6-Methyl­flavone

In the title mol­ecule, C₁₆H₁₂O₂, the phenyl and quinone rings are effectively planar, with maximum deviations from planarity of 0.007 (2) and 0.008 (1) Å, respectively. The γ-pyrone ring makes a dihedral angle of 8.9 (3)° with the 2-phenyl substituent.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.045
• wR factor = 0.127
• Data-to-parameter ratio = 16.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           28.30
         From the CIF: _reflns_number_total               2758
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         2922
         Completeness (_total/calc)             94.39%
          Alert C: < 95% complete


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Flavones and related compounds are known to exhibit a wide range of interesting biological activities. (Agullo et al., 1997; Carlo et al., 1993; Miksicek, 1993; Wang et al., 1999). 6-Methylflavone is one of a number of flavones that have interesting modulatory activities at GABA-A receptors. (Medina et al., 1998; Campbell, 2001). The title compound, (I), was synthesized as part of an on-going structure–activity study to determine the properties of these compounds that confer this activity in order to aid the design of more active compounds.

All bond lengths and angles in (I) (Fig. 1) are as expected. Rings AC and B are planar; the maximum deviations are 0.008 (2) and 0.007 (1) Å from the ring planes AC and B, respectively.

The average C—C bond length for rings A and B are 1.394 (2) and 1.383 (2) Å, respectively. The dihedral angle between the phenyl and the γ-pyrone ring is small (8.9 (3) Å) as expected in the generally preferred conformation of flavones. The small dihedral angle results in a relatively short C3—C10 bond length of 1.472 (2) Å which is consistent with bond lengths and dihedral angles found in other flavones. Flavone-3'sulfonamide has a dihedral angle of 8.2 (3)° and the C3—C10 bond length of 1.478 (3) Å. (Kendi et al., 2000). In 5-hydroxyflavone, the dihedral angle is 5.2 (9)° and the C3—C10 bond length is 1.465 (4) Å. (Shoja, 1990). 5,7-Dihydroxy-4'-methoxyflavone with a dihedral angle of 3.1° has a C3—C10 bond length of 1.453 (9) Å. (Shoja, 1992). However, in 2'-methyl-3'-nitroflavone, the dihedral angle is 139.8 (2)° and the C3—C10 bond length is 1.491 (8) Å. (Kendi et al., 1996) and in 5,4'-dihydroxy-3,6,7,8-tetramethoxyflavone a large dihedral of angle of 164.4 (6)° and a C2—C10 bond length of 1.503 (8) Å are found (Vijayalakshmi et al., 1986).

The small dihedral angle between the phenyl and the γ-pyrone ring and shorter C1'-C2 bond length results in less delocalization of the π electrons in C3—C2—C1—O2, resulting in longer C2=C3 and C4=O2 bond lengths. 6-Methylflavone has a C2=C3 bond length of 1.348 (2) Å and a C4=O2 bond length of 1.237 (2) Å, a situation which is similar to flavone 3'-sulfonamide with a dihedral angle of 5.2 (9)°, and C2=C3 and C4=O2 bond lengths of 1.346 (3) and 1.247 (3) Å, respectively (Kendi et al., 2000). Conversely, 2'-methyl-3'nitro-flavone with the larger dihedral angle of 139.8 (2)° and longer C3—C10 bond length, has shorter C2=C3 and C4=O2 bond lengths of 1.322 (9) and 1.227 (8) Å, respectively (Kendi et al., 1996).

The widening of the O1—C4—C5 angle to 122.32 (13)° and the narrowing of the C2—C1—C5 angle to 114.51 (14)° in the γ-pyrone ring may be attributed to the ring strain caused by the neighbouring Csp² - Csp² atoms.

