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In the title compound, C6H12O3, which has a sterically demanding tert-butyl group attached to a hydroxy­acetic acid residue, centrosymmetric hydrogen-bonded dimers are formed; the hydr­oxy OH group functions as the donor and the double-bonded O atom of the carboxyl group functions as the acceptor. The dimer engages in inter­dimer bonding through four shorter hydrogen bonds involving two donors (the carboxyl OH) and two acceptors (the hydroxyl O atom). A three-dimensional system of hydrogen bonds is established that has channels for the hydro­phobic butyl groups along (0, 0, z) and (1\over2, 1\over2, z). There are two independent mol­ecules in the asymmetric unit.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807046156/ng2330sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536807046156/ng2330Isup2.hkl
Contains datablock I

CCDC reference: 663824

Key indicators

  • Single-crystal X-ray study
  • T = 200 K
  • Mean [sigma](C-C) = 0.003 Å
  • R factor = 0.048
  • wR factor = 0.142
  • Data-to-parameter ratio = 16.0

checkCIF/PLATON results

No syntax errors found



Alert level C PLAT242_ALERT_2_C Check Low Ueq as Compared to Neighbors for C13 PLAT242_ALERT_2_C Check Low Ueq as Compared to Neighbors for C23
Alert level G PLAT793_ALERT_1_G Check the Absolute Configuration of C12 = ... R PLAT793_ALERT_1_G Check the Absolute Configuration of C22 = ... S
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 2 ALERT level C = Check and explain 2 ALERT level G = General alerts; check 2 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 2 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 0 ALERT type 5 Informative message, check

Comment top

tert-Butylglycolic acid was prepared as a chelating molecule bearing the sterically demanding tert-butyl group as a substituent. In order to estimate the influence of chelation on structural parameters of the chelating molecule, the structure of the parent compound was investigated.

The molecular structure of (I) comprises a tert-butyl group attached to hydroxy acetic acid (glycolic acid). The two molecules present in the asymmetric unit differ only slightly from each other by the arrangement of the tert-butyl group relative to the carboxyl group.

Hydrogen bonds between hydroxyl donors and carboxyl-O acceptors connect pairs of molecules to centrosymmetric dimers. Each dimer is incorporated in three-dimensional network by means of two carboxyl-donor and two hydroxyl-acceptor sites. Figure 2 shows hydrophobic channels along 0,0,z and 1/2,1/2,z running through the hydrogen-bonded network of the hydrophilic functions.

Related literature top

For synthesis of the title compound, see Reetz & Heimbach (1983). For the crystal structures of 1-hydroxy-1-carboxylic acids with hydrophobic residues of similar size, see Betz & Klüfers (2007a, 2007b, 2007c).

Experimental top

The title compound was prepared according to a published procedure (Reetz & Heimbach, 1983) upon addition of tert-butyl chloride to tris(trimethylsilyloxyethene). Crystals suitable for X-ray analysis were directly obtained from the crystallized reaction product.

Refinement top

All H atoms were located in a difference map. Methyl H atoms were refined as riding with one common isotropic temperature parameter. Individual isotropic temperature parameters were refined for the other H atoms. The positional parameters of O-bonded H atoms were refined freely.

Structure description top

tert-Butylglycolic acid was prepared as a chelating molecule bearing the sterically demanding tert-butyl group as a substituent. In order to estimate the influence of chelation on structural parameters of the chelating molecule, the structure of the parent compound was investigated.

The molecular structure of (I) comprises a tert-butyl group attached to hydroxy acetic acid (glycolic acid). The two molecules present in the asymmetric unit differ only slightly from each other by the arrangement of the tert-butyl group relative to the carboxyl group.

Hydrogen bonds between hydroxyl donors and carboxyl-O acceptors connect pairs of molecules to centrosymmetric dimers. Each dimer is incorporated in three-dimensional network by means of two carboxyl-donor and two hydroxyl-acceptor sites. Figure 2 shows hydrophobic channels along 0,0,z and 1/2,1/2,z running through the hydrogen-bonded network of the hydrophilic functions.

For synthesis of the title compound, see Reetz & Heimbach (1983). For the crystal structures of 1-hydroxy-1-carboxylic acids with hydrophobic residues of similar size, see Betz & Klüfers (2007a, 2007b, 2007c).

