Crystallographic and spectroscopic characterization of (R)-O-acetyl­mandelic acid

Cirbes, C.; Tanski, J.M.

doi:10.1107/S2056989016008653

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Volume 72| Part 7| July 2016| Pages 901-903

https://doi.org/10.1107/S2056989016008653

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Crystallographic and spectroscopic characterization of (R)-O-acetylmandelic acid

Cady Cirbes ^a and Joseph M. Tanski ^a ^*

^aDepartment of Chemistry, Vassar College, Poughkeepsie, NY 12604, USA
^*Correspondence e-mail: jotanski@vassar.edu

Edited by S. Parkin, University of Kentucky, USA (Received 25 May 2016; accepted 29 May 2016; online 10 June 2016)

The title compound [systematic name: (R)-(−)-2-acetoxy-2-phenylacetic acid], C₁₀H₁₀O₄, is a resolved chiral ester derivative of mandelic acid. The compound contains an acetate group and a carboxylic acid group, which engage in intermolecular hydrogen bonding, forming chains extending parallel to [001] with a short donor–acceptor hydrogen-bonding distance of 2.676 (2) Å.

Keywords: crystal structure; absolute structure; hydrogen bonding; mandelic acid ester derivative.

CCDC reference: 1482445

1. Chemical context

Chiral, resolved carboxylic acids have played an important role as chiral NMR shift reagents (Lovely & Wenzel, 2008 ; Parker, 1991 ). The title compound, (R)-(−)-2-acetoxy-2-phenylacetic acid (I), commonly known as (R)-O-acetylmandelic acid, is a chiral, resolved derivative of mandelic acid. The compound may be synthesized by acetylation of the parent α-hydroxy acid with acetic anhydride in pyridine (Ornelas et al., 2013 ). When racemic, resolution of the compound with free amino acids has been demonstrated (Szeleczky et al., 2015 ). The title compound has been employed as a chiral NMR shift reagent (Parker, 1991).

2. Structural commentary

The molecular structure of the title compound (Fig. 1) shows the R confguration about carbon atom C1, and that the molecule does not engage in intramolecular or pairwise hydrogen bonding. The absolute structure parameters confirm the R assignment, with Flack x = −0.01 (4) and Hooft y = −0.02 (4), calculated with PLATON (Spek, 2009 ).

Figure 1
A view of (R)-(−)-2-acetoxy-2-phenylacetic acid (I)

with the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level.

3. Supramolecular features

The molecules pack together in the solid state via van der Waals forces and hydrogen bonding between the carboxylic acid OH group and the carbonyl oxygen atom of the ester on a neighboring molecule, O1—H1⋯O4ⁱ [symmetry code (i) −x + $[{1\over 2}]$ , −y + 1, z − $[{1\over 2}]$ ] with a donor–acceptor distance of 2.676 (2) Å (Table 1). These interactions create zigzag hydrogen-bonded chains that extend parallel to the c axis of the unit cell (Fig. 2). Notably, there is no face-to-face or edge-to-face π-stacking.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1⋯O4ⁱ	0.85 (2)	1.84 (2)	2.6761 (16)	165 (2)
Symmetry code: (i) $[-x+{\script{1\over 2}}, -y+1, z-{\script{1\over 2}}]$ .

Figure 2
A view of the intermolecular hydrogen bonding in (R)-(−)-2-acetoxy-2-phenylacetic acid (I)

that forms a one-dimensional chain. Symmetry code: (i) −x + $[{1\over 2}]$ , −y + 1, z − $[{1\over 2}]$ .

4. Database survey

The Cambridge Structural Database (Groom et al., 2016 ) contains several related mandelic acid ester structures. Related structures of resolved mandelic acid esters that differ by the nature of the ester group include (2S)-[(2S)-2-hydroxy-2-phenylethanoyloxy]phenylacetic acid (Mughal et al., 2004 ) and (1R,2R,3S,4S)-2-[(R)-mandeloxycarbonyl]bicyclo(2.2.1)heptane-3-carboxylic acid (Ohtani et al., 1991 ). The hydrogen bonding in the former differs from (I), forming an intermolecular chain with the carboxylic acid groups further cross-linked by hydrogen bonding of the alcohol moiety with the ester, whereas the latter compound exhibits pairwise dimerization of the carboxylic acid groups. A related structure with a tert-butyl ester and substituents on the phenyl ring, (S,E)-2-[2-(3-methoxy-3-oxoprop-1-en-1-yl)-4-(trifluoromethyl)phenyl]-2-(pivaloyloxy)acetic acid (Xiao et al., 2016 ), exhibits a similar one-dimensional intermolecular carboxylic acid OH⋯ester carbonyl hydrogen-bonding motif to that found in the title compound.

