13H-Dibenzo­[a,i]­fluoren-13-one

Molecules of 13H-dibenzo­[a,i]­fluoren-13-one, C₂₁H₁₂O, strad­dle a crystallographic mirror plane and are essentially planar, with a dihedral angle of only 1.9 (1)° between the two naphtha­lene ring systems. Repulsive intramolecular C=O...H interactions therefore do not explain the larger distortions found in isomeric ketones.

S1. Comment

In a recent publication (Morris et al., 1998) we described the crystal structure of 13H-dibenzo[a,g]fluoren-13-one (C·A·S. Registry No. [63041–47-4]), (I), which had previously been shown by Harvey et al. (1992) to exhibit an anomolously low field resonance in the ¹H NMR spectrum for the H atom (H4) closest to the carbonyl O.

Molecules of (I) show small but significant distortions from planarity: the two naphthalene ring systems define a dihedral angle of 6.0 (1)° and are themselves slightly ruffled (r.m.s. deviations for the two C₁₀ planes are 0.019 and 0.012 Å). Repulsive intramolecular C=O···H interactions (O···H 2.48 Å and O···C—H 124°) were considered to be the most likely cause of these distortions (Morris et al., 1998). However, the geometry of the C=O···H sub-unit in (I) falls in the region where it is difficult to discriminate between `repulsive forced interactions' and weak C—H···O hydrogen bonds (Jeffrey, 1997). The bay region of (I) also contains a short intramolecular C10—H···H—C14 contact of 2.07 Å which is indicative of overcrowding. In order to investigate this point we have determined the structure of the isomeric compound 13H-dibenzo[a,i]fluoren-13-one, (II) (C·A·S. Registry No. [86854–01-5]), in which there are no short H···H contacts but two C=O···H interactions of the type found in (I). \scheme

Molecules of (II) straddle a crystallographic mirror plane which is normal to the five-membered ring, passing through C1, O and the midpoint of the C11—C11ⁱ bond [symmetry code: (i) x, 1/2 - y, z]. Bond lengths and angles in (II) are unexceptional (Table 1) and agree with comparable values in (I). The single independent naphthalene ring system in (II), defined by C2—C11, has an r.m.s. deviation from planarity of only 0.007 Å and the angle between the two mirror-related ring systems within the same molecule is only 1.9 (1)°. Compound (II) is therefore planar almost to within experimental error; only one skeletal torsion angle deviates from 0° or 180° by more than 1° [C3—C2—C1—O = -1.4 (3)°]. However, the C=O.·H contact in (II) [O···H4 = 2.47 (5) Å and O···H4—C4 = 125 (2)°] is very similar to the corresponding contact in (I). This is consistent with the observation of low field signals in the ¹H NMR spectra of both molecules. Taken together, the structural and NMR results for (I) and (II) suggest that the C=O···H interactions in both molecules are not strongly repulsive and indeed may be indicative of weak intramolecular hydrogen bonding. The slight distortion observed in (I) probably helps to relieve H···H steric crowding.

S2. Experimental

Compound (II) was made by coupling the Grignard reagent from 1-bromonaphthalene (Blicke, 1927) with ethyl formate to give 1,1-dinaphthylmethanol. This was converted to 13H-dibenzo[a,i]fluorene (m.p. 505–506 K; literature value 504–506 K; Harvey et al., 1991) by the action of meta-phosphoric acid at 448 K (other dehydrating agents were unsuccessful). Reaction of the hydrocarbon with potassium methoxide and acetone gave compound (II) (m.p. 544–545 K Query; literature value 544 K; Harvey et al., 1991). The ¹H NMR of compound (II) in CDCl₃ was determined with a Bruker DPX 400 spectrometer at 9.4 T, and chemical shifts in p.p.m. were referenced to chloroform at 7.25. Spectroscopic analysis: ¹H NMR: 8.89 (d, J = 8.44 Hz), 2.89 (d, J = 8.16 Hz), 7.70 (d, J = 8.32 Hz), 7.59 (d, J = 8.20 Hz), 7.50 (d, J = 7.60 Hz), 7.33 (d, J = 7.56 Hz). All absorptions were equally intense. The low field absorption is assigned to the protons closest to the lone pairs of the carbonyl O. We have, for convenience, numbered the C atoms of (II) so that the oxygen-bearing C atom is defined as C1 (Fig. 1). However, this is at variance with IUPAC nomenclature which defines C4 in Fig. 1 as C1, with other C atoms numbered in sequence around the ring away from the carbonyl C atom.