S2. Experimental

6-Methylflavone was obtained by the Baker-Venkataraman method and the structure confirmed by ¹H, and ¹³C NMR, mass spectrometry and infra-red spectroscopy. The product was recrystallized by slow evaporation from methanol (1.64 g, 60%), m.p. 397–400. λmax/cm^-1 2900 (ArC-H), 1640 (C=O), 1450, 1375, 1300, 1220, 1165, 1130, 1085, 1040, 1025, 975, 900, 850, 835, 815, 770, 720, 660; δH (300 MHz; CDCl₃) 2.48 (3H, s, CH3), 6.83 (1H, s, C(3)—H), 7.49–7.57 (5H, m, C(2')-H, C(3')-H, C(4')-H), 7.92–7.96 (2H, m, C(7)—H, C(8)—H), 8.03 (1H, symm. m, C(5)—H); δC (75 MHz; CDCl₃) 21.01 (CH₃), 107.50 (C-8), 117.93 (C-3), 123.72 (C-5a), 125.14 (C-4), 126.33 (C-3'), 129.09 (C-2'), 131.56 (C-5), 132.00 (C-1'), 135.04 (C-7), 135.26 (C-6), 154.63 (C-2), 163.29 (C-8a), 178.55 (C-4); m/z 236 ([M]+, 100%), 235 (31), 208 (51), 134 (29), 106 (19), 105 (28), 78 (12), 77 (14).

Crystals of (I) were mounted using silicone oil which acted as both a coating and an adhesive.

S3. Refinement

H atoms were included in calculated positions (riding model) with U_iso set at 1.2(CH) and 1.5(CH₃) times the U_eq of the parent atoms.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997).

Figures

Fig. 1. A general view of the molecular structure of (I). The ellipsoids are drawn at the 50% probability level (Farrugia, 1997).

(I)

Crystal data

C16H12O2	Dx = 1.335 Mg m^−3
Mr = 236.26	Melting point = 124–127 K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 4.7103 (8) Å	Cell parameters from 999 reflections
b = 11.684 (2) Å	θ = 1.9–28.3°
c = 21.352 (4) Å	µ = 0.09 mm^−1
β = 90.043 (3)°	T = 150 K
V = 1175.1 (3) Å^3	Prism, colourless
Z = 4	0.25 × 0.15 × 0.15 mm
F(000) = 496

Data collection

Bruker SMART 1000 CCD diffractometer	1644 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.033
Graphite monochromator	θmax = 28.3°, θmin = 1.9°
ω–scan	h = −6→6
7396 measured reflections	k = −10→15
2758 independent reflections	l = −28→28

