1-(4-Bromo­phenyl)-3-(4-methyl­phenyl)­prop-2-en-1-one

In the mol­ecule of the title compound, C₁₆H₁₃BrO, the two benzene rings are rotated in opposite directions with respect to the central C—C=C—C part of the mol­ecule. The phenone O atom deviates from the least-squares plane of the mol­ecule by 0.300 (3) Å. In the crystal structure, mol­ecules are paired through C—H...π interactions. The molecular pairs along [001] are hydrogen bonded through three translation-related co-operative hydrogen bonds in the `bay area', forming molecular chains, which are further hydrogen bonded through C—H...Br weak interactions, forming (010) molecular layers. In the third direction, there are only weak van der Waals interactions. The co-operative hydrogen bonds in the `bay area' are discussed briefly.

S1. Comment

Chalcones with the general formula Ar—CH═CH—CO—Ar belong to an important class of compounds. The common and interesting part in the molecules of these compounds is the central part, i.e. –CH═CH—C═O–, in which the H atoms may or may not be substituted. The –C═C– double bond can be photoreactive, in which case it can react with suitable reagents through photocycloaddition to synthesize various products, and is therefore widely used in organic solid photochemistry (Satish Goud et al., 1995). On the other hand, with appropriate substitutents, chalcones are a class of non-linear optical materials (Indira et al., 2002).

In these materials, the C═O bond acts as the electron-withdrawing group, and the electron-rich substituents in the aromatic rings serve as electron-donating groups, forming a so-called D-π···A type molecule. When the electron-rich groups are located on the 4 and/or 4' positions, the electron flow follows a Λ-shaped path, and therefore the molecule is called a Λ-shaped molecule (Devia et al., 1999). During our search for chalcone non-linear optical materials, the title compound, (I), was synthesized. We present here a study of the molecular packing in the crystal of (I), and a brief study of the C—H···O hydrogen bonds in (I) and some similar crystals. \sch

The molecule of (I) is not planar. Taking the C1—C6 phenyl ring as plane 1, the C7—C12 phenyl ring as plane 2 and the central C1—C13═C14—C15 as plane 3, the dihedral angles between them, A₁₂, A₁₃ and A₂₃, are 47.0 (1), 11.7 (0) and 35.4 (1)°, respectively, showing that the two phenyl rings are rotated in opposite directions with respect to the central part, plane 3. The C1—C13═C14—C15 torsion angle is 175.1 (3)°. The angle between the C═O bond and plane 3 is 14.2 (3)°.

In the crystal of (I), molecules are paired through C—H···π interactions (Suezawa et al., 2001; Table 3). The shortest distance between the parallel C═C double bonds is 4.557 (4) Å, much longer than the 4.2 Å reference value for a photoreactive crystal (Reference?). The dihedral angle between plane 3 and the plane formed by the two C═C double bonds is 45.6 (3)°, which deviates significantly from the perfect value of 90° for 2 + 2 photocycloaddition. This is consistent with the fact that the crystal of (I) is photoinert.

The molecules along [001] interact via three C—H···O interactions (Desiraju, 1991), namely C12—H12···O1, C2—H2···O1 and C14—H14···O1 (Table 2), and form hydrogen-bonded molecular chains. These chains interact further through C5—H5···Br1 and C16—H16A···Br1 hydrogen bonds (Table 2), forming (010) molecular layers. In the third direction, [010], there are only weak ordinary van der Waals interactions.

The most interesting features in the structure of (I) are the above-mentioned cooperative hydrogen bonds, formed by the phenone O atom and the three C—H bonds in the `bay area', namely the area encricled by C2'-C1'-C_e—C_a═C_b—C1—C2. From the scheme, one can see that the three C—H bonds almost point to the same site. When this site is occupied by a phenone O atom from a neighbouring molecule, the formation of three C—H···O hydrogen bonds with nearly perfect geometries can be expected. Depending on the mutual arrangement of the two molecules involved, the most favourable symmetry relation between them is a translation vector, the size of which is dependent on the size of the substituents, followed by a screw axis and a glide plane. It is almost impossible for a centre of symmetry to connect the molecules in such a manner.

From the viewpoint of designing second-harmonic generating crystals (Desiraju, 1989), which must not be centrosymmetric, the above molecular self-assembling mode is desirable. Therefore, a brief study of some similar 4,4'-substituted chalcones was carried out, and the results are summarized in Tables 4 and 5.

