Two phases of C₉H₁₂O₄: why is the structure at 295 K so complicated?

Molecules of 4,4′-dimethyl-2-hydroxy-6-oxocyclohexene-1-carboxylic acid, C₉H₁₂O₄, crystallize at 295 K in a modulated superstructure with five half-molecules in the asymmetric unit; each molecule is located on one of the mirror planes of the space group Cmc2₁. Reflections with k ≠ 5n are systematically weak; a satisfactory refinement can be obtained in a Cmcm pseudocell having b′ = b/5. The important modulation involves small rotations of the molecules around axes perpendicular to the mirror plane; there is also an up/down disorder of the CMe₂ fragment in four of the five molecules (two molecules with occupancy factors ca 4:1; two with occupancy factors ca 3:2). The modulation is a response to packing problems that can be traced to the differences between the thin, electron- and oxygen-rich `head' of the molecule and the thicker, methyl-rich `tail'. At 130 K the length of b is reduced by 2/5 and the Pmnb structure is ordered. Both structures can be described as modulated variants of the Cmcm substructure; the wavevectors are 2b′*/5 for the room-temperature structure and b′*/2 for the low-temperature structure, where b′* is the reciprocal axis of the subcell. The structure at room temperature can also be understood as a hybrid of the fully disordered pseudocell structure and the ordered structure that is found at low temperature.

Computing details

Data collection: COLLECT software (Nonius, 1998) for cmc21; CAD4-VAX (ENRAF-Nonius, 1988) for pmnb. Cell refinement: DENZO-SMN (Otwinowski & Minor, 1997) for cmc21; CAD4-VAX (ENRAF-Nonius, 1988) for pmnb. Data reduction: SCALEPACK (Otwinowski & Minor, 1997) for cmc21. Program(s) used to solve structure: SIR92 (Altomare, Cascarano, Giacovazzo, Guagliardi, Burla, Polidori & Camalli, 1994) in maXus (Mackay, Gilmore, Edwards, Tremayne, Stewart & Shankland, 1998); SHELXS97 (Sheldrick, 1990) in maXus (Mackay, Gilmore, Edwards, Tremayne, Stewart & Shankland, 1998) for cmc21; From structure at 295 K for pmnb. For both compounds, program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL PC (Sheldrick, 1990).

(cmc21) 4,4'-dimethyl-2-hydroxy-6-oxo-cyclohexene-1-carboxylic acid

Crystal data

C9H12O4	Dx = 1.323 Mg m^−3
Mr = 184.19	Melting point: 123_C K
Orthorhombic, Cmc21	Mo Kα radiation, λ = 0.71073 Å
a = 10.474 (5) Å	Cell parameters from 23801 reflections
b = 66.24 (3) Å	θ = 1.0–27.5°
c = 6.662 (3) Å	µ = 0.10 mm^−1
V = 4622 (4) Å^3	T = 295 K
Z = 20	Laths, colourless
F(000) = 1960	0.50 × 0.30 × 0.15 mm

Data collection

Nonius Kappa-CCD diffractometer	1388 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.048
Graphite monochromator	θmax = 27.5°, θmin = 2.1°
Detector resolution: 18 pixels mm^-1	h = 0→13
φ and ω scans with 2.0° steps	k = 0→85
11377 measured reflections	l = −8→8
2987 independent reflections

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)] = 0.070	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.191	H-atom parameters constrained
S = 1.50	w = 1/[σ^2(Fo^2) + (0.06P)^2] where P = (Fo^2 + 2Fc^2)/3
2987 reflections	(Δ/σ)max = 0.001
388 parameters	Δρmax = 0.17 e Å^−3
430 restraints	Δρmin = −0.15 e Å^−3

Special details

Experimental. The crystal-to-detector distance was 60 mm. Each frame was measured for 90 s. The number of scan sets measured was 3; the total number of frames measured was 236.

