ap-9-(o-Methyl­phenyl)-9-fluorenol, a structure exhibiting several aryl-H...π(arene) intermolecular interactions

The title compound, C₂₀H₁₆O, (I), which crystallized exclusively as its ap rotamer, exhibits several intermolecular aryl-H...π(arene) interactions, resulting in planar molecular arrays in which each mol­ecule interacts with six adjacent mol­ecules. Surprisingly, there were no O—H...O—H or O—H...π(arene) interactions within hydrogen-bonding distances. Crystalline (I) melted sharply without molecular decomposition (NMR), but the cooled melt recrystallized only after several hours.

S1. Comment

ap-9-(o-Methylphenyl)-9-fluorenol, (I), prepared from the reaction of fluorenone with o-tolylmagnesium bromide, crystallized as its ap rotamer, as illustrated with the atom-numbering in Fig. 1, which was also its exclusive conformation in solution, determined by NMR resonance. Several intermolecular aryl-H···π(arene) interactions were observed, resulting in planar molecular arrays in which each molecule interacts with six adjacent molecules, shown in Fig. 2. Surprisingly, there were no O—H···OH or O—H···π(arene) interactions within hydrogen-bonding distances, the only remote possibility being the latter in which a near interaction with an H···A distance of 3.02 Å, a D···A distance of 3.783 (3) Å, and a D—H···A angle of 157° was observed. While (I) exhibited a sharp melting point, the melt recrystallized only after standing at room temperature overnight, and the melting point of the reformed crystals was identical to that of the original crystals, showing that no decomposition had occurred during melting. The fact that the cooled melt recrystallized within several hours but not immediately may be associated with the extensive intermolecular aryl-H···π(arene) interactions in the absence of stronger interactions involving O—H···O—H hydrogen bonds. Like (I), related 9-(o-isopropylphenyl)-9-fluorenol, (II), crystallized as its ap rotamer, which also was shown by NMR to be its only rotamer in solution (Hou et al., 1999). However, while crystalline (II), like (I), exhibited no O—H···O—H hydrogen bonding, it did provide parameters suggesting O—H···π(fluorene) intermolecular hydrogen bonding. Also like (I), the cooled melt of (II) recrystallized only after about 24 h, and the NMR spectra of the melts of (I) and (II) were identical to that of their crystals, again showing that molecular decomposition did not occur on melting. In the case of (II), it is suggested that this phenomenon is associated with the weak O—H···π(fluorene) intermolecular hydrogen bonding in the absence of stronger O—H···O—H hydrogen-bonding interactions. In contrast, related 9-(o-tert-butylphenyl)-9-fluorenol, (III), crystallized exclusively as its sp rotamer, which was also true of its solution, the very large barrier restricting rotation of the 9-(o-tert-butylphenyl) group being responsible for the absence of its ap rotamer even in solution (Robinson et al., 1998). In further contrast, the molecular packing of (III) exhibited O—H···O—H as well as O—H···π(fluorene) intermolecular hydrogen bonding, and its melt failed to recrystallize on cooling even after long standing, in line with the suggested explanation of the behavior of (I) and (II).

As seen from the torsion angles O1—C9—C10—C11 of −177.60 (14)°, O1—C9—C10—C15 of 3.2 (2)°, and C9—C10—C11—C16 of 2.1 (2)°, the 9-aryl plane is essentially perpendicular to the fluorene plane. In this ap conformation of (I), therefore, the ortho-methyl C atom (C16) is virtually touching the fluorene ring, clearly illustrated in Fig. 1 and by the observed parameters: C16···C8a = 3.140 (3) Å (0.26 Å less than the sum of their van der Waals radii) and C16···C9a = 3.182 (3) Å (0.22 Å less than the sum of their van der Waals radii). In spite of these proximities, it must be assumed, therefore, that the ap rotamer of (I) affords the greatest rotational thermodynamic favorability. This characteristic may be an intrinsically molecular feature, since it is exhibited by crystalline (I) as well as (II) in solution, the spectrum of the latter also indicating the presence of the ap rotamer exclusively, viz. the shielded methyl resonance of (I), δ 1.31, compared to that of the related meta-methyl compound, δ 2.29 (McLean et al., 2003).