As shown by the Tables 4 and 5, the symmetry elements involved are indeed translation vectors and their size is around 6 Å. The cooperative C—H···O hydrogen bonds in the `bay area' certainly play an important role in the crystal packing, as shown by the ESM% column in Table 5, which expresses the interaction energy between the molecules involved as a percentage of the total packing energy, as calculated using program OPEC (Gavezzotti, 1983). However, this is not the unique factor determining the crystal packing. The dipole moment of the molecule of (I) is relatively large when compared with the others in Table 4, which leads to the molecules of (I) being arranged in an antiparallel fashion in the crystal. This may be the reason that the crystal of (I) is centrosymmetric.

S2. Experimental

The synthesis of the (I) was carried out using the procedure of Migrdichian (1957). An aqueous solution of sodium hydroxide (10%, 10 ml) was added to a solution of 4-bromoacetophenone (0.02 mol) and 4-methylbenzaldehyde (0.02 mol) in 95% ethanol (30 ml). The reaction mixture was stirred at room temperature for 4 h and yielded a light-yellow solid, and was then neutralized with hydrochloric acid (10%) and water. The product was recrystallized three times from dry acetone. After 3 d, light-yellow crystals of (I) were obtained by slow evaporation from dry acetone at 286 K. Elemental analysis (Perkin-Elmer 240 C elemental analyzer): calculated for C₁₆H₁₃BrO: C 63.79, H 4.32%; found: C 63.66, H 4.19%. IR spectroscopy (KBr pellets, ν, cm⁻¹): 3030 (Ar—H), 2914 (C—H), 1658 (–C═O), 1598 (–CH═CH–), 1563 (Ph), 1332 (–CH₃), 1007 (–CH═C—H), 810 (Ar—H), 737 (Ar—H). ¹H NMR spectroscopy (Bruker AV-400 NMR spectrometer, CDCl₃, 399.97 MHz, ambient temperature, δ, p.p.m.): 2.40 (s, 3H, –CH₃), 7.25 (d, 2H, Ph), 7.45 (d, 1H, –CH═CH–), 7.55 (d, 2H, Ph), 7.64 (d, 2H, Ph), 7.81 (d, 1H, –CH═CH–), 7.89 (d, 2H, Ph).

S3. Refinement

H atoms were placed in geometrical positions and treated as riding, with C—H distances in the range 0.95–0.98 Å and with U_iso(H) = 1.2U_eq(C). Please check added text.

Computing details

Data collection: CrystalClear (Rigaku, 2001); cell refinement: CrystalClear; data reduction: CrystalStructure (Rigaku, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997b); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b); molecular graphics: SHELXL97; software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A packing diagram for (I), viewed down the c axis.

1-(4-Bromophenyl)-3-(4-methylphenyl)prop-2-en-1-one

Crystal data

C16H13BrO	F(000) = 608
Mr = 301.17	Dx = 1.538 Mg m^−3
Monoclinic, P21/c	Melting point = 437–439 K
Hall symbol: -p 2ybc	Mo Kα radiation, λ = 0.71070 Å
a = 15.600 (3) Å	Cell parameters from 4569 reflections
b = 14.235 (3) Å	θ = 3.2–25.0°
c = 5.8621 (11) Å	µ = 3.14 mm^−1
β = 92.029 (4)°	T = 193 K
V = 1301.0 (4) Å^3	Block, light-yellow
Z = 4	0.35 × 0.31 × 0.30 mm

Data collection

Rigaku MercuryCCD area-detector diffractometer	2267 independent reflections
Radiation source: fine-focus sealed tube	2144 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.051
Detector resolution: 7.31 pixels mm^-1	θmax = 25.0°, θmin = 3.2°
ω scans	h = −18→18
Absorption correction: multi-scan (Jacobson, 1998)	k = −16→16
Tmin = 0.356, Tmax = 0.382	l = −6→6
12258 measured reflections

