2-Hydroxy­bicyclo­[2.2.1]heptane-2-endo-carboxylic acid

In the title compound, C₈H₁₂O₃, the methyl­ene function of glycolic acid is incorporated in the sterically demanding lipophilic norbornane backbone. Pairs of longer inter­molecular hydroxyl OH...carboxyl O hydrogen bonds lead to the formation of centrosymmetric dimers. The dimers are connected to form sheets parallel to the bc plane by shorter carboxyl OH...hydroxyl O bonds. Hydro­phobic contacts connect the hydrogen-bonded sheets.

Key indicators

• Single-crystal X-ray study
• T = 200 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.045
• wR factor = 0.119
• Data-to-parameter ratio = 17.1

checkCIF/PLATON results

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Alert level G
PLAT793_ALERT_1_G Check the Absolute Configuration of C1     = ...          S
PLAT793_ALERT_1_G Check the Absolute Configuration of C2     = ...          S
PLAT793_ALERT_1_G Check the Absolute Configuration of C4     = ...          R

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   0 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
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S1. Comment

2-Hydroxybicyclo[2.2.1]heptane-2-endo-carboxylic acid (2-hydroxynorbornane-2-endo-carboxylic acid) was prepared as the parent acid of a potentially chelating ligand bearing the sterically demanding norbornane group as a substituent. In the molecule a carboxy group and a hydroxy group are attached to the 2-position of the bicyclic norbornane framework. The carboxy groups is oriented away from the bridge-head methylene group. Bond lengths are in good agreement with literature values.

In the crystal structure, hydrophobic and hydrophilic building blocks are separated (Figure 2). In the hydrophilic blocks, a two-dimensional hydrogen-bond system is constructed by two types of bonds: pairs of longer hydroxyl-OH···carboxyl-O hydrogen bonds are found in centrosymmetric dimers. Shorter carboxyl-OH···hydroxyl-O bonds connect the dimers to form an infinite sheet (Figure 3). A three-dimensional analogue of the same connectivity pattern has been found recently for the related tert-butylglycolic acid (Betz et al., 2007).

Related literature

For synthesis of the title compound, see Kwart & Null (1960). For the crystal structures of 1-hydroxy-1-carboxylic acids with hydrophobic residues of similar size, see Betz & Klüfers (2007a,b,c). The same hydrogen-bond donor–acceptor pattern has been found for tert-butylglycolic acid but forming a three-dimensionally connected network instead of the two-dimensional array in the title compound (Betz et al., 2007).

S2. Experimental

The title compound was prepared according to a published procedure (Kwart & Null, 1960) by aqueous alkaline oxidation of norbornane-2-carboxylic acid with potassium permanganate. Crystals suitable for X-ray analysis were obtained by recrystallization of the crude reaction product from boiling benzene.

S3. Refinement

All H atoms were located in a difference map and refined as riding on their parent atoms. One common isotropic displacement parameter for all H atoms was refined to U_iso(H) = 0.0485 (16) Ų.

Computing details

Data collection: COLLECT (Nonius, 2004); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. The molecular structure of (I), with atom labels and anisotropic displacement ellipsoids (drawn at the 50% probability level) for non-H atoms.
	Fig. 2. Hydrophobic and hydrophilic sheets alternating along [100], viewed along [010].
	Fig. 3. View of a hydrophilic sheet, projected onto the (100) plane (twice the unit vectors in b and c). Norbornane-C atoms including their H atoms are omitted except for C2. Hydroxyl-OH···carboxyl-O bonds are drawn in green, the shorter carboxyl-OH···hydroxyl-O bonds are drawn in yellow.

