2-Formylthymol oxime

The structure of the title compound [systematic name: 2-hy­droxy-6-methyl-3-(1-methylethyl)benzaldehyde oxime] C₁₁H₁₅NO₂, exhibits intra- as well as inter­molecular hydrogen bonding, involving participation of the phenolic OH group in intra­molecular hydrogen bonding and the hydroxyl group of the oxime in inter­molecular hydrogen bonding. The H atom of the phenolic hydroxyl group forms a strong O—H...N intra­molecular hydrogen bond with an O...N distance of 2.5788 (14) Å, which is in the middle of the expected range for such hydrogen bonds. The H atom of the hydroxyl group (in the oxime functionality) forms a weaker hydrogen bond with the phenolic hydroxyl group of a neighboring mol­ecule [O...O = 2.8317 (14) Å], forming an extended chain, as expected for phenolic aldoximes which have bulky substituents on the aryl ring.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.045
• wR factor = 0.137
• Data-to-parameter ratio = 19.6

checkCIF/PLATON results

No syntax errors found



Alert level C
ABSTM02_ALERT_3_C  The ratio of expected to reported Tmax/Tmin(RR') is < 0.90
            Tmin and Tmax reported:      0.716     0.928
            Tmin(prime) and Tmax expected:      0.954     0.974
            RR(prime) =      0.787
            Please check that your absorption correction is appropriate.
PLAT061_ALERT_3_C Tmax/Tmin Range Test RR' too Large .............       0.79
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       1.05
PLAT125_ALERT_4_C No _symmetry_space_group_name_Hall Given .......          ?
PLAT199_ALERT_1_C Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_C Check the Reported _diffrn_ambient_temperature .        293 K

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

   2 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
   2 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion

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S1. Comment

Thymol is a naturally occurring phenolic monoterpenoid. It possesses an ecological role and shows a broad spectrum of biological activities (Desai & Shah, 2003). In order to enhance the overall biological activity of thymol, derivatives such as nitroso, amino, azomethine, 4-thiazolidinones, 2-azetidinones and 4-imidazolinones have been prepared (Vashai et al., 1995). On the other hand, derivatization of the hydroxyl group of thymol to ether and esters has resulted in an increase in biological activities. A structure–activity correlation has also been established in this series of compounds and the overall activity has been found to depend on the nature and position of the functional groups. Thus, thymol was derivatized to 2-formyl thymol oxime, (I), to utilize it for the preparation of metal complexes, as a number of metal–oxime complexes are known to have biological significance (Chakravorty, 1974; Lumme et al., 1984; Jayaraju & Kondapi, 2001). We present the structure of (I) here.

Compound (I) is a member of a general class of phenolic oximes (Smith et al., 2003). These compounds have found extensive use in industry, mainly as extractants for copper (Kordosky, 2002), but also as anticorrosives in protective coatings (Thorpe et al., 1999). Another feature of the phenolic oxime ligands is their propensity (Chaudhuri et al., 1993; Bill et al., 1997) to form polynuclear complexes in which both the oxime and phenolate functions can act as bridging units.

Elemental analysis for (I) gave a satisfactory fit to the formula C₁₁H₁₅NO₂. Table 1 contains selected bond lengths and angles. A view of the molecule and unit-cell content are shown in Figs. 1 and 2. The average length of the benzene ring bonds is 1.396 (12) Å, which is in good agreement with generally accepted values.

Hydrogen bonding is a major feature of the structures of phenolic oximes. This results from the high density of hydrogen-bonding donors and acceptors per molecule. Invariably, the phenolic H atom forms an intramolecular hydrogen bond to the N atom of the oxime group, giving a six-membered ring. Since the phenolic H atom is often not found in Fourier difference maps, this interaction is usually characterized in terms of the phenolic O to oximic N separation. This distance varies little between structures, with a maximum value of 2.65 Å and a minimum of 2.51 Å. However, a general trend is that aldoximes have a greater phenolic O···N distance than the ketoximes (Smith et al., 2003). In all of the free ligand structures, the molecules associate via intermolecular hydrogen bonding. These structures fall into two categories. Dimers result from the interaction of the oximic H atom with an adjacent phenolic O atom to produce a pseudomacrocyclic ligand with a 14-membered inner great ring. This structure is only seen for aldoximes with no substituents or only monatomic substituents on the aromatic ring (Smith et al., 2003).

