α-Methyl­styrene

The crystal structure of α-methyl­styrene, C₉H₁₀, has been determined at 180 (2) K following in situ crystal growth from the liquid. In space group P2₁/n, the structure consists of herring-bone-packed layers within which intermolecular C—H...π interactions are evident.

Key indicators

• Single-crystal X-ray study
• T = 180 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.085
• wR factor = 0.250
• Data-to-parameter ratio = 10.8

checkCIF results

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ADDSYM reports no extra symmetry


 Alert Level A:



THETM_01  Alert A The value of sine(theta_max)/wavelength is less than 0.550
          Calculated sin(theta_max)/wavelength =    0.5344


 1 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

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S1. Comment

As part of a study devoted to improving techniques for determining the crystal structures of substances that are liquid at room temperature, we have recently reported the structure of styrene, C₈H₈ (Bond & Davies, 2001; Yasuda et al., 2001). We report here the crystal structure of the α-methyl derivative, C₉H₁₀, determined at 180 (2) K following in situ crystal growth from the liquid.

α-Methylstyrene, (I), crystallizes in the monoclinic space group P2₁/n with one whole molecule in the asymmetric unit (Fig. 1). The propenyl substituent lies approximately coplanar with the phenyl ring [the angle between the least-squares planes through C1–C6 and C7–C9 is 1.8 (3)°]. Molecules of (I) form herring-bone packed layers parallel to (001) (Fig. 2). These layers may be considered to stack in an ABAB arrangement (Fig. 3). C—H···π interactions are evident between molecules within layers [H5···cent(C7–C8)ⁱ = 3.06 Å, C5—H5···cent(C7–C8)ⁱ = 153°; H6···cent(C1–C6)ⁱ = 3.06 Å, C6—H6···cent(C1–C6)ⁱ = 137°; H8B···cent(C1–C6)ⁱⁱ = 3.03 Å, C8—H8B···cent(C1–C6)ⁱⁱ = 138°; symmetry codes: (i) -0.5 - x, 0.5 + y, 0.5 - z; (ii) 0.5 - x, -0.5 + y, 0.5 - z; cent denotes the centroid of the indicated ring]. A similar arrangement is observed in styrene itself, but in that case, the α-hydrogen also acts as a C—H···π donor; this interaction is clearly prohibited in (I).

S2. Experimental

The sample (99%) was obtained from the Lancaster company and used without further purification. The crystal was grown in a 0.3 mm glass capillary tube at ca 247.4 K (a temperature only slightly less than the melting point of the solid in the capillary) using a technique described earlier (Davies & Bond, 2001). Once grown, the crystal was cooled to 180 (2) K for data collection. The length of the cylindrical crystal was not estimated, but it exceeded the diameter of the collimator (0.35 mm).

S3. Refinement

H atoms were placed geometrically and allowed to ride during subsequent refinement with U_iso(H) = xU_eq(C) (x = 1.2 for alkene and phenyl H, and 1.5 for methyl H). The methyl group was allowed to rotate about its local threefold axis. No significant diffracted intensity was observed beyond 22.5° in θ (equivalent to 0.93 Å resolution) and the data were truncated at this point; the precision of the result is reduced accordingly.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Sheldrick, 1993) and CAMERON (Watkin et al., 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular unit in (I), showing displacement ellipsoids at the 50% probability level for non-H atoms (XP; Sheldrick, 1993).
	Fig. 2. Projection on to (001) of a single layer of (I), showing the herring-bone packing arrangement (CAMERON; Watkin et al., 1996).
	Fig. 3. Projection of (I) on to (100). C—H···π interactions are indicated by dotted lines (CAMERON; Watkin et al., 1996).

isopropenylbenzene

Crystal data

C9H10	Dx = 1.095 Mg m^−3
Mr = 118.17	Melting point: 250 K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.7107 Å
a = 5.795 (1) Å	Cell parameters from 2680 reflections
b = 7.829 (1) Å	θ = 1.0–22.5°
c = 15.820 (1) Å	µ = 0.06 mm^−1
β = 93.23 (1)°	T = 180 K
V = 716.60 (16) Å^3	Cylinder, colourless
Z = 4	0.15 mm (radius)
F(000) = 256

Data collection

Nonius KappaCCD diffractometer	676 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.089
Graphite monochromator	θmax = 22.3°, θmin = 3.7°
Thin–slice ω and ϕ scans	h = −5→6
3208 measured reflections	k = −7→8
895 independent reflections	l = −15→16

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)] = 0.085	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.250	H-atom parameters constrained
S = 1.15	w = 1/[σ^2(Fo^2) + (0.1448P)^2 + 0.2267P] where P = (Fo^2 + 2Fc^2)/3
895 reflections	(Δ/σ)max < 0.001
83 parameters	Δρmax = 0.37 e Å^−3
0 restraints	Δρmin = −0.27 e Å^−3

Special details

Experimental. Crystal grown in situ at 247.4 K in 0.3 mm diameter glass capillary tube.