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis RED (Oxford Diffraction, 2005); data reduction: CrysAlis RED (Oxford Diffraction, 2005); 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 top
[Figure 1] Fig. 1. The structure of the molecules of (I) in the asymmetric unit, with atom labels and anisotropic displacement ellipsoids (drawn at the 50% probability level) for non-H atoms.
[Figure 2] Fig. 2. The molecular packing of (I) viewed along [0 0 1].
tert-Butylglycolic acid top
Crystal data top
C6H12O3Z = 16
Mr = 132.16F(000) = 1152
Monoclinic, C2/cDx = 1.156 Mg m3
Hall symbol: -C 2ycMo Kα radiation, λ = 0.71073 Å
a = 21.236 (2) Åθ = 3.9–26.0°
b = 13.4486 (13) ŵ = 0.09 mm1
c = 11.4351 (13) ÅT = 200 K
β = 111.537 (10)°Block, colourless
V = 3037.8 (6) Å30.44 × 0.36 × 0.16 mm
Data collection top
Oxford Diffraction XCalibur
diffractometer
3003 independent reflections
Radiation source: fine-focus sealed tube2266 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.025
ω scansθmax = 26.0°, θmin = 4.5°
Absorption correction: analytical
(de Meulenaer & Tompa, 1965)
h = 1926
Tmin = 0.972, Tmax = 0.988k = 1612
7814 measured reflectionsl = 1414
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.048Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.142H atoms treated by a mixture of independent and constrained refinement
S = 1.10 w = 1/[σ2(Fo2) + (0.0759P)2 + 0.3594P]
where P = (Fo2 + 2Fc2)/3
3003 reflections(Δ/σ)max < 0.001
188 parametersΔρmax = 0.19 e Å3
0 restraintsΔρmin = 0.21 e Å3
Crystal data top
C6H12O3V = 3037.8 (6) Å3
Mr = 132.16Z = 16
Monoclinic, C2/cMo Kα radiation
a = 21.236 (2) ŵ = 0.09 mm1
b = 13.4486 (13) ÅT = 200 K
c = 11.4351 (13) Å0.44 × 0.36 × 0.16 mm
β = 111.537 (10)°
Data collection top
Oxford Diffraction XCalibur
diffractometer
3003 independent reflections
Absorption correction: analytical
(de Meulenaer & Tompa, 1965)
2266 reflections with I > 2σ(I)
Tmin = 0.972, Tmax = 0.988Rint = 0.025
7814 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0480 restraints
wR(F2) = 0.142H atoms treated by a mixture of independent and constrained refinement
S = 1.10Δρmax = 0.19 e Å3
3003 reflectionsΔρmin = 0.21 e Å3
188 parameters
Special details top

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. Treatment of H atoms: GEOM for methyl Hs, 1 common isotropic U. GEOM for methylidine Hs, individual isotropic Us All H-atom parameters refined for O-bonded Hs

