2,4,5,7-Tetra­methyl­phenanthrene at 150 K

The title compound, C₁₈H₁₈, crystallized in the centrosymmetric space group P2₁/c with one mol­ecule as the asymmetric unit. The methyl-group H atoms at the 4 and 5 positions are ordered, while those at the 2 and 7 positions are disordered. The torsion of the bay region of the core is notably similar to that of other 4,5-di­methyl­phenanthrenes. No substantial C—H...π interaction occurs in this structure.

S1. Comment

2,4,5,7-Tetramethylphenanthrene, (I), was of interest because of its potential for C—H···π interactions as well as for structural comparisons with 4,5-dimethylphenanthrene [(IIa); Armstrong et al., 1987; (IIb); Cosmo et al., 1987; (IIc) Imashiro et al., 1987], and with 3,4,5,6-tetramethylphenanthrene [(III); Armstrong et al., 1987], which are identically substituted in the (crowded) bay region. Compound (I) crystallized in the centrosymmetric space group P2₁/c with one molecule as the asymmetric unit. The refined molecule and the labelling scheme are given in Fig. 1. The fully refined methyl groups at the 4 and 5 positions are ordered, while those at the 2 and 7 positions, refined with only their U_iso's fixed, have their H atoms disordered over two sets of sites with refined populations 0.54 (3) and 0.46 and 0.66 (2) and 0.34, respectively. The most striking molecular feature is, as expected, the departure of the core from the near planarity of phenanthrene itself (e.g. Kay et al., 1971), due to crowding in the bay region. A satisfactory measure of this departure is the magnitude of the bay torsion angle C4—C12—C13—C5, which is 32.4 (2)° in (I). This result is in very good accord with the values reported for 4,5-dimethylphenanthrene at room temperature: 31.5 (3), 33.0 and 32.2° for (IIa,b and c), respectively. It is also in very good accord with the corresponding value for 3,4,5,6-tetramethylphenanthrene (III), 32.9 (2)°, further confirming the evidence from Armstrong et al. (1987) that the placement of additional methyl groups in a 4,5-dimethylphenanthrene is of little importance in determining this torsion angle. In 4,5-diiodophenanthrene at 150 K (hereafter, DIP) (present labelling; Bock et al., 1998) the bay torsion angle is enlarged to 63°. However, other aspects of the ring geometries are very similar to those found in (I). Thus, C9—C10 and C12—C13 measure 1.348 (2) and 1.466 (2) Å in (I), and 1.348 (7) and 1.461 (5) Å (mean values) in DIP. Also, the mean values of C16—C4—C12 and C17—C5—C13 and of C4—C12—C13 and C5—C13—C12 are 123.39 (9) and 124.88 (9)° in (I), while the corresponding mean values (I—C—C and C—C—C) are given for DIP as 123.0 (3) and 126.2 (3)°. Thus, the geometric distortion of the individual rings is not significantly correlated with the torsion angle of the bay region. No substantial C—H···π interaction occurs in this structure. \sch

Selected bond distances and angles of (I) are given in Table 1. In (I) the molecular core displays very nearly twofold symmetry with respect to an axis through the midpoints of the C9—C10 and C12—C13 bonds. Thus, for example, the r.m.s. difference within the seven corresponding pairs of distances, which range from 1.378 (2) to 1.439 (2) Å, is 0.002 Å, while the r.m.s. difference within the eleven corresponding pairs of core carbon angles, which range from 116.81 (9) to 124.90 (9)°, is 0.2°. The packing diagram, Fig. 2, makes clear the molecular orientations, which place the terminal methyl group H atoms no farther than 1.76 Å from the bc faces of the unit cell. The closest intermolecular approaches are between H15A and H17Cⁱ (i = x, 3/2 − y, −1/2 + z) and fall short of the corresponding Bondi (1964) van der Waals radius sum by 0.20 Å. This suggests some preference for pairing of H15A,B,C occupancy with H17D,E,F occupancy, and vice versa.

S2. Experimental

Compound (I) was obtained as coarse, colorless crystals from a sample in Dr M. S. Newman's chemical collection. Evaporation of a solution of these in ethanol/acetone produced satisfactory crystals. A synthesis is described by Karnes et al. (1965).