The introduction of groups which remove planarity in the molecule appears to stop efficient packing of dimeric units in the crystal structure and, instead, a polymeric structure, [(H₂sal)_n], is observed. This is true for all phenolic ketoximes and for phenolic aldoximes which have bulky substituents on the aryl ring (Smith et al., 2003).

The title compound exhibits intra- as well as intermolecular hydrogen bonding (Table 2), involving participation of the phenolic OH moiety in intramolecular hydrogen bonding and the hydroxyl group of the oxime in intermolecular hydrogen bonding, as indicated above. The H atom of the phenolic hydroxyl group forms a strong O1—H···N1 intramolecular hydrogen bond with an O1···N1 distance of 2.5788 (14) Å, which is in the middle of the expected range for such hydrogen bonds (Smith et al., 2003).

The H atom of the hydroxyl group (in the oxime functionality) attached to atom N1 forms a weaker hydrogen bond with the phenolic hydroxyl group of a neighboring molecule [O2···O1 = 2.8317 (14) Å], forming an extended chain, as expected for phenolic aldoximes which have bulky substituents on the aryl ring (Smith et al., 2003).

S2. Experimental

The title compound was prepared by the condensation of 2-formyl thymol (obtained by ortho-formylation of thymol) with hydroxylamine hydrochloride in ethanol. [Please give brief details of quantities or molar ratios] Yellow crystals of (I) suitable for X-ray diffraction were obtained upon slow evaporation of the reaction mixture.

S3. Refinement

H atoms were included in their idealized geometries and constrained to ride on their attached atoms. Methyl H atoms were constrained to an ideal geometry, with C—H distances of 0.96 Å and U_iso(H) = 1.5U_eq(C), but each group was allowed to rotate freely about its C—C bond. All other H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with O—H = 0.82 Å, aromatic C—H = 0.93 Å and methine C—H = 0.98 Å; for these H atoms, U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1998); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the title compound, showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 20% probability level and H atoms are represented by circles of arbitrary size.
	Fig. 2. The molecular packing of the title compound, viewed along the b axis. Dotted lines indicate the hydrogen-bonding interactions.

2-Formyl thymol oxime

Crystal data

C11H15NO2	F(000) = 416
Mr = 193.24	Dx = 1.208 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 8.8517 (7) Å	Cell parameters from 4359 reflections
b = 9.0145 (7) Å	θ = 2.5–28.2°
c = 13.5956 (10) Å	µ = 0.08 mm^−1
β = 101.698 (2)°	T = 293 K
V = 1062.31 (14) Å^3	Irregular, pale yellow
Z = 4	0.55 × 0.45 × 0.32 mm

Data collection

Bruker SMART 1K CCD area-detector diffractometer	2592 independent reflections
Radiation source: fine-focus sealed tube	1897 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
ϕ and ω scans	θmax = 28.3°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	h = −10→11
Tmin = 0.716, Tmax = 0.928	k = −10→11
8098 measured reflections	l = −17→18