Computing details

Data collection: CAD-4 EXPRESS (Enraf Nonius, 1992); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids and with H atoms drawn as arbitrary spheres.

13H-dibenzo[a,i]fluoren-13-one

Crystal data

C21H12O	Dx = 1.415 Mg m^−3
Mr = 280.31	Melting point = 543–544 K
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
a = 13.2543 (9) Å	Cell parameters from 25 reflections
b = 25.7694 (18) Å	θ = 19.0–23.4°
c = 3.8521 (2) Å	µ = 0.09 mm^−1
V = 1315.71 (15) Å^3	T = 293 K
Z = 4	Plate, red
F(000) = 584	0.63 × 0.34 × 0.13 mm

Data collection

Enraf Nonius CAD-4 diffractometer	Rint = 0.018
Radiation source: fine-focus sealed tube	θmax = 32.9°, θmin = 3.1°
Graphite monochromator	h = −20→2
ω scans	k = −3→39
3713 measured reflections	l = −5→1
2502 independent reflections	3 standard reflections every 120 min
1371 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.054	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.167	All H-atom parameters refined
S = 1.00	Calculated w = 1/[σ^2(Fo^2) + (0.0846P)^2 + 0.1556P] where P = (Fo^2 + 2Fc^2)/3
2502 reflections	(Δ/σ)max < 0.001
127 parameters	Δρmax = 0.36 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

Special details

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.

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
O	−0.00758 (11)	1/4	0.7656 (5)	0.0454 (4)
C1	−0.09098 (13)	1/4	0.6299 (5)	0.0317 (4)
C2	−0.15223 (9)	0.29630 (5)	0.5289 (4)	0.0312 (3)
C3	−0.13214 (9)	0.34980 (5)	0.5674 (4)	0.0316 (3)
C4	−0.04258 (11)	0.36996 (6)	0.7197 (4)	0.0369 (3)
H4	0.0078 (15)	0.3456 (8)	0.798 (5)	0.050 (5)*
C5	−0.02961 (12)	0.42241 (6)	0.7480 (5)	0.0435 (4)
H5	0.0337 (16)	0.4350 (8)	0.843 (5)	0.062 (6)*
C6	−0.10376 (13)	0.45715 (6)	0.6308 (5)	0.0471 (4)
H6	−0.0908 (14)	0.4945 (7)	0.660 (4)	0.052 (5)*
C7	−0.19056 (12)	0.43907 (6)	0.4844 (5)	0.0437 (4)
H7	−0.2427 (13)	0.4642 (7)	0.407 (5)	0.053 (5)*
C8	−0.20742 (10)	0.38497 (6)	0.4463 (4)	0.0359 (3)
C9	−0.29675 (11)	0.36547 (6)	0.2929 (4)	0.0408 (4)
H9	−0.3454 (14)	0.3906 (8)	0.212 (5)	0.054 (5)*
C10	−0.31426 (10)	0.31342 (6)	0.2597 (4)	0.0385 (4)
H10	−0.3762 (14)	0.3003 (6)	0.147 (5)	0.046 (5)*
C11	−0.24108 (9)	0.27878 (6)	0.3801 (4)	0.0321 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O	0.0312 (7)	0.0413 (8)	0.0636 (11)	0	−0.0137 (7)	0
C1	0.0257 (8)	0.0371 (9)	0.0324 (10)	0	0.0010 (8)	0
C2	0.0257 (5)	0.0383 (7)	0.0296 (7)	0.0015 (5)	0.0014 (5)	0.0001 (6)
C3	0.0287 (6)	0.0374 (7)	0.0288 (7)	0.0027 (5)	0.0031 (5)	0.0007 (6)
C4	0.0336 (6)	0.0397 (7)	0.0374 (8)	0.0009 (6)	0.0004 (6)	−0.0012 (7)
C5	0.0431 (8)	0.0417 (8)	0.0456 (9)	−0.0045 (7)	0.0010 (7)	−0.0052 (7)
C6	0.0514 (9)	0.0362 (7)	0.0536 (11)	0.0003 (7)	0.0079 (8)	−0.0020 (8)
C7	0.0461 (8)	0.0391 (8)	0.0459 (10)	0.0084 (7)	0.0054 (7)	0.0035 (7)
C8	0.0330 (6)	0.0406 (7)	0.0340 (8)	0.0058 (6)	0.0041 (6)	0.0031 (6)
C9	0.0324 (7)	0.0492 (9)	0.0406 (9)	0.0096 (6)	−0.0001 (6)	0.0052 (7)
C10	0.0274 (6)	0.0519 (9)	0.0362 (8)	0.0035 (6)	−0.0023 (6)	0.0024 (7)
C11	0.0262 (6)	0.0423 (7)	0.0278 (7)	0.0011 (5)	0.0013 (5)	0.0011 (6)