5. Synthesis and crystallization

(R)-(−)-2-acetoxy-2-phenylacetic acid (99%) was purchased from Aldrich Chemical Company, USA, and was used as received.

6. Analytical data

¹H NMR (Bruker Avance 300 MHz, CDCl₃): δ 2.19 (s, 3 H, CH₃), 5.93 (s, 1H, CH), 7.36–7.42 (m, 3 H, C_arylH), 7.45–7.51 (m, 2H, C_arylH), 11.76 (br s, 1H, OH). ¹³C NMR (¹³C{¹H}, 75.5 MHz, CDCl₃): δ 20.59 (CH₃), 74.02 (CH), 127.62 (C_arylH), 128.86 (C_arylH), 129.49 (C_arylH), 132.98 (C_aryl), 170.38 (CO), 174.55 (CO). IR (Thermo Nicolet iS50, ATR, cm⁻¹): 3483 (w), 3014 (v br, O—H str), 2708 (w), 2588 (w), 1752 (v s, C=O str), 1686 (v s, C=O str), 1498 (w), 1461 (w), 1412 (m), 1382 (s), 1321 (m), 1277 (s), 1259 (s), 1206 (s), 1182 (s), 1045 (s), 996 (m), 967 (m), 919 (m), 888 (m), 767 (s), 734 (s), 700 (s), 642 (m), 616 (w), 603 (w), 583 (w), 525 (s), 487 (w). GC/MS (Hewlett-Packard MS 5975/GC 7890): M-18⁺ = 176 (calc. exact mass 194.06 - water = 176).

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms on carbon were included in calculated positions and refined using a riding model with C–H = 0.95, 0.98 and 1.00 Å and U_iso(H) = 1.2, 1.5 and 1.2 × U_eq(C) of the aryl, methyl and methine C atoms, respectively. The position of the carboxylic acid hydrogen atom was found in the difference map and the atom refined semi-freely using a distance restraint d(O—H) = 0.84 Å, and U_iso(H) = 1.2U_eq(O).

Table 2
Experimental details

Crystal data
Chemical formula	C₁₀H₁₀O₄
M_r	194.18
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	125
a, b, c (Å)	9.1047 (10), 10.0086 (11), 10.5871 (11)
V (Å³)	964.75 (18)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	0.88
Crystal size (mm)	0.26 × 0.26 × 0.17

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2013 )
T_min, T_max	0.74, 0.86
No. of measured, independent and observed [I > 2σ(I)] reflections	8953, 1698, 1693
R_int	0.030
(sin θ/λ)_max (Å⁻¹)	0.595

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.025, 0.062, 1.10
No. of reflections	1698
No. of parameters	131
No. of restraints	1
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.19, −0.19
Absolute structure	Flack x determined using 691 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 ); Hooft y calculated with PLATON (Spek, 2009)
Absolute structure parameter	−0.01 (4)
Computer programs: APEX2 and SAINT (Bruker, 2013), SHELXT (Sheldrick, 2015a ), SHELXL2014 (Sheldrick, 2015b ), SHELXTL (Sheldrick, 2008 ), OLEX2 (Dolomanov et al., 2009 ), Mercury (Macrae et al., 2008 ) and PLATON (Spek, 2009).

Supporting information

CCDC reference: 1482445

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989016008653/pk2580sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016008653/pk2580Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989016008653/pk2580Isup3.cml

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008), OLEX2 (Dolomanov et al., 2009), Mercury (Macrae et al., 2008) and PLATON (Spek, 2009).

