organic compounds
one, which crystallizes as a four-component twin (Bolotina et
al., 2005).
In the asymmetric unit of (II), the molecules are positioned
pairwise with intermolecular NÐHÁ Á ÁO hydrogen bonds
between molecules A and B and between molecules C and D
However, the lattice perspective examined along the b axis
(Fig. 3) shows that molecules B and D at the short a-axis edges
of the lattice are in more similar conformations than molecules
A and C, with the offset penta¯uorophenyl rings in the middle
of the unit cell. A closer inspection of the molecular confor-
mations reveals that all four molecules differ: torsion angles
N1ÐC3ÐC5ÐC6 in molecules A±D and in the molecule of
(II) with its geometry optimized at the pbe1pbe/6-31+G* level
of theory (II-DFT) (GAUSSIAN03; Frisch et al., 2004) are
(
Fig. 1). The donor±acceptor NÁ Á ÁO separations fall in the
Ê
range 2.8380 (15)±2.8855 (15) A, with NÐHÁ Á ÁO angles
ꢀ
between 156 and 172 . These relatively strong hydrogen bonds
are thought to be the driving force for the crystallization of
ꢀ
(
II).
The hydrogen-bonding motif in (II) is C(4) (Bernstein et al.,
995) in all cases. The parallel hydrogen-bonded chains of the
55.23 (17), 64.47 (16), 47.80 (16), 66.39 (16) and 52.3 ,
respectively. A somewhat smaller variation is observed for
torsion angles C2ÐN1ÐC3ÐC5 for the ®ve molecules in the
same order: 74.23 (14), 87.95 (15), 81.32 (15), 84.22 (15) and
1
same chiral con®guration propagate in the [120] direction and
are stacked in planes with alternating chiral con®gurations
along the crystallographic c axis. While there are no interchain
hydrogen bonds, there is a number of FÁ Á ÁF contacts that are
ꢀ
89.0 .
Ê
The average CÐF bond length of 1.341 (3) A for molecules
A±D is statistically equivalent to the corresponding averaged
Ê
distance in (II-DFT) [1.334 (6) A]. A scrutiny of the amide
link shows that the delocalization of electron density in the
planar HÐNÐC O unit due to the n(N1)!ꢁ*(C2 O1)
donation is more prominent in the experimental data [N1Ð
shorter than the sum of the F `zero-point energy' radius of
Ê
2
.826 A, de®ned as the distance at which the FÁ Á ÁF inter-
actions become predominantly repulsive (Guzei & Wendt,
006). The contacts are between chains A and A(1 + x, y, z), A
2
Ê Ê
and C(2 � x, � y, 1 � z), A and C(1 � x, � y, 1 � z), B and
C2 = 1.340 (3) A and C2 O1 = 1.232 (2) A] than in the
Ê
Ê
D(x, 1 + y, z), and C and C(1 + x, y, z), with the shortest
Ê
distance being 2.7722 (11) A between atoms F3A and
theoretical model (N1ÐC2 = 1.37 A and C2 O1 = 1.22 A),
where the differences are statistically signi®cant. This may in
part be attributed to the intermolecular hydrogen bonding,
F4C(1 � x, � y, 1 � z). The energy required to reposition two
Ê
F atoms from 2.826 to 2.772 A has been estimated with a
which would elongate the experimentally observed C
O
Morse potential and found to be ꢁ0.04 kcal mol�
1
double bonds relative to that in the theoretical model, in
which intermolecular effects were absent. A natural bond-
orbital analysis of (II-DFT) computed the bond orders for
bonds N1ÐC2 and C2 O1 to be 1.1 and 1.9, respectively.
�
1
1 kcal mol = 4.184 kJ mol ).
� 1
(
Interestingly, molecules B and D have similar geometries,
while those of A and C are noticeably different. Thus, two
different hydrogen-bonded chains are present. It is important
to compare Figs. 2 and 3. The lattice content viewed along the
a axis (Fig. 2) seems to reveal a regular packing pattern.
Experimental
2 2
Piperidine (245 ml, 2.48 mmol) was dissolved in CH Cl (25 ml) in a
dry 25 ml ¯ask to which triethylamine (380 ml, 2.73 mmol) was added.
The solution was cooled to 273 K and bromoacetyl bromide (216 ml,
2.48 mmol) was added dropwise to the stirred solution. After 15 min,
the solution was placed in a separatory funnel and washed with water
(
(
20 ml), 5% citric acid (20 ml) and saturated sodium bicarbonate
20 ml). The organic layer was dried over sodium sulfate and ®ltered.
Removal of the solvent in vacuo yielded 425 mg of a dark-brown
liquid. A 200 mg (0.97 mmol) portion of this liquid was dissolved in
0
N,N -dimethylformamide (DMF, 20 ml) and stirred at 273 K.
Racemic 1-(penta¯uorophenyl)ethylamine (225 mg, 1.07 mmol) was
dissolved in DMF (15 ml) and added dropwise to this solution. The
solution was stirred for 10 min after the addition was complete, then
heated to 343 K for 40 min in an oil bath to afford a mixture of
products, presumably including (I). After cooling to room tempera-
ture, acetyl chloride (345 ml, 4.85 mmol) and pyridine (118 ml,
1
.46 mmol) were added to the crude mixture. The reaction was stirred
overnight and the solution was concentrated in vacuo to yield a
brown oil. The oil was dissolved in CH Cl (10 ml). Pyridine (156 ml,
.94 mmol) was added to the solution, followed by acetyl chloride
345 ml, 4.85 mmol). The solution was stirred for 15 min, followed by
removal of the solvent in vacuo to yield a gray solid. The solid was
redissolved in CH Cl (15 ml), placed in a separatory funnel, and
2
2
1
(
2
2
washed with 10% citric acid (15 ml) and saturated sodium bicarbon-
ate (15 ml). The organic layer was dried over sodium sulfate, ®ltered
and concentrated in vacuo to yield a brown oil. Puri®cation by silica-
gel chromatography using ethyl acetate as eluent afforded the desired
Figure 3
A packing diagram of (II), viewed along the b axis. All H atoms, except
the amide NH atoms, have been omitted for clarity. Hydrogen-bonding
interactions are shown as dashed lines.
ꢂ
Acta Cryst. (2006). C62, o286±o288
Guzei et al.
10 8
C H F
5
NO o287
Guzei, Ilia A.
