C4A—C10A | 1.5411 (18) |
C1—C2 | 1.5328 (18) | C4A—H4AA | 1.0000 |
C1—C10A | 1.5481 (17) | C5—C6 | 1.3923 (19) |
C1—H1A | 0.9900 | C5—H5A | 0.9500 |
C1—H1B | 0.9900 | C6—C7 | 1.387 (2) |
O2—C11 | 1.2121 (17) | C6—H6A | 0.9500 |
C2—C3 | 1.4979 (19) | C7—C8 | 1.382 (2) |
C2—H2A | 0.9900 | C7—H7A | 0.9500 |
C2—H2B | 0.9900 | C8A—C8 | 1.3996 (19) |
O3—C11 | 1.3232 (17) | C8A—C9 | 1.516 (2) |
O3—H3 | 0.8400 | C8—H8A | 0.9500 |
C3—C4 | 1.5043 (18) | C9—C10 | 1.5324 (18) |
C4B—C5 | 1.397 (2) | C9—H9A | 0.9900 |
C4B—C8A | 1.4034 (19) | C9—H9B | 0.9900 |
C4B—C4A | 1.5258 (17) | C10A—C11 | 1.5276 (18) |
C4—C4A | 1.5280 (18) | C10A—C10 | 1.5331 (17) |
C4—H4A | 0.9900 | C10—H10A | 0.9900 |
C4—H4B | 0.9900 | C10—H10B | 0.9900 |
C2—C1—C10A | 113.87 (10) | C7—C6—C5 | 119.64 (13) |
C2—C1—H1A | 108.8 | C7—C6—H6A | 120.2 |
C10A—C1—H1A | 108.8 | C5—C6—H6A | 120.2 |
C2—C1—H1B | 108.8 | C8—C7—C6 | 119.55 (12) |
C10A—C1—H1B | 108.8 | C8—C7—H7A | 120.2 |
H1A—C1—H1B | 107.7 | C6—C7—H7A | 120.2 |
C3—C2—C1 | 113.12 (11) | C8—C8A—C4B | 119.06 (13) |
C3—C2—H2A | 109.0 | C8—C8A—C9 | 118.61 (12) |
C1—C2—H2A | 109.0 | C4B—C8A—C9 | 122.31 (12) |
C3—C2—H2B | 109.0 | C7—C8—C8A | 121.55 (13) |
C1—C2—H2B | 109.0 | C7—C8—H8A | 119.2 |
H2A—C2—H2B | 107.8 | C8A—C8—H8A | 119.2 |
C11—O3—H3 | 109.5 | C8A—C9—C10 | 114.65 (11) |
O1—C3—C2 | 121.08 (12) | C8A—C9—H9A | 108.6 |
O1—C3—C4 | 120.85 (12) | C10—C9—H9A | 108.6 |
C2—C3—C4 | 117.93 (11) | C8A—C9—H9B | 108.6 |
C5—C4B—C8A | 118.84 (12) | C10—C9—H9B | 108.6 |
C5—C4B—C4A | 121.57 (12) | H9A—C9—H9B | 107.6 |
C8A—C4B—C4A | 119.54 (12) | C11—C10A—C10 | 112.27 (10) |
C3—C4—C4A | 114.37 (11) | C11—C10A—C4A | 111.45 (10) |
C3—C4—H4A | 108.7 | C10—C10A—C4A | 107.07 (10) |
C4A—C4—H4A | 108.7 | C11—C10A—C1 | 107.74 (10) |
C3—C4—H4B | 108.7 | C10—C10A—C1 | 109.50 (10) |
C4A—C4—H4B | 108.7 | C4A—C10A—C1 | 108.76 (10) |
H4A—C4—H4B | 107.6 | C9—C10—C10A | 112.81 (11) |
C4B—C4A—C4 | 113.46 (11) | C9—C10—H10A | 109.0 |
C4B—C4A—C10A | 111.46 (11) | C10A—C10—H10A | 109.0 |
C4—C4A—C10A | 114.84 (11) | C9—C10—H10B | 109.0 |
C4B—C4A—H4AA | 105.4 | C10A—C10—H10B | 109.0 |
C4—C4A—H4AA | 105.4 | H10A—C10—H10B | 107.8 |
C10A—C4A—H4AA | 105.4 | O2—C11—O3 | 122.73 (12) |
C6—C5—C4B | 121.35 (13) | O2—C11—C10A | 123.85 (12) |
C6—C5—H5A | 119.3 | O3—C11—C10A | 113.33 (11) |
C4B—C5—H5A | 119.3 | ||
C10A—C1—C2—C3 | 49.48 (16) | C8—C8A—C9—C10 | −174.95 (11) |
C1—C2—C3—O1 | 143.89 (14) | C4B—C8A—C9—C10 | 7.00 (18) |
C1—C2—C3—C4 | −40.45 (16) | C4B—C4A—C10A—C11 | 64.36 (13) |
O1—C3—C4—C4A | −146.29 (14) | C4—C4A—C10A—C11 | −66.43 (14) |
C2—C3—C4—C4A | 38.04 (17) | C4B—C4A—C10A—C10 | −58.77 (13) |