S3. Refinement

Fourier difference methods were used to locate initial H-atom positions, and these H atoms were refined. It was then apparent that the methyl-H atoms on C15 and C18 are disordered, and two sets of H-atom sites, and occupancies, were refined on each. Absence of any further disorder was obvious since none of the subsequent top twenty-five difference peaks was suitable as a potential H atom. Refined C—H distances for the twelve full-occupancy H atoms ranged from 0.98 (1) to 1.02 (1) Å, with mean value 1.00 (2) Å; their U_iso values ranged from 1.0 to 1.6 times the U_eq values of the attached C atoms. The ring H atoms were then made canonical, with C—H = 0.98 Å and U_iso = 1.2 × U_eq of the attached C atom, and U_iso of the partial-occupancy H-atoms was fixed at 1.2 × U_eq of the attached C atom. Final refined C—H distances for the twelve partial-occupancy H-atoms ranged from 0.94 (4) to 1.07 (4) Å, with mean value 1.03 (4) Å.

Computing details

Data collection: COLLECT (Nonius, 1999); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: TEXSAN (Molecular Structure Corporation, 1995); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN and PLATON (Spek, 1990).

Figures

	Fig. 1. The molecular structure of (I) showing the labelling scheme, with displacement ellipsoids at the 50% probability level. Shaded spheres depict partial-occupancy H atoms.
	Fig. 2. Packing diagram of (I) viewed nearly down the a axis, with displacement ellipsoids at the 50% probability level. Shaded spheres depict partial-occupancy H atoms.

(I)

Crystal data

C18H18	F(000) = 504
Mr = 234.34	Dx = 1.198 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.3604 (2) Å	Cell parameters from 25832 reflections
b = 8.1567 (1) Å	θ = 2.1–27.5°
c = 19.1388 (4) Å	µ = 0.07 mm^−1
β = 95.467 (1)°	T = 150 K
V = 1299.20 (4) Å^3	Irregular hexagonal slab, colorless
Z = 4	0.38 × 0.27 × 0.15 mm

Data collection

Nonius KappaCCD diffractometer	2381 reflections with I > 2σI
Radiation source: X-ray tube	Rint = 0.036
Graphite monochromator	θmax = 27.5°
ω scans with κ offsets	h = −10→10
25832 measured reflections	k = −10→10
2981 independent reflections	l = −24→24

Refinement

Refinement on F^2	H atoms treated by a mixture of independent and constrained refinement
Least-squares matrix: full	Weighting scheme based on measured s.u.'s 1/[σ^2cs + (0.027 I)^2]
R[F^2 > 2σ(F^2)] = 0.043	(Δ/σ)max = 0.002
wR(F^2) = 0.096	Δρmax = 0.24 e Å^−3
S = 1.92	Δρmin = −0.21 e Å^−3
2981 reflections	Extinction correction: Zachariasen (1963, 1968)
226 parameters	Extinction coefficient: 13 (3) × 10^-7

Special details

Experimental. The Laue group assignment, the systematic absences and the centrosymmetry indicated by the intensity statistics led to assignment of the space group uniquely as P2₁/c (No. 14); since refinement proceeded well, it was adopted. In the later stages of refinement an extinction coefficient was included in the model. The maximum peak in the final difference map occurs ~0.4 Å from C6, the maximum negative peak ~0.8 Å from C8.

Geometry. Table of Least-Squares Planes ——————————

————– Plane number 1 —————

Atoms Defining Plane Distance e.s.d. C1 (1) −0.0187 0.0010 C2 (1) 0.0542 0.0010 C3 (1) −0.0250 0.0010 C4 (1) −0.0489 0.0009 C11 (1) −0.0461 0.0009 C12 (1) 0.0815 0.0009

Mean deviation from plane is 0.0457 angstroms Chi-squared: 18134.2

————– Plane number 2 —————

Atoms Defining Plane Distance e.s.d. C9 (1) −0.0648 0.0010 C10 (1) 0.0692 0.0010 C11 (1) 0.0239 0.0009 C12 (1) −0.1047 0.0009 C13 (1) 0.1109 0.0009 C14 (1) −0.0428 0.0009

Mean deviation from plane is 0.0694 angstroms Chi-squared: 39218.5

Dihedral angles between least-squares planes plane plane angle 2 1 13.24

————– Plane number 3 —————

Atoms Defining Plane Distance e.s.d. C5 (1) 0.0530 0.0009 C6 (1) 0.0273 0.0010 C7 (1) −0.0535 0.0010 C8 (1) 0.0118 0.0009 C13 (1) −0.0825 0.0009 C14 (1) 0.0483 0.0009

Mean deviation from plane is 0.0461 angstroms Chi-squared: 18680.8

Dihedral angles between least-squares planes plane plane angle 3 1 27.52 3 2 14.65

————– Plane number 4 —————

Atoms Defining Plane Distance e.s.d. C1 (2) 0.0187 0.0010 C2 (2) −0.0542 0.0010 C3 (2) 0.0250 0.0010 C4 (2) 0.0489 0.0009 C11 (2) 0.0461 0.0009 C12 (2) −0.0815 0.0009