Refinement. Modulated superstructure. Highly restrained refinement.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1B	−0.1061 (3)	0.11439 (4)	0.0317 (6)	0.0900 (10)
O3B	−0.2235 (2)	0.08179 (4)	−0.0112 (4)	0.0862 (11)
H1B	−0.1884	0.0995	0.0155	0.155 (8)*
C7B	0.0000	0.10493 (7)	0.0207 (9)	0.0632 (15)
C1B	0.0000	0.08312 (6)	−0.0120 (7)	0.0505 (12)
C2B	−0.1161 (3)	0.07262 (5)	−0.0243 (6)	0.0650 (11)
C3B	−0.1180 (3)	0.05065 (5)	−0.0819 (8)	0.0602 (12)	0.765 (5)
H3B1	−0.1272	0.0492	−0.2249	0.072*	0.765 (5)
H3B2	−0.1912	0.0445	−0.0201	0.072*	0.765 (5)
C4B	0.0000	0.03938 (6)	−0.0116 (7)	0.0610 (15)	0.765 (5)
C8B	0.0000	0.01810 (8)	−0.0994 (13)	0.082 (2)	0.765 (5)
H8B1	0.0000	0.0193	−0.2433	0.123*	0.765 (5)
H8B2	0.0749	0.0109	−0.0572	0.123*	0.765 (5)
C9B	0.0000	0.03771 (9)	0.2204 (8)	0.070 (2)	0.765 (5)
H9B1	0.0000	0.0510	0.2774	0.105*	0.765 (5)
H9B2	0.0749	0.0306	0.2639	0.105*	0.765 (5)
C3B'	−0.1150 (10)	0.05104 (11)	0.0652 (18)	0.0602 (12)	0.24
H3B3	−0.1925	0.0441	0.0303	0.072*	0.235 (5)
H3B4	−0.1103	0.0519	0.2092	0.072*	0.235 (5)
C4B'	0.0000	0.03938 (6)	−0.0116 (7)	0.0610 (15)	0.24
C8B'	0.0000	0.01773 (15)	0.066 (3)	0.089 (8)*	0.235 (5)
H8B3	0.0000	0.0167	0.2099	0.134*	0.235 (5)
H8B4	0.0749	0.0113	0.0129	0.134*	0.235 (5)
C9B'	0.0000	0.0395 (2)	−0.2459 (12)	0.053 (5)*	0.235 (5)
H9B3	0.0000	0.0531	−0.2955	0.080*	0.235 (5)
H9B4	0.0749	0.0326	−0.2933	0.080*	0.235 (5)
O1E	0.6052 (3)	0.18556 (4)	0.5225 (5)	0.0892 (10)
O3E	0.7225 (2)	0.21837 (4)	0.5527 (6)	0.0941 (14)
H1E	0.6885	0.2013	0.5246	0.155 (8)*
C7E	0.5000	0.19492 (7)	0.5337 (9)	0.0688 (16)
C1E	0.5000	0.21687 (6)	0.5507 (10)	0.0603 (16)
C2E	0.6162 (3)	0.22730 (5)	0.5685 (8)	0.0736 (14)
C3E	0.6193 (3)	0.24942 (5)	0.6278 (9)	0.0792 (16)	0.870 (6)
H3E1	0.6940	0.2558	0.5735	0.095*	0.870 (6)
H3E2	0.6245	0.2501	0.7718	0.095*	0.870 (6)
C4E	0.5000	0.26064 (6)	0.5607 (9)	0.0673 (17)	0.870 (6)
C8E	0.5000	0.28216 (8)	0.6476 (15)	0.108 (3)	0.870 (6)
H8E1	0.5000	0.2814	0.7918	0.162*	0.870 (6)
H8E2	0.5749	0.2893	0.6032	0.162*	0.870 (6)
C9E	0.5000	0.26222 (12)	0.3270 (10)	0.109 (3)	0.870 (6)
H9E1	0.5000	0.2488	0.2712	0.163*	0.870 (6)
H9E2	0.5749	0.2693	0.2827	0.163*	0.870 (6)
C3E'	0.6164 (17)	0.24906 (17)	0.488 (3)	0.0792 (16)	0.13
H3E3	0.6152	0.2485	0.3433	0.119*	0.130 (6)
H3E4	0.6927	0.2560	0.5285	0.119*	0.130 (6)
C4E'	0.5000	0.26064 (6)	0.5607 (9)	0.0673 (17)	0.13
C8E'	0.5000	0.2823 (2)	0.485 (5)	0.085 (17)*	0.130 (6)
H8E3	0.5000	0.2827	0.3404	0.127*	0.130 (6)
H8E4	0.5748	0.2891	0.5349	0.127*	0.130 (6)
C9E'	0.5000	0.2609 (5)	0.7953 (16)	0.074 (14)*	0.130 (6)
H9E3	0.5000	0.2472	0.8411	0.111*	0.130 (6)
H9E4	0.5731	0.2682	0.8448	0.111*	0.130 (6)
O1A	0.3947 (3)	0.01473 (4)	−0.0030 (5)	0.0888 (11)
O3A	0.2769 (2)	−0.01821 (4)	−0.0064 (5)	0.0890 (11)
H1A	0.3145	−0.0011	0.0014	0.155 (8)*
C7A	0.5000	0.00507 (7)	−0.0007 (8)	0.0640 (15)
C1A	0.5000	−0.01680 (6)	−0.0100 (8)	0.0557 (14)
C2A	0.3840 (3)	−0.02742 (5)	−0.0069 (8)	0.0808 (16)
C3A	0.3804 (5)	−0.04966 (7)	0.0565 (11)	0.0692 (16)	0.591 (5)
H3A1	0.3064	−0.0562	0.0017	0.083*	0.591 (5)
H3A2	0.3744	−0.0501	0.2006	0.083*	0.591 (5)
C4A	0.5000	−0.06076 (11)	−0.0092 (14)	0.0616 (16)	0.591 (5)