C5—C4B—C4A—C4 | −18.50 (18) | C4—C4A—C10A—C10 | 170.44 (11) |
C8A—C4B—C4A—C4 | 164.19 (12) | C4B—C4A—C10A—C1 | −177.00 (10) |
C5—C4B—C4A—C10A | −150.00 (12) | C4—C4A—C10A—C1 | 52.20 (14) |
C8A—C4B—C4A—C10A | 32.69 (16) | C2—C1—C10A—C11 | 66.13 (14) |
C3—C4—C4A—C4B | −174.25 (11) | C2—C1—C10A—C10 | −171.50 (11) |
C3—C4—C4A—C10A | −44.43 (16) | C2—C1—C10A—C4A | −54.81 (14) |
C8A—C4B—C5—C6 | 1.67 (19) | C8A—C9—C10—C10A | −35.51 (16) |
C4A—C4B—C5—C6 | −175.66 (12) | C11—C10A—C10—C9 | −61.41 (14) |
C4B—C5—C6—C7 | −0.7 (2) | C4A—C10A—C10—C9 | 61.21 (14) |
C5—C6—C7—C8 | −0.6 (2) | C1—C10A—C10—C9 | 178.96 (11) |
C5—C4B—C8A—C8 | −1.36 (19) | C10—C10A—C11—O2 | 159.27 (12) |
C4A—C4B—C8A—C8 | 176.02 (11) | C4A—C10A—C11—O2 | 39.16 (17) |
C5—C4B—C8A—C9 | 176.67 (12) | C1—C10A—C11—O2 | −80.08 (15) |
C4A—C4B—C8A—C9 | −5.94 (18) | C10—C10A—C11—O3 | −24.00 (15) |
C6—C7—C8—C8A | 0.8 (2) | C4A—C10A—C11—O3 | −144.12 (11) |
C4B—C8A—C8—C7 | 0.13 (19) | C1—C10A—C11—O3 | 96.65 (12) |
C9—C8A—C8—C7 | −177.98 (12) |
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O1i | 0.84 | 1.84 | 2.6675 (14) | 170 |
C2—H2A···O2ii | 0.99 | 2.45 | 3.3817 (16) | 156 |
C4—H4B···O2iii | 0.99 | 2.60 | 3.5273 (18) | 156 |
C8—H8A···O1iv | 0.95 | 2.55 | 3.2625 (17) | 132 |
Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) x−1/2, −y+3/2, z−1/2; (iii) −x+1/2, y−1/2, −z+1/2; (iv) x, y, z+1. |
Experimental details
Crystal data | |
Chemical formula | C15H16O3 |
Mr | 244.28 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 100 |
a, b, c (Å) | 9.7172 (4), 12.2735 (6), 10.4867 (5) |
β (°) | 102.6764 (19) |
V (Å3) | 1220.20 (10) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 0.74 |
Crystal size (mm) | 0.41 × 0.38 × 0.36 |
Data collection | |
Diffractometer | Bruker SMART CCD APEXII area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2001) |
Tmin, Tmax | 0.750, 0.775 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7219, 2106, 2019 |
Rint | 0.019 |
(sin θ/λ)max (Å−1) | 0.601 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.039, 0.108, 1.05 |
No. of reflections | 2106 |
No. of parameters | 165 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.25, −0.20 |
Computer programs: APEX2 (Bruker, 2006), SAINT (Bruker, 2005), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
O3—H3···O1i | 0.84 | 1.84 | 2.6675 (14) | 170 |
C2—H2A···O2ii | 0.99 | 2.45 | 3.3817 (16) | 156 |
C4—H4B···O2iii | 0.99 | 2.60 | 3.5273 (18) | 156 |
C8—H8A···O1iv | 0.95 | 2.55 | 3.2625 (17) | 132 |
Symmetry codes: (i) −x+1/2, y+1/2, −z+1/2; (ii) x−1/2, −y+3/2, z−1/2; (iii) −x+1/2, y−1/2, −z+1/2; (iv) x, y, z+1. |
