sp-9-(o-Methyl­phenyl)­fluorene

While the barriers of rotation of the sp and ap rotamers of 9-(o-methyl­phenyl)­fluorene, C₂₀H₁₆, are sufficiently similar to permit them to equilibrate, both being observed (NMR) in solution, crystallization provides the sp rotamer, (I), exclusively. Although in the sp conformation the intramolecular distance between adjacent C atoms of the phenyl and fluorene rings is small [3.382 (4) Å, within 0.02 Å of the sum of the van der Waals radii], in the ap conformation the distance between the adjacent o-CH₃ group on the phenyl ring and C atom of the fluorene ring would be much closer, based on that exhibited in the crystalline ap progenitor 9-(o-methyl­phenyl)-9-fluorenol. The angle between the fluorene and 9-aryl planes of (I) is 75.82 (10)°.

S1. Comment

Crystalline 9-(o-methylphenyl)fluorene, (I), prepared from ap-9-(o-methylphenyl)-9-fluorenol, (II) (Meyers Robinson & McLean, 2003), is entirely composed of the sp rotamer. The structure of sp-(I), with the atom-numbering scheme, is shown in Fig. 1. The angle between the fluorene and 9-aryl planes is 75.82 (10)°. \sch

Geometric intermolecular calculations suggest the possible presence of a weak C4—H4···Cg1ⁱ interaction [where Cg1 is the centroid of the C1—C4/C4a/C9a ring; symmetry code: (i) 1 − x, 1/2 + y, 1/2 − z] with an H—A distance of 2.82 Å, a D—A distance of 3.634 (3) Å and a D—H···A angle of 146°. This rather poor geometry suggests only a possible weak interaction at best. In addition, the fact that, after melting, (I) recrystallizes immediately at room temperature suggests the absence of any effective intermolecular hydrogen bonding, based on the tentative correlations raised by our related studies (McLean et al., 2004; Meyers Robinson & McLean, 2003; Robinson et al., 2003a,b; McLean et al., 2003a,b; Meyers McLean & Robinson, 2003).

Although in this sp conformation the intramolecular distance between atoms C15 and C8 of (I) is small [3.382 (4) Å, 0.02 Å within the sum of the van der Waals radii], in the ap conformation the distance between the CH₃ group (C16) and the fluorene ring (C8a) would be much closer, e.g. near the value of 3.140 (3) Å, 0.26 Å within the sum of the van der Waals radii, of its crystalline ap progenitor (II). The latter's sp conformation is so sterically hindered by the 9-OH group that it is not observed in solution (although the ¹H NMR resonance of the o-CH₃ is broad; Meyers Robinson & McLean, 2003). This restriction is alleviated in (I) by the replacement of the 9-OH by H. These factors plausibly account for the equilibration of (I)-sp (60%) and (I)-ap (40%) in solution, in which the rotation is allowed but is slow enough to permit each to be observed. In turn, this interpretation appears much more valid than one suggesting that it is the intramolecular attractive interaction (van der Waals forces) between the o-methyl H atoms and the fluorene ring in (II) that promotes its ap rotamer exclusivity even in solution.

This explanation is strengthened by our earlier observations with the corresponding o-isopropyl compounds, which parallel those described above. Thus, like (I), 9-(o-isopropylphenyl)fluorene (Meyers et al., 1997) in solution also exhibited equilibrating sp [(III), 70%] and ap [(IIIa), 30%] rotamers, but crystallization provided the sp rotamer exclusively, while the corresponding 9-fluorenol, (IV) (Hou et al., 1999), like 9-fluorenol, (II), exists entirely as the ap rotamer both in solution and in the crystal. In contrast with these examples, the greater magnitude of steric hindrance between an o-tert-butyl group and the fluorene ring in the ap conformation (V) reduces the rotational barrier of that rotamer substantially, forcing 9-(o-tert-butylphenyl)fluorene, (Va), and its corresponding 9-fluorenol, (VI), to exist exclusively in their sp rotamers in solution as well as in their crystalline forms (Robinson et al., 1998). The very low rotational barrier of the highly hindered ap-9-(o-tert-butylphenyl)fluorene rotamer, (V), has been shown by the observation that, although it is exclusively formed via deprotonation-reprotonation inversion of the sp rotamer (Va), it rapidly rotates back to 100% of the sp rotamer (Hou & Meyers, 2004).

