(4-tert-Butyl­phenyl)­acetic acid

In the title compound, C₁₂H₁₆O₂, the plane of the carboxylic acid group is almost perpendicular to the benzene ring [dihedral angle 80.9 (3)°] and the tert-butyl unit is disordered over two sets of sites in a 0.503 (6):0.497 (6) ratio. In the crystal structure, centrosymmetric dimers arise from pairs of O—H...O hydrogen bonds involving the carboxylic acid groups.

Key indicators

• Single-crystal X-ray study
• T = 295 K
• Mean [sigma](C-C) = 0.005 Å
• Disorder in main residue
• R factor = 0.075
• wR factor = 0.220
• Data-to-parameter ratio = 15.6

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT241_ALERT_2_B Check High      Ueq as Compared to Neighbors for         C7
PLAT242_ALERT_2_B Check Low       Ueq as Compared to Neighbors for         C8
PLAT242_ALERT_2_B Check Low       Ueq as Compared to Neighbors for         C9

Alert level C
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C1
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C4
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.21
PLAT301_ALERT_3_C Main Residue  Disorder .........................      18.00 Perc.
PLAT340_ALERT_3_C Low Bond Precision on C-C Bonds (x 1000) Ang ...          5

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

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   6 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 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

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S1. Comment

As part of investigation on the nature of aromatic stacking (Liu et al., 2006), the title compound, (I), has recently been prepared in Prof. Liu's laboratory by the hydrolization reaction of 2-(4-tert-butylphenyl)-1-morpholinoethanethione. Herein we present its X-ray structure (Fig. 1).

The C8—O1 bond distance of 1.309 (3) Å is significantly longer than the C8—O2 bond distance of 1.191 (3) Å. The carboxyl group is nearly perpendicular to the benzene plane, the dihedral angle being 80.9 (3)°. The adjacent molecules are linked together via O—H···O hydrogen bonding (Table 1) to form a centrosymmetric supramolecular dimer as shown in Fig. 2, which is comparable to that found in 4-tert-butylbenzoic acid (van Koningsveld, 1982).

Related literature

For general background, see: Liu et al. (2006). For a related structure, see: van Koningsveld (1982).

S2. Experimental

The title compound was prepared by a hydrolization reaction of 2-(4-tert-butylphenyl)-1-morpholinoethanethione (55 g) in a solution containing CH₃COOH (150 ml), H₂SO₄ (25 ml, 98%) and water (30 ml) at 390 K until the reaction mixture changed colour to dark-green. After cooling to room temperature, the solid product was separated from the reaction mixture, and colourless prisms of (I) were obtained by recrystallization of the solid product from an ethanol–water solution (1:1 v/v) after 2 months.

S3. Refinement

The carboxyl H atom was located in a difference Fourier map and refined as riding in its as-found relative position with U_iso(H) = 1.5U_eq(O). The methyl H atoms were placed in calculated positions with C—H = 0.96 Å and torsion angles were refined to fit the electron density with U_iso(H) = 1.5U_eq(C). The other H atoms were placed in calculated positions with C—H = 0.97 Å (methylene) or 0.93 Å (aromatic), and refined in riding mode with U_iso(H) = 1.2U_eq(C). The tert-butyl group is disordered over two positions. Occupancies were initially refined and converged to 0.503 (6) and 0.497 (6), respectively; in the final cycles of refinement, the occupancies were fixed at 0.5, and displacement parameters for the disordered carbon atoms were constrained to be identical.

Computing details

Data collection: SMART (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. The molecular structure of (I) with 30% probability displacement ellipsoids (arbitrary spheres for H atoms). Double dashed lines indicate one of disordered components.
	Fig. 2. The unit cell packing diagram showing the supra-molecular dimeric structure linked by the hydrogen bonding (dashed lines).

(4-tert-Butylphenyl)acetic acid

Crystal data

C12H16O2	F(000) = 832
Mr = 192.25	Dx = 1.097 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 2180 reflections
a = 11.209 (2) Å	θ = 2.8–25.0°
b = 12.442 (3) Å	µ = 0.07 mm^−1
c = 17.250 (5) Å	T = 295 K
β = 104.625 (12)°	Prism, colourless
V = 2327.8 (10) Å^3	0.30 × 0.23 × 0.16 mm
Z = 8