Mean deviation from plane is 0.0457 angstroms Chi-squared: 18133.4

Dihedral angles between least-squares planes plane plane angle 4 1 87.98 4 2 99.39 4 3 113.69

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
C1	0.58428 (12)	0.78224 (12)	0.00185 (5)	0.0272 (3)
C2	0.73549 (12)	0.71663 (12)	−0.00079 (5)	0.0272 (3)
C3	0.77962 (12)	0.58835 (12)	0.04543 (5)	0.0278 (3)
C4	0.68624 (11)	0.53535 (12)	0.09707 (5)	0.0259 (3)
C5	0.49965 (12)	0.54262 (12)	0.23311 (5)	0.0271 (3)
C6	0.39107 (12)	0.50012 (12)	0.28030 (5)	0.0291 (3)
C7	0.22461 (12)	0.51057 (12)	0.26513 (6)	0.0299 (3)
C8	0.16887 (12)	0.58020 (12)	0.20181 (6)	0.0296 (3)
C9	0.21744 (12)	0.72549 (13)	0.09283 (5)	0.0289 (3)
C10	0.31955 (12)	0.78616 (12)	0.04892 (5)	0.0286 (3)
C11	0.48433 (12)	0.73300 (12)	0.05310 (5)	0.0247 (3)
C12	0.54118 (11)	0.62029 (11)	0.10648 (5)	0.0239 (3)
C13	0.44091 (11)	0.59115 (11)	0.16405 (5)	0.0241 (3)
C14	0.27369 (11)	0.62650 (12)	0.15223 (5)	0.0259 (3)
C15	0.84542 (16)	0.77056 (17)	−0.05426 (6)	0.0359 (4)
C16	0.73303 (15)	0.37554 (14)	0.13321 (6)	0.0330 (3)
C17	0.67335 (14)	0.55761 (16)	0.26180 (6)	0.0360 (3)
C18	0.11348 (17)	0.46007 (17)	0.31876 (7)	0.0397 (4)
H1	0.5455	0.8651	−0.0328	0.033*
H3	0.8822	0.5328	0.0411	0.033*
H6	0.4332	0.4606	0.3268	0.035*
H8	0.0532	0.5978	0.1912	0.036*
H9	0.1024	0.7494	0.0840	0.035*
H10	0.2810	0.8677	0.0136	0.034*
H15A	0.790 (3)	0.860 (4)	−0.0856 (13)	0.043*	0.54 (3)
H15B	0.883 (4)	0.677 (3)	−0.0859 (14)	0.043*	0.54
H15C	0.949 (3)	0.827 (4)	−0.0291 (12)	0.043*	0.54
H15D	0.967 (3)	0.743 (5)	−0.0403 (15)	0.043*	0.46
H15E	0.811 (4)	0.709 (4)	−0.1023 (15)	0.043*	0.46
H15F	0.837 (4)	0.888 (4)	−0.0669 (17)	0.043*	0.46
H16A	0.7551 (13)	0.2923 (15)	0.0953 (6)	0.051 (4)*
H16B	0.6466 (14)	0.3284 (12)	0.1596 (6)	0.043 (3)*
H16C	0.8348 (13)	0.3834 (13)	0.1649 (6)	0.044 (3)*
H17A	0.7452 (13)	0.6109 (13)	0.2284 (5)	0.041 (3)*
H17B	0.7232 (12)	0.4475 (15)	0.2753 (6)	0.048 (3)*
H17C	0.6790 (13)	0.6279 (15)	0.3055 (6)	0.053 (4)*
H18A	0.171 (2)	0.398 (3)	0.3583 (10)	0.047*	0.66 (14)
H18B	0.057 (3)	0.560 (2)	0.3382 (11)	0.047*	0.66
H18C	0.022 (2)	0.384 (3)	0.2942 (10)	0.047*	0.66
H18D	0.152 (5)	0.513 (5)	0.369 (2)	0.047*	0.34
H18E	0.119 (5)	0.331 (5)	0.330 (2)	0.047*	0.34
H18F	0.004 (5)	0.485 (6)	0.307 (2)	0.047*	0.34