S2. Experimental

A solution of I₂ (0.018 g, 0.071 mmol), 50% aqueous H₃PO₂ (1.4 ml, 13.52 mmol) and glacial acetic acid (10 ml) was heated under argon until it became colorless, and 9-(o-methylphenyl)-9-fluorenol (Meyers Robinson & McLean, 2003; 0.317 g, 0.663 mmol) was then added. The yellow mixture was refluxed under argon for 5 h, cooled, water (50 ml) was added and the mixture was extracted with ether. The combined extracts were washed with saturated aqueous sodium bicarbonate, dried (anhydrous MgSO₄) and concentrated in vacuo to give a pale-yellow solid (0.283 g, 95% yield). Recrystallization (hexanes/methanol; Ratio?) afforded pale-yellow crystals of (I) [m.p. 363–364 K; literature m.p. 365–367.5 K (Bordwell et al., 1982)]. The melt crystallized immediately upon cooling, the resulting crystals having the same m.p. as those prior to melting. Spectroscopic analysis: ¹H NMR (CDCl₃, δ, p.p.m.): 1.14 (s, ap, 1.2H), 2.79 (s, sp, 1.8H, CH₃, two rotamers), 5.03 (s, ap, 0.4H), 5.43 (s, sp, 0.6H, 9-H, two rotamers), 6.37–6.39 (m, 1H), 6.89–6.99 (m, 1H), 7.09–7.14 (m, 1H), 7.22–7.41 (m, 2H), 7.61–7.64 (m, 1H), 7.81–7.84 (m, 2H); ¹³C NMR (Solvent?, δ, p.p.m.): 20.47, 49.92, 56.19, 98.98, 119.89, 124.69, 125.06, 125.72, 126.48, 126.58, 127.13, 127.27, 127.49, 130.32, 131.59, 132.63.

S3. Refinement

The rotational orientation of the methyl group was refined by the circular Fourier method available in SHELXL97 (Sheldrick, 1997). All H atoms were treated as riding, with C—H distances ranging from 0.93 to 0.98 Å and U_iso(H) values equal to 1.5 (methyl H atoms) or 1.2 (all other H atoms) times U_eq of the parent atom.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1996); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: PROCESS in TEXSAN (Molecular Structure Corporation, 1997); program(s) used to solve structure: SIR92 (Burla et al., 1989); program(s) used to refine structure: LS in TEXSAN and SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: TEXSAN, SHELXL97 and PLATON (Spek, 2003).

Figures

Fig. 1. The molecular structure and atom numbering scheme for (I), with displacement ellipsoids drawn at the 30% probability level.

sp-9-(o-Methylphenyl)fluorene

Crystal data

C20H16	F(000) = 544
Mr = 256.33	Dx = 1.187 Mg m^−3
Monoclinic, P21/c	Melting point = 363–364 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71069 Å
a = 12.9887 (17) Å	Cell parameters from 25 reflections
b = 6.075 (2) Å	θ = 14.8–19.2°
c = 18.7903 (16) Å	µ = 0.07 mm^−1
β = 104.701 (8)°	T = 296 K
V = 1434.1 (5) Å^3	Irregular fragment, colorless
Z = 4	0.49 × 0.46 × 0.35 mm

Data collection

Rigaku AFC-5S diffractometer	Rint = 0.018
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 2.2°
Graphite monochromator	h = 0→15
ω scans	k = 0→7
2659 measured reflections	l = −22→21
2539 independent reflections	3 standard reflections every 100 reflections
1515 reflections with I > 2σ(I)	intensity decay: 4.2%

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)] = 0.050	H-atom parameters constrained
wR(F^2) = 0.166	w = 1/[σ^2(Fo^2) + (0.0776P)^2 + 0.3078P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
2539 reflections	Δρmax = 0.33 e Å^−3
183 parameters	Δρmin = −0.16 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.016 (3)

