(E)-2-Methyl-4-[(4-propyl­phen­yl)diazen­yl]phenol

The title compound, C₁₆H₁₈N₂O, was produced when 4-propyl­benzene­diazo­nium chloride, prepared from a 4-propyl­aniline and NaNO₂–HCl mixture, was treated with 2-methyl­phenol in an approximately 1:1 molar ratio. The mol­ecules of the title compound are stabilized by inversion-related O—H...N and C—H...O inter­molecular hydrogen bonds. The O—H...N and C—H...O hydrogen bonds generate two edge-fused R₂²(6) ring motifs. The dihedral angle between the aromatic rings is 15.28 (10)°. The N atoms are disordered approximately equally over two positions.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C) = 0.004 Å
• Disorder in main residue
• R factor = 0.053
• wR factor = 0.177
• Data-to-parameter ratio = 16.0

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT201_ALERT_2_B Isotropic non-H Atoms in Main Residue(s) .......          2

Alert level C
RINTA01_ALERT_3_C  The value of Rint is greater than 0.10
            Rint given   0.128
PLAT020_ALERT_3_C The value of Rint is greater than 0.10 .........       0.13
PLAT026_ALERT_3_C Ratio Observed / Unique Reflections too Low ....         47 Perc.
PLAT031_ALERT_4_C Refined Extinction Parameter within Range ......       3.15 Sigma
PLAT063_ALERT_3_C Crystal Probably too Large for Beam Size .......       0.72 mm
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        N1A
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        C11
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for        N2A
PLAT301_ALERT_3_C Main Residue  Disorder .........................      10.00 Perc.
PLAT366_ALERT_2_C Short? C(sp?)-C(sp?) Bond  C1     -   C2     ...       1.38 Ang.
PLAT366_ALERT_2_C Short? C(sp?)-C(sp?) Bond  C1     -   C6     ...       1.39 Ang.
PLAT366_ALERT_2_C Short? C(sp?)-C(sp?) Bond  C8     -   C9     ...       1.35 Ang.
PLAT366_ALERT_2_C Short? C(sp?)-C(sp?) Bond  C8     -   C13    ...       1.38 Ang.
PLAT480_ALERT_4_C Long H...A H-Bond Reported H6     ..  O1      ..       2.63 Ang.
PLAT480_ALERT_4_C Long H...A H-Bond Reported H9     ..  O1      ..       2.77 Ang.

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
  15 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
   8 ALERT type 2 Indicator that the structure model may be wrong or deficient
   5 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

Azobenzene derivatives have been the most widely used class of dyes due to their versatile application in various fields, such as dyeing textile fibers, biomedical studies, advanced applications in organic synthesis, and high technology areas as laser, liquid crystalline displays, electro-optical devices, and ink-jet printers (Peters & Freeman, 1991). In the azo class of dye molecules, azo compounds are an important type of organic colorants and consist of at least a conjugated chromophore azo group and two or more aromatic rings. The colour of an azo dye is mainly due to the interaction of the azo group with incident light. The pharmaceutical importance of compounds including an arylazo group has been extensively reported in the literature (Garg & Sharma, 1969). The oxidation-reduction behaviors of these compounds play an important role in its biological activity (Ravindranath et al., 1983). In view of the importance of the title compound, (I), a crystal structure is investigated. The present work is part of a structural study of compounds of phenolicazobenzene (Albayrak et al., 2007, 2004; Odabaşoğlu et al., 2003; Şahin et al., 2005a,b,c,d,e) and we report here the structure of the title compound (Fig. 1).

The molecular structure of (I) is shown in Fig. 1, with the atom-numbering scheme. Selected bond distances and angles are given in Table 1. The a rings aromatic adopt a trans configuration about the azo functional group and dihedral angle between the rings is 15.28 (10)°. All the C—C bond lengths in the C1—C6 and C8—C13 rings have typical C_sp2—C_sp2 values. The average C—C bond lengths within these two rings are 1.380 (4) and 1.369 (4) A °, respectively. In the azo group, the C—N and N═N bond lenghths different normal C—N and N═N bonds and angles of around the N atoms are abnormal because of orientational disorder (Fig. 1). The title molecules are stabilized by O—H···N and C—H···O intermolecular hydrogen bonds and O—H···N and C—H···O hydrogen bonds generate hydrogen bonded chain which have edge-fussed [R₂²(6)R₂²(6)] ring motifs (Fig. 2, Table 2) (Etter, 1990). The hydrogen bonded chains arranged as forming quardrangle tunnels (Fig. 3).