(R)-(-)-2-Acetoxy-2-phenylacetic acid top

Crystal data top

C₁₀H₁₀O₄	D_x = 1.337 Mg m⁻³
M_r = 194.18	Cu Kα radiation, λ = 1.54178 Å
Orthorhombic, P2₁2₁2₁	Cell parameters from 8300 reflections
a = 9.1047 (10) Å	θ = 4.2–66.6°
b = 10.0086 (11) Å	µ = 0.88 mm⁻¹
c = 10.5871 (11) Å	T = 125 K
V = 964.75 (18) Å³	Block, colourless
Z = 4	0.26 × 0.26 × 0.17 mm
F(000) = 408

Data collection top

Bruker APEXII CCD diffractometer	1698 independent reflections
Radiation source: Cu IuS micro-focus source	1693 reflections with I > 2σ(I)
Detector resolution: 8.3333 pixels mm^-1	R_int = 0.030
φ and ω scans	θ_max = 66.6°, θ_min = 6.1°
Absorption correction: multi-scan (SADABS; Bruker, 2013)	h = −10→10
T_min = 0.74, T_max = 0.86	k = −11→11
8953 measured reflections	l = −12→12

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.025	w = 1/[σ²(F_o²) + (0.0336P)² + 0.1385P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.062	(Δ/σ)_max < 0.001
S = 1.10	Δρ_max = 0.19 e Å⁻³
1698 reflections	Δρ_min = −0.19 e Å⁻³
131 parameters	Absolute structure: Flack x determined using 691 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013); Hooft y calculated with PLATON (Spek, 2009)
1 restraint	Absolute structure parameter: −0.01 (4)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.42132 (13)	0.46237 (13)	0.08956 (12)	0.0329 (3)
H1	0.355 (2)	0.479 (2)	0.035 (2)	0.039*
O2	0.35211 (12)	0.66275 (12)	0.16115 (11)	0.0286 (3)
O3	0.50941 (12)	0.63319 (11)	0.37499 (9)	0.0235 (3)
O4	0.29716 (12)	0.53107 (12)	0.42058 (10)	0.0273 (3)
C1	0.53382 (16)	0.53625 (15)	0.27588 (13)	0.0200 (3)
H1A	0.5199	0.4438	0.3097	0.024*
C2	0.69072 (15)	0.55447 (14)	0.23211 (13)	0.0184 (3)
C3	0.79939 (18)	0.47071 (16)	0.27844 (16)	0.0272 (4)
H3A	0.7744	0.3988	0.3329	0.033*
C4	0.94513 (18)	0.49242 (17)	0.2450 (2)	0.0346 (4)
H4A	1.0198	0.4358	0.2776	0.042*
C5	0.98206 (18)	0.59621 (18)	0.16417 (17)	0.0326 (4)
H5A	1.0818	0.6109	0.1418	0.039*
C6	0.87356 (18)	0.67809 (18)	0.11641 (16)	0.0303 (4)
H6A	0.8985	0.7482	0.0599	0.036*
C7	0.72770 (17)	0.65833 (17)	0.15078 (14)	0.0242 (3)
H7A	0.6534	0.7157	0.1187	0.029*
C8	0.42388 (15)	0.56275 (15)	0.16993 (14)	0.0201 (3)
C9	0.38220 (17)	0.62321 (16)	0.43773 (14)	0.0237 (3)
C10	0.3600 (2)	0.7365 (2)	0.52655 (17)	0.0364 (4)
H10A	0.4523	0.7555	0.5707	0.055*
H10B	0.2842	0.7128	0.5883	0.055*
H10C	0.329	0.8158	0.4792	0.055*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0273 (6)	0.0350 (6)	0.0363 (6)	0.0053 (5)	−0.0144 (5)	−0.0139 (5)
O2	0.0270 (6)	0.0289 (6)	0.0298 (6)	0.0060 (5)	−0.0008 (5)	−0.0001 (5)
O3	0.0209 (5)	0.0298 (6)	0.0198 (5)	−0.0061 (4)	0.0051 (4)	−0.0055 (4)
O4	0.0232 (5)	0.0335 (6)	0.0253 (6)	−0.0066 (5)	0.0058 (4)	0.0003 (5)
C1	0.0197 (7)	0.0209 (7)	0.0193 (7)	−0.0032 (6)	0.0012 (6)	−0.0020 (6)
C2	0.0171 (7)	0.0207 (7)	0.0173 (7)	−0.0019 (6)	−0.0001 (5)	−0.0046 (6)
C3	0.0249 (8)	0.0232 (8)	0.0334 (8)	0.0001 (7)	−0.0030 (7)	0.0014 (7)
C4	0.0214 (7)	0.0329 (9)	0.0496 (11)	0.0066 (7)	−0.0035 (8)	−0.0042 (8)
C5	0.0184 (7)	0.0424 (9)	0.0370 (9)	−0.0037 (7)	0.0061 (7)	−0.0119 (8)
C6	0.0276 (8)	0.0394 (9)	0.0238 (8)	−0.0093 (8)	0.0042 (7)	0.0016 (7)
C7	0.0215 (7)	0.0301 (8)	0.0210 (7)	−0.0005 (6)	−0.0010 (6)	0.0037 (6)
C8	0.0149 (7)	0.0237 (7)	0.0216 (7)	−0.0034 (6)	0.0036 (5)	−0.0010 (6)
C9	0.0213 (7)	0.0315 (8)	0.0184 (7)	−0.0036 (7)	0.0033 (6)	0.0021 (6)
C10	0.0390 (10)	0.0389 (10)	0.0311 (9)	−0.0082 (9)	0.0139 (8)	−0.0076 (8)