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.137	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0689P)^2 + 0.1206P] where P = (Fo^2 + 2Fc^2)/3
2592 reflections	(Δ/σ)max = 0.007
132 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.17 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
O1	0.10567 (11)	0.43403 (10)	0.72775 (7)	0.0449 (3)
H1O	0.1386	0.3528	0.7149	0.067*
O2	0.17161 (13)	0.04888 (11)	0.61086 (9)	0.0596 (3)
H2O	0.2440	0.0243	0.6556	0.089*
N1	0.11426 (14)	0.18593 (12)	0.63462 (9)	0.0427 (3)
C1	−0.02431 (14)	0.46760 (14)	0.65762 (9)	0.0335 (3)
C2	−0.08023 (14)	0.36816 (13)	0.57850 (9)	0.0328 (3)
C21	−0.00284 (15)	0.22718 (14)	0.56953 (10)	0.0389 (3)
H21A	−0.0400	0.1660	0.5149	0.047*
C3	−0.21369 (15)	0.40662 (14)	0.50728 (9)	0.0370 (3)
C31	−0.28054 (18)	0.30561 (17)	0.42058 (11)	0.0483 (4)
H31A	−0.3700	0.3513	0.3803	0.073*
H31B	−0.3091	0.2127	0.4461	0.073*
H31C	−0.2049	0.2886	0.3802	0.073*
C4	−0.28386 (16)	0.54065 (15)	0.51771 (11)	0.0449 (4)
H4A	−0.3713	0.5676	0.4708	0.054*
C5	−0.22720 (16)	0.63643 (16)	0.59653 (11)	0.0444 (3)
H5A	−0.2779	0.7257	0.6011	0.053*
C6	−0.09694 (15)	0.60262 (14)	0.66870 (10)	0.0368 (3)
C61	−0.03602 (17)	0.70251 (15)	0.75815 (11)	0.0441 (3)
H61A	0.0766	0.7046	0.7672	0.053*
C62	−0.0929 (2)	0.86189 (18)	0.74286 (15)	0.0673 (5)
H62A	−0.0397	0.9223	0.7971	0.101*
H62B	−0.2017	0.8650	0.7414	0.101*
H62C	−0.0731	0.8988	0.6804	0.101*
C63	−0.0748 (2)	0.6381 (2)	0.85431 (12)	0.0634 (5)
H63A	−0.0372	0.5381	0.8633	0.095*
H63B	−0.1846	0.6387	0.8491	0.095*
H63C	−0.0268	0.6972	0.9108	0.095*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0445 (5)	0.0375 (5)	0.0444 (5)	0.0053 (4)	−0.0104 (4)	−0.0082 (4)
O2	0.0600 (7)	0.0405 (6)	0.0675 (7)	0.0174 (5)	−0.0130 (5)	−0.0116 (5)
N1	0.0456 (6)	0.0319 (6)	0.0464 (6)	0.0046 (5)	−0.0009 (5)	−0.0042 (5)
C1	0.0318 (6)	0.0333 (7)	0.0333 (6)	−0.0012 (5)	0.0014 (5)	0.0005 (5)
C2	0.0337 (6)	0.0309 (6)	0.0327 (6)	−0.0015 (5)	0.0040 (5)	0.0000 (5)
C21	0.0403 (7)	0.0351 (7)	0.0382 (7)	−0.0007 (5)	0.0005 (5)	−0.0048 (5)
C3	0.0362 (7)	0.0393 (7)	0.0334 (6)	−0.0020 (5)	0.0022 (5)	0.0009 (5)
C31	0.0472 (8)	0.0516 (9)	0.0400 (7)	−0.0009 (6)	−0.0059 (6)	−0.0066 (6)
C4	0.0378 (7)	0.0458 (8)	0.0457 (8)	0.0056 (6)	−0.0042 (6)	0.0019 (6)
C5	0.0421 (7)	0.0364 (7)	0.0527 (8)	0.0081 (6)	0.0051 (6)	−0.0012 (6)
C6	0.0370 (7)	0.0334 (7)	0.0400 (7)	−0.0019 (5)	0.0077 (5)	−0.0035 (5)
C61	0.0431 (7)	0.0377 (7)	0.0502 (8)	−0.0022 (6)	0.0062 (6)	−0.0109 (6)
C62	0.0791 (12)	0.0423 (9)	0.0757 (12)	0.0060 (8)	0.0039 (9)	−0.0190 (8)
C63	0.0747 (12)	0.0678 (11)	0.0490 (9)	−0.0089 (9)	0.0155 (8)	−0.0172 (8)

Geometric parameters (Å, º)