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

	x	y	z	Uiso*/Ueq
C1	0.47360 (17)	0.4216 (4)	0.39627 (13)	0.0623 (7)
C2	0.55518 (19)	0.5692 (5)	0.39790 (14)	0.0724 (8)
C3	0.5442 (2)	0.7322 (5)	0.34593 (15)	0.0764 (8)
C4	0.4512 (2)	0.7534 (4)	0.29098 (14)	0.0705 (7)
C4a	0.36868 (18)	0.6061 (4)	0.28905 (11)	0.0551 (6)
C4b	0.26137 (18)	0.5909 (4)	0.23986 (12)	0.0583 (6)
C5	0.2098 (2)	0.7248 (5)	0.18170 (14)	0.0780 (8)
C6	0.1062 (3)	0.6768 (6)	0.14583 (14)	0.0918 (10)
C7	0.0542 (2)	0.4980 (7)	0.16644 (14)	0.0893 (10)
C8	0.10501 (19)	0.3642 (5)	0.22441 (13)	0.0756 (8)
C8a	0.20878 (17)	0.4130 (4)	0.26142 (11)	0.0572 (6)
C9	0.27986 (16)	0.3003 (4)	0.32818 (11)	0.0531 (6)
C9a	0.38099 (16)	0.4391 (4)	0.34154 (12)	0.0515 (6)
C10	0.23389 (16)	0.2900 (4)	0.39546 (11)	0.0539 (6)
C11	0.25802 (19)	0.1221 (4)	0.44706 (14)	0.0676 (7)
C12	0.2123 (2)	0.1281 (6)	0.50783 (14)	0.0787 (8)
C13	0.1495 (2)	0.3029 (6)	0.51686 (16)	0.0859 (9)
C14	0.1284 (2)	0.4708 (6)	0.46847 (15)	0.0854 (9)
C15	0.16843 (17)	0.4625 (5)	0.40754 (13)	0.0687 (7)
C16	0.3297 (3)	−0.0595 (5)	0.44158 (19)	0.1017 (10)
H1	0.4813	0.3119	0.4318	0.075*
H2	0.6182	0.5579	0.4346	0.087*
H3	0.6000	0.8296	0.3477	0.092*
H4	0.4440	0.8643	0.2559	0.085*
H5	0.2447	0.8441	0.1674	0.094*
H6	0.0704	0.7658	0.1071	0.110*
H7	−0.0157	0.4675	0.1411	0.107*
H8	0.0701	0.2440	0.2382	0.091*
H9	0.2956	0.1506	0.3146	0.064*
H12	0.2248	0.0135	0.5418	0.094*
H13	0.1208	0.3052	0.5575	0.103*
H14	0.0875	0.5899	0.4762	0.103*
H15	0.1516	0.5752	0.3730	0.082*
H16A	0.3126	−0.1140	0.3920	0.153*
H16B	0.3216	−0.1757	0.4744	0.153*
H16C	0.4019	−0.0079	0.4548	0.153*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0531 (13)	0.0756 (17)	0.0583 (13)	−0.0021 (12)	0.0142 (11)	0.0058 (13)
C2	0.0563 (14)	0.096 (2)	0.0649 (15)	−0.0114 (15)	0.0157 (12)	−0.0004 (15)
C3	0.0658 (16)	0.092 (2)	0.0765 (17)	−0.0238 (15)	0.0279 (14)	−0.0057 (16)
C4	0.0800 (18)	0.0718 (18)	0.0688 (16)	−0.0058 (14)	0.0352 (14)	0.0049 (13)
C4a	0.0564 (13)	0.0647 (15)	0.0501 (12)	0.0042 (12)	0.0243 (10)	−0.0003 (11)
C4b	0.0617 (14)	0.0725 (16)	0.0460 (12)	0.0121 (12)	0.0232 (11)	0.0021 (12)
C5	0.0829 (19)	0.097 (2)	0.0582 (15)	0.0223 (16)	0.0259 (14)	0.0165 (15)
C6	0.087 (2)	0.134 (3)	0.0544 (16)	0.039 (2)	0.0168 (15)	0.0165 (18)
C7	0.0618 (16)	0.151 (3)	0.0522 (16)	0.0203 (19)	0.0087 (13)	−0.0058 (18)
C8	0.0592 (15)	0.114 (2)	0.0534 (14)	−0.0002 (16)	0.0131 (12)	−0.0049 (15)
C8a	0.0517 (12)	0.0780 (17)	0.0432 (11)	0.0073 (12)	0.0147 (10)	−0.0030 (12)
C9	0.0505 (12)	0.0593 (14)	0.0510 (12)	0.0005 (11)	0.0157 (10)	−0.0019 (11)
C9a	0.0494 (12)	0.0604 (14)	0.0492 (12)	0.0023 (11)	0.0209 (10)	−0.0029 (11)
C10	0.0470 (12)	0.0682 (16)	0.0450 (12)	−0.0147 (11)	0.0088 (9)	−0.0003 (11)
C11	0.0606 (15)	0.0704 (17)	0.0679 (16)	−0.0177 (13)	0.0095 (12)	0.0047 (14)
C12	0.0755 (17)	0.094 (2)	0.0626 (16)	−0.0289 (17)	0.0104 (14)	0.0114 (15)
C13	0.0716 (18)	0.122 (3)	0.0673 (18)	−0.0227 (19)	0.0234 (15)	−0.0060 (19)
C14	0.0678 (16)	0.120 (3)	0.0744 (18)	−0.0059 (17)	0.0284 (14)	−0.0142 (19)
C15	0.0519 (13)	0.100 (2)	0.0594 (14)	−0.0103 (14)	0.0238 (11)	−0.0147 (14)
C16	0.123 (3)	0.072 (2)	0.116 (3)	−0.005 (2)	0.041 (2)	0.0086 (19)