2-Hydroxybicyclo[2.2.1]heptane-2-endo-carboxylic acid

Crystal data

C8H12O3	F(000) = 336
Mr = 156.18	Dx = 1.339 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 17661 reflections
a = 11.4780 (6) Å	θ = 3.1–27.5°
b = 6.8145 (3) Å	µ = 0.10 mm^−1
c = 10.1444 (5) Å	T = 200 K
β = 102.506 (2)°	Platelet, colourless
V = 774.64 (7) Å^3	0.20 × 0.18 × 0.01 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	1314 reflections with I > 2σ(I)
Radiation source: rotating anode	Rint = 0.040
MONTEL, graded multilayered X-ray optics monochromator	θmax = 27.4°, θmin = 3.5°
thick–slice ω and φ scans	h = −14→14
6408 measured reflections	k = −8→8
1765 independent reflections	l = −13→13

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) = 0.119	Only H-atom displacement parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0509P)^2 + 0.3026P] where P = (Fo^2 + 2Fc^2)/3
1765 reflections	(Δ/σ)max < 0.001
103 parameters	Δρmax = 0.23 e Å^−3
0 restraints	Δρmin = −0.21 e Å^−3

Special details

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. Comment on the refU data value for H atoms: H atoms were refined as riding on their parent atoms (AFIX 147). One common isotropic displacement parameter for all H atoms was refined to U_iso = 0.050 (3) Ų.

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

	x	y	z	Uiso*/Ueq
O2	0.38046 (10)	−0.21347 (15)	0.39994 (10)	0.0309 (3)
H2	0.4087	−0.1587	0.4742	0.0485 (16)*
O81	0.53499 (10)	0.0669 (2)	0.34527 (11)	0.0448 (4)
O82	0.43585 (10)	0.06668 (17)	0.13284 (11)	0.0380 (3)
H82	0.4970	0.1269	0.1221	0.0485 (16)*
C1	0.26245 (14)	0.0878 (2)	0.35726 (16)	0.0327 (4)
H1	0.2991	0.1347	0.4504	0.0485 (16)*
C2	0.33717 (13)	−0.0665 (2)	0.29946 (14)	0.0271 (3)
C3	0.24406 (14)	−0.1625 (2)	0.18421 (15)	0.0318 (4)
H31	0.2641	−0.1386	0.0954	0.0485 (16)*
H32	0.2391	−0.3057	0.1983	0.0485 (16)*
C4	0.12712 (15)	−0.0606 (3)	0.19329 (18)	0.0397 (4)
H4	0.0533	−0.1354	0.1518	0.0485 (16)*
C5	0.13144 (17)	0.1498 (3)	0.14017 (19)	0.0469 (5)
H51	0.0523	0.2139	0.1270	0.0485 (16)*
H52	0.1581	0.1514	0.0537	0.0485 (16)*
C6	0.22312 (17)	0.2516 (3)	0.2530 (2)	0.0446 (5)
H61	0.2916	0.3019	0.2183	0.0485 (16)*
H62	0.1861	0.3618	0.2926	0.0485 (16)*
C7	0.14432 (15)	−0.0255 (3)	0.34493 (18)	0.0391 (4)
H71	0.1540	−0.1487	0.3978	0.0485 (16)*
H72	0.0801	0.0557	0.3682	0.0485 (16)*
C8	0.44562 (13)	0.0280 (2)	0.26121 (15)	0.0280 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2	0.0344 (6)	0.0338 (6)	0.0236 (5)	0.0030 (5)	0.0044 (5)	0.0023 (4)
O81	0.0329 (7)	0.0722 (9)	0.0275 (6)	−0.0141 (6)	0.0027 (5)	−0.0006 (6)
O82	0.0385 (7)	0.0480 (7)	0.0271 (6)	−0.0141 (5)	0.0060 (5)	0.0024 (5)
C1	0.0329 (9)	0.0341 (8)	0.0320 (8)	0.0027 (7)	0.0090 (7)	−0.0024 (7)
C2	0.0272 (8)	0.0296 (8)	0.0238 (7)	0.0014 (6)	0.0039 (6)	0.0012 (6)
C3	0.0316 (8)	0.0342 (8)	0.0286 (8)	−0.0041 (7)	0.0039 (6)	−0.0023 (6)
C4	0.0264 (8)	0.0508 (11)	0.0397 (10)	−0.0029 (7)	0.0023 (7)	0.0011 (8)
C5	0.0409 (10)	0.0539 (11)	0.0442 (11)	0.0122 (9)	0.0057 (8)	0.0107 (9)
C6	0.0451 (10)	0.0369 (9)	0.0545 (11)	0.0084 (8)	0.0168 (9)	0.0055 (8)
C7	0.0319 (9)	0.0452 (10)	0.0425 (10)	0.0024 (7)	0.0129 (7)	0.0024 (8)
C8	0.0288 (8)	0.0299 (8)	0.0252 (8)	0.0014 (6)	0.0052 (6)	−0.0021 (6)