C8A	0.5000	−0.08250 (12)	0.0652 (19)	0.098 (4)	0.591 (5)
H8A1	0.5000	−0.0825	0.2096	0.147*	0.591 (5)
H8A2	0.5734	−0.0895	0.0133	0.147*	0.591 (5)
C9A	0.5000	−0.06100 (14)	−0.2441 (11)	0.095 (4)	0.591 (5)
H9A1	0.5000	−0.0475	−0.2979	0.142*	0.591 (5)
H9A2	0.5744	−0.0682	−0.2894	0.142*	0.591 (5)
C3A'	0.3822 (7)	−0.04903 (10)	−0.0892 (14)	0.0692 (16)	0.41
H3A3	0.3793	−0.0487	−0.2336	0.083*	0.409 (5)
H3A4	0.3071	−0.0558	−0.0414	0.083*	0.409 (5)
C4A'	0.5000	−0.06029 (16)	−0.018 (2)	0.0616 (16)	0.41
C8A'	0.5000	−0.08153 (18)	−0.106 (3)	0.094 (5)	0.409 (5)
H8A4	0.5000	−0.0796	−0.2489	0.141*	0.409 (5)
H8A5	0.5757	−0.0889	−0.0693	0.141*	0.409 (5)
C9A'	0.5000	−0.06164 (17)	0.2152 (16)	0.067 (3)	0.409 (5)
H9A3	0.5000	−0.0482	0.2692	0.101*	0.409 (5)
H9A4	0.5751	−0.0686	0.2603	0.101*	0.409 (5)
O1D	0.3937 (3)	0.21446 (4)	0.0497 (6)	0.0944 (13)
O3D	0.2773 (2)	0.18190 (5)	0.0267 (5)	0.0945 (11)
H1D	0.3121	0.1990	0.0329	0.155 (8)*
C7D	0.5000	0.20525 (7)	0.0471 (9)	0.0667 (16)
C1D	0.5000	0.18330 (6)	0.0279 (9)	0.0585 (14)
C2D	0.3840 (3)	0.17277 (5)	0.0251 (8)	0.0761 (13)
C3D	0.3832 (5)	0.15096 (8)	−0.0485 (11)	0.0677 (14)	0.535 (4)
H3D1	0.3859	0.1506	−0.1929	0.081*	0.535 (4)
H3D2	0.3063	0.1443	−0.0056	0.081*	0.535 (4)
C4D	0.5000	0.13937 (12)	0.0266 (14)	0.0619 (15)	0.535 (4)
C8D	0.5000	0.11848 (13)	−0.0671 (17)	0.082 (3)	0.535 (4)
H8D1	0.5000	0.1195	−0.2108	0.123*	0.535 (4)
H8D2	0.5719	0.1110	−0.0171	0.123*	0.535 (4)
C9D	0.5000	0.13831 (13)	0.2584 (12)	0.067 (3)	0.535 (4)
H9D1	0.5000	0.1517	0.3137	0.100*	0.535 (4)
H9D2	0.5749	0.1312	0.3028	0.100*	0.535 (4)
C3D'	0.3819 (6)	0.15068 (8)	0.1025 (12)	0.0677 (14)	0.47
H3D3	0.3078	0.1441	0.0473	0.081*	0.465 (4)
H3D4	0.3750	0.1503	0.2465	0.081*	0.465 (4)
C4D'	0.5000	0.13930 (14)	0.0304 (16)	0.0619 (15)	0.47
C8D'	0.5000	0.11765 (13)	0.105 (2)	0.095 (4)	0.465 (4)
H8D3	0.5000	0.1175	0.2491	0.142*	0.465 (4)
H8D4	0.5729	0.1107	0.0510	0.142*	0.465 (4)
C9D'	0.5000	0.13887 (17)	−0.2054 (13)	0.088 (4)	0.465 (4)
H9D3	0.5000	0.1526	−0.2530	0.132*	0.465 (4)
H9D4	0.5757	0.1323	−0.2538	0.132*	0.465 (4)
O1C	0.1048 (3)	0.08525 (4)	0.4893 (5)	0.0831 (10)
O3C	0.2231 (2)	0.11797 (5)	0.5323 (5)	0.0922 (11)
H1C	0.1928	0.1012	0.5049	0.155 (8)*
C7C	0.0000	0.09461 (7)	0.5047 (8)	0.0655 (15)
C1C	0.0000	0.11654 (7)	0.5298 (9)	0.0575 (13)
C2C	0.1165 (3)	0.12689 (5)	0.5501 (7)	0.0722 (12)
C3C	0.1171 (3)	0.14905 (5)	0.5979 (8)	0.0861 (14)
H3C1	0.1256	0.1503	0.7411	0.103*
H3C2	0.1913	0.1551	0.5376	0.103*
C4C	0.0000	0.16041 (6)	0.5324 (9)	0.0660 (15)
C8C	0.0000	0.18185 (8)	0.6170 (14)	0.125 (3)
H8C1	0.0000	0.1807	0.7610	0.187*
H8C2	0.0749	0.1891	0.5746	0.187*
C9C	0.0000	0.16199 (10)	0.2982 (9)	0.110 (2)
H9C1	0.0000	0.1487	0.2413	0.165*
H9C2	0.0749	0.1691	0.2546	0.165*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1B	0.108 (2)	0.0648 (17)	0.097 (2)	0.0240 (17)	−0.001 (2)	−0.0067 (16)
O3B	0.0475 (15)	0.090 (2)	0.121 (3)	0.0200 (14)	−0.0053 (17)	0.000 (2)
C7B	0.083 (4)	0.059 (3)	0.048 (3)	0.000	0.000	−0.001 (3)
C1B	0.051 (3)	0.052 (3)	0.048 (3)	0.000	0.000	0.008 (2)
C2B	0.047 (2)	0.071 (2)	0.077 (3)	0.0047 (18)	−0.008 (2)	0.002 (2)
C3B	0.041 (2)	0.064 (3)	0.076 (3)	−0.0059 (18)	−0.006 (3)	−0.009 (2)