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.091	H-atom parameters constrained
S = 1.24	w = 1/[σ^2(Fo^2) + (0.0295P)^2 + 1.5303P] where P = (Fo^2 + 2Fc^2)/3
2267 reflections	(Δ/σ)max = 0.001
166 parameters	Δρmax = 0.53 e Å^−3
0 restraints	Δρmin = −0.34 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
Br1	−0.38335 (2)	0.37129 (3)	0.22424 (7)	0.04250 (16)
O1	0.01755 (15)	0.38037 (19)	−0.1995 (4)	0.0432 (6)
C1	0.22169 (19)	0.3884 (2)	0.3007 (5)	0.0228 (6)
C2	0.2183 (2)	0.3475 (2)	0.5172 (5)	0.0249 (7)
H2	0.1650	0.3260	0.5705	0.030*
C3	0.2920 (2)	0.3382 (2)	0.6551 (5)	0.0262 (7)
H3	0.2885	0.3095	0.8008	0.031*
C4	0.3711 (2)	0.3702 (2)	0.5832 (5)	0.0265 (7)
C5	0.3741 (2)	0.4126 (2)	0.3704 (5)	0.0292 (7)
H5	0.4272	0.4363	0.3201	0.035*
C6	0.30137 (19)	0.4210 (2)	0.2304 (5)	0.0252 (7)
H6	0.3054	0.4493	0.0844	0.030*
C7	−0.09306 (19)	0.3758 (2)	0.0649 (5)	0.0236 (6)
C8	−0.1539 (2)	0.3431 (2)	−0.0966 (5)	0.0269 (7)
H8	−0.1358	0.3213	−0.2403	0.032*
C9	−0.2397 (2)	0.3422 (2)	−0.0500 (5)	0.0273 (7)
H9	−0.2807	0.3195	−0.1601	0.033*
C10	−0.26536 (19)	0.3747 (2)	0.1584 (5)	0.0261 (6)
C11	−0.2069 (2)	0.4095 (2)	0.3208 (5)	0.0277 (7)
H11	−0.2257	0.4336	0.4615	0.033*
C12	−0.12066 (19)	0.4086 (2)	0.2744 (5)	0.0266 (7)
H12	−0.0798	0.4304	0.3861	0.032*
C13	0.1473 (2)	0.3945 (2)	0.1434 (5)	0.0248 (7)
H13	0.1581	0.4145	−0.0075	0.030*
C14	0.06604 (19)	0.3753 (2)	0.1870 (5)	0.0271 (7)
H14	0.0510	0.3597	0.3380	0.033*
C15	−0.0012 (2)	0.3780 (2)	0.0020 (6)	0.0296 (7)
C16	0.4515 (2)	0.3583 (2)	0.7358 (5)	0.0315 (7)
H16A	0.4992	0.3379	0.6432	0.047*
H16B	0.4410	0.3110	0.8530	0.047*
H16C	0.4660	0.4183	0.8092	0.047*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0243 (2)	0.0459 (2)	0.0575 (3)	0.00039 (15)	0.00448 (15)	−0.00353 (18)
O1	0.0326 (13)	0.0721 (19)	0.0251 (13)	−0.0003 (12)	0.0043 (10)	0.0009 (12)
C1	0.0261 (16)	0.0183 (15)	0.0242 (15)	0.0022 (12)	0.0034 (12)	−0.0006 (12)
C2	0.0247 (16)	0.0223 (16)	0.0279 (16)	−0.0027 (12)	0.0042 (12)	−0.0004 (12)
C3	0.0333 (17)	0.0250 (16)	0.0206 (15)	0.0010 (13)	0.0033 (13)	0.0023 (12)
C4	0.0258 (16)	0.0262 (16)	0.0273 (16)	0.0024 (13)	−0.0010 (12)	−0.0017 (13)
C5	0.0238 (16)	0.0326 (18)	0.0313 (17)	−0.0026 (13)	0.0048 (13)	0.0013 (14)
C6	0.0286 (17)	0.0231 (16)	0.0240 (16)	−0.0009 (12)	0.0045 (12)	0.0020 (12)
C7	0.0249 (16)	0.0230 (15)	0.0228 (15)	0.0012 (12)	−0.0015 (12)	0.0030 (12)
C8	0.0304 (17)	0.0258 (16)	0.0244 (16)	0.0023 (13)	−0.0014 (13)	−0.0030 (12)
C9	0.0286 (17)	0.0240 (16)	0.0288 (17)	−0.0002 (13)	−0.0080 (13)	−0.0037 (13)
C10	0.0241 (16)	0.0208 (15)	0.0332 (17)	−0.0015 (12)	0.0006 (12)	0.0030 (13)
C11	0.0341 (18)	0.0268 (16)	0.0223 (16)	0.0015 (14)	0.0027 (13)	−0.0017 (12)
C12	0.0283 (17)	0.0278 (16)	0.0232 (16)	−0.0028 (13)	−0.0036 (12)	0.0006 (13)
C13	0.0296 (17)	0.0221 (15)	0.0228 (15)	0.0031 (12)	0.0035 (12)	0.0028 (12)
C14	0.0246 (16)	0.0300 (17)	0.0267 (16)	0.0007 (13)	0.0007 (12)	0.0036 (13)
C15	0.0295 (17)	0.0290 (17)	0.0300 (18)	0.0000 (13)	−0.0012 (13)	0.0000 (13)
C16	0.0238 (16)	0.041 (2)	0.0294 (17)	0.0026 (14)	−0.0020 (13)	0.0033 (14)

Geometric parameters (Å, º)