Geometric parameters (Å, º)

C1—C9a	1.374 (3)	C12—C13	1.376 (4)
C1—C2	1.382 (3)	C13—C14	1.348 (4)
C2—C3	1.372 (4)	C14—C15	1.374 (3)
C3—C4	1.381 (4)	C1—H1	0.9300
C4—C4a	1.390 (3)	C2—H2	0.9300
C4a—C9a	1.396 (3)	C3—H3	0.9300
C4a—C4b	1.467 (3)	C4—H4	0.9300
C4b—C5	1.390 (3)	C5—H5	0.9300
C4b—C8a	1.393 (3)	C6—H6	0.9300
C5—C6	1.375 (4)	C7—H7	0.9300
C6—C7	1.385 (5)	C8—H8	0.9300
C7—C8	1.385 (4)	C9—H9	0.9800
C8a—C8	1.383 (3)	C12—H12	0.9300
C8a—C9	1.519 (3)	C13—H13	0.9300
C9a—C9	1.527 (3)	C14—H14	0.9300
C9—C10	1.530 (3)	C15—H15	0.9300
C10—C11	1.387 (3)	C16—H16A	0.9600
C10—C15	1.403 (3)	C16—H16B	0.9600
C11—C12	1.415 (4)	C16—H16C	0.9600
C11—C16	1.464 (4)
C9a—C1—C2	119.1 (2)	C9a—C1—H1	120.4
C3—C2—C1	120.7 (2)	C2—C1—H1	120.4
C2—C3—C4	120.9 (2)	C3—C2—H2	119.6
C3—C4—C4a	118.8 (2)	C1—C2—H2	119.6
C4—C4a—C9a	120.0 (2)	C2—C3—H3	119.6
C4—C4a—C4b	131.3 (2)	C4—C3—H3	119.6
C9a—C4a—C4b	108.7 (2)	C3—C4—H4	120.6
C5—C4b—C8a	120.6 (2)	C4a—C4—H4	120.6
C5—C4b—C4a	130.5 (2)	C6—C5—H5	120.7
C8a—C4b—C4a	108.9 (2)	C4b—C5—H5	120.7
C6—C5—C4b	118.5 (3)	C5—C6—H6	119.5
C5—C6—C7	121.0 (3)	C7—C6—H6	119.5
C8—C7—C6	120.7 (3)	C8—C7—H7	119.6
C8—C8a—C4b	120.5 (2)	C6—C7—H7	119.6
C8—C8a—C9	129.0 (2)	C8a—C8—H8	120.7
C4b—C8a—C9	110.48 (19)	C7—C8—H8	120.7
C8a—C8—C7	118.6 (3)	C8a—C9—H9	109.1
C1—C9a—C4a	120.4 (2)	C9a—C9—H9	109.1
C1—C9a—C9	129.3 (2)	C10—C9—H9	109.1
C4a—C9a—C9	110.21 (19)	C13—C12—H12	119.9
C8a—C9—C9a	101.79 (19)	C11—C12—H12	119.9
C8a—C9—C10	114.70 (18)	C14—C13—H13	119.1
C9a—C9—C10	112.73 (17)	C12—C13—H13	119.1
C11—C10—C15	118.3 (2)	C13—C14—H14	120.7
