organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
Molecules of (II) straddle a crystallographic mirror plane
which is normal to the ®ve-membered ring, passing through
1
C1, O and the midpoint of the C11ÐC11(x, 2 � y, z). Bond
ISSN 0108-2701
lengths and angles in (II) are unexceptional (Table 1) and
agree with comparable values in (I). The single independent
naphthalene ring system in (II), de®ned by C2±C11, has an
Ê
1
3H-Dibenzo[a,i]fluoren-13-one
r.m.s. deviation from planarity of only 0.007 A and the angle
between the two mirror-related ring systems within the same
ꢁ
a
a
b
molecule is only 1.9 (1) . Compound (II) is therefore planar
David G. Morris, * Sean Higgins, Karl S. Ryder, R. Alan
b
a
almost to within experimental error; only one skeletal torsion
ꢁ
Howie and Kenneth W. Muir
ꢁ
angle deviates from 0 or 180 by more than 1 [C3ÐC2ÐC1Ð
ꢁ
a
O � 1.4 (3) ]. However, the C OÁ Á ÁH contact in (II) [OÁ Á ÁH4
Department of Chemistry, University of Glasgow, Glasgow, G12 8QQ, Scotland,
b
Ê
ꢁ
and Department of Chemistry, Meston Walk, University of Aberdeen, Old
2.47 (5) A and OÁ Á ÁH4ÐC4 125 (2) ] is very similar to the
Aberdeen, AB24 3UE, Scotland
corresponding contact in (I). This is consistent with the
1
observation of low ®eld signals in the H NMR spectra of both
molecules. Taken together, the structural and NMR results for
Received 8 October 1999
Accepted 18 January 2000
(
I) and (II) suggest that the C OÁ Á ÁH 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
HÁ Á ÁH steric crowding.
Molecules of 13H-dibenzo[a,i]¯uoren-13-one, C H O, strad-
1
2
12
dle a crystallographic mirror plane and are essentially planar,
ꢁ
with a dihedral angle of only 1.9 (1) between the two naph-
thalene ring systems. Repulsive intramolecular C OÁ Á ÁH
interactions therefore do not explain the larger distortions
found in isomeric ketones.
Comment
In a recent publication (Morris et al., 1998) we described the
crystal structure of 13H-dibenzo[a,g]¯uoren-13-one (CAS
Registry No. [63041-47-4]), (I), which had previously been
shown by Harvey et al. (1992) to exhibit an anomolously low
1
eld resonance in the H NMR spectrum for the H atom (H4)
®
closest to the carbonyl O.
Figure 1
The molecular structure of (II) showing 50% probability displacement
ellipsoids and with H atoms drawn as arbitrary spheres.
Molecules of (I) show small but signi®cant distortions from
planarity: the two naphthalene ring systems de®ne a dihedral
ꢁ
angle of 6.0 (1) and are themselves slightly ruf¯ed (r.m.s.
Ê
deviations for the two C10 planes are 0.019 and 0.012 A).
Experimental
Repulsive intramolecular C OÁ Á ÁH interactions (OÁ Á ÁH
Ê
ꢁ
2
.48 A and OÁ Á ÁCÐH 124 ) were considered to be the most
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]¯uorene
(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 potas-
sium methoxide and acetone gave compound (II) (m.p. 544±545 K;
likely cause of these distortions (Morris et al., 1998). However,
the geometry of the C OÁ Á ÁH sub-unit in (I) falls in the
region where it is dif®cult to discriminate between `repulsive
forced interactions' and weak CÐHÁ Á ÁO hydrogen bonds
(
Jeffrey, 1997). The bay region of (I) also contains a short
Ê
intramolecular C10ÐHÁ Á ÁHÐC14 contact of 2.07 A, which is
1
literature value 542±543 K; Harvey et al., 1991). The H NMR spec-
trum of compound (II) in CDCl
indicative of overcrowding. In order to investigate this point
3
was determined with a Bruker DPX
4
00 spectrometer at 9.4 T, and chemical shifts in p.p.m. were refer-
1
enced to chloroform at 7.25. Spectroscopic analysis, H 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-®eld absorption is assigned to the
protons closest to the lone pairs of the carbonyl-O atom. We have, for
convenience, numbered the C atoms of (II) so that the oxygen-
bearing C atom is de®ned as C1 (Fig. 1). However, this is at variance
with IUPAC nomenclature, which de®nes C4 in Fig. 1 as C1, with the
other C atoms numbered in sequence around the ring away from the
carbonyl-C atom.
we have determined the structure of the isomeric compound
1
3H-dibenzo[a,i]¯uoren-13-one, (II) (CAS Registry No.
86854-01-5]), in which there are no short HÁ Á ÁH contacts but
two C OÁ Á ÁH interactions of the type found in (I).
[
5
70 # 2000 International Union of Crystallography ꢀ Printed in Great Britain ± all rights reserved
Acta Cryst. (2000). C56, 570±571