Data collection

Bruker APEXII CCD diffractometer	1375 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.025
Graphite monochromator	θmax = 25.0°, θmin = 2.4°
Detector resolution: 10 pixels mm^-1	h = −13→12
ϕ and ω scans	k = −11→14
5829 measured reflections	l = −20→17
2047 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)] = 0.075	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.220	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0943P)^2 + 2.2585P] where P = (Fo^2 + 2Fc^2)/3
2047 reflections	(Δ/σ)max = 0.003
131 parameters	Δρmax = 0.30 e Å^−3
0 restraints	Δρmin = −0.25 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. 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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.3924 (2)	0.7974 (2)	0.56682 (15)	0.1086 (10)
H1	0.3088	0.7959	0.5607	0.163*
O2	0.35115 (18)	0.70221 (19)	0.45614 (13)	0.0801 (7)
C1	0.6042 (2)	0.6780 (3)	0.45859 (19)	0.0733 (9)
C2	0.6468 (3)	0.5756 (3)	0.4707 (2)	0.0904 (11)
H2	0.6448	0.5403	0.5179	0.108*
C3	0.6930 (3)	0.5233 (3)	0.41409 (19)	0.0838 (10)
H3	0.7216	0.4532	0.4244	0.101*
C4	0.6984 (2)	0.5702 (2)	0.34325 (15)	0.0582 (7)
C5	0.6512 (3)	0.6719 (3)	0.33048 (18)	0.0714 (9)
H5	0.6498	0.7060	0.2823	0.086*
C6	0.6056 (3)	0.7253 (3)	0.3870 (2)	0.0819 (10)
H6	0.5753	0.7948	0.3764	0.098*
C7	0.5608 (3)	0.7390 (4)	0.5219 (2)	0.1051 (14)
H7A	0.5971	0.7062	0.5735	0.126*
H7B	0.5917	0.8120	0.5237	0.126*
C8	0.4244 (3)	0.7432 (3)	0.51024 (17)	0.0653 (8)
C9	0.7547 (3)	0.5128 (3)	0.28348 (18)	0.0732 (9)
C10A	0.8271 (11)	0.6028 (9)	0.2430 (6)	0.1125 (15)	0.497 (6)
H10A	0.8575	0.5698	0.2015	0.169*	0.497 (6)
H10B	0.8950	0.6315	0.2833	0.169*	0.497 (6)
H10C	0.7713	0.6598	0.2207	0.169*	0.497 (6)
C11A	0.8538 (13)	0.4343 (11)	0.3166 (9)	0.1125 (15)	0.497 (6)
H11A	0.8187	0.3714	0.3344	0.169*	0.497 (6)
H11B	0.9124	0.4660	0.3611	0.169*	0.497 (6)
H11C	0.8944	0.4147	0.2759	0.169*	0.497 (6)
C12A	0.6605 (9)	0.4711 (9)	0.2153 (6)	0.1125 (15)	0.497 (6)
H12A	0.6206	0.5299	0.1829	0.169*	0.497 (6)
H12B	0.6006	0.4309	0.2344	0.169*	0.497 (6)
H12C	0.6985	0.4251	0.1838	0.169*	0.497 (6)
C10B	0.7561 (11)	0.5733 (9)	0.2101 (6)	0.1125 (15)	0.503 (6)
H10D	0.7923	0.5297	0.1761	0.169*	0.503 (6)
H10E	0.8037	0.6377	0.2243	0.169*	0.503 (6)
H10F	0.6732	0.5917	0.1823	0.169*	0.503 (6)
C11B	0.8802 (13)	0.4692 (11)	0.3269 (8)	0.1125 (15)	0.503 (6)
H11D	0.8717	0.4232	0.3698	0.169*	0.503 (6)
H11E	0.9342	0.5279	0.3482	0.169*	0.503 (6)
H11F	0.9142	0.4289	0.2900	0.169*	0.503 (6)
C12B	0.6679 (9)	0.4091 (9)	0.2531 (6)	0.1125 (15)	0.503 (6)
H12D	0.5836	0.4318	0.2348	0.169*	0.503 (6)
H12E	0.6756	0.3592	0.2965	0.169*	0.503 (6)
H12F	0.6931	0.3750	0.2099	0.169*	0.503 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0599 (14)	0.172 (3)	0.0991 (17)	−0.0057 (14)	0.0303 (12)	−0.0708 (17)
O2	0.0532 (12)	0.1151 (18)	0.0758 (14)	−0.0020 (11)	0.0231 (10)	−0.0310 (12)
C1	0.0408 (15)	0.112 (3)	0.0682 (19)	0.0018 (15)	0.0160 (13)	−0.0220 (18)
C2	0.098 (3)	0.114 (3)	0.068 (2)	0.007 (2)	0.0381 (19)	0.0096 (19)
C3	0.105 (3)	0.078 (2)	0.078 (2)	0.0180 (19)	0.0417 (19)	0.0145 (17)
C4	0.0506 (15)	0.0689 (17)	0.0574 (15)	0.0100 (13)	0.0178 (12)	0.0069 (13)
C5	0.0659 (18)	0.084 (2)	0.0675 (18)	0.0235 (16)	0.0221 (14)	0.0174 (15)
C6	0.064 (2)	0.086 (2)	0.094 (2)	0.0292 (16)	0.0180 (17)	−0.0029 (18)
C7	0.0542 (19)	0.171 (4)	0.091 (2)	0.003 (2)	0.0214 (17)	−0.053 (3)
C8	0.0546 (17)	0.086 (2)	0.0594 (16)	0.0042 (14)	0.0218 (14)	−0.0110 (15)
C9	0.0687 (19)	0.091 (2)	0.0630 (17)	0.0215 (16)	0.0231 (15)	0.0022 (16)
C10A	0.116 (3)	0.136 (4)	0.098 (3)	0.029 (3)	0.050 (3)	−0.008 (2)
C11A	0.116 (3)	0.136 (4)	0.098 (3)	0.029 (3)	0.050 (3)	−0.008 (2)
C12A	0.116 (3)	0.136 (4)	0.098 (3)	0.029 (3)	0.050 (3)	−0.008 (2)
C10B	0.116 (3)	0.136 (4)	0.098 (3)	0.029 (3)	0.050 (3)	−0.008 (2)
C11B	0.116 (3)	0.136 (4)	0.098 (3)	0.029 (3)	0.050 (3)	−0.008 (2)
C12B	0.116 (3)	0.136 (4)	0.098 (3)	0.029 (3)	0.050 (3)	−0.008 (2)