C4B	0.049 (3)	0.051 (3)	0.082 (4)	0.000	0.000	0.004 (3)
C8B	0.070 (5)	0.065 (4)	0.110 (6)	0.000	0.000	−0.021 (4)
C9B	0.080 (5)	0.057 (4)	0.072 (4)	0.000	0.000	0.003 (3)
C3B'	0.041 (2)	0.064 (3)	0.076 (3)	−0.0059 (18)	−0.006 (3)	−0.009 (2)
C4B'	0.049 (3)	0.051 (3)	0.082 (4)	0.000	0.000	0.004 (3)
O1E	0.104 (2)	0.0665 (17)	0.097 (2)	0.0196 (16)	0.005 (2)	0.0023 (16)
O3E	0.0533 (17)	0.088 (2)	0.141 (4)	0.0151 (14)	−0.001 (2)	−0.001 (2)
C7E	0.086 (4)	0.062 (3)	0.059 (3)	0.000	0.000	0.000 (3)
C1E	0.053 (3)	0.058 (3)	0.070 (4)	0.000	0.000	−0.010 (3)
C2E	0.049 (2)	0.065 (2)	0.107 (4)	0.0140 (18)	0.001 (2)	0.008 (3)
C3E	0.057 (3)	0.063 (3)	0.117 (4)	−0.0063 (18)	−0.017 (3)	−0.004 (3)
C4E	0.056 (3)	0.059 (3)	0.086 (4)	0.000	0.000	−0.008 (3)
C8E	0.095 (6)	0.055 (4)	0.174 (10)	0.000	0.000	−0.010 (5)
C9E	0.119 (7)	0.091 (6)	0.116 (6)	0.000	0.000	0.043 (4)
C3E'	0.057 (3)	0.063 (3)	0.117 (4)	−0.0063 (18)	−0.017 (3)	−0.004 (3)
C4E'	0.056 (3)	0.059 (3)	0.086 (4)	0.000	0.000	−0.008 (3)
O1A	0.096 (2)	0.0680 (17)	0.102 (3)	0.0214 (15)	−0.004 (2)	−0.0050 (16)
O3A	0.0416 (14)	0.093 (2)	0.132 (3)	0.0179 (13)	−0.0084 (17)	−0.008 (2)
C7A	0.075 (3)	0.070 (4)	0.047 (3)	0.000	0.000	−0.001 (3)
C1A	0.046 (3)	0.062 (3)	0.059 (3)	0.000	0.000	0.010 (3)
C2A	0.040 (2)	0.068 (2)	0.135 (5)	0.0030 (18)	−0.007 (3)	−0.001 (3)
C3A	0.040 (2)	0.077 (3)	0.091 (4)	−0.007 (2)	0.013 (3)	0.003 (3)
C4A	0.049 (3)	0.058 (3)	0.078 (4)	0.000	0.000	0.010 (3)
C8A	0.098 (8)	0.060 (5)	0.135 (10)	0.000	0.000	0.022 (6)
C9A	0.131 (10)	0.068 (6)	0.085 (5)	0.000	0.000	−0.022 (5)
C3A'	0.040 (2)	0.077 (3)	0.091 (4)	−0.007 (2)	0.013 (3)	0.003 (3)
C4A'	0.049 (3)	0.058 (3)	0.078 (4)	0.000	0.000	0.010 (3)
C8A'	0.063 (10)	0.088 (8)	0.131 (14)	0.000	0.000	−0.034 (10)
C9A'	0.059 (8)	0.055 (7)	0.088 (7)	0.000	0.000	−0.004 (6)
O1D	0.110 (2)	0.0657 (18)	0.108 (4)	0.0223 (16)	0.008 (2)	0.0069 (17)
O3D	0.0516 (16)	0.089 (2)	0.143 (3)	0.0191 (14)	−0.0012 (19)	0.006 (2)
C7D	0.085 (4)	0.063 (3)	0.052 (4)	0.000	0.000	−0.003 (3)
C1D	0.056 (3)	0.056 (3)	0.064 (3)	0.000	0.000	0.008 (3)
C2D	0.051 (2)	0.070 (2)	0.108 (4)	0.0107 (19)	−0.006 (2)	0.002 (2)
C3D	0.044 (2)	0.074 (3)	0.084 (3)	−0.007 (2)	0.009 (3)	0.005 (3)
C4D	0.045 (3)	0.063 (3)	0.078 (3)	0.000	0.000	0.009 (3)
C8D	0.078 (8)	0.065 (5)	0.104 (8)	0.000	0.000	−0.002 (6)
C9D	0.064 (6)	0.042 (5)	0.094 (6)	0.000	0.000	0.000 (5)
C3D'	0.044 (2)	0.074 (3)	0.084 (3)	−0.007 (2)	0.009 (3)	0.005 (3)
C4D'	0.045 (3)	0.063 (3)	0.078 (3)	0.000	0.000	0.009 (3)
C8D'	0.094 (9)	0.053 (5)	0.136 (11)	0.000	0.000	0.001 (6)
C9D'	0.116 (11)	0.078 (8)	0.069 (5)	0.000	0.000	−0.032 (5)
O1C	0.102 (2)	0.0679 (17)	0.079 (2)	0.0211 (16)	0.0022 (18)	0.0030 (14)
O3C	0.0469 (15)	0.0927 (19)	0.137 (3)	0.0162 (14)	0.0076 (19)	0.007 (2)
C7C	0.082 (4)	0.064 (3)	0.051 (3)	0.000	0.000	0.020 (3)
C1C	0.052 (3)	0.062 (3)	0.059 (3)	0.000	0.000	0.003 (3)
C2C	0.052 (2)	0.071 (2)	0.094 (3)	0.0081 (19)	0.003 (2)	0.012 (2)
C3C	0.053 (2)	0.071 (2)	0.134 (4)	−0.0081 (18)	−0.017 (2)	−0.003 (2)
C4C	0.050 (3)	0.049 (3)	0.099 (4)	0.000	0.000	−0.002 (3)
C8C	0.109 (5)	0.057 (3)	0.209 (9)	0.000	0.000	−0.018 (5)
C9C	0.116 (6)	0.099 (5)	0.115 (4)	0.000	0.000	0.039 (4)