S2. Experimental

After a mixture of magnesium (0.36 g, 14.71 mmol), freshly distilled tetrahydrofuran (15 ml), and 1,2-dibromoethane (0.30 ml, 3.48 mmol), was stirred and gently heated under an atmosphere of argon until bubbles appeared on the surface of the magnesium, o-bromotoluene (1.90 g, 11.11 mmol) was added and heating was continued until all of the magnesium had been consumed. A solution of fluorenone (1.06 g, 5.89 mmol) in tetrahydrofuran (20 ml) was then added and the reaction mixture, which immediately turned dark brown, was refluxed for 6 h. After being cooled to 298 K, the mixture was diluted with water, then with an excess saturated aqueous ammonium chloride solution, and extracted with ether. The dried extracts (anhydrous MgSO₄), concentrated in vacuo, yielded a tan-colored oil which solidified after several days (yield 1.41 g, 88.3%). Recrystallization from hexanes provided colorless crystals [m.p.392–393 K; literature m.p. 394–395 K (Chandross & Sheley, 1968)]. The melted crystals failed to recrystallize on standing several hours at room temperature, but very slowly crystallized overnight, providing crystals whose melting point was identical to that of the original crystals. The NMR spectra of the crystals and their melt were identical, showing that no decomposition had occurred on melting. ¹H NMR (CDCl₃): δ 1.31 (broad s, 3H), 2.32 (s, 1H), 6.94–6.96 (m, 1H), 7.15–7.25 (m, 6H), 7.34–7.41 (m, 2H), 7.67–7.70 (m, 2H), 8.31–8.33 (m, 1H); ¹³C NMR: δ 19.42, 82.66, 120.20, 124.29, 125.67, 126.52, 127.51, 128.55, 129.10, 131.43, 135.12, 139.99, 140.20, 149.31.

S3. Refinement

The rotational orientations of the methyl and hydroxyl groups were determined by the circular Fourier refinement methods available in SHELXL97 (Sheldrick, 1997). The location calculated for the hydroxyl H atom is essentially identical to its initial position which was easily determined from a difference Fourier synthesis. Thus, we feel confident that this atom is correctly located. All H atoms were treated as riding, with an O—H distance of 0.82 Å, C—H distances in the range 0.93–0.96 Å, and U_iso(H) values equal to 1.5 (hydroxyl and methyl H atoms) or 1.2 times (all other H atoms) 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) and PLATON (Spek, 2003); software used to prepare material for publication: TEXSAN, SHELXL97, and PLATON.

Figures

Fig. 1. The molecular structure and atom-numbering scheme for (I), with displacement ellipsoids drawn at the 50% probablilty level.

Fig. 2. The molecular packing and aryl-H···π(arene) interactions in (I). Note that there are three crystallographically distinct interactions which form tightly knit planar arrays of molecules normal to [010]. Only one of the two parallel planes that pass through the unit cell is shown. Cg1 and Cg2 represent the centroids of rings C10–C15 and C1–C9a, respectively. [Symmetry codes: (i) 1 + x, 1/2 − y, 1/2 + z; (ii) x, 1/2 − y, z − 1/2; (iii) x − 1, y, z.]

ap-9-(o-Methylphenyl)-9-fluorenol

Crystal data

C20H16O	F(000) = 576
Mr = 272.33	Dx = 1.240 Mg m^−3
Monoclinic, P21/c	Melting point = 392–393 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71069 Å
a = 7.991 (3) Å	Cell parameters from 25 reflections
b = 14.211 (3) Å	θ = 17.8–20.0°
c = 13.3274 (19) Å	µ = 0.08 mm^−1
β = 105.501 (17)°	T = 296 K
V = 1458.4 (7) Å^3	Prism, colorless
Z = 4	0.43 × 0.33 × 0.21 mm

Data collection

Rigaku AFC-5S diffractometer	Rint = 0.013
Radiation source: fine-focus sealed tube	θmax = 25.1°, θmin = 2.1°
Graphite monochromator	h = 0→9
ω scans	k = 0→16
2780 measured reflections	l = −15→15
2587 independent reflections	3 standard reflections every 100 reflections
1640 reflections with I > 2σ(I)	intensity decay: 0.7%

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)] = 0.035	H-atom parameters constrained
wR(F^2) = 0.104	w = 1/[σ^2(Fo^2) + (0.0479P)^2 + 0.2124P] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max < 0.001
2587 reflections	Δρmax = 0.15 e Å^−3
193 parameters	Δρmin = −0.15 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0150 (18)