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.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

3.0239 (0.0069) x + 6.6056 (0.0061) y + 1.5219 (0.0192) z = 1.4245 (0.0060)

* 0.0002 (0.0019) C1 * -0.0008 (0.0020) C2 * -0.0005 (0.0022) C3 * 0.0024 (0.0022) C4 * -0.0030 (0.0021) C5 * 0.0018 (0.0020) C6

Rms deviation of fitted atoms = 0.0018

3.0744 (0.0127) x + 6.5936 (0.0096) y + 1.0447 (0.0850) z = 1.3655 (0.0095)

Angle to previous plane (with approximate e.s.d.) = 1.78 (0.27)

* 0.0000 (0.0000) C7 * 0.0000 (0.0000) C8 * 0.0000 (0.0000) C9

Rms deviation of fitted atoms = 0.0000

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
C1	0.0133 (5)	0.1575 (3)	0.22612 (18)	0.0411 (10)
C2	0.1594 (5)	0.0765 (4)	0.2865 (2)	0.0529 (11)
H2	0.2931	0.0192	0.2690	0.064*
C3	0.1140 (6)	0.0778 (4)	0.3716 (2)	0.0579 (11)
H3	0.2161	0.0216	0.4116	0.070*
C4	−0.0787 (6)	0.1603 (4)	0.3982 (2)	0.0593 (11)
H4	−0.1095	0.1618	0.4565	0.071*
C5	−0.2261 (6)	0.2404 (4)	0.3398 (2)	0.0563 (11)
H5	−0.3602	0.2967	0.3576	0.068*
C6	−0.1790 (6)	0.2391 (4)	0.2549 (2)	0.0535 (11)
H6	−0.2817	0.2960	0.2153	0.064*
C7	0.0638 (6)	0.1560 (4)	0.1350 (2)	0.0518 (11)
C8	0.2540 (6)	0.0716 (5)	0.1078 (2)	0.0685 (12)
H8A	0.2814	0.0681	0.0492	0.082*
H8B	0.3581	0.0167	0.1477	0.082*
C9	−0.0938 (7)	0.2390 (5)	0.0749 (2)	0.0731 (13)
H9A	−0.0436	0.2199	0.0175	0.110*
H9B	−0.0961	0.3618	0.0867	0.110*
H9C	−0.2492	0.1918	0.0795	0.110*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0422 (19)	0.0306 (16)	0.050 (2)	−0.0042 (12)	−0.0015 (14)	−0.0005 (12)
C2	0.048 (2)	0.0472 (18)	0.063 (2)	0.0071 (14)	−0.0020 (16)	−0.0025 (14)
C3	0.066 (2)	0.055 (2)	0.051 (2)	0.0043 (16)	−0.0110 (17)	0.0051 (15)
C4	0.075 (3)	0.053 (2)	0.050 (2)	−0.0062 (17)	0.0070 (17)	−0.0032 (15)
C5	0.050 (2)	0.057 (2)	0.062 (2)	0.0041 (15)	0.0075 (17)	−0.0044 (15)
C6	0.051 (2)	0.0481 (19)	0.060 (2)	0.0013 (14)	−0.0086 (17)	0.0020 (14)
C7	0.060 (2)	0.0428 (18)	0.052 (2)	−0.0090 (14)	−0.0020 (16)	−0.0013 (13)
C8	0.077 (3)	0.070 (2)	0.061 (2)	0.0117 (19)	0.0174 (19)	0.0002 (17)
C9	0.073 (3)	0.093 (3)	0.053 (3)	0.001 (2)	−0.0033 (19)	0.0014 (18)

Geometric parameters (Å, º)

C1—C6	1.384 (4)	C5—H5	0.950
C1—C2	1.393 (4)	C6—H6	0.950
C1—C7	1.487 (4)	C7—C8	1.375 (5)
C2—C3	1.386 (5)	C7—C9	1.436 (5)
C2—H2	0.950	C8—H8A	0.950
C3—C4	1.376 (5)	C8—H8B	0.950
C3—H3	0.950	C9—H9A	0.980
C4—C5	1.374 (5)	C9—H9B	0.980
C4—H4	0.950	C9—H9C	0.980
C5—C6	1.385 (5)
C6—C1—C2	117.0 (3)	C1—C6—C5	121.9 (3)
C6—C1—C7	121.9 (3)	C1—C6—H6	119.0
C2—C1—C7	121.1 (3)	C5—C6—H6	119.0
C3—C2—C1	121.4 (3)	C8—C7—C9	120.1 (3)
C3—C2—H2	119.3	C8—C7—C1	120.8 (3)
C1—C2—H2	119.3	C9—C7—C1	119.1 (3)
C4—C3—C2	120.1 (3)	C7—C8—H8A	120.0
C4—C3—H3	119.9	C7—C8—H8B	120.0
C2—C3—H3	119.9	H8A—C8—H8B	120.0
C5—C4—C3	119.5 (3)	C7—C9—H9A	109.5
C5—C4—H4	120.2	C7—C9—H9B	109.5
C3—C4—H4	120.2	H9A—C9—H9B	109.5
C4—C5—C6	120.0 (3)	C7—C9—H9C	109.5
C4—C5—H5	120.0	H9A—C9—H9C	109.5
C6—C5—H5	120.0	H9B—C9—H9C	109.5
C6—C1—C2—C3	0.0 (4)	C7—C1—C6—C5	179.9 (3)
C7—C1—C2—C3	179.8 (3)	C4—C5—C6—C1	0.6 (5)
C1—C2—C3—C4	−0.1 (5)	C6—C1—C7—C8	−178.9 (3)
C2—C3—C4—C5	0.4 (5)	C2—C1—C7—C8	1.3 (4)
C3—C4—C5—C6	−0.6 (5)	C6—C1—C7—C9	−1.2 (4)
C2—C1—C6—C5	−0.3 (4)	C2—C1—C7—C9	179.1 (3)