Geometric parameters (Å, º)

O1A—C7A	1.275 (3)	O3C—H1C	1.17
O1B—C7B	1.278 (3)	O3D—H1D	1.19
O1C—C7C	1.265 (3)	O3E—H1E	1.20
O1D—C7D	1.270 (3)	C3A—H3A1	0.96
O1E—C7E	1.267 (3)	C3A—H3A2	0.96
O3A—C2A	1.277 (3)	C3A'—H3A3	0.96
O3B—C2B	1.282 (3)	C3A'—H3A4	0.96
O3C—C2C	1.268 (4)	C3B—H3B1	0.96
O3D—C2D	1.270 (4)	C3B—H3B2	0.96
O3E—C2E	1.265 (3)	C3B'—H3B3	0.96
C1A—C2A	1.404 (4)	C3B'—H3B4	0.96
C1B—C2B	1.403 (3)	C3C—H3C1	0.96
C1C—C2C	1.407 (4)	C3C—H3C2	0.96
C1D—C2D	1.402 (4)	C3D—H3D1	0.96
C1E—C2E	1.404 (4)	C3D—H3D2	0.96
C1A—C7A	1.450 (5)	C3D'—H3D3	0.96
C1B—C7B	1.461 (5)	C3D'—H3D4	0.96
C1C—C7C	1.462 (5)	C3E—H3E1	0.96
C1D—C7D	1.459 (5)	C3E—H3E2	0.96
C1E—C7E	1.459 (5)	C3E'—H3E3	0.96
C2A—C3A	1.533 (5)	C3E'—H3E4	0.96
C2B—C3B	1.505 (4)	C8A—H8A1	0.96
C2C—C3C	1.502 (4)	C8A—H8A2	0.96
C2D—C3D	1.526 (5)	C8A'—H8A3	0.96
C2E—C3E	1.518 (4)	C8A'—H8A4	0.96
C2A—C3A'	1.534 (6)	C8B—H8B1	0.96
C2B—C3B'	1.548 (7)	C8B—H8B2	0.96
C2D—C3D'	1.552 (6)	C8B'—H8B3	0.96
C2E—C3E'	1.538 (8)	C8B'—H8B4	0.96
C3A—C4A	1.517 (5)	C8C—H8C1	0.96
C3B—C4B	1.518 (4)	C8C—H8C2	0.96
C3C—C4C	1.504 (4)	C8D—H8D1	0.96
C3D—C4D	1.529 (6)	C8D—H8D2	0.96
C3E—C4E	1.521 (4)	C8D'—H8D3	0.96
C3A'—C4A'	1.518 (6)	C8D'—H8D4	0.96
C3D'—C4D'	1.526 (6)	C8E—H8E1	0.96
C4A—C8A	1.523 (7)	C8E—H8E2	0.96
C4B—C8B	1.526 (5)	C8E'—H8E3	0.96
C4C—C8C	1.528 (5)	C8E'—H8E4	0.96
C4D—C8D	1.518 (7)	C9A—H9A1	0.96
C4E—C8E	1.539 (5)	C9A—H9A2	0.96
C4A'—C8A'	1.525 (7)	C9A'—H9A3	0.96
C4D'—C8D'	1.518 (7)	C9A'—H9A4	0.96
C4A—C9A	1.565 (8)	C9B—H9B1	0.96
C4B—C9B	1.549 (5)	C9B—H9B2	0.96
C4C—C9C	1.564 (6)	C9B'—H9B3	0.96
C4D—C9D	1.545 (8)	C9B'—H9B4	0.96
C4E—C9E	1.561 (6)	C9C—H9C1	0.96
C4A'—C9A'	1.553 (8)	C9C—H9C2	0.96
C4D'—C9D'	1.571 (8)	C9D—H9D1	0.96
O1A—H1A	1.35	C9D—H9D2	0.96
O1B—H1B	1.31	C9D'—H9D3	0.96
O1C—H1C	1.40	C9D'—H9D4	0.96
O1D—H1D	1.34	C9E—H9E1	0.96
O1E—H1E	1.36	C9E—H9E2	0.96
O3A—H1A	1.20	C9E'—H9E3	0.96
O3B—H1B	1.24	C9E'—H9E4	0.96
C2A—C1A—C2A^i	119.8 (4)	C2E—O3E—H1E	101.1
C2B—C1B—C2B^ii	120.1 (4)	C2A—C3A—H3A1	110.5
C2C—C1C—C2C^ii	120.4 (4)	C2A—C3A—H3A2	107.6
C2D—C1D—C2D^i	120.3 (4)	C2B—C3B—H3B1	110.5
C2E—C1E—C2E^i	120.1 (4)	C2B—C3B—H3B2	108.2
C2A—C1A—C7A	120.0 (2)	C2C—C3C—H3C1	107.3
C2B—C1B—C7B	119.9 (2)	C2C—C3C—H3C2	108.8
C2C—C1C—C7C	119.7 (2)	C2D—C3D—H3D1	110.0
C2D—C1D—C7D	119.8 (2)	C2D—C3D—H3D2	110.0
C2E—C1E—C7E	119.8 (2)	C2E—C3E—H3E1	110.2
O3A—C2A—C1A	121.4 (3)	C2E—C3E—H3E2	108.0
O3B—C2B—C1B	121.5 (3)	C2A—C3A'—H3A3	109.9
O3C—C2C—C1C	121.9 (3)	C2A—C3A'—H3A4	109.3
O3D—C2D—C1D	121.7 (3)	C2B—C3B'—H3B3	110.0
O3E—C2E—C1E	121.7 (3)	C2B—C3B'—H3B4	109.4
O3A—C2A—C3A	115.9 (3)	C2D—C3D'—H3D3	108.0
O3B—C2B—C3B	117.6 (3)	C2D—C3D'—H3D4	110.7
O3C—C2C—C3C	118.1 (3)	C2E—C3E'—H3E3	108.4
O3D—C2D—C3D	116.7 (4)	C2E—C3E'—H3E4	110.5
O3E—C2E—C3E	117.0 (3)	C4A—C3A—H3A1	109.7
O3A—C2A—C3A'	115.9 (4)	C4A—C3A—H3A2	109.2
