2-(2-Oxazolin-2-yl)benzene-1,4-diol: X-ray and density functional theory studies

In the crystal structure of the title compound, C₉H₉NO₃, there are strong intra­molecular O—H...N and inter­molecular O—H...O hydrogen bonds which, together with weak inter­molecular C—H...O hydrogen bonds, lead to the formation of infinite chains of mol­ecules. The calculated inter­molecular hydrogen-bond energies are −11.3 and −2.7 kJ mol⁻¹, respectively, showing the dominant role of the O—H...O hydrogen bonding. A natural bond orbital analysis revealed the electron contribution of the lone pairs of the oxazoline N and O atoms, and of the two hydr­oxy O atoms, to the order of the relevant bonds.

S1. Comment

The present study of the title compound, (I), is a continuation of our previous studies of bifunctional monophenols (Langer et al., 2005, 2006), which are monomers of the AB type that provide linear poly(etheramide)s in a thermally initiated polymerization (Lustoň et al., 2006). According to Flory (1952), analogous compounds containing two phenolic groups, hence compounds of the AB₂ type, provide hyperbranched polymers during thermal treatment (Lustoň & Kronek, 2007; Huber et al., 1999). Therefore, it was of interest to study also the crystal structure of these monomers, compounds with two phenolic groups and a 2-oxazoline ring. In this paper, we present the results for (I), one of the six possible isomers.

The atom-numbering scheme, together with the corresponding atomic displacement ellipsoid plot for (I), are shown in Fig. 1. Selected geometric parameters for (I) are listed in Table 1. The C1—C4 bond in (I) is significantly shorter than the usual single C—C bond (Table 1; Standard reference?), indicating weak conjugation between the 2-oxazoline ring substituted at the C-2 position (C1) and the benzene ring. The acute angle between the planes of the oxazoline and benzene rings is 2.76 (15)°. The 2-oxazoline ring in (I) is almost planar [χ² = 63.5, maximum deviation 0.012 (2) Å], as it is, for example, for 2-(2-hydroxyphenyl)-2-oxazoline and 2-(4-hydroxyphenyl)-2-oxazoline (Langer et al., 2005).

A natural bond orbital (NBO) analysis (Foster & Weinhold, 1980) reveals that the electrons of the lone pairs of atoms N1, O1, O5 and O8 participate in the electron density within the N1═C1, O1—C1, O5—C5 and O8—C8 bonds. The Wiberg indices illustrated in Fig. 2 show bond orders in the molecule of (I).

There are strong hydrogen bonds in the structure of (I), of the O—H···N (intramolecular) and O—H···O (intermolecular) types, as well as weak hydrogen bonds of the C—H···O type (intermolecular) (Fig.3. and Table 2). Calculations using the GAUSSIAN98 program package (Frisch et al., 1998) confirmed the experimental data, with more realistic H···A distances and D—H···A angles (Table 2).

The hydrogen-bonding pattern can be described using graph theory (Bernstein et al., 1995; Grell et al., 1999). On the first-level graph set, S(6) intramolecular strings formed by hydrogen bonds a, C(7) chains formed by hydrogen bonds b and C(6) chains formed by hydrogen bonds c were identified (see Fig. 3 for definitions of hydrogen bonds). On the second-level graph set, chains C²₂(11) and rings R⁴₄(22), formed by hydrogen bonds b and c, could be recognized.

The energy of the intermolecular hydrogen bonds was calculated and corrected to BSSE [Please define] using a standard procedure (Boys & Bernardi, 1970). The energy of hydrogen bond b was estimated to be approximately -11.3 kJ mol^-1, and that of hydrogen bond c - 2.7 kJ mol^-1. Hydrogen bond b plays a dominant role in the intermolecular interactions in the structure of (I) (Fig. 3).

Related literature

For related literature, see: Becke (1993); Bernstein et al. (1995); Boys & Bernardi (1970); Flory (1952); Foster & Weinhold (1980); Frisch (1998); Glendening et al. (1993); Grell et al. (1999); Huber et al. (1999); Langer et al. (2005, 2006); Lustoň & Kronek (2007); Lustoň et al. (2006).

S2. Experimental

The relevant data for the synthetic and analytical methods, as well as a description of the instruments and materials used for the preparation and characterization of 2-(2,5-dihydroxyfenyl)-2-oxazoline, have been reported previously (Lustoň & Kronek, 2007). After recrystallization from toluene, well developed yellow needles of the (I) were obtained (m.p. 388–389 K).

S3. Refinement

H atoms were constrained to ideal geometry using an appropriate riding model and refined isotropically. For the hydroxyl groups, the O—H distances (0.84 Å) and C—O—H angles (109.5°) were kept fixed, while the torsion angles were allowed to refine, with the starting positions based on the circular Fourier synthesis.

In the absence of significant anomalous scattering, the absolute configuration could not be reliably determined. Therefore, Friedel pairs were merged and any references to the Flack parameter have been removed.