Geometric parameters (Å, º)

O—C1	1.223 (2)	C8—C3	1.427 (2)
C1—C2^i	1.495 (2)	C7—C6	1.363 (2)
C1—C2	1.495 (2)	C7—H7	0.992 (19)
C11—C2	1.386 (2)	C6—C5	1.404 (2)
C11—C10	1.397 (2)	C6—H6	0.984 (18)
C11—C11^i	1.483 (3)	C5—C4	1.367 (2)
C10—C9	1.367 (2)	C5—H5	0.97 (2)
C10—H10	0.988 (18)	C4—C3	1.422 (2)
C9—C8	1.416 (2)	C4—H4	0.97 (2)
C9—H9	0.96 (2)	C3—C2	1.412 (2)
C8—C7	1.419 (2)
O—C1—C2^i	127.04 (8)	C8—C7—H7	120.0 (11)
O—C1—C2	127.04 (8)	C7—C6—C5	120.38 (15)
C2^i—C1—C2	105.92 (15)	C7—C6—H6	122.0 (11)
C2—C11—C10	121.28 (14)	C5—C6—H6	117.6 (11)
C2—C11—C11^i	109.01 (8)	C4—C5—C6	121.12 (16)
C10—C11—C11^i	129.71 (9)	C4—C5—H5	118.0 (12)
C9—C10—C11	118.55 (14)	C6—C5—H5	120.8 (12)
C9—C10—H10	121.2 (10)	C5—C4—C3	119.95 (14)
C11—C10—H10	120.2 (10)	C5—C4—H4	122.1 (12)
C10—C9—C8	121.96 (14)	C3—C4—H4	117.9 (12)
C10—C9—H9	121.0 (11)	C2—C3—C4	123.87 (12)
C8—C9—H9	117.1 (11)	C2—C3—C8	117.02 (13)
C9—C8—C7	121.58 (13)	C4—C3—C8	119.11 (13)
C9—C8—C3	119.73 (14)	C11—C2—C3	121.46 (12)
C7—C8—C3	118.69 (14)	C11—C2—C1	108.03 (12)
C6—C7—C8	120.75 (14)	C3—C2—C1	130.51 (12)
C6—C7—H7	119.2 (11)
C2—C11—C10—C9	−0.3 (2)	C9—C8—C3—C4	179.75 (14)
C11^i—C11—C10—C9	179.27 (10)	C7—C8—C3—C4	−0.4 (2)
C11—C10—C9—C8	−0.3 (2)	C10—C11—C2—C3	0.4 (2)
C10—C9—C8—C7	−179.03 (16)	C11^i—C11—C2—C3	−179.21 (11)
C10—C9—C8—C3	0.8 (2)	C10—C11—C2—C1	179.85 (14)
C9—C8—C7—C6	−179.57 (16)	C11^i—C11—C2—C1	0.22 (13)
C3—C8—C7—C6	0.6 (2)	C4—C3—C2—C11	179.66 (13)
C8—C7—C6—C5	−0.3 (3)	C8—C3—C2—C11	0.0 (2)
C7—C6—C5—C4	−0.2 (3)	C4—C3—C2—C1	0.4 (3)
C6—C5—C4—C3	0.4 (3)	C8—C3—C2—C1	−179.26 (16)
C5—C4—C3—C2	−179.68 (15)	O—C1—C2—C11	179.27 (19)
C5—C4—C3—C8	−0.1 (2)	C2^i—C1—C2—C11	−0.4 (2)
C9—C8—C3—C2	−0.6 (2)	O—C1—C2—C3	−1.4 (3)
C7—C8—C3—C2	179.20 (14)	C2^i—C1—C2—C3	179.01 (9)

Symmetry code: (i) x, −y+1/2, z.