O3B—C2B—C3B'	114.7 (4)	C4B—C3B—H3B1	109.8
O3D—C2D—C3D'	115.7 (4)	C4B—C3B—H3B2	107.9
O3E—C2E—C3E'	114.1 (5)	C4C—C3C—H3C1	108.6
C1A—C2A—C3A	120.4 (4)	C4C—C3C—H3C2	109.2
C1B—C2B—C3B	120.4 (3)	C4D—C3D—H3D1	107.0
C1C—C2C—C3C	120.0 (3)	C4D—C3D—H3D2	110.1
C1D—C2D—C3D	118.7 (4)	C4E—C3E—H3E1	110.1
C1E—C2E—C3E	121.0 (3)	C4E—C3E—H3E2	108.4
C1A—C2A—C3A'	118.2 (4)	C4A'—C3A'—H3A3	110.5
C1B—C2B—C3B'	115.4 (5)	C4A'—C3A'—H3A4	109.3
C1D—C2D—C3D'	118.5 (4)	C4D'—C3D'—H3D3	108.2
C1E—C2E—C3E'	115.6 (9)	C4D'—C3D'—H3D4	111.3
C2A—C3A—C4A	111.5 (4)	C4A—C8A—H8A1	109.0
C2B—C3B—C4B	112.7 (3)	C4A—C8A—H8A2	109.7
C2C—C3C—C4C	115.1 (3)	C4B—C8B—H8B1	107.6
C2D—C3D—C4D	111.5 (5)	C4B—C8B—H8B2	110.4
C2E—C3E—C4E	112.2 (3)	C4C—C8C—H8C1	107.0
C2A—C3A'—C4A'	109.7 (6)	C4D—C8D—H8D1	110.1
C2D—C3D'—C4D'	110.5 (6)	C4D—C8D—H8D2	109.2
C3A—C4A—C3A^i	111.3 (7)	C4E—C8E—H8E1	109.0
C3B—C4B—C3B^ii	109.0 (4)	C4E—C8E—H8E2	109.7
C3C—C4C—C3C^ii	109.3 (4)	C4A'—C8A'—H8A3	111.6
C3D—C4D—C3D^i	106.3 (7)	C4A'—C8A'—H8A4	104.9
C3E—C4E—C3E^i	110.5 (5)	C4D'—C8D'—H8D3	109.7
C3A'—C4A'—C3A'^i	108.7 (9)	C4D'—C8D'—H8D4	109.3
C3D'—C4D'—C3D'^i	108.3 (8)	C4A—C9A—H9A1	111.3
C3A—C4A—C8A	111.4 (4)	C4A—C9A—H9A2	108.6
C3B—C4B—C8B	109.7 (3)	C4B—C9B—H9B1	109.2
C3C—C4C—C8C	111.0 (3)	C4B—C9B—H9B2	109.6
C3D—C4D—C8D	108.8 (5)	C4C—C9C—H9C1	109.5
C3E—C4E—C8E	110.0 (3)	C4D—C9D—H9D1	109.9
C3A'—C4A'—C8A'	109.4 (6)	C4D—C9D—H9D2	109.3
C3D'—C4D'—C8D'	111.4 (5)	C4E—C9E—H9E1	108.9
C3A—C4A—C9A	107.1 (5)	C4E—C9E—H9E2	109.8
C3B—C4B—C9B	110.0 (3)	C4A'—C9A'—H9A3	108.7
C3C—C4C—C9C	108.8 (3)	C4A'—C9A'—H9A4	109.9
C3D—C4D—C9D	110.5 (5)	C4D'—C9D'—H9D3	108.2
C3E—C4E—C9E	109.0 (3)	C4D'—C9D'—H9D4	110.1
C3A'—C4A'—C9A'	110.0 (6)	H3A1—C3A—H3A2	108.3
C3D'—C4D'—C9D'	108.9 (5)	H3B1—C3B—H3B2	107.6
C8A—C4A—C9A	108.5 (6)	H3C1—C3C—H3C2	107.6
C8B—C4B—C9B	108.4 (5)	H3D1—C3D—H3D2	108.2
C8C—C4C—C9C	107.8 (5)	H3E1—C3E—H3E2	107.9
C8D—C4D—C9D	111.7 (7)	H3A3—C3A'—H3A4	108.3
C8E—C4E—C9E	108.3 (5)	H3B3—C3B'—H3B4	108.1
C8A'—C4A'—C9A'	109.3 (8)	H3D3—C3D'—H3D4	108.1
C8D'—C4D'—C9D'	108.0 (8)	H3E3—C3E'—H3E4	108.1
O1A—C7A—O1A^i	119.7 (4)	H8A1—C8A—H8A2	111.1
O1B—C7B—O1B^ii	120.8 (5)	H8B1—C8B—H8B2	109.5
O1C—C7C—O1C^ii	120.4 (5)	H8C1—C8C—H8C2	109.5
O1D—C7D—O1D^i	122.5 (5)	H8D1—C8D—H8D2	112.6
O1E—C7E—O1E^i	120.9 (5)	H8E1—C8E—H8E2	109.5
O1A—C7A—C1A	120.1 (2)	H8A3—C8A'—H8A4	108.6
O1B—C7B—C1B	119.6 (2)	H8B3—C8B'—H8B4	109.5
O1C—C7C—C1C	119.8 (2)	H8D3—C8D'—H8D4	111.5
O1D—C7D—C1D	118.7 (2)	H8E3—C8E'—H8E4	109.6
O1E—C7E—C1E	119.5 (2)	H9A1—C9A—H9A2	110.0
C7A—O1A—H1A	98.5	H9B1—C9B—H9B2	109.5
C7B—O1B—H1B	101.4	H9C1—C9C—H9C2	109.5
C7C—O1C—H1C	101.3	H9D1—C9D—H9D2	109.5
C7D—O1D—H1D	100.9	H9E1—C9E—H9E2	109.5
C7E—O1E—H1E	100.5	H9A3—C9A'—H9A4	109.3
C2A—O3A—H1A	99.3	H9B3—C9B'—H9B4	109.4
C2B—O3B—H1B	101.3	H9D3—C9D'—H9D4	108.6
C2C—O3C—H1C	102.6	H9E3—C9E'—H9E4	111.3
C2D—O3D—H1D	100.6