Br1—C10	1.895 (3)	C7—C15	1.493 (4)
O1—C15	1.228 (4)	C8—C9	1.375 (4)
C1—C2	1.398 (4)	C8—H8	0.9500
C1—C6	1.403 (4)	C9—C10	1.379 (4)
C1—C13	1.460 (4)	C9—H9	0.9500
C2—C3	1.388 (4)	C10—C11	1.387 (4)
C2—H2	0.9500	C11—C12	1.381 (4)
C3—C4	1.394 (4)	C11—H11	0.9500
C3—H3	0.9500	C12—H12	0.9500
C4—C5	1.389 (5)	C13—C14	1.330 (4)
C4—C16	1.524 (4)	C13—H13	0.9500
C5—C6	1.382 (4)	C14—C15	1.482 (4)
C5—H5	0.9500	C14—H14	0.9500
C6—H6	0.9500	C16—H16A	0.9800
C7—C12	1.396 (4)	C16—H16B	0.9800
C7—C8	1.397 (4)	C16—H16C	0.9800
C2—C1—C6	117.8 (3)	C10—C9—H9	120.4
C2—C1—C13	122.9 (3)	C9—C10—C11	121.5 (3)
C6—C1—C13	119.2 (3)	C9—C10—Br1	119.1 (2)
C3—C2—C1	120.8 (3)	C11—C10—Br1	119.3 (2)
C3—C2—H2	119.6	C12—C11—C10	118.9 (3)
C1—C2—H2	119.6	C12—C11—H11	120.6
C2—C3—C4	121.0 (3)	C10—C11—H11	120.6
C2—C3—H3	119.5	C11—C12—C7	120.6 (3)
C4—C3—H3	119.5	C11—C12—H12	119.7
C5—C4—C3	118.2 (3)	C7—C12—H12	119.7
C5—C4—C16	121.4 (3)	C14—C13—C1	127.5 (3)
C3—C4—C16	120.3 (3)	C14—C13—H13	116.3
C6—C5—C4	121.2 (3)	C1—C13—H13	116.3
C6—C5—H5	119.4	C13—C14—C15	120.6 (3)
C4—C5—H5	119.4	C13—C14—H14	119.7
C5—C6—C1	121.0 (3)	C15—C14—H14	119.7
C5—C6—H6	119.5	O1—C15—C14	121.3 (3)
C1—C6—H6	119.5	O1—C15—C7	120.1 (3)
C12—C7—C8	119.0 (3)	C14—C15—C7	118.6 (3)
C12—C7—C15	122.6 (3)	C4—C16—H16A	109.5
C8—C7—C15	118.3 (3)	C4—C16—H16B	109.5
C9—C8—C7	120.7 (3)	H16A—C16—H16B	109.5
C9—C8—H8	119.6	C4—C16—H16C	109.5
C7—C8—H8	119.6	H16A—C16—H16C	109.5
C8—C9—C10	119.2 (3)	H16B—C16—H16C	109.5
C8—C9—H9	120.4
C6—C1—C2—C3	−1.3 (4)	C9—C10—C11—C12	−2.1 (5)
C13—C1—C2—C3	176.0 (3)	Br1—C10—C11—C12	177.7 (2)
C1—C2—C3—C4	0.8 (5)	C10—C11—C12—C7	2.0 (5)
C2—C3—C4—C5	0.6 (5)	C8—C7—C12—C11	−0.6 (5)
C2—C3—C4—C16	−179.3 (3)	C15—C7—C12—C11	176.7 (3)
C3—C4—C5—C6	−1.6 (5)	C2—C1—C13—C14	9.5 (5)
C16—C4—C5—C6	178.3 (3)	C6—C1—C13—C14	−173.3 (3)
C4—C5—C6—C1	1.1 (5)	C1—C13—C14—C15	−175.1 (3)
C2—C1—C6—C5	0.3 (4)	C13—C14—C15—O1	13.8 (5)
C13—C1—C6—C5	−177.1 (3)	C13—C14—C15—C7	−167.5 (3)
C12—C7—C8—C9	−0.6 (5)	C12—C7—C15—O1	−154.7 (3)
C15—C7—C8—C9	−178.1 (3)	C8—C7—C15—O1	22.7 (5)
C7—C8—C9—C10	0.5 (5)	C12—C7—C15—C14	26.5 (4)
C8—C9—C10—C11	0.9 (5)	C8—C7—C15—C14	−156.1 (3)
C8—C9—C10—Br1	−178.9 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2^i—H2^i···O1	0.95	2.82	3.627 (3)	144
C14^i—H14^i···O1	0.95	2.80	3.702 (4)	160
C12^i—H12^i···O1	0.95	2.91	3.722 (4)	145
C5^ii—H5^ii···Br1	0.95	3.17	3.953 (5)	141
C16^ii—H16A^ii···Br1	0.98	3.15	4.026 (4)	149

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