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.127	H-atom parameters constrained
S = 0.93	w = 1/[σ^2(Fo^2) + (0.0696P)^2] where P = (Fo^2 + 2Fc^2)/3
2758 reflections	(Δ/σ)max < 0.001
164 parameters	Δρmax = 0.26 e Å^−3
0 restraints	Δρmin = −0.20 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	0.1397 (2)	0.74957 (9)	0.14860 (5)	0.0299 (3)
O2	−0.2213 (3)	0.43274 (10)	0.13297 (6)	0.0443 (4)
C1	−0.1137 (4)	0.52883 (14)	0.13807 (7)	0.0310 (4)
C2	0.0931 (3)	0.57314 (14)	0.09453 (7)	0.0310 (4)
H2	0.1488	0.5274	0.0611	0.037*
C3	0.2090 (3)	0.67804 (14)	0.10033 (7)	0.0270 (4)
C4	−0.0587 (3)	0.71459 (13)	0.19192 (7)	0.0271 (4)
C5	−0.1869 (3)	0.60763 (13)	0.18931 (7)	0.0269 (4)
C6	−0.3861 (3)	0.57969 (14)	0.23574 (7)	0.0299 (4)
H6	−0.4718	0.5080	0.2349	0.036*
C7	−0.4586 (3)	0.65577 (14)	0.28278 (7)	0.0295 (4)
C8	−0.3264 (4)	0.76346 (14)	0.28275 (7)	0.0325 (4)
H8	−0.3748	0.8163	0.3135	0.039*
C9	−0.1273 (4)	0.79302 (14)	0.23852 (7)	0.0326 (4)
H9	−0.0399	0.8644	0.2398	0.039*
C10	0.4199 (3)	0.73010 (14)	0.05827 (7)	0.0280 (4)
C11	0.5532 (4)	0.83208 (15)	0.07408 (8)	0.0371 (4)
H11	0.5062	0.8689	0.1113	0.045*
C12	0.7551 (4)	0.87919 (16)	0.03500 (9)	0.0470 (5)
H12	0.8431	0.9475	0.0460	0.056*
C13	0.8275 (4)	0.82568 (16)	−0.02031 (8)	0.0428 (5)
H13	0.9649	0.8575	−0.0463	0.051*
C14	0.6961 (4)	0.72534 (15)	−0.03687 (8)	0.0385 (4)
H14	0.7444	0.6892	−0.0742	0.046*
C15	0.4930 (4)	0.67802 (15)	0.00156 (8)	0.0347 (4)
H15	0.4032	0.6105	−0.0103	0.042*
C16	−0.6683 (4)	0.62485 (15)	0.33332 (8)	0.0376 (4)
H16A	−0.8012	0.5698	0.3173	0.056*
H16B	−0.7682	0.6923	0.3464	0.056*
H16C	−0.5689	0.5927	0.3684	0.056*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0366 (7)	0.0238 (6)	0.0294 (6)	−0.0026 (5)	0.0080 (5)	−0.0034 (4)
O2	0.0555 (9)	0.0298 (7)	0.0475 (7)	−0.0131 (6)	0.0152 (6)	−0.0094 (6)
C1	0.0349 (10)	0.0252 (9)	0.0328 (9)	0.0004 (7)	0.0032 (7)	−0.0013 (7)
C2	0.0353 (10)	0.0283 (9)	0.0295 (8)	0.0016 (7)	0.0065 (7)	−0.0062 (7)
C3	0.0291 (9)	0.0276 (9)	0.0245 (8)	0.0046 (7)	0.0019 (7)	−0.0017 (6)
C4	0.0302 (9)	0.0261 (9)	0.0249 (8)	0.0016 (7)	0.0040 (7)	0.0011 (6)
C5	0.0289 (9)	0.0242 (9)	0.0276 (8)	0.0018 (7)	0.0020 (7)	0.0004 (6)
C6	0.0294 (9)	0.0280 (9)	0.0324 (9)	−0.0016 (7)	0.0022 (7)	0.0007 (7)
C7	0.0275 (9)	0.0325 (9)	0.0287 (8)	0.0039 (7)	0.0012 (7)	0.0039 (7)
C8	0.0423 (11)	0.0288 (9)	0.0263 (8)	0.0060 (8)	0.0054 (8)	−0.0028 (7)
C9	0.0423 (11)	0.0242 (9)	0.0313 (9)	−0.0011 (7)	0.0031 (8)	−0.0017 (7)
C10	0.0296 (9)	0.0263 (9)	0.0282 (8)	0.0031 (7)	0.0008 (7)	0.0025 (7)
C11	0.0442 (11)	0.0315 (10)	0.0356 (9)	−0.0023 (8)	0.0097 (8)	−0.0050 (8)
C12	0.0560 (13)	0.0359 (11)	0.0492 (11)	−0.0126 (9)	0.0181 (9)	−0.0044 (9)
C13	0.0466 (12)	0.0402 (11)	0.0418 (10)	−0.0028 (9)	0.0160 (9)	0.0068 (8)
C14	0.0489 (12)	0.0370 (11)	0.0297 (9)	0.0051 (9)	0.0090 (8)	0.0011 (8)
C15	0.0422 (11)	0.0310 (10)	0.0309 (8)	−0.0007 (8)	0.0043 (8)	−0.0022 (7)
C16	0.0373 (11)	0.0405 (11)	0.0351 (9)	0.0023 (8)	0.0091 (8)	0.0015 (8)

Geometric parameters (Å, º)