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O120.19291 (6)0.25485 (9)0.62987 (11)0.0395 (3)
H120.2237 (12)0.2390 (17)0.608 (2)0.073 (7)*
O220.05822 (6)0.37302 (10)0.12597 (12)0.0476 (3)
H220.0265 (11)0.4000 (15)0.074 (2)0.051 (6)*
O1110.17753 (5)0.27864 (10)0.38322 (12)0.0534 (4)
O1120.06607 (5)0.27901 (10)0.33272 (12)0.0508 (4)
H1120.0644 (11)0.3065 (18)0.267 (2)0.072 (7)*
O2110.07378 (6)0.56407 (9)0.05469 (13)0.0541 (4)
O2120.18526 (5)0.54759 (10)0.15797 (12)0.0487 (4)
H2120.1857 (13)0.612 (2)0.156 (2)0.090 (8)*
C110.12818 (7)0.26207 (11)0.40870 (15)0.0358 (4)
C120.13211 (7)0.21920 (11)0.53441 (14)0.0347 (4)
H1210.09320.24720.55310.035 (4)*
C130.12590 (8)0.10491 (12)0.53469 (16)0.0400 (4)
C140.18576 (10)0.05486 (14)0.5147 (2)0.0636 (6)
H1410.22790.07390.58280.0897 (19)*
H1420.18750.07610.43400.0897 (19)*
H1430.18030.01750.51460.0897 (19)*
C150.06016 (9)0.07141 (15)0.4313 (2)0.0570 (5)
H1510.05480.00050.43740.0897 (19)*
H1520.06180.08750.34890.0897 (19)*
H1530.02180.10580.44130.0897 (19)*
C160.12455 (12)0.07342 (17)0.6625 (2)0.0714 (7)
H1610.08660.10600.67620.0897 (19)*
H1620.16710.09300.72920.0897 (19)*
H1630.11920.00110.66400.0897 (19)*
C210.12311 (8)0.51224 (12)0.10414 (15)0.0387 (4)
C220.11975 (7)0.40017 (12)0.11120 (15)0.0380 (4)
H2210.15780.37860.18890.031 (4)*
C230.12843 (9)0.34628 (13)0.00079 (17)0.0464 (4)
C240.07322 (13)0.3743 (2)0.1234 (2)0.0892 (8)
H2410.02900.35950.11880.0897 (19)*
H2420.07870.33600.19200.0897 (19)*
H2430.07610.44550.13900.0897 (19)*
C250.19713 (11)0.37017 (18)0.0065 (2)0.0713 (6)
H2510.19960.44140.02260.0897 (19)*
H2520.20330.33190.07440.0897 (19)*
H2530.23280.35270.07370.0897 (19)*
C260.12598 (15)0.23381 (17)0.0209 (3)0.0888 (8)
H2610.16340.21520.09830.0897 (19)*
H2620.13020.19780.05040.0897 (19)*
H2630.08280.21670.02860.0897 (19)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O120.0292 (6)0.0446 (7)0.0392 (7)0.0007 (5)0.0061 (5)0.0006 (5)
O220.0284 (6)0.0597 (8)0.0526 (8)0.0021 (5)0.0122 (6)0.0249 (6)
O1110.0270 (6)0.0774 (9)0.0543 (8)0.0029 (5)0.0130 (6)0.0266 (6)
O1120.0255 (6)0.0817 (10)0.0420 (7)0.0054 (5)0.0087 (6)0.0214 (6)
O2110.0310 (6)0.0446 (7)0.0766 (9)0.0029 (5)0.0080 (6)0.0077 (6)
O2120.0310 (6)0.0433 (8)0.0611 (8)0.0029 (5)0.0044 (6)0.0050 (6)
C110.0262 (8)0.0383 (9)0.0396 (9)0.0010 (6)0.0082 (7)0.0058 (6)
C120.0254 (7)0.0407 (9)0.0357 (8)0.0006 (6)0.0085 (7)0.0019 (6)
C130.0348 (8)0.0396 (9)0.0437 (9)0.0042 (7)0.0123 (8)0.0049 (7)
C140.0508 (11)0.0393 (10)0.1000 (17)0.0027 (8)0.0269 (12)0.0026 (10)
C150.0463 (10)0.0557 (12)0.0621 (12)0.0151 (8)0.0116 (10)0.0018 (9)
C160.0837 (16)0.0688 (14)0.0574 (13)0.0183 (11)0.0210 (12)0.0173 (10)
C210.0301 (8)0.0464 (10)0.0381 (9)0.0002 (7)0.0107 (7)0.0042 (7)
C220.0261 (8)0.0447 (9)0.0401 (9)0.0005 (6)0.0085 (7)0.0124 (7)
C230.0378 (9)0.0447 (10)0.0552 (11)0.0003 (7)0.0153 (8)0.0006 (8)
C240.0748 (16)0.135 (2)0.0494 (13)0.0289 (15)0.0132 (12)0.0139 (13)
C250.0602 (13)0.0745 (15)0.0925 (17)0.0056 (10)0.0437 (13)0.0153 (12)
C260.106 (2)0.0496 (13)0.126 (2)0.0121 (12)0.0607 (19)0.0130 (13)
Geometric parameters (Å, º) top
O12—C121.4331 (18)C15—H1520.9800
O12—H120.81 (2)C15—H1530.9800
O22—C221.4253 (18)C16—H1610.9800
O22—H220.80 (2)C16—H1620.9800
O111—C111.2071 (18)C16—H1630.9800
O112—C111.3058 (18)C21—C221.512 (2)
O112—H1120.82 (2)C22—C231.540 (2)
O211—C211.2116 (19)C22—H2211.0000
O212—C211.3230 (19)C23—C241.508 (3)
O212—H2120.87 (3)C23—C251.519 (3)
C11—C121.522 (2)C23—C261.537 (3)
C12—C131.543 (2)C24—H2410.9800
C12—H1211.0000C24—H2420.9800
C13—C141.528 (2)C24—H2430.9800
C13—C151.529 (2)C25—H2510.9800
C13—C161.532 (3)C25—H2520.9800
C14—H1410.9800C25—H2530.9800
C14—H1420.9800C26—H2610.9800
C14—H1430.9800C26—H2620.9800
C15—H1510.9800C26—H2630.9800
C12—O12—H12106.5 (17)H161—C16—H163109.5
C22—O22—H22110.7 (14)H162—C16—H163109.5
C11—O112—H112112.3 (16)O211—C21—O212123.66 (16)
C21—O212—H212111.4 (17)O211—C21—C22123.27 (14)
O111—C11—O112124.16 (14)O212—C21—C22113.06 (13)
O111—C11—C12123.12 (14)O22—C22—C21108.95 (12)
O112—C11—C12112.72 (13)O22—C22—C23111.89 (14)
O12—C12—C11108.32 (12)C21—C22—C23113.71 (13)
O12—C12—C13112.68 (12)O22—C22—H221107.3
C11—C12—C13113.84 (13)C21—C22—H221107.3
O12—C12—H121107.2C23—C22—H221107.3
C11—C12—H121107.2C24—C23—C25109.8 (2)
C13—C12—H121107.2C24—C23—C26109.5 (2)
C14—C13—C15109.16 (16)C25—C23—C26107.77 (18)
C14—C13—C16109.19 (17)C24—C23—C22111.46 (15)
C15—C13—C16108.95 (15)C25—C23—C22110.27 (15)
C14—C13—C12111.24 (13)C26—C23—C22107.92 (17)
C15—C13—C12110.27 (14)C23—C24—H241109.5
C16—C13—C12107.99 (15)C23—C24—H242109.5
C13—C14—H141109.5H241—C24—H242109.5
C13—C14—H142109.5C23—C24—H243109.5
H141—C14—H142109.5H241—C24—H243109.5
C13—C14—H143109.5H242—C24—H243109.5
H141—C14—H143109.5C23—C25—H251109.5
H142—C14—H143109.5C23—C25—H252109.5
C13—C15—H151109.5H251—C25—H252109.5
C13—C15—H152109.5C23—C25—H253109.5
H151—C15—H152109.5H251—C25—H253109.5
C13—C15—H153109.5H252—C25—H253109.5
H151—C15—H153109.5C23—C26—H261109.5
H152—C15—H153109.5C23—C26—H262109.5
C13—C16—H161109.5H261—C26—H262109.5
C13—C16—H162109.5C23—C26—H263109.5
H161—C16—H162109.5H261—C26—H263109.5
C13—C16—H163109.5H262—C26—H263109.5
O111—C11—C12—O1232.7 (2)O211—C21—C22—O2234.9 (2)
O112—C11—C12—O12147.03 (13)O212—C21—C22—O22144.80 (14)
O111—C11—C12—C1393.44 (19)O211—C21—C22—C2390.67 (19)
O112—C11—C12—C1386.80 (16)O212—C21—C22—C2389.66 (17)
O12—C12—C13—C1458.85 (19)O22—C22—C23—C2462.7 (2)
C11—C12—C13—C1464.99 (18)C21—C22—C23—C2461.3 (2)
O12—C12—C13—C15179.89 (14)O22—C22—C23—C25175.10 (15)
C11—C12—C13—C1556.26 (18)C21—C22—C23—C2560.93 (19)
O12—C12—C13—C1660.95 (18)O22—C22—C23—C2657.62 (19)
C11—C12—C13—C16175.21 (15)C21—C22—C23—C26178.40 (16)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O12—H12···O111i0.81 (2)2.08 (2)2.8456 (17)159 (2)
O22—H22···O211ii0.80 (2)2.15 (2)2.9308 (18)163.4 (19)
O112—H112···O220.82 (2)1.81 (3)2.6317 (18)177 (2)
O212—H212···O12iii0.87 (3)1.82 (3)2.6883 (18)170 (2)
Symmetry codes: (i) x+1/2, y+1/2, z+1; (ii) x, y+1, z; (iii) x, y+1, z1/2.

