sp-9-(o-Methylphenyl)fluorene

Article abstract of DOI:10.1107/S010827010400040X

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, (

Full text of DOI:10.1107/S010827010400040X

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
radii], in the ap conformation the distance between the CH3
group (C16) and the ¯uorene ring (C8a) would be much
Ê
Ê
closer, e.g. near the value of 3.140 (3) A (within 0.26 A of the
sum of the van der Waals radii) in its crystalline ap progenitor
ISSN 0108-2701
(II). The sp conformation of the latter is so sterically hindered
by the 9-OH group that it is not observed in solution (although
1
the H NMR resonance of o-CH is broad; Meyers, Robinson
sp-9-(o-Methylphenyl)fluorene
3
&
McLean, 2003). This restriction is alleviated in (I) by
a
b
replacement of 9-OH by H. These factors plausibly account
for the equilibration of sp-(I) (60%) and ap-(I) (40%) in
solution, in which 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 ¯uorene ring in (II)
that promotes its ap rotamer exclusivity even in solution.
Cal Y. Meyers, Paul D. Robinson * and Aaron W.
a
McLean
a
Meyers Institute for Interdisciplinary Research in Organic and Medicinal Chemistry,
and the Department of Chemistry and Biochemistry, Southern Illinois University-
b
4
409, Carbondale, IL 62901, USA, and Department of Geology, Southern Illinois
University-4324, Carbondale, IL 62901, USA
Correspondence e-mail: robinson@geo.siu.edu
Received 22 December 2003
Accepted 6 January 2004
Online 31 January 2004
While the barriers of rotation of the sp and ap rotamers of
9
-(o-methylphenyl)¯uorene, C H , are suf®ciently similar to
20 16
permit them to equilibrate, both being observed (NMR) in
solution, crystallization provides the sp rotamer, (I), exclu-
sively. Although in the sp conformation the intramolecular
distance between adjacent C atoms of the phenyl and ¯uorene
Ê
Ê
rings is small [3.382 (4) A, within 0.02 A of the sum of the van
der Waals radii], in the ap conformation the distance between
the adjacent o-CH group on the phenyl ring and C atom of
3
the ¯uorene ring would be much closer, based on that
exhibited in the crystalline ap progenitor 9-(o-methylphenyl)-
9-¯uorenol. The angle between the ¯uorene and 9-aryl planes
ꢀ
of (I) is 75.82 (10) .
Comment
Crystalline 9-(o-methylphenyl)¯uorene, (I), prepared from
ap-9-(o-methylphenyl)-9-¯uorenol, (II) (Meyers, Robinson &
McLean, 2003), is entirely composed of the sp rotamer (Fig. 1).
The angle between the ¯uorene and 9-aryl planes is
ꢀ
7
5.82 (10) .
Geometric intermolecular calculations suggest the possible
i
presence of a weak C4ÐH4Á Á ÁCg1 interaction [where Cg1 is
the centroid of the C1±C4/C4a/C9a ring; symmetry code: (i)
1
1
2
Ê
1
� x, + y, � z], with an HÁ Á ÁA distance of 2.82 A, a DÁ Á ÁA
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)-
¯uorene (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-¯uorenol, (IV) (Hou et al., 1999), like
9-¯uorenol (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 ¯uorene ring in ap conformation (V) reduces
the rotational barrier of that rotamer substantially, forcing
9-(o-tert-butylphenyl)¯uorene, (Va), and its corresponding
2
Ê
ꢀ
distance of 3.634 (3) A and a DÐHÁ Á ÁA angle of 146 . This
rather poor geometry suggests only a possible weak interac-
tion 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 (Meyers, Robinson & McLean, 2003; Robinson et al.,
2
Robinson, 2003).
Although in this sp conformation, the intramolecular
distance between atoms C15 and C8 of (I) is small
003a,b; McLean et al., 2003a,b, 2004; Meyers, McLean &
Ê Ê
3.382 (4) A, within 0.02 A of the sum of the van der Waals
[
o156 # 2004 International Union of Crystallography
DOI: 10.1107/S010827010400040X
Acta Cryst. (2004). C60, o156±o157