Geometric parameters (Å, º) top

O1—C8	1.3168 (19)	C3—H3A	0.95
O1—H1	0.852 (19)	C4—C5	1.387 (3)
O2—C8	1.1989 (19)	C4—H4A	0.95
O3—C9	1.3389 (18)	C5—C6	1.380 (3)
O3—C1	1.4463 (17)	C5—H5A	0.95
O4—C9	1.218 (2)	C6—C7	1.391 (2)
C1—C2	1.5128 (19)	C6—H6A	0.95
C1—C8	1.527 (2)	C7—H7A	0.95
C1—H1A	1.0	C9—C10	1.487 (2)
C2—C3	1.386 (2)	C10—H10A	0.98
C2—C7	1.391 (2)	C10—H10B	0.98
C3—C4	1.391 (2)	C10—H10C	0.98

C8—O1—H1	107.2 (15)	C4—C5—H5A	120.1
C9—O3—C1	116.28 (11)	C5—C6—C7	120.22 (16)
O3—C1—C2	106.65 (11)	C5—C6—H6A	119.9
O3—C1—C8	108.41 (11)	C7—C6—H6A	119.9
C2—C1—C8	111.91 (12)	C6—C7—C2	119.95 (14)
O3—C1—H1A	109.9	C6—C7—H7A	120.0
C2—C1—H1A	109.9	C2—C7—H7A	120.0
C8—C1—H1A	109.9	O2—C8—O1	125.26 (14)
C3—C2—C7	119.87 (14)	O2—C8—C1	124.01 (14)
C3—C2—C1	119.51 (13)	O1—C8—C1	110.72 (12)
C7—C2—C1	120.54 (13)	O4—C9—O3	122.18 (14)
C2—C3—C4	119.76 (15)	O4—C9—C10	125.84 (14)
C2—C3—H3A	120.1	O3—C9—C10	111.98 (13)
C4—C3—H3A	120.1	C9—C10—H10A	109.5
C5—C4—C3	120.37 (16)	C9—C10—H10B	109.5
C5—C4—H4A	119.8	H10A—C10—H10B	109.5
C3—C4—H4A	119.8	C9—C10—H10C	109.5
C6—C5—C4	119.83 (15)	H10A—C10—H10C	109.5
C6—C5—H5A	120.1	H10B—C10—H10C	109.5

C9—O3—C1—C2	−172.13 (12)	C4—C5—C6—C7	1.1 (3)
C9—O3—C1—C8	67.21 (15)	C5—C6—C7—C2	−1.0 (3)
O3—C1—C2—C3	98.10 (15)	C3—C2—C7—C6	−0.2 (2)
C8—C1—C2—C3	−143.51 (14)	C1—C2—C7—C6	176.71 (15)
O3—C1—C2—C7	−78.78 (16)	O3—C1—C8—O2	13.69 (19)
C8—C1—C2—C7	39.62 (18)	C2—C1—C8—O2	−103.65 (16)
C7—C2—C3—C4	1.1 (2)	O3—C1—C8—O1	−167.43 (12)
C1—C2—C3—C4	−175.84 (16)	C2—C1—C8—O1	75.23 (15)
C2—C3—C4—C5	−0.9 (3)	C1—O3—C9—O4	6.3 (2)
C3—C4—C5—C6	−0.2 (3)	C1—O3—C9—C10	−173.19 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O4ⁱ	0.85 (2)	1.84 (2)	2.6761 (16)	165 (2)
C10—H10B···O1ⁱⁱ	0.98	2.56	3.312 (2)	133

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

Acknowledgements

This work was supported by Vassar College. X-ray facilities were provided by the US National Science Foundation (Grant Nos. 0521237 and 0911324 to JMT). We acknowledge the Salmon Fund of Vassar College for funding publication expenses.

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