Related literature

For related literature, see: Albayrak et al. (2004, 2007); Etter (1990); Garg & Sharma (1969); Odabaşoğlu et al. (2003); Peters & Freeman (1991); Ravindranath et al. (1983); Şahin et al. (2005a,b,c,d,e).

S2. Experimental

A mixture of 4-propylaniline (1.352 g, 10 mmol), water (50 ml) and concentrated hydrochloric acid (2.5 ml, 30 mmol) was heated with stirring until a clear solution was obtained. This solution was cooled down to 273–278 K and a solution of sodium nitrite (0.96 g, 14 mmol) in water was added dropwise while the temperature was maintained below 278 K. The resulting mixture was stirred for 30 min in an ice bath. 2-methylphenol (1.081 g, 10 mmol) solution (pH 9) was gradually added to a cooled solution of 4-propylbenzenediazonium chloride, prepared as described above, and the resulting mixture was stirred at 273–278 K for 60 min in an ice bath. The product was recrystallized from acetonitrile to obtain solid (E)-2-methyl-4-[(4-propylphenyl) diazenyl]phenol (Yield 31%; m.p. 384–386 K).

S3. Refinement

All C-bound H atoms were refined using the riding model approximation with d(C—H) = 0.93 for aromatic, d(C—H) = 0.97 for methylene and d(C—H) = 0.96 for methyl C—H [U_iso(H) = 1.2U_eq(C) or 1.5U_eq(methyl C)]. O-bound H atom was located in Fourier difference map and refined freely due to its taking part in H-bond. The two N atoms in the azo group are orientational disorder. The relative occupancies for the disordered components were refined freely to yield relative occupancies of 0.501 (8) and 0.499 (8), respectively, for N1A (N1B) and N2A (N2B).

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A view of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level..
	Fig. 2. Part of the crystal structure of (I), showing the formation of R2^2(6)R2^2(6) motifs. [Symmetry code: (i) -x, 3/2 - y, 1 - z].
	Fig. 3. A packing diagram of (I), showing the quardrangle tunnels. H atoms not involved in intramolecular interactions have been ommited for clarity.

(E)-2-Methyl-4-[(4-propylphenyl)diazenyl]phenol

Crystal data

C16H18N2O	F(000) = 1088
Mr = 254.32	Dx = 1.179 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 22722 reflections
a = 9.9032 (7) Å	θ = 1.7–26.0°
b = 12.0663 (8) Å	µ = 0.08 mm^−1
c = 23.984 (2) Å	T = 296 K
V = 2866.0 (4) Å^3	Prism, brown
Z = 8	0.72 × 0.51 × 0.19 mm

Data collection

Stoe IPDS2 diffractometer	2813 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	1315 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.129
Detector resolution: 6.67 pixels mm^-1	θmax = 26.0°, θmin = 1.7°
ω scan rotation method	h = −12→12
Absorption correction: integration (X-RED32; Stoe & Cie, 2002)	k = −14→14
Tmin = 0.958, Tmax = 0.986	l = −29→29
30080 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.053	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.177	w = 1/[σ^2(Fo^2) + (0.0964P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.91	(Δ/σ)max < 0.001
2813 reflections	Δρmax = 0.19 e Å^−3
176 parameters	Δρmin = −0.15 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0041 (13)