Symmetry codes: (i) −x+1, y, z; (ii) −x, y, z.

(pmnb) 4,4'-dimethyl-2-hydroxy-6-oxo-cyclohexene-1-carboxylic acid

Crystal data

C9H12O4	Dx = 1.384 Mg m^−3
Mr = 184.19	Melting point: 123_C K
Orthorhombic, Pmnb	Mo Kα radiation, λ = 0.71073 Å
a = 10.471 (3) Å	Cell parameters from 23 reflections
b = 26.240 (9) Å	θ = 8.6–15.7°
c = 6.434 (2) Å	µ = 0.11 mm^−1
V = 1767.8 (10) Å^3	T = 130 K
Z = 8	Laths, colourless
F(000) = 784	0.38 × 0.35 × 0.10 mm

Data collection

ENRAF-Nonius CAD4-VAX diffractometer	Rint = 0.131
Radiation source: fine-focus sealed tube	θmax = 16.0°, θmin = 2.5°
Graphite monochromator	h = 0→8
ω scans	k = 0→20
960 measured reflections	l = −4→4
465 independent reflections	2 standard reflections every 60 min
250 reflections with I > 2σ(I)	intensity decay: <1.

Refinement

Refinement on F^2	8 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.081	H-atom parameters constrained
wR(F^2) = 0.214	w = 1/[σ^2(Fo^2) + (0.06P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.43	(Δ/σ)max = 0.001
465 reflections	Δρmax = 0.42 e Å^−3
20 parameters	Δρmin = −0.35 e Å^−3

Special details

Experimental. The crystal fell off the diffractometer after data to /q=16° had been measured.

Geometry. Rigid-group refinement. All geometric parameters were fixed.

Refinement. Rigid-group refinement.

