Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103023503/fg1712sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270103023503/fg1712Isup2.hkl |
CCDC reference: 229116
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.
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 Uiso(H) values equal to 1.5 (hydroxyl and methyl H atoms) or 1.2 times (all other H atoms) Ueq of the parent atom.
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.
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) Å3 | Prism, colorless |
Z = 4 | 0.43 × 0.33 × 0.21 mm |
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 on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.035 | H-atom parameters constrained |
wR(F2) = 0.104 | w = 1/[σ2(Fo2) + (0.0479P)2 + 0.2124P] where P = (Fo2 + 2Fc2)/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+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0150 (18) |
C20H16O | V = 1458.4 (7) Å3 |
Mr = 272.33 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 7.991 (3) Å | µ = 0.08 mm−1 |
b = 14.211 (3) Å | T = 296 K |
c = 13.3274 (19) Å | 0.43 × 0.33 × 0.21 mm |
β = 105.501 (17)° |
Rigaku AFC-5S diffractometer | Rint = 0.013 |
2780 measured reflections | 3 standard reflections every 100 reflections |
2587 independent reflections | intensity decay: 0.7% |
1640 reflections with I > 2σ(I) |
R[F2 > 2σ(F2)] = 0.035 | 0 restraints |
wR(F2) = 0.104 | H-atom parameters constrained |
S = 1.00 | Δρmax = 0.15 e Å−3 |
2587 reflections | Δρmin = −0.15 e Å−3 |
193 parameters |
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* |
U11 | U22 | U33 | U12 | U13 | U23 | |
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) |
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) |
D—H···A | D—H | H···A | D···A | D—H···A |
C3—H3···Cg1i | 0.93 | 2.84 | 3.723 (3) | 159 |
C7—H7···Cg1ii | 0.93 | 2.81 | 3.606 (2) | 145 |
C12—H12···Cg2iii | 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. |
Experimental details
Crystal data | |
Chemical formula | C20H16O |
Mr | 272.33 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 296 |
a, b, c (Å) | 7.991 (3), 14.211 (3), 13.3274 (19) |
β (°) | 105.501 (17) |
V (Å3) | 1458.4 (7) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.08 |
Crystal size (mm) | 0.43 × 0.33 × 0.21 |
Data collection | |
Diffractometer | Rigaku AFC-5S diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2780, 2587, 1640 |
Rint | 0.013 |
(sin θ/λ)max (Å−1) | 0.596 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.035, 0.104, 1.00 |
No. of reflections | 2587 |
No. of parameters | 193 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.15, −0.15 |
Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1996), MSC/AFC Diffractometer Control Software, PROCESS in TEXSAN (Molecular Structure Corporation, 1997), SIR92 (Burla et al., 1989), LS in TEXSAN and SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2003), TEXSAN, SHELXL97, and PLATON.
D—H···A | D—H | H···A | D···A | D—H···A |
C3—H3···Cg1i | 0.93 | 2.84 | 3.723 (3) | 159 |
C7—H7···Cg1ii | 0.93 | 2.81 | 3.606 (2) | 145 |
C12—H12···Cg2iii | 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. |
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).