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)
C1	0.2475 (3)	0.5850 (3)	0.51406 (13)	0.1011 (9)
C2	0.1876 (3)	0.5164 (2)	0.47522 (13)	0.0972 (9)
H2	0.2122	0.4420	0.4746	0.117*
C3	0.0941 (3)	0.55263 (18)	0.43763 (11)	0.0814 (7)
C4	0.0579 (2)	0.66430 (19)	0.43955 (10)	0.0721 (6)
C5	0.1156 (3)	0.7349 (2)	0.47817 (10)	0.0815 (7)
H5	0.0906	0.8092	0.4791	0.098*
C6	0.2098 (3)	0.6956 (3)	0.51507 (11)	0.0952 (8)
H6	0.2486	0.7434	0.5409	0.114*
C7	0.0314 (3)	0.4775 (2)	0.39447 (13)	0.1125 (10)
H7A	0.0512	0.5053	0.3579	0.135*
H7B	−0.0646	0.4753	0.3998	0.135*
H7C	0.0678	0.4042	0.3983	0.135*
C8	0.4872 (3)	0.4888 (4)	0.61056 (13)	0.1068 (10)
C9	0.5234 (4)	0.5440 (3)	0.65733 (15)	0.1279 (11)
H9	0.4860	0.6132	0.6647	0.153*
C10	0.6148 (4)	0.4991 (3)	0.69411 (13)	0.1197 (10)
H10	0.6376	0.5387	0.7260	0.144*
C11	0.6733 (3)	0.3979 (2)	0.68518 (11)	0.0897 (7)
C12	0.6357 (3)	0.3422 (2)	0.63816 (12)	0.0965 (8)
H12	0.6731	0.2730	0.6309	0.116*
C13	0.5443 (3)	0.3858 (3)	0.60142 (12)	0.1081 (10)
H13	0.5203	0.3456	0.5699	0.130*
C14	0.7710 (3)	0.3489 (3)	0.72635 (14)	0.1183 (10)
H14A	0.8407	0.3098	0.7059	0.142*
H14B	0.8143	0.4090	0.7464	0.142*
C15	0.7113 (3)	0.2718 (3)	0.76744 (13)	0.1191 (11)
H15A	0.6711	0.2102	0.7475	0.143*
H15B	0.6393	0.3100	0.7870	0.143*
C16	0.8075 (3)	0.2271 (3)	0.80925 (12)	0.1238 (11)
H16A	0.8469	0.2872	0.8298	0.149*
H16B	0.8774	0.1864	0.7906	0.149*
H16C	0.7603	0.1788	0.8344	0.149*
N1A	0.3301 (5)	0.5099 (4)	0.54315 (18)	0.0729 (15)*	0.501 (8)
N2A	0.3998 (5)	0.5696 (4)	0.5811 (2)	0.0699 (14)*	0.499 (8)
N1B	0.3534 (6)	0.5833 (4)	0.5619 (2)	0.0784 (15)*	0.501 (8)
N2B	0.3897 (6)	0.4875 (4)	0.5616 (2)	0.0814 (16)*	0.499 (8)
O1	−0.03469 (18)	0.70055 (15)	0.40199 (7)	0.0866 (5)
H1	−0.066 (3)	0.774 (3)	0.4090 (13)	0.134 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0825 (17)	0.130 (3)	0.0903 (19)	0.0218 (17)	0.0118 (15)	0.0385 (19)
C2	0.0960 (19)	0.0829 (18)	0.113 (2)	0.0185 (15)	0.0253 (18)	0.0296 (17)
C3	0.0844 (16)	0.0634 (14)	0.0964 (18)	−0.0017 (12)	0.0231 (14)	0.0035 (13)
C4	0.0757 (14)	0.0680 (13)	0.0726 (14)	0.0016 (11)	0.0078 (12)	0.0051 (12)
C5	0.0899 (16)	0.0750 (14)	0.0795 (15)	0.0021 (13)	0.0030 (14)	−0.0058 (13)
C6	0.0883 (18)	0.123 (2)	0.0737 (16)	−0.0010 (17)	0.0014 (14)	−0.0001 (15)
C7	0.126 (2)	0.0725 (17)	0.139 (3)	−0.0154 (16)	0.028 (2)	−0.0195 (17)
C8	0.0867 (19)	0.148 (3)	0.086 (2)	0.0006 (19)	0.0052 (15)	0.031 (2)
C9	0.155 (3)	0.115 (2)	0.114 (2)	0.040 (2)	−0.010 (2)	0.012 (2)
C10	0.159 (3)	0.098 (2)	0.102 (2)	0.011 (2)	−0.028 (2)	−0.0089 (18)
C11	0.0880 (17)	0.0883 (18)	0.0927 (18)	−0.0064 (14)	−0.0056 (15)	0.0112 (15)
C12	0.109 (2)	0.0877 (17)	0.0931 (19)	−0.0100 (15)	0.0084 (17)	0.0004 (16)
C13	0.107 (2)	0.142 (3)	0.0756 (18)	−0.040 (2)	0.0029 (17)	0.0059 (19)
C14	0.097 (2)	0.129 (2)	0.129 (2)	−0.0041 (18)	−0.0163 (19)	0.019 (2)
C15	0.096 (2)	0.161 (3)	0.101 (2)	0.0069 (19)	−0.0072 (17)	0.033 (2)
C16	0.114 (2)	0.156 (3)	0.102 (2)	0.009 (2)	−0.0160 (18)	0.016 (2)
O1	0.0941 (12)	0.0756 (11)	0.0902 (12)	0.0075 (9)	−0.0089 (10)	−0.0095 (9)