Geometric parameters (Å, º)

O1—C8	1.309 (3)	C9—C11B	1.517 (15)
O1—H1	0.9169	C9—C12B	1.621 (11)
O2—C8	1.191 (3)	C9—C10A	1.639 (11)
C1—C2	1.358 (5)	C10A—H10A	0.9600
C1—C6	1.371 (5)	C10A—H10B	0.9600
C1—C7	1.508 (4)	C10A—H10C	0.9600
C2—C3	1.379 (4)	C11A—H11A	0.9600
C2—H2	0.9300	C11A—H11B	0.9600
C3—C4	1.369 (4)	C11A—H11C	0.9600
C3—H3	0.9300	C12A—H12A	0.9600
C4—C5	1.368 (4)	C12A—H12B	0.9600
C4—C9	1.517 (4)	C12A—H12C	0.9600
C5—C6	1.381 (4)	C10B—H10D	0.9600
C5—H5	0.9300	C10B—H10E	0.9600
C6—H6	0.9300	C10B—H10F	0.9600
C7—C8	1.491 (4)	C11B—H11D	0.9600
C7—H7A	0.9700	C11B—H11E	0.9600
C7—H7B	0.9700	C11B—H11F	0.9600
C9—C12A	1.463 (10)	C12B—H12D	0.9600
C9—C10B	1.476 (10)	C12B—H12E	0.9600
C9—C11A	1.480 (15)	C12B—H12F	0.9600
C8—O1—H1	111.6	C10B—C9—C12B	105.3 (5)
C2—C1—C6	117.3 (3)	C4—C9—C12B	106.0 (4)
C2—C1—C7	121.7 (3)	C11B—C9—C12B	106.3 (6)
C6—C1—C7	121.0 (4)	C12A—C9—C10A	103.5 (6)
C1—C2—C3	120.9 (3)	C11A—C9—C10A	102.2 (7)
C1—C2—H2	119.5	C4—C9—C10A	107.7 (4)
C3—C2—H2	119.5	C9—C10A—H10A	109.5
C4—C3—C2	122.7 (3)	C9—C10A—H10B	109.5
C4—C3—H3	118.7	C9—C10A—H10C	109.5
C2—C3—H3	118.7	C9—C11A—H11A	109.5
C5—C4—C3	115.8 (3)	C9—C11A—H11B	109.5
C5—C4—C9	122.4 (3)	C9—C11A—H11C	109.5
C3—C4—C9	121.7 (3)	C9—C12A—H12A	109.5
C4—C5—C6	121.9 (3)	C9—C12A—H12B	109.5
C4—C5—H5	119.0	C9—C12A—H12C	109.5
C6—C5—H5	119.0	C9—C10B—H10D	109.5
C1—C6—C5	121.3 (3)	C9—C10B—H10E	109.5
C1—C6—H6	119.4	H10D—C10B—H10E	109.5
C5—C6—H6	119.4	C9—C10B—H10F	109.5
C8—C7—C1	115.3 (3)	H10D—C10B—H10F	109.5
C8—C7—H7A	108.5	H10E—C10B—H10F	109.5
C1—C7—H7A	108.5	C9—C11B—H11D	109.5
C8—C7—H7B	108.5	C9—C11B—H11E	109.5
C1—C7—H7B	108.5	H11D—C11B—H11E	109.5
H7A—C7—H7B	107.5	C9—C11B—H11F	109.5
O2—C8—O1	122.7 (3)	H11D—C11B—H11F	109.5
O2—C8—C7	124.9 (3)	H11E—C11B—H11F	109.5
O1—C8—C7	112.4 (3)	C9—C12B—H12D	109.5
C12A—C9—C11A	113.3 (6)	C9—C12B—H12E	109.5
C12A—C9—C4	112.0 (4)	H12D—C12B—H12E	109.5
C10B—C9—C4	116.0 (4)	C9—C12B—H12F	109.5
C11A—C9—C4	116.6 (6)	H12D—C12B—H12F	109.5
C10B—C9—C11B	113.3 (7)	H12E—C12B—H12F	109.5
C4—C9—C11B	109.0 (5)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^i	0.92	1.74	2.659 (3)	176

Symmetry code: (i) −x+1/2, −y+3/2, −z+1.