O1—C3	1.3667 (18)	C8—H8	0.9300
O1—C4	1.3773 (18)	C9—H9	0.9300
O2—C1	1.2365 (19)	C10—C11	1.388 (2)
C1—C2	1.443 (2)	C10—C15	1.398 (2)
C1—C5	1.471 (2)	C11—C12	1.380 (2)
C2—C3	1.347 (2)	C11—H11	0.9300
C2—H2	0.9300	C12—C13	1.379 (2)
C3—C10	1.471 (2)	C12—H12	0.9300
C4—C5	1.389 (2)	C13—C14	1.372 (3)
C4—C9	1.391 (2)	C13—H13	0.9300
C5—C6	1.404 (2)	C14—C15	1.377 (2)
C6—C7	1.384 (2)	C14—H14	0.9300
C6—H6	0.9300	C15—H15	0.9300
C7—C8	1.404 (2)	C16—H16A	0.9600
C7—C16	1.507 (2)	C16—H16B	0.9600
C8—C9	1.375 (2)	C16—H16C	0.9600
C3—O1—C4	119.18 (12)	C8—C9—H9	120.5
O2—C1—C2	123.07 (15)	C4—C9—H9	120.5
O2—C1—C5	122.52 (15)	C11—C10—C15	118.19 (15)
C2—C1—C5	114.41 (14)	C11—C10—C3	120.79 (14)
C3—C2—C1	122.72 (14)	C15—C10—C3	121.03 (15)
C3—C2—H2	118.6	C12—C11—C10	120.46 (15)
C1—C2—H2	118.6	C12—C11—H11	119.8
C2—C3—O1	121.92 (14)	C10—C11—H11	119.8
C2—C3—C10	126.41 (14)	C13—C12—C11	120.51 (18)
O1—C3—C10	111.67 (13)	C13—C12—H12	119.7
O1—C4—C5	122.36 (13)	C11—C12—H12	119.7
O1—C4—C9	116.30 (14)	C14—C13—C12	119.76 (16)
C5—C4—C9	121.34 (14)	C14—C13—H13	120.1
C4—C5—C6	118.14 (14)	C12—C13—H13	120.1
C4—C5—C1	119.39 (14)	C13—C14—C15	120.20 (16)
C6—C5—C1	122.47 (14)	C13—C14—H14	119.9
C7—C6—C5	121.90 (15)	C15—C14—H14	119.9
C7—C6—H6	119.0	C14—C15—C10	120.86 (16)
C5—C6—H6	119.0	C14—C15—H15	119.6
C6—C7—C8	117.75 (14)	C10—C15—H15	119.6
C6—C7—C16	121.85 (15)	C7—C16—H16A	109.5
C8—C7—C16	120.40 (14)	C7—C16—H16B	109.5
C9—C8—C7	121.87 (15)	H16A—C16—H16B	109.5
C9—C8—H8	119.1	C7—C16—H16C	109.5
C7—C8—H8	119.1	H16A—C16—H16C	109.5
C8—C9—C4	118.99 (15)	H16B—C16—H16C	109.5
O2—C1—C2—C3	179.85 (17)	C5—C6—C7—C16	−178.81 (15)
C5—C1—C2—C3	−0.1 (2)	C6—C7—C8—C9	−1.2 (3)
C1—C2—C3—O1	0.7 (3)	C16—C7—C8—C9	177.86 (15)
C1—C2—C3—C10	−179.86 (15)	C7—C8—C9—C4	1.1 (3)
C4—O1—C3—C2	−1.4 (2)	O1—C4—C9—C8	179.32 (14)
C4—O1—C3—C10	179.06 (13)	C5—C4—C9—C8	0.0 (2)
C3—O1—C4—C5	1.6 (2)	C2—C3—C10—C11	−170.71 (17)
C3—O1—C4—C9	−177.71 (14)	O1—C3—C10—C11	8.8 (2)
O1—C4—C5—C6	179.81 (14)	C2—C3—C10—C15	8.9 (3)
C9—C4—C5—C6	−0.9 (2)	O1—C3—C10—C15	−171.61 (14)
O1—C4—C5—C1	−1.1 (2)	C15—C10—C11—C12	−0.9 (3)
C9—C4—C5—C1	178.21 (14)	C3—C10—C11—C12	178.66 (17)
O2—C1—C5—C4	−179.66 (16)	C10—C11—C12—C13	0.0 (3)
C2—C1—C5—C4	0.3 (2)	C11—C12—C13—C14	0.5 (3)
O2—C1—C5—C6	−0.6 (3)	C12—C13—C14—C15	−0.1 (3)
C2—C1—C5—C6	179.39 (15)	C13—C14—C15—C10	−0.9 (3)
C4—C5—C6—C7	0.8 (2)	C11—C10—C15—C14	1.4 (3)
C1—C5—C6—C7	−178.28 (15)	C3—C10—C15—C14	−178.20 (16)
C5—C6—C7—C8	0.2 (2)