organic compounds
Figure 3
The intermolecular hydrogen bonding in (III), forming a molecular chain
that propogates along the a direction. The atom labelled with an asterisk
1
1
2
(
*) is at symmetry position (x + , y, � z).
2
Figure 4
planar arrangement, as shown by the pseudo-torsion angle
between the two carbonyl groups [O1ÐC2Á Á ÁC4ÐO2
Aview of the asymmetric unit of (IV), showing the twisted nature of both
crystallographically independent molecules and their atom-numbering
schemes. Displacement ellipsoids are drawn at the 50% probability level
and H atoms are shown as small spheres of arbitrary radii.
ꢁ
�
179.0 (2) ]. The meta- and para-substituted compounds,
however, feature intermolecular hydrogen bonding between
NÐH and the amide carbonyl group (Fig. 3). Here, the
requirement to adopt a planar arrangement is lifted and the
group in preventing the close approach of a second molecule
to form an intermolecular hydrogen bond.
ꢁ
equivalent torsion angles are � 62.2 (2) for (III), and
ꢁ
�
64.0 (2) and � 74.8 (2) for the two independent conforma-
tions of (IV). A further difference is that, in (II), the aromatic
ring plane is approximately coplanar with the amide plane,
whilst both (III) and (IV) exhibit more twisted geometries
Experimental
All starting materials were purchased from Aldrich and used as
received, except for xylene (mixture of isomers), which was puri®ed
by washing with concentrated sulfuric acid and dried over anhydrous
(
see torsion angles in Tables 1, 3 and 5).
Thus, the three compounds are differentiated by the relative
2
CaCl . The general synthesis used for the preparation of (II), (III)
conformations of both the aromatic and ketone groups with
respect to the amide, and by differences in hydrogen bonding.
Similar effects were observed in previous work on methyl-
substituted analogues (Chisholm et al., 2000). Therein, we
rationalized that a methyl substituent ortho to the NÐH group
sterically disfavoured intermolecular interactions and forced
the adoption of a sterically disfavoured planar conformation.
That this is a disfavoured strained conformation is shown by a
widening of the C2ÐC3ÐC4 angle, with values of 122.13 (9)
and (IV) was carried out as follows. A 250 ml three-necked round-
bottomed ¯ask was ®tted with a magnetic stirrer, a dropping funnel,
and a still head and condenser set for downward distillation. To this
apparatus were added ethyl acetoacetate (12.9 g, 0.1 mol) and xylene
(25 ml). The ¯ask was heated in an oil bath at 420 K with stirring. The
appropriate ¯uorinated aniline (0.09 mol) was then added via the
dropping funnel and ethanol began to distil. The reaction was
continued until the temperature at the still head dropped below the
boiling point of ethanol. On cooling to room temperature, off-white
crystalline needles formed, which were isolated by ®ltration and
washed with a small amount of petroleum ether (333±353 K), with
typical yields of 55±65%. For (II), m.p. 332±334 K; IR spectroscopic
ꢁ
and 122.5 (2) in, respectively, planar (II) and its methyl
ꢁ
analogue, compared with values of 112.6 (2) for (III), and
ꢁ
1
10.6 (1) or 110.2 (2) for (IV). A steric explanation is less
�
1
data (ꢀmax, nujol, cm ): 1707 (C O), 1675 (amide 1), 1620
likely to be the case with F substitution, due to the similarity in
van der Waals radii between H and F. In (II), an explanation
may be the high electronegativity of F, which disfavours the
approach of the O atom to form an intermolecular hydrogen
bond. The coplanarity of the amide group and the aromatic
(
aromatic), 1551 (amide 2). For (III), m.p. 339±341 K; IR spectro-
� 1
scopic data (ꢀmax, nujol, cm ): 1720 (C O), 1663 (amide 1), 1614
(
aromatic), 1548 (amide 2). For (IV), m.p. 364±366 K; IR spectro-
1
�
scopic data (ꢀmax, nujol, cm ): 1720 (C O), 1665 (amide 1), 1618
(aromatic), 1552 (amide 2).
Ê
ring is stabilized by an F1Á Á ÁH1N close contact of 2.29 (2) A.
That this is attractive and not incidental may be indicated by
ꢁ
the closure of the N1ÐC5ÐC10 angle to 117.2 (1) . We ®nd
no evidence of intermolecular HÁ Á ÁF interactions in any of
Table 1
Ê
ꢁ
Selected geometric parameters (A, ) for (II).
these compounds.
F1ÐC10
O1ÐC2
O2ÐC4
1.3621 (12)
1.2189 (13)
1.2205 (13)
N1ÐC4
N1ÐC5
1.3571 (13)
1.4011 (14)
In conclusion, the structures presented herein provide
further evidence for two broad conformational motifs for
acetoacetanilides, namely a planar intramolecular hydrogen-
bonded structure and a non-planar intermolecular hydrogen-
bonded structure. Which motif is present is dependent on the
position of the substituents on the phenyl ring. Whilst the
small size of ¯ourine may mitigate against steric effects, its
high electronegativity may serve to mimic the effect of a larger
C4ÐN1ÐC5
C2ÐC3ÐC4
N1ÐC4ÐC3
C10ÐC5ÐC6
128.08 (9)
122.13 (9)
116.26 (9)
117.14 (10)
C10ÐC5ÐN1
C6ÐC5ÐN1
C9ÐC10ÐC5
117.20 (10)
125.66 (10)
123.35 (10)
O1ÐC2ÐC3ÐC4
C5ÐN1ÐC4ÐO2
2.63 (16)
0.84 (17)
C4ÐN1ÐC5ÐC10
C4ÐN1ÐC5ÐC6
� 176.57 (9)
4.27 (17)
ꢀ
o646 Greig Chisholm et al.
Three isomers of C10
H10FNO
2
Acta Cryst. (2002). C58, o645±o648
Chisholm, Greig