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

	x	y	z	Uiso*/Ueq
O1	0.30750 (17)	0.14583 (9)	0.07847 (11)	0.0602 (4)
C1	0.4211 (2)	0.19404 (15)	0.32093 (15)	0.0558 (5)
C2	0.5447 (3)	0.23389 (18)	0.40359 (16)	0.0674 (6)
C3	0.6050 (3)	0.32352 (17)	0.39580 (16)	0.0682 (6)
C4	0.5431 (2)	0.37661 (14)	0.30620 (16)	0.0577 (5)
C4A	0.4200 (2)	0.33711 (12)	0.22367 (13)	0.0446 (4)
C4B	0.3269 (2)	0.37547 (12)	0.12148 (14)	0.0454 (4)
C5	0.3357 (2)	0.46276 (14)	0.07699 (16)	0.0600 (5)
C6	0.2264 (3)	0.48139 (15)	−0.02025 (17)	0.0673 (6)
C7	0.1092 (3)	0.41541 (16)	−0.07231 (15)	0.0628 (6)
C8	0.1003 (2)	0.32794 (14)	−0.02851 (14)	0.0535 (5)
C8A	0.2103 (2)	0.30795 (12)	0.06785 (13)	0.0424 (4)
C9	0.2301 (2)	0.21655 (11)	0.12969 (13)	0.0424 (4)
C9A	0.3606 (2)	0.24561 (12)	0.23141 (13)	0.0430 (4)
C10	0.0621 (2)	0.17438 (11)	0.14415 (12)	0.0388 (4)
C11	−0.0499 (2)	0.22628 (12)	0.18855 (13)	0.0423 (4)
C12	−0.2005 (2)	0.18293 (14)	0.19860 (14)	0.0511 (5)
C13	−0.2413 (2)	0.09133 (14)	0.16796 (14)	0.0553 (5)
C14	−0.1314 (2)	0.04064 (13)	0.12552 (14)	0.0529 (5)
C15	0.0192 (2)	0.08198 (12)	0.11396 (14)	0.0478 (4)
C16	−0.0129 (3)	0.32513 (13)	0.22845 (16)	0.0562 (5)
H1	0.3849	0.1697	0.0572	0.090*
H1A	0.3800	0.1335	0.3261	0.067*
H2	0.5869	0.1997	0.4647	0.081*
H3	0.6888	0.3490	0.4516	0.082*
H4	0.5834	0.4374	0.3017	0.069*
H5	0.4137	0.5080	0.1120	0.072*
H6	0.2321	0.5396	−0.0511	0.081*
H7	0.0356	0.4297	−0.1373	0.075*
H8	0.0211	0.2832	−0.0636	0.064*
H12	−0.2763	0.2169	0.2270	0.061*
H13	−0.3427	0.0641	0.1760	0.066*
H14	−0.1579	−0.0213	0.1046	0.063*
H15	0.0934	0.0471	0.0853	0.057*
H16A	−0.1087	0.3479	0.2522	0.084*
H16B	0.0031	0.3649	0.1735	0.084*
H16C	0.0907	0.3257	0.2852	0.084*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0529 (8)	0.0562 (8)	0.0811 (9)	−0.0014 (6)	0.0343 (7)	−0.0201 (7)
C1	0.0422 (10)	0.0653 (12)	0.0607 (12)	0.0090 (9)	0.0151 (9)	0.0076 (10)
C2	0.0529 (12)	0.0953 (17)	0.0513 (12)	0.0142 (12)	0.0093 (10)	0.0058 (12)
C3	0.0492 (11)	0.0950 (18)	0.0539 (12)	0.0046 (12)	0.0022 (10)	−0.0207 (12)
C4	0.0437 (10)	0.0628 (13)	0.0634 (13)	−0.0033 (9)	0.0085 (9)	−0.0188 (10)
C4A	0.0347 (9)	0.0495 (10)	0.0499 (10)	0.0002 (8)	0.0121 (8)	−0.0089 (8)
C4B	0.0384 (9)	0.0491 (11)	0.0506 (10)	−0.0043 (8)	0.0151 (8)	−0.0054 (8)
C5	0.0564 (12)	0.0510 (11)	0.0730 (14)	−0.0110 (10)	0.0183 (11)	−0.0005 (10)
C6	0.0715 (14)	0.0623 (13)	0.0703 (14)	0.0005 (11)	0.0229 (12)	0.0157 (11)
C7	0.0634 (13)	0.0770 (15)	0.0477 (11)	0.0031 (11)	0.0143 (10)	0.0066 (10)
C8	0.0500 (11)	0.0672 (13)	0.0438 (10)	−0.0078 (9)	0.0136 (9)	−0.0073 (9)
C8A	0.0380 (9)	0.0507 (10)	0.0418 (9)	−0.0026 (8)	0.0164 (8)	−0.0054 (8)
C9	0.0375 (9)	0.0437 (10)	0.0481 (10)	−0.0008 (7)	0.0151 (8)	−0.0092 (8)
C9A	0.0310 (8)	0.0499 (10)	0.0491 (10)	0.0034 (8)	0.0123 (8)	−0.0036 (8)
C10	0.0344 (8)	0.0406 (9)	0.0396 (9)	−0.0001 (7)	0.0069 (7)	−0.0005 (7)
C11	0.0384 (9)	0.0461 (10)	0.0420 (9)	0.0025 (8)	0.0103 (7)	0.0020 (8)
C12	0.0383 (9)	0.0629 (12)	0.0529 (11)	0.0039 (9)	0.0138 (8)	0.0055 (9)
C13	0.0417 (10)	0.0665 (13)	0.0553 (11)	−0.0112 (10)	0.0087 (9)	0.0105 (10)
C14	0.0559 (11)	0.0439 (10)	0.0536 (11)	−0.0112 (9)	0.0055 (9)	0.0040 (9)
C15	0.0471 (10)	0.0439 (10)	0.0515 (10)	−0.0002 (8)	0.0117 (8)	−0.0029 (8)
C16	0.0543 (11)	0.0505 (11)	0.0712 (13)	0.0045 (9)	0.0298 (10)	−0.0071 (9)