The theoretical investigation of the hydrogen bonds was performed using the GAUSSIAN98 program package (Frisch et al., 1998) at the B3LYP/6–31G** level of theory (Becke, 1993). A cluster (66 atoms) consisted of three neighbouring molecules of (I), which represented hydrogen bonds existing in this compound. Only partial optimization of the positions of the H atoms participating in the hydrogen bonds was carried out. Natural bond orbital (NBO) calculations were carried out by means of the NBO program (Glendening et al., 1993) included in the GAUSSIAN98 package.

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT and SADABS (Sheldrick, 2003); program(s) used to solve structure: SHELXTL (Bruker, 2003); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented as small spheres of arbitrary radii.
	Fig. 2. Wiberg bond orders calculated for an isolated molecule of (I) using NBO formalism. Arrows indicate predicted transfers of electron density from lone pairs.
	Fig. 3. The hydrogen-bonding pattern in the crystal structure of (I). See Table 2 for symbols and symmetry codes.

2-(2-Oxazolin-2-yl)benzene-1,4-diol

Crystal data

C9H9NO3	Dx = 1.383 Mg m^−3
Mr = 179.17	Melting point: 389 K
Orthorhombic, Fdd2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: F 2 -2d	Cell parameters from 3265 reflections
a = 24.4297 (3) Å	θ = 2.6–26.4°
b = 31.7167 (7) Å	µ = 0.11 mm^−1
c = 4.4409 (1) Å	T = 173 K
V = 3440.94 (12) Å^3	Needle, yellow
Z = 16	1.00 × 0.06 × 0.04 mm
F(000) = 1504

Data collection

Bruker SMART CCD area-detector diffractometer	1010 independent reflections
Radiation source: fine-focus sealed tube	840 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.073
ω scans	θmax = 26.4°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −30→30
Tmin = 0.513, Tmax = 0.996	k = −39→38
9919 measured reflections	l = −5→5

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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.096	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.055P)^2 + 2.545P] where P = (Fo^2 + 2Fc^2)/3
1010 reflections	(Δ/σ)max < 0.001
129 parameters	Δρmax = 0.20 e Å^−3
1 restraint	Δρmin = −0.18 e Å^−3

Special details

Experimental. Data were collected at 173 K using a Siemens SMART CCD diffractometer equipped with an LT-2a low-temperature device. An almost-full sphere of reciprocal space was scanned by 0.3° steps in ω with a crystal-to-detector distance of 3.97 cm, 30 s per frame. The preliminary orientation matrix was obtained from the first 100 frames using SMART (Bruker, 2003). The collected frames were integrated using the preliminary orientation matrix, which was updated every 100 frames. Final cell parameters were obtained by refinement on the position of 3265 reflections with I>10σ(I), after integration of all the frames data using SAINT (Bruker, 2003).

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
O1	−0.13506 (6)	0.06136 (5)	0.5991 (5)	0.0329 (5)
O5	0.02876 (7)	0.06893 (6)	0.3460 (5)	0.0382 (5)
H5	0.0134	0.0532	0.4727	0.065 (12)*
O8	−0.11289 (7)	0.19201 (6)	−0.0585 (6)	0.0433 (6)
H8	−0.1454	0.1875	−0.0050	0.056 (11)*
N1	−0.04979 (8)	0.03503 (6)	0.6357 (6)	0.0330 (6)
C1	−0.08141 (9)	0.06343 (7)	0.5294 (6)	0.0250 (6)
C2	−0.08311 (11)	0.00695 (8)	0.8252 (7)	0.0342 (7)
H2A	−0.0707	0.0079	1.0374	0.045 (9)*
H2B	−0.0812	−0.0225	0.7523	0.034 (7)*
C3	−0.14114 (11)	0.02448 (8)	0.7942 (8)	0.0385 (7)
H3A	−0.1658	0.0034	0.7015	0.060 (10)*
H3B	−0.1561	0.0327	0.9931	0.050 (10)*
C4	−0.06306 (10)	0.09721 (7)	0.3334 (6)	0.0248 (6)
C5	−0.00738 (9)	0.09864 (7)	0.2496 (7)	0.0287 (6)
C6	0.01071 (10)	0.13077 (7)	0.0664 (7)	0.0340 (7)
H6	0.0482	0.1318	0.0096	0.028 (7)*
C7	−0.02479 (10)	0.16149 (8)	−0.0358 (8)	0.0345 (7)
H7	−0.0118	0.1834	−0.1631	0.031 (7)*
C8	−0.07983 (10)	0.16025 (7)	0.0484 (7)	0.0304 (6)
C9	−0.09858 (10)	0.12836 (7)	0.2298 (7)	0.0275 (6)
H9	−0.1361	0.1275	0.2853	0.025 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0230 (9)	0.0299 (9)	0.0459 (12)	0.0017 (7)	0.0112 (9)	0.0110 (10)
O5	0.0211 (9)	0.0378 (10)	0.0557 (14)	0.0069 (8)	0.0053 (9)	0.0138 (11)
O8	0.0261 (10)	0.0389 (10)	0.0650 (17)	0.0037 (8)	0.0027 (10)	0.0225 (11)
N1	0.0292 (11)	0.0287 (11)	0.0411 (15)	0.0045 (9)	0.0029 (11)	0.0086 (11)
C1	0.0204 (11)	0.0264 (12)	0.0283 (15)	0.0003 (9)	0.0045 (11)	−0.0032 (12)
C2	0.0375 (15)	0.0275 (12)	0.0376 (17)	0.0008 (11)	0.0080 (14)	0.0043 (14)
C3	0.0376 (15)	0.0319 (14)	0.0460 (19)	−0.0023 (12)	0.0113 (14)	0.0124 (15)
C4	0.0208 (11)	0.0243 (11)	0.0293 (14)	−0.0003 (9)	0.0039 (10)	−0.0026 (12)
C5	0.0198 (12)	0.0284 (13)	0.0380 (17)	0.0008 (10)	0.0015 (12)	−0.0014 (13)
C6	0.0189 (11)	0.0380 (14)	0.0450 (18)	−0.0011 (11)	0.0049 (13)	0.0070 (15)
C7	0.0286 (13)	0.0333 (13)	0.0414 (17)	−0.0053 (11)	0.0042 (13)	0.0105 (13)
C8	0.0234 (12)	0.0293 (12)	0.0385 (17)	0.0000 (10)	−0.0016 (12)	0.0052 (13)
C9	0.0193 (11)	0.0291 (12)	0.0342 (16)	−0.0011 (10)	0.0018 (11)	0.0005 (12)