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0334 (6)	0.0242 (6)	0.0235 (5)	0.0004 (5)	−0.0002 (5)	0.0011 (4)
C2	0.0313 (6)	0.0261 (6)	0.0242 (5)	−0.0021 (5)	0.0018 (4)	−0.0034 (4)
C3	0.0266 (6)	0.0262 (6)	0.0306 (6)	0.0026 (4)	0.0029 (5)	−0.0024 (5)
C4	0.0279 (6)	0.0223 (5)	0.0271 (5)	0.0002 (4)	−0.0001 (4)	−0.0005 (4)
C5	0.0308 (6)	0.0210 (5)	0.0292 (6)	0.0005 (4)	0.0021 (5)	−0.0001 (4)
C6	0.0370 (7)	0.0238 (6)	0.0266 (6)	0.0003 (5)	0.0034 (5)	0.0022 (4)
C7	0.0351 (6)	0.0205 (6)	0.0352 (6)	−0.0026 (5)	0.0097 (5)	−0.0033 (5)
C8	0.0264 (6)	0.0243 (6)	0.0386 (6)	−0.0010 (5)	0.0046 (5)	−0.0048 (5)
C9	0.0247 (6)	0.0295 (6)	0.0316 (6)	0.0036 (5)	−0.0020 (5)	−0.0041 (5)
C10	0.0322 (6)	0.0262 (6)	0.0263 (5)	0.0050 (5)	−0.0026 (5)	−0.0007 (4)
C11	0.0283 (6)	0.0205 (5)	0.0245 (5)	0.0007 (4)	−0.0011 (4)	−0.0035 (4)
C12	0.0257 (5)	0.0203 (5)	0.0250 (5)	−0.0025 (4)	−0.0005 (4)	−0.0026 (4)
C13	0.0268 (6)	0.0188 (5)	0.0267 (6)	−0.0015 (4)	0.0014 (4)	−0.0014 (4)
C14	0.0277 (6)	0.0213 (5)	0.0284 (6)	0.0000 (4)	0.0013 (4)	−0.0044 (4)
C15	0.0387 (7)	0.0391 (8)	0.0310 (6)	0.0025 (6)	0.0090 (6)	0.0042 (6)
C16	0.0330 (7)	0.0283 (6)	0.0379 (7)	0.0054 (5)	0.0049 (6)	0.0048 (5)
C17	0.0331 (7)	0.0433 (8)	0.0306 (7)	−0.0018 (6)	−0.0018 (5)	0.0061 (6)
C18	0.0406 (8)	0.0364 (8)	0.0442 (8)	−0.0032 (6)	0.0150 (6)	0.0033 (6)

Geometric parameters (Å, º)