Geometric parameters (Å, º)

O1—C9	1.4439 (19)	C11—C16	1.503 (2)
C1—C9A	1.373 (3)	C12—C13	1.377 (3)
C1—C2	1.389 (3)	C13—C14	1.369 (3)
C2—C3	1.376 (3)	C14—C15	1.385 (2)
C3—C4	1.387 (3)	O1—H1	0.8200
C4—C4A	1.383 (2)	C1—H1A	0.9300
C4B—C5	1.385 (3)	C2—H2	0.9300
C4B—C8A	1.394 (2)	C3—H3	0.9300
C4B—C4A	1.471 (2)	C4—H4	0.9300
C4A—C9A	1.398 (2)	C5—H5	0.9300
C5—C6	1.381 (3)	C6—H6	0.9300
C6—C7	1.375 (3)	C7—H7	0.9300
C7—C8	1.383 (3)	C8—H8	0.9300
C8—C8A	1.378 (2)	C12—H12	0.9300
C8A—C9	1.524 (2)	C13—H13	0.9300
C9—C10	1.528 (2)	C14—H14	0.9300
C9—C9A	1.530 (2)	C15—H15	0.9300
C10—C15	1.389 (2)	C16—H16A	0.9600
C10—C11	1.406 (2)	C16—H16B	0.9600
C11—C12	1.390 (2)	C16—H16C	0.9600
C9A—C1—C2	118.8 (2)	C13—C14—C15	119.68 (18)
C3—C2—C1	120.5 (2)	C14—C15—C10	121.56 (17)
C2—C3—C4	121.12 (19)	C9—O1—H1	109.5
C4A—C4—C3	118.57 (19)	C9A—C1—H1A	120.6
C5—C4B—C8A	120.01 (17)	C2—C1—H1A	120.6
C5—C4B—C4A	131.11 (17)	C3—C2—H2	119.8
C8A—C4B—C4A	108.85 (15)	C1—C2—H2	119.8
C4—C4A—C9A	120.15 (17)	C2—C3—H3	119.4
C4—C4A—C4B	131.45 (17)	C4—C3—H3	119.4
C9A—C4A—C4B	108.38 (14)	C4A—C4—H4	120.7
C6—C5—C4B	118.81 (18)	C3—C4—H4	120.7
C7—C6—C5	121.16 (19)	C6—C5—H5	120.6
C6—C7—C8	120.32 (19)	C4B—C5—H5	120.6
C8A—C8—C7	119.11 (18)	C7—C6—H6	119.4
C8—C8A—C4B	120.56 (17)	C5—C6—H6	119.4
C8—C8A—C9	128.90 (16)	C6—C7—H7	119.8
C4B—C8A—C9	110.53 (15)	C8—C7—H7	119.8
O1—C9—C8A	109.47 (14)	C8A—C8—H8	120.4
O1—C9—C10	106.77 (13)	C7—C8—H8	120.4
C8A—C9—C10	115.77 (13)	C13—C12—H12	118.9
O1—C9—C9A	109.27 (13)	C11—C12—H12	118.9
C8A—C9—C9A	101.35 (13)	C14—C13—H13	120.2
C10—C9—C9A	114.07 (14)	C12—C13—H13	120.2
C1—C9A—C4A	120.86 (17)	C13—C14—H14	120.2
C1—C9A—C9	128.61 (16)	C15—C14—H14	120.2
C4A—C9A—C9	110.52 (15)	C14—C15—H15	119.2
C15—C10—C11	118.81 (15)	C10—C15—H15	119.2
C15—C10—C9	119.41 (15)	C11—C16—H16A	109.5
C11—C10—C9	121.77 (14)	C11—C16—H16B	109.5