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

	x	y	z	Uiso*/Ueq
C7A	0.2500	0.3891 (3)	0.2542 (14)	0.014 (6)*
O1A	0.145030 (2)	0.4125 (3)	0.2346 (17)	0.026 (4)*
O3A	0.026950 (8)	0.3301 (3)	0.2852 (10)	0.022 (4)*
H1A	0.0571	0.3723	0.2533	0.027*
C1A	0.250000 (7)	0.3339 (3)	0.2853 (10)	0.017 (6)*
C2A	0.133552 (6)	0.3078 (3)	0.3071 (10)	0.025 (5)*
C3A	0.133009 (10)	0.2521 (3)	0.3617 (15)	0.021 (5)*
H3AA	0.1238	0.2496	0.5102	0.025*
H3AB	0.0593	0.2364	0.2998	0.025*
C4A	0.25000 (5)	0.2232 (3)	0.2982 (18)	0.012 (6)*
C8A	0.25000 (2)	0.1695 (3)	0.391 (3)	0.024 (6)*
H8AA	0.2500	0.1733	0.5395	0.035*
H8AB	0.1759	0.1510	0.3475	0.035*
C9A	0.2500 (2)	0.2178 (4)	0.0561 (19)	0.026 (7)*
H9AA	0.2500	0.2512	−0.0059	0.038*
H9AB	0.1774	0.1995	0.0116	0.038*
C7B	0.2500	0.3611 (3)	0.7687 (15)	0.014 (6)*
O1B	0.145080 (2)	0.3375 (3)	0.7859 (17)	0.026 (4)*
O3B	0.026947 (8)	0.4201 (3)	0.7410 (10)	0.022 (4)*
H1B	0.0572	0.3777	0.7698	0.027*
C1B	0.250000 (7)	0.4164 (3)	0.7419 (11)	0.017 (6)*
C2B	0.133553 (6)	0.4426 (3)	0.7214 (10)	0.025 (5)*
C3B	0.133018 (10)	0.4985 (4)	0.6710 (13)	0.021 (5)*
H3BA	0.1241	0.5016	0.5227	0.025*
H3BB	0.0591	0.5138	0.7337	0.025*
C4B	0.25000 (5)	0.5271 (3)	0.7374 (16)	0.012 (6)*
C8B	0.25000 (2)	0.5812 (4)	0.649 (2)	0.024 (6)*
H8BA	0.2500	0.5781	0.4999	0.035*
H8BB	0.1757	0.5995	0.6932	0.035*
C9B	0.2500 (2)	0.5314 (4)	0.9798 (16)	0.026 (7)*
H9BA	0.2500	0.4977	1.0393	0.038*
H9BB	0.1765	0.5495	1.0253	0.038*

Geometric parameters (Å, º)

O1A—C7A	1.266	O1A—H1A	1.40
O3A—C2A	1.268	O3A—H1A	1.17
C1A—C7A	1.462	C3A—H3AA	0.96
C1A—C2A	1.406	C3A—H3AB	0.96
C2A—C3A	1.502	C8A—H8AA	0.96
C3A—C4A	1.500	C8A—H8AB	0.96
C4A—C8A	1.528	C9A—H9AA	0.96
C4A—C9A	1.564	C9A—H9AB	0.94
O1B—C7B	1.266	O1B—H1B	1.40
O3B—C2B	1.268	O3B—H1B	1.17
C1B—C7B	1.462	C3B—H3BA	0.96
C1B—C2B	1.406	C3B—H3BB	0.96
C2B—C3B	1.502	C8B—H8BA	0.96
C3B—C4B	1.500	C8B—H8BB	0.96
C4B—C8B	1.528	C9B—H9BA	0.96
C4B—C9B	1.564	C9B—H9BB	0.95
C2A—C1A—C2A^i	120.3	C2A—O3A—H1A	102.6
C2A—C1A—C7A	119.8	C7B—O1B—H1B	101.3
O3A—C2A—C1A	121.8	C2B—O3B—H1B	102.6
O3A—C2A—C3A	118.1	C2A—C3A—H3AA	107.3
C1A—C2A—C3A	120.0	C2A—C3A—H3AB	108.8
C2A—C3A—C4A	115.2	C4A—C3A—H3AA	108.6
C3A—C4A—C3A^i	109.7	C4A—C3A—H3AB	109.1
C3A—C4A—C8A	111.1	C4A—C8A—H8AA	107.0
C3A—C4A—C9A	108.5	C4A—C8A—H8AB	110.7
C8A—C4A—C9A	107.8	C4A—C9A—H9AA	109.4
O1A^i—C7A—O1A	120.5	C4A—C9A—H9AB	110.3
O1A—C7A—C1A	119.7	C2B—C3B—H3BA	107.3
C2B^i—C1B—C2B	120.3	C2B—C3B—H3BB	108.8
C2B—C1B—C7B	119.8	C4B—C3B—H3BA	108.6
O3B—C2B—C1B	121.8	C4B—C3B—H3BB	109.1
O3B—C2B—C3B	118.1	C4B—C8B—H8BA	107.0
C1B—C2B—C3B	120.0	C4B—C8B—H8BB	110.8
C2B—C3B—C4B	115.2	C4B—C9B—H9BA	109.4
C3B^i—C4B—C3B	109.5	C4B—C9B—H9BB	110.0
C3B—C4B—C8B	111.1	H3AA—C3A—H3AB	107.6
C3B—C4B—C9B	108.6	H8AA—C8A—H8AB	110.0
C8B—C4B—C9B	107.8	H9AA—C9A—H9AB	109.7
O1B—C7B—O1B^i	120.5	H3BA—C3B—H3BB	107.6
O1B—C7B—C1B	119.7	H8BA—C8B—H8BB	109.8
C7A—O1A—H1A	101.3	H9BA—C9B—H9BB	109.7

Symmetry code: (i) −x+1/2, y, z.