organic compounds
Data collection
Rigaku AFC-5S diffractometer
!
h = 0 ! 15
scans
k = 0 ! 7
2
2
1
659 measured re¯ections
539 independent re¯ections
515 re¯ections with I > 2ꢅ(I)
l = � 22 ! 21
3 standard re¯ections
every 100 re¯ections
intensity decay: 4.2%
R
int = 0.018
ꢀ
ꢃ
max = 25.0
Re®nement
2
2
2
2
Re®nement on F
2
o
w = 1/[ꢅ (F ) + (0.0776P)
2
R[F > 2ꢅ(F )] = 0.050
wR(F ) = 0.166
S = 1.07
+ 0.3078P]
where P = (F
(Á/ꢅ)max < 0.001
2
2
2
c
o
+ 2F
)/3
Ê
� 3
2
1
539 re¯ections
83 parameters
Áꢆmax = 0.33 e A
Ê
� 3
Áꢆmin = � 0.16 e A
H-atom parameters constrained
Extinction correction: SHELXL97
Extinction coef®cient: 0.016 (3)
The rotational orientation of the methyl group was re®ned by the
circular Fourier method available in SHELXL97 (Sheldrick, 1997).
Figure 1
The molecular structure and atom-numbering scheme for (I), with
displacement ellipsoids drawn at the 30% probability level.
All H atoms were treated as riding, with CÐH distances ranging from
Ê
0.93 to 0.98 A and Uiso(H) values equal to 1.5 (methyl H atoms) or 1.2
(
all other H atoms) times Ueq of the parent atom.
9
-¯uorenol, (VI), to exist exclusively in their sp rotamers in
solution as well as in their crystalline forms (Robinson et al.,
998). The very low rotational barrier of the highly hindered
Data collection and cell re®nement: MSC/AFC Diffractometer
Control Software (Molecular Structure Corporation, 1996); data
reduction: TEXSAN (Molecular Structure Corporation, 1997);
structure solution: SIR92 (Burla et al., 1989); structure re®nement:
TEXSAN and SHELXL97; molecular graphics: ORTEP-3 (Farrugia,
1997); software used to prepare material for publication: TEXSAN,
SHELXL97 and PLATON (Spek, 2003).
1
ap-9-(o-tert-butylphenyl)¯uorene rotamer, (V), has been
shown by the observation that, although it is exclusively
formed via deprotonation±reprotonation inversion of sp
rotamer (Va), it rapidly rotates back to 100% of the sp
rotamer (Hou & Meyers, 2004).
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FR1463). Services for accessing these data are
described at the back of the journal.
Experimental
A solution of I
3.52 mmol) and glacial acetic acid (10 ml) was heated under argon
until it became colorless, and 9-(o-methylphenyl)-9-¯uorenol
Meyers, Robinson & McLean, 2003; 0.317 g, 0.663 mmol) was then
2 3 2
(0.018 g, 0.071 mmol), 50% aqueous H PO (1.4 ml,
1
References
(
Bordwell, F. G., Drucker, G. E. & McCollum, G. J. (1982). J. Org. Chem. 47,
2
504±2510.
added. The yellow mixture was re¯uxed under argon for 5 h and
cooled. Water (50 ml) was added and the mixture was extracted with
ether. The combined extracts were washed with saturated aqueous
Burla, M. C., Camalli, M., Cascarano, G., Giacovazzo, C., Polidori, G., Spagna,
R. & Viterbo, D. (1989). J. Appl. Cryst. 22, 389±393.
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.
sodium bicarbonate, dried (anhydrous MgSO ) and concentrated in
vacuo to give a pale-yellow solid (0.283 g, 95% yield). Recrystalli-
zation (hexanes/methanol ꢁ1:1) afforded pale-yellow crystals of (I)
4
Hou, Y. & Meyers, C. Y. (2004). J. Org. Chem. In the press.
Hou, Y., Robinson, P. D. & Meyers, C. Y. (1999). Acta Cryst. C55, IUC9900144.
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o1228±o1230.
McLean, A. W., Meyers, C. Y. & Robinson, P. D. (2003b). Acta Cryst. E59,
o891±o893.
[m.p. 363±364 K; literature melting point 365±367.5 K (Bordwell et
al., 1982)]. The melt crystallized immediately upon cooling, the
resulting crystals having the same melting point as those formed prior
, ꢀ): 1.14 (s, ap,
1.2H), 2.79 (s, sp, 1.8H, CH , two rotamers), 5.03 (s, ap, 0.4H), 5.43 (s,
3
sp, 0.6H, 9-H, two rotamers), 6.37±6.39 (m, 1H), 6.89±6.99 (m, 1H),
McLean, A. W., Meyers, C. Y. & Robinson, P. D. (2004). Acta Cryst. E60, o75±
o76.
Meyers, C. Y., Hou, Y., Scott, D. & Robinson, P. D. (1997). Acta Cryst. C53,
1
to melting. Spectroscopic analysis, H NMR (CDCl
3
1149±1151.
Meyers, C. Y., McLean, A. W. & Robinson, P. D. (2003). Acta Cryst. E59, o978±
o980.
Meyers, C. Y., Robinson, P. D. & McLean, A. W. (2003). Acta Cryst. C59, o712±
o714.
Molecular Structure Corporation (1996). MSC/AFC Diffractometer Control
Software. MSC, 3200 Research Forest Drive, The Woodlands, TX 77381,
USA.
Molecular Structure Corporation (1997). TEXSAN. MSC, 3200 Research
Forest Drive, The Woodlands, TX 77381, USA.
Robinson, P. D., Hou, Y., Lut®, H. G. & Meyers, C. Y. (1998). Acta Cryst. C54,
73±77.
Robinson, P. D., McLean, A. W. & Meyers, C. Y. (2003a). Acta Cryst. E59,
o1915±o1917.
Robinson, P. D., McLean, A. W. & Meyers, C. Y. (2003b). Acta Cryst. C59,
o539±o540.
Sheldrick, G. M. (1997). SHELXL97. University of G oÈ ttingen, Germany.
Spek, A. L. (2003). J. Appl. Cryst. 36, 7±13.
7
2
1
1
.09±7.14 (m, 1H), 7.22±7.41 (m, 2H), 7.61±7.64 (m, 1H), 7.81±7.84 (m,
, ꢀ): 20.47, 49.92, 56.19, 98.98, 119.89, 124.69,
25.06, 125.72, 126.48, 126.58, 127.13, 127.27, 127.49, 130.32, 131.59,
32.63.
1
H); C NMR (CDCl
3
3
Crystal data
�
3
C
20
H
16
D
x
= 1.187 Mg m
r
M = 256.33
Mo Kꢂ radiation
Monoclinic, P2 =c
Cell parameters from 25
re¯ections
1
Ê
a = 12.9887 (17) A
Ê
b = 6.075 (2) A
ꢀ
ꢃ = 14.8±19.2
Ê
c = 18.7903 (16) A
� 1
ꢄ = 0.07 mm
T = 296 K
ꢀ
Ê
ꢁ
= 104.701 (8)
3
V = 1434.1 (5) A
Z = 4
Irregular fragment, colorless
0.49 Â 0.46 Â 0.35 mm
ꢂ
Acta Cryst. (2004). C60, o156±o157
Cal Y. Meyers et al.
20
C H16 o157