C12—C11—C10	118.23 (16)	H16A—C16—H16B	109.5
C12—C11—C16	118.27 (16)	C11—C16—H16C	109.5
C10—C11—C16	123.48 (15)	H16A—C16—H16C	109.5
C13—C12—C11	122.17 (17)	H16B—C16—H16C	109.5
C14—C13—C12	119.54 (17)
C9A—C1—C2—C3	0.1 (3)	C4—C4A—C9A—C1	0.8 (2)
C1—C2—C3—C4	0.7 (3)	C4B—C4A—C9A—C1	−177.50 (15)
C2—C3—C4—C4A	−0.8 (3)	C4—C4A—C9A—C9	−178.22 (15)
C3—C4—C4A—C9A	0.0 (3)	C4B—C4A—C9A—C9	3.43 (18)
C3—C4—C4A—C4B	177.89 (17)	O1—C9—C9A—C1	−69.2 (2)
C5—C4B—C4A—C4	0.5 (3)	C8A—C9—C9A—C1	175.36 (16)
C8A—C4B—C4A—C4	−177.51 (18)	C10—C9—C9A—C1	50.2 (2)
C5—C4B—C4A—C9A	178.62 (18)	O1—C9—C9A—C4A	109.83 (15)
C8A—C4B—C4A—C9A	0.59 (19)	C8A—C9—C9A—C4A	−5.66 (17)
C8A—C4B—C5—C6	0.5 (3)	C10—C9—C9A—C4A	−130.78 (15)
C4A—C4B—C5—C6	−177.33 (18)	O1—C9—C10—C15	3.2 (2)
C4B—C5—C6—C7	0.6 (3)	C8A—C9—C10—C15	125.33 (16)
C5—C6—C7—C8	−0.9 (3)	C9A—C9—C10—C15	−117.61 (17)
C6—C7—C8—C8A	0.0 (3)	O1—C9—C10—C11	−177.60 (14)
C7—C8—C8A—C4B	1.2 (3)	C8A—C9—C10—C11	−55.5 (2)
C7—C8—C8A—C9	−177.35 (17)	C9A—C9—C10—C11	61.6 (2)
C5—C4B—C8A—C8	−1.4 (3)	C15—C10—C11—C12	−1.0 (2)
C4A—C4B—C8A—C8	176.86 (15)	C9—C10—C11—C12	179.74 (15)
C5—C4B—C8A—C9	177.33 (15)	C15—C10—C11—C16	177.15 (16)
C4A—C4B—C8A—C9	−4.38 (19)	C9—C10—C11—C16	−2.1 (2)
C8—C8A—C9—O1	69.3 (2)	C10—C11—C12—C13	0.9 (3)
C4B—C8A—C9—O1	−109.31 (15)	C16—C11—C12—C13	−177.41 (17)
C8—C8A—C9—C10	−51.4 (2)	C11—C12—C13—C14	−0.4 (3)
C4B—C8A—C9—C10	129.99 (15)	C12—C13—C14—C15	0.0 (3)
C8—C8A—C9—C9A	−175.35 (16)	C13—C14—C15—C10	−0.2 (3)
C4B—C8A—C9—C9A	6.02 (17)	C11—C10—C15—C14	0.7 (3)
C2—C1—C9A—C4A	−0.9 (3)	C9—C10—C15—C14	179.98 (15)
C2—C1—C9A—C9	178.01 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···Cg1^i	0.93	2.84	3.723 (3)	159
C7—H7···Cg1^ii	0.93	2.81	3.606 (2)	145
C12—H12···Cg2^iii	0.93	2.68	3.599 (2)	170

Symmetry codes: (i) x+1, −y+1/2, z+1/2; (ii) x, −y+1/2, z−1/2; (iii) x−1, y, z.