C1—C2	1.3782 (14)	C10—H10	0.98
C1—C11	1.4064 (13)	C11—C12	1.4220 (13)
C1—H1	0.98	C12—C13	1.4661 (13)
C2—C3	1.3969 (14)	C13—C14	1.4242 (13)
C2—C15	1.5048 (15)	C15—H15A	1.03 (3)
C3—C4	1.3857 (13)	C15—H15B	1.04 (3)
C3—H3	0.98	C15—H15C	1.06 (3)
C4—C12	1.4229 (13)	C15—H15D	1.05 (3)
C4—C16	1.5096 (14)	C15—H15E	1.06 (3)
C5—C6	1.3843 (13)	C15—H15F	0.99 (3)
C5—C13	1.4216 (13)	C16—H16A	1.023 (12)
C5—C17	1.5078 (14)	C16—H16B	0.997 (11)
C6—C7	1.3969 (14)	C16—H16C	0.999 (11)
C6—H6	0.98	C17—H17A	1.016 (11)
C7—C8	1.3786 (14)	C17—H17B	1.013 (12)
C7—C18	1.5060 (15)	C17—H17C	1.011 (12)
C8—C14	1.4034 (13)	C18—H18A	1.00 (2)
C8—H8	0.98	C18—H18B	1.03 (2)
C9—C10	1.3477 (14)	C18—H18C	1.06 (2)
C9—C14	1.4365 (14)	C18—H18D	1.07 (4)
C9—H9	0.98	C18—H18E	1.07 (4)
C10—C11	1.4391 (14)	C18—H18F	0.94 (4)
C2—C1—C11	121.51 (9)	C8—C14—C9	120.53 (9)
C2—C1—H1	119.2	C8—C14—C13	120.32 (9)
C11—C1—H1	119.2	C9—C14—C13	118.81 (9)
C1—C2—C3	117.09 (9)	C2—C15—H15A	109.4 (14)
C1—C2—C15	122.22 (10)	C2—C15—H15B	114.7 (12)
C3—C2—C15	120.54 (10)	C2—C15—H15C	110.2 (12)
C2—C3—C4	123.55 (9)	C2—C15—H15D	113.8 (14)
C2—C3—H3	118.2	C2—C15—H15E	108.5 (14)
C4—C3—H3	118.2	C2—C15—H15F	114.4 (16)
C3—C4—C12	118.89 (9)	H15A—C15—H15B	109.2 (18)
C3—C4—C16	117.20 (9)	H15A—C15—H15C	105.1 (17)
C12—C4—C16	123.31 (9)	H15B—C15—H15C	107.8 (16)
C6—C5—C13	119.10 (9)	H15D—C15—H15E	107.0 (18)
C6—C5—C17	116.83 (9)	H15D—C15—H15F	108 (2)
C13—C5—C17	123.47 (9)	H15E—C15—H15F	104 (2)
C5—C6—C7	123.46 (9)	C4—C16—H16A	107.8 (7)
C5—C6—H6	118.3	C4—C16—H16B	113.4 (6)
C7—C6—H6	118.3	C4—C16—H16C	113.0 (6)
C6—C7—C8	117.03 (9)	H16A—C16—H16B	106.9 (9)
C6—C7—C18	120.58 (10)	H16A—C16—H16C	105.8 (8)
C8—C7—C18	122.20 (10)	H16B—C16—H16C	109.5 (8)
C7—C8—C14	121.65 (9)	C5—C17—H17A	114.3 (6)
C7—C8—H8	119.2	C5—C17—H17B	112.3 (6)
C14—C8—H8	119.2	C5—C17—H17C	108.3 (6)
C10—C9—C14	121.38 (9)	H17A—C17—H17B	106.7 (8)
C10—C9—H9	119.3	H17A—C17—H17C	107.1 (8)
C14—C9—H9	119.3	H17B—C17—H17C	107.8 (9)
C9—C10—C11	120.97 (9)	C7—C18—H18A	111.9 (10)
C9—C10—H10	119.5	C7—C18—H18B	111.2 (10)
C11—C10—H10	119.5	C7—C18—H18C	108.9 (10)
C1—C11—C10	120.29 (9)	C7—C18—H18D	110.4 (17)
C1—C11—C12	120.37 (9)	C7—C18—H18E	112.8 (18)
C10—C11—C12	119.17 (9)	C7—C18—H18F	115 (2)
C4—C12—C11	117.03 (9)	H18A—C18—H18B	109.4 (15)
C4—C12—C13	124.85 (9)	H18A—C18—H18C	108.5 (14)
C11—C12—C13	117.95 (8)	H18B—C18—H18C	106.8 (13)
C5—C13—C12	124.90 (9)	H18D—C18—H18E	102 (3)
C5—C13—C14	116.81 (9)	H18D—C18—H18F	109 (3)
C12—C13—C14	118.08 (9)	H18E—C18—H18F	107 (3)
C1—C2—C3—C4	−6.06 (15)	C6—C5—C13—C14	13.01 (14)
C1—C11—C10—C9	172.40 (9)	C6—C7—C8—C14	5.03 (15)
C1—C11—C12—C4	−12.92 (14)	C7—C6—C5—C13	−3.59 (15)
C1—C11—C12—C13	171.52 (8)	C7—C6—C5—C17	167.85 (10)
C2—C1—C11—C10	−171.41 (9)	C7—C8—C14—C9	−168.44 (9)
C2—C1—C11—C12	3.76 (15)	C7—C8—C14—C13	4.72 (15)
C2—C3—C4—C12	−3.31 (15)	C8—C14—C9—C10	172.62 (9)
C2—C3—C4—C16	168.19 (10)	C8—C14—C13—C12	171.28 (8)
C3—C2—C1—C11	5.76 (15)	C9—C10—C11—C12	−2.82 (15)
C3—C4—C12—C11	12.57 (14)	C9—C14—C13—C12	−15.45 (13)
C3—C4—C12—C13	−172.21 (8)	C10—C9—C14—C13	−0.64 (15)
C4—C3—C2—C15	178.25 (10)	C10—C11—C12—C13	−13.26 (13)
C4—C12—C11—C10	162.31 (9)	C11—C1—C2—C15	−178.62 (9)
C4—C12—C13—C5	32.43 (15)	C11—C10—C9—C14	10.09 (16)
C4—C12—C13—C14	−152.97 (9)	C11—C12—C4—C16	−158.38 (10)
C5—C6—C7—C8	−5.66 (15)	C11—C12—C13—C14	22.21 (13)
C5—C6—C7—C18	179.18 (10)	C12—C13—C5—C17	16.83 (16)
C5—C13—C12—C11	−152.38 (9)	C13—C12—C4—C16	16.84 (15)
C5—C13—C14—C8	−13.68 (14)	C14—C8—C7—C18	−179.90 (10)
C5—C13—C14—C9	159.59 (9)	C14—C13—C5—C17	−157.83 (10)
C6—C5—C13—C12	−172.33 (9)