O1—C1	1.3710 (14)	C4—C5	1.388 (2)
O1—H1O	0.8200	C4—H4A	0.9300
O2—N1	1.3982 (14)	C5—C6	1.3879 (19)
O2—H2O	0.8200	C5—H5A	0.9300
N1—C21	1.2743 (16)	C6—C61	1.5213 (18)
C1—C6	1.3989 (18)	C61—C62	1.523 (2)
C1—C2	1.4105 (17)	C61—C63	1.531 (2)
C2—C3	1.4105 (17)	C61—H61A	0.9800
C2—C21	1.4605 (18)	C62—H62A	0.9600
C21—H21A	0.9300	C62—H62B	0.9600
C3—C4	1.3790 (19)	C62—H62C	0.9600
C3—C31	1.5119 (18)	C63—H63A	0.9600
C31—H31A	0.9600	C63—H63B	0.9600
C31—H31B	0.9600	C63—H63C	0.9600
C31—H31C	0.9600
C1—O1—H1O	109.5	C6—C5—C4	121.83 (13)
N1—O2—H2O	109.5	C6—C5—H5A	119.1
C21—N1—O2	112.32 (11)	C4—C5—H5A	119.1
O1—C1—C6	117.15 (11)	C5—C6—C1	116.68 (12)
O1—C1—C2	120.36 (11)	C5—C6—C61	122.97 (12)
C6—C1—C2	122.49 (11)	C1—C6—C61	120.33 (12)
C3—C2—C1	118.87 (11)	C6—C61—C62	113.30 (13)
C3—C2—C21	119.89 (11)	C6—C61—C63	110.71 (12)
C1—C2—C21	121.24 (11)	C62—C61—C63	110.44 (14)
N1—C21—C2	121.68 (11)	C6—C61—H61A	107.4
N1—C21—H21A	119.2	C62—C61—H61A	107.4
C2—C21—H21A	119.2	C63—C61—H61A	107.4
C4—C3—C2	118.48 (12)	C61—C62—H62A	109.5
C4—C3—C31	119.64 (12)	C61—C62—H62B	109.5
C2—C3—C31	121.88 (12)	H62A—C62—H62B	109.5
C3—C31—H31A	109.5	C61—C62—H62C	109.5
C3—C31—H31B	109.5	H62A—C62—H62C	109.5
H31A—C31—H31B	109.5	H62B—C62—H62C	109.5
C3—C31—H31C	109.5	C61—C63—H63A	109.5
H31A—C31—H31C	109.5	C61—C63—H63B	109.5
H31B—C31—H31C	109.5	H63A—C63—H63B	109.5
C3—C4—C5	121.64 (12)	C61—C63—H63C	109.5
C3—C4—H4A	119.2	H63A—C63—H63C	109.5
C5—C4—H4A	119.2	H63B—C63—H63C	109.5
O1—C1—C2—C3	−179.59 (11)	C31—C3—C4—C5	179.52 (14)
C6—C1—C2—C3	0.55 (19)	C3—C4—C5—C6	0.2 (2)
O1—C1—C2—C21	0.55 (19)	C4—C5—C6—C1	0.6 (2)
C6—C1—C2—C21	−179.31 (12)	C4—C5—C6—C61	−177.47 (14)
O2—N1—C21—C2	−179.12 (12)	O1—C1—C6—C5	179.15 (12)
C3—C2—C21—N1	−177.13 (13)	C2—C1—C6—C5	−0.99 (19)
C1—C2—C21—N1	2.7 (2)	O1—C1—C6—C61	−2.70 (19)
C1—C2—C3—C4	0.29 (19)	C2—C1—C6—C61	177.16 (12)
C21—C2—C3—C4	−179.85 (12)	C5—C6—C61—C62	−20.2 (2)
C1—C2—C3—C31	−179.89 (13)	C1—C6—C61—C62	161.78 (14)
C21—C2—C3—C31	−0.03 (19)	C5—C6—C61—C63	104.51 (16)
C2—C3—C4—C5	−0.6 (2)	C1—C6—C61—C63	−73.52 (17)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O···N1	0.82	1.85	2.5788 (14)	148
O2—H2O···O1^i	0.82	2.02	2.8317 (14)	169

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