Geometric parameters (Å, º)

O2—C2	1.4385 (17)	C3—H31	0.990
O2—H2	0.840	C3—H32	0.990
O81—C8	1.2127 (18)	C4—C7	1.527 (2)
O82—C8	1.3094 (19)	C4—C5	1.536 (3)
O82—H82	0.840	C4—H4	1.000
C1—C6	1.537 (2)	C5—C6	1.541 (3)
C1—C7	1.542 (2)	C5—H51	0.990
C1—C2	1.550 (2)	C5—H52	0.990
C1—H1	1.000	C6—H61	0.990
C2—C8	1.525 (2)	C6—H62	0.990
C2—C3	1.548 (2)	C7—H71	0.990
C3—C4	1.532 (2)	C7—H72	0.990
C2—O2—H2	109.5	C3—C4—H4	114.6
C8—O82—H82	109.5	C5—C4—H4	114.6
C6—C1—C7	100.70 (14)	C4—C5—C6	103.19 (14)
C6—C1—C2	109.66 (13)	C4—C5—H51	111.1
C7—C1—C2	100.28 (13)	C6—C5—H51	111.1
C6—C1—H1	114.8	C4—C5—H52	111.1
C7—C1—H1	114.8	C6—C5—H52	111.1
C2—C1—H1	114.8	H51—C5—H52	109.1
O2—C2—C8	107.39 (12)	C1—C6—C5	103.65 (15)
O2—C2—C3	108.50 (12)	C1—C6—H61	111.0
C8—C2—C3	117.04 (12)	C5—C6—H61	111.0
O2—C2—C1	109.80 (12)	C1—C6—H62	111.0
C8—C2—C1	111.01 (12)	C5—C6—H62	111.0
C3—C2—C1	102.96 (12)	H61—C6—H62	109.0
C4—C3—C2	103.53 (12)	C4—C7—C1	94.58 (13)
C4—C3—H31	111.1	C4—C7—H71	112.8
C2—C3—H31	111.1	C1—C7—H71	112.8
C4—C3—H32	111.1	C4—C7—H72	112.8
C2—C3—H32	111.1	C1—C7—H72	112.8
H31—C3—H32	109.0	H71—C7—H72	110.3
C7—C4—C3	102.00 (13)	O81—C8—O82	122.18 (14)
C7—C4—C5	101.54 (15)	O81—C8—C2	121.75 (14)
C3—C4—C5	107.87 (14)	O82—C8—C2	116.06 (13)
C7—C4—H4	114.6
C6—C1—C2—O2	176.39 (13)	C7—C1—C6—C5	−35.60 (16)
C7—C1—C2—O2	−78.23 (14)	C2—C1—C6—C5	69.49 (17)
C6—C1—C2—C8	57.80 (17)	C4—C5—C6—C1	0.73 (18)
C7—C1—C2—C8	163.18 (12)	C3—C4—C7—C1	55.55 (15)
C6—C1—C2—C3	−68.22 (16)	C5—C4—C7—C1	−55.76 (15)
C7—C1—C2—C3	37.16 (14)	C6—C1—C7—C4	55.89 (15)
O2—C2—C3—C4	113.76 (13)	C2—C1—C7—C4	−56.58 (14)
C8—C2—C3—C4	−124.61 (14)	O2—C2—C8—O81	−40.91 (19)
C1—C2—C3—C4	−2.57 (15)	C3—C2—C8—O81	−163.13 (15)
C2—C3—C4—C7	−33.46 (16)	C1—C2—C8—O81	79.12 (19)
C2—C3—C4—C5	73.00 (16)	O2—C2—C8—O82	139.88 (13)
C7—C4—C5—C6	34.87 (17)	C3—C2—C8—O82	17.66 (19)
C3—C4—C5—C6	−71.91 (17)	C1—C2—C8—O82	−100.09 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O81^i	0.84	1.91	2.7447 (16)	172
O82—H82···O2^ii	0.84	1.83	2.6653 (15)	173

Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x+1, y+1/2, −z+1/2.