C11—C10—C9	122.8 (2)	C15—C14—H14	120.7
C15—C10—C9	118.8 (2)	C14—C15—H15	118.8
C10—C11—C12	118.6 (3)	C10—C15—H15	118.8
C10—C11—C16	122.7 (2)	C11—C16—H16A	109.5
C12—C11—C16	118.7 (3)	C11—C16—H16B	109.5
C13—C12—C11	120.2 (3)	H16A—C16—H16B	109.5
C14—C13—C12	121.8 (3)	C11—C16—H16C	109.5
C13—C14—C15	118.6 (3)	H16A—C16—H16C	109.5
C14—C15—C10	122.4 (3)	H16B—C16—H16C	109.5
C9a—C1—C2—C3	0.3 (4)	C4b—C4a—C9a—C9	0.8 (2)
C1—C2—C3—C4	0.3 (4)	C8—C8a—C9—C9a	−178.4 (2)
C2—C3—C4—C4a	−0.1 (4)	C4b—C8a—C9—C9a	−0.2 (2)
C3—C4—C4a—C9a	−0.7 (3)	C8—C8a—C9—C10	−56.4 (3)
C3—C4—C4a—C4b	177.9 (2)	C4b—C8a—C9—C10	121.8 (2)
C4—C4a—C4b—C5	−2.1 (4)	C1—C9a—C9—C8a	177.8 (2)
C9a—C4a—C4b—C5	176.6 (2)	C4a—C9a—C9—C8a	−0.4 (2)
C4—C4a—C4b—C8a	−179.7 (2)	C1—C9a—C9—C10	54.4 (3)
C9a—C4a—C4b—C8a	−1.0 (2)	C4a—C9a—C9—C10	−123.8 (2)
C8a—C4b—C5—C6	−0.3 (4)	C8a—C9—C10—C11	150.5 (2)
C4a—C4b—C5—C6	−177.7 (2)	C9a—C9—C10—C11	−93.7 (3)
C4b—C5—C6—C7	−0.6 (4)	C8a—C9—C10—C15	−32.6 (3)
C5—C6—C7—C8	0.8 (4)	C9a—C9—C10—C15	83.3 (2)
C5—C4b—C8a—C8	1.2 (3)	C15—C10—C11—C12	2.4 (3)
C4a—C4b—C8a—C8	179.1 (2)	C9—C10—C11—C12	179.4 (2)
C5—C4b—C8a—C9	−177.2 (2)	C15—C10—C11—C16	−176.9 (2)
C4a—C4b—C8a—C9	0.7 (2)	C9—C10—C11—C16	0.1 (4)
C4b—C8a—C8—C7	−1.1 (4)	C10—C11—C12—C13	−3.1 (4)
C9—C8a—C8—C7	177.0 (2)	C16—C11—C12—C13	176.3 (3)
C6—C7—C8—C8a	0.1 (4)	C11—C12—C13—C14	0.9 (4)
C2—C1—C9a—C4a	−1.2 (3)	C12—C13—C14—C15	1.9 (4)
C2—C1—C9a—C9	−179.2 (2)	C13—C14—C15—C10	−2.6 (4)
C4—C4a—C9a—C1	1.4 (3)	C11—C10—C15—C14	0.4 (4)
C4b—C4a—C9a—C1	−177.54 (19)	C9—C10—C15—C14	−176.8 (2)
C4—C4a—C9a—C9	179.7 (2)