Geometric parameters (Å, º)

C1—C2	1.380 (4)	C9—H9	0.9300
C1—C6	1.386 (4)	C10—C11	1.368 (4)
C1—N1A	1.406 (6)	C10—H10	0.9300
C1—N1B	1.554 (8)	C11—C12	1.364 (4)
C2—C3	1.365 (4)	C11—C14	1.504 (4)
C2—H2	0.9300	C12—C13	1.368 (4)
C3—C4	1.395 (3)	C12—H12	0.9300
C3—C7	1.509 (4)	C13—H13	0.9300
C4—O1	1.358 (3)	C14—C15	1.478 (4)
C4—C5	1.383 (3)	C14—H14A	0.9700
C5—C6	1.370 (3)	C14—H14B	0.9700
C5—H5	0.9300	C15—C16	1.485 (4)
C6—H6	0.9300	C15—H15A	0.9700
C7—H7A	0.9600	C15—H15B	0.9700
C7—H7B	0.9600	C16—H16A	0.9600
C7—H7C	0.9600	C16—H16B	0.9600
C8—C9	1.353 (5)	C16—H16C	0.9600
C8—C13	1.383 (5)	N1A—N2A	1.350 (6)
C8—N2A	1.483 (7)	N1B—N2B	1.211 (6)
C8—N2B	1.521 (7)	O1—H1	0.95 (4)
C9—C10	1.376 (4)
C2—C1—C6	118.3 (3)	C11—C10—H10	119.0
C2—C1—N1A	101.4 (3)	C9—C10—H10	119.0
C6—C1—N1A	140.2 (4)	C12—C11—C10	117.0 (3)
C2—C1—N1B	141.3 (3)	C12—C11—C14	121.6 (3)
C6—C1—N1B	100.5 (3)	C10—C11—C14	121.4 (3)
C3—C2—C1	123.1 (3)	C11—C12—C13	121.6 (3)
C3—C2—H2	118.5	C11—C12—H12	119.2
C1—C2—H2	118.5	C13—C12—H12	119.2
C2—C3—C4	117.5 (2)	C12—C13—C8	120.9 (3)
C2—C3—C7	122.7 (3)	C12—C13—H13	119.5
C4—C3—C7	119.8 (3)	C8—C13—H13	119.5
O1—C4—C5	121.7 (2)	C15—C14—C11	115.3 (2)
O1—C4—C3	117.6 (2)	C15—C14—H14A	108.4
C5—C4—C3	120.7 (2)	C11—C14—H14A	108.4
C6—C5—C4	120.1 (2)	C15—C14—H14B	108.4
C6—C5—H5	120.0	C11—C14—H14B	108.4
C4—C5—H5	120.0	H14A—C14—H14B	107.5
C5—C6—C1	120.4 (3)	C14—C15—C16	115.0 (3)
C5—C6—H6	119.8	C14—C15—H15A	108.5
C1—C6—H6	119.8	C16—C15—H15A	108.5
C3—C7—H7A	109.5	C14—C15—H15B	108.5
C3—C7—H7B	109.5	C16—C15—H15B	108.5
H7A—C7—H7B	109.5	H15A—C15—H15B	107.5
C3—C7—H7C	109.5	C15—C16—H16A	109.5
H7A—C7—H7C	109.5	C15—C16—H16B	109.5
H7B—C7—H7C	109.5	H16A—C16—H16B	109.5