Experimental details

Crystal data
Chemical formulaC6H12O3
Mr132.16
Crystal system, space groupMonoclinic, C2/c
Temperature (K)200
a, b, c (Å)21.236 (2), 13.4486 (13), 11.4351 (13)
β (°) 111.537 (10)
V3)3037.8 (6)
Z16
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.44 × 0.36 × 0.16
Data collection
DiffractometerOxford Diffraction XCalibur
Absorption correctionAnalytical
(de Meulenaer & Tompa, 1965)
Tmin, Tmax0.972, 0.988
No. of measured, independent and
observed [I > 2σ(I)] reflections
7814, 3003, 2266
Rint0.025
(sin θ/λ)max1)0.617
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.048, 0.142, 1.10
No. of reflections3003
No. of parameters188
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.19, 0.21

Computer programs: CrysAlis CCD (Oxford Diffraction, 2005), CrysAlis RED (Oxford Diffraction, 2005), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPIII (Burnett & Johnson, 1996).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O12—H12···O111i0.81 (2)2.08 (2)2.8456 (17)159 (2)
O22—H22···O211ii0.80 (2)2.15 (2)2.9308 (18)163.4 (19)
O112—H112···O220.82 (2)1.81 (3)2.6317 (18)177 (2)
O212—H212···O12iii0.87 (3)1.82 (3)2.6883 (18)170 (2)
Symmetry codes: (i) x+1/2, y+1/2, z+1; (ii) x, y+1, z; (iii) x, y+1, z1/2.
 

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