Geometric parameters (Å, º)

O1—C1	1.348 (3)	C3—H3A	0.9900
N1—C1	1.277 (3)	C3—H3B	0.9900
C1—C4	1.451 (3)	C4—C9	1.393 (3)
O1—C3	1.463 (3)	C4—C5	1.411 (3)
O5—C5	1.361 (3)	C5—C6	1.377 (3)
O5—H5	0.8400	C6—C7	1.381 (4)
O8—C8	1.375 (3)	C6—H6	0.9500
O8—H8	0.8400	C7—C8	1.396 (3)
N1—C2	1.471 (3)	C7—H7	0.9500
C2—C3	1.529 (4)	C8—C9	1.372 (4)
C2—H2A	0.9900	C9—H9	0.9500
C2—H2B	0.9900
C1—O1—C3	105.88 (18)	C9—C4—C5	119.4 (2)
C5—O5—H5	109.5	C9—C4—C1	121.9 (2)
C8—O8—H8	109.5	C5—C4—C1	118.7 (2)
C1—N1—C2	107.7 (2)	O5—C5—C6	119.4 (2)
N1—C1—O1	117.9 (2)	O5—C5—C4	121.4 (2)
N1—C1—C4	123.7 (2)	C6—C5—C4	119.3 (2)
O1—C1—C4	118.3 (2)	C5—C6—C7	121.0 (2)
N1—C2—C3	104.0 (2)	C5—C6—H6	119.5
N1—C2—H2A	111.0	C7—C6—H6	119.5
C3—C2—H2A	111.0	C8—C7—C6	119.8 (2)
N1—C2—H2B	111.0	C8—C7—H7	120.1
C3—C2—H2B	111.0	C6—C7—H7	120.1
H2A—C2—H2B	109.0	C9—C8—O8	123.1 (2)
O1—C3—C2	104.5 (2)	C9—C8—C7	120.0 (2)
O1—C3—H3A	110.9	O8—C8—C7	116.9 (2)
C2—C3—H3A	110.9	C8—C9—C4	120.6 (2)
O1—C3—H3B	110.9	C8—C9—H9	119.7
C2—C3—H3B	110.9	C4—C9—H9	119.7
H3A—C3—H3B	108.9
C2—N1—C1—O1	−1.9 (4)	C1—C4—C5—O5	0.7 (4)
C2—N1—C1—C4	179.4 (2)	C9—C4—C5—C6	−0.1 (4)
C3—O1—C1—N1	0.7 (3)	C1—C4—C5—C6	−179.3 (2)
C3—O1—C1—C4	179.5 (2)	O5—C5—C6—C7	180.0 (3)
C1—N1—C2—C3	2.2 (3)	C4—C5—C6—C7	0.0 (4)
C1—O1—C3—C2	0.7 (3)	C5—C6—C7—C8	0.4 (4)
N1—C2—C3—O1	−1.7 (3)	C6—C7—C8—C9	−0.6 (4)
N1—C1—C4—C9	−178.0 (3)	C6—C7—C8—O8	179.3 (3)
O1—C1—C4—C9	3.4 (4)	O8—C8—C9—C4	−179.5 (3)
N1—C1—C4—C5	1.2 (4)	C7—C8—C9—C4	0.5 (4)
O1—C1—C4—C5	−177.5 (3)	C5—C4—C9—C8	−0.1 (4)
C9—C4—C5—O5	179.9 (2)	C1—C4—C9—C8	179.0 (3)