Acknowledgements
HWT is grateful to Professor Gree Loober Spoog for helpful consultations. The authors acknowledge support by NSF-CRIF grant No. 0443538.
References
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In ketocarboxylic acids the bias toward centrosymmetric acid pairing (Leiserowitz, 1976; Gavezzotti & Filippini, 1994; Allen et al., 1999) may be suppressed when molecular inflexibility diminishes the repertoire of conformational options. Keto acids with few fully rotatable bonds thus display an increased tendency to form acid-to-ketone H-bonding chains. In this context, we describe the title compound (I), which aggregates in the less common catemer mode.
Fig. 1 shows the asymmetric unit for (I) with its numbering. The sole option for full bond rotation involves the carboxyl group, which is turned so that its carbonyl lies over the ring system, with a C4A—C10A—C11—O2 torsion angle of 39.16 (17)°. Within the asymmetric unit, the dihedral angle for ketone (C2—C3—C4—O1) versus carboxyl (C10A—C11—O2—O3) is 86.06 (6)°. Because (I) is not dimeric, averaging of C—O bond lengths and C—C—O angles by disorder is precluded, and these values [1.2121 (17) & 1.3232 (17) Å] resemble ones typical for highly ordered carboxyls (Borthwick, 1980).
Fig. 2 illustrates the packing. The carboxyl-to-ketone H bonds proceed among molecules screw-related in b, generating two parallel single-strand helical catemers for each cell. These chains are centrosymmetrically related and thus counter-directional. For the ketone and carboxyl groups involved in each intermolecular H bond (Table 1), the C2—C3—C4—O1 versus C10A'-C11'-O2'-O3' [symmetry = 0.5 - x,-1/2 + y,0.5 - z] dihedral angle is 69.01 (6)°.
We characterize the geometry of H bonding to carbonyls using a combination of the H···O=C angle and the H···O=C—C torsion angle. These describe the approach of the H atom to the O in terms of its deviation from, respectively, C=O axiality and planarity with the carbonyl. In (I) these angles are 117° for H···O=C and -6.5° for H···O=C—C, extremely close to the "ideal" angles of 120 and 0°.
Within the 2.6 Å range we survey (Steiner, 1997), three intermolecular C—H···O=C close contacts were found in the packing, involving both the ketone and the carboxyl group. (Table 1).
Compound (I) is derived from the Δ4 isoskeletal unsaturated keto acid whose structure we have previously reported (Miller et al., 1999), and the molecular shapes of these two compounds are so similar that (I) was found to be isomorphous with the prior material.