C9—C8—C13	117.8 (3)	C15—C16—H16C	109.5
C9—C8—N2A	103.0 (4)	H16A—C16—H16C	109.5
C13—C8—N2A	138.9 (4)	H16B—C16—H16C	109.5
C9—C8—N2B	144.4 (4)	N2A—N1A—C1	106.7 (4)
C13—C8—N2B	97.3 (3)	N1A—N2A—C8	105.6 (4)
C8—C9—C10	120.8 (3)	N2B—N1B—C1	102.0 (5)
C8—C9—H9	119.6	N1B—N2B—C8	100.0 (5)
C10—C9—H9	119.6	C4—O1—H1	114 (2)
C11—C10—C9	122.0 (3)
C6—C1—C2—C3	0.5 (4)	C14—C11—C12—C13	178.4 (3)
N1A—C1—C2—C3	178.2 (2)	C11—C12—C13—C8	0.5 (4)
N1B—C1—C2—C3	−179.0 (3)	C9—C8—C13—C12	−0.9 (5)
C1—C2—C3—C4	−0.5 (4)	N2A—C8—C13—C12	172.1 (4)
C1—C2—C3—C7	178.6 (2)	N2B—C8—C13—C12	−175.1 (3)
C2—C3—C4—O1	179.7 (2)	C12—C11—C14—C15	−83.1 (4)
C7—C3—C4—O1	0.5 (3)	C10—C11—C14—C15	94.8 (4)
C2—C3—C4—C5	0.2 (3)	C11—C14—C15—C16	−177.8 (3)
C7—C3—C4—C5	−179.0 (2)	C2—C1—N1A—N2A	177.0 (3)
O1—C4—C5—C6	−179.3 (2)	C6—C1—N1A—N2A	−6.2 (6)
C3—C4—C5—C6	0.2 (3)	N1B—C1—N1A—N2A	−0.3 (3)
C4—C5—C6—C1	−0.2 (4)	C1—N1A—N2A—C8	−179.3 (3)
C2—C1—C6—C5	−0.1 (4)	C9—C8—N2A—N1A	−162.7 (3)
N1A—C1—C6—C5	−176.5 (3)	C13—C8—N2A—N1A	23.7 (6)
N1B—C1—C6—C5	179.6 (2)	N2B—C8—N2A—N1A	4.9 (3)
C13—C8—C9—C10	0.5 (5)	C2—C1—N1B—N2B	0.5 (6)
N2A—C8—C9—C10	−174.8 (3)	C6—C1—N1B—N2B	−179.2 (3)
N2B—C8—C9—C10	170.7 (4)	N1A—C1—N1B—N2B	4.7 (3)
C8—C9—C10—C11	0.3 (6)	C1—N1B—N2B—C8	−177.3 (2)
C9—C10—C11—C12	−0.7 (5)	C9—C8—N2B—N1B	19.9 (7)
C9—C10—C11—C14	−178.8 (3)	C13—C8—N2B—N1B	−168.9 (3)
C10—C11—C12—C13	0.4 (4)	N2A—C8—N2B—N1B	−1.2 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···N2A^i	0.95 (4)	1.94 (4)	2.877 (4)	170 (3)
O1—H1···N1B^i	0.95 (4)	2.03 (4)	2.964 (5)	169 (3)
C6—H6···O1^ii	0.93	2.63	3.454 (3)	147
C9—H9···O1^ii	0.93	2.77	3.443 (4)	131

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