N-(n-Decyl)-4-nitroaniline

N-(n-Decyl)-4-nitroaniline, C16H26N2O2, crystallizes with two essentially planar molecules in the asymmetric unit. The decyl chains are fully extended in an anti conformation. The molecules pack in planar layers, within which molecules are linked into chains by two approximately linear N—H⋯O hydrogen bonds between the amine N atom and one O atom of the nitro group of an adjacent molecule. These molecular chains propagate via interleaving of the decyl chains to form the two dimensional sheets. The sheets are associated exclusively via non-bonded contacts. The structure has features in common with those of other N-alkyl-4-nitroanilines, but also subtle differences in packing.

N-(n-Decyl)-4-nitroaniline, C 16 H 26 N 2 O 2 , crystallizes with two essentially planar molecules in the asymmetric unit. The decyl chains are fully extended in an anti conformation. The molecules pack in planar layers, within which molecules are linked into chains by two approximately linear N-HÁ Á ÁO hydrogen bonds between the amine N atom and one O atom of the nitro group of an adjacent molecule. These molecular chains propagate via interleaving of the decyl chains to form the two dimensional sheets. The sheets are associated exclusively via non-bonded contacts. The structure has features in common with those of other N-alkyl-4-nitroanilines, but also subtle differences in packing.
undertaken the preparation of polyamines containing one aromatic nitro group in contrast to two such groups. The syntheses and properties of these polymers using both 2,6-difluoronitrobenzene and isomeric 2,4-difluoronitrobenzene, and a series of aliphatic diamines, will be reported elsewhere. In the course of these studies, it was necessary to prepare model compounds prior to the preparation of the polymers. This was accomplished by the reactions of either mono-or difluoro-substituted nitrobenzene with a homologous series of n-alkyl amines. The X-ray crystal structures of N-methyl-4-nitroaniline (Panunto et al., 1987) and N-alkyl-4-nitroanilines with alkyl groups ranging from n-propyl to n-pentyl (Gangopadhyay et al., 1999) have been reported. The N-decyl-4-nitroaniline (I) reported herein represents the longest chain N-alkyl-4-nitroaniline derivative thus far characterized by single-crystal X-ray methods.
The asymmetric unit of the title compound (I) contains two independent molecules which do not differ significantly in conformation (Figure 1). Both molecules are essentially planar and have the decyl tails in the characteristic zigzag anti conformations. The molecules are packed into layers that are parallel to and at the same intervals as the (202) lattice planes ( Figure 2). Within each of these layers, the molecules are linked by two N-H···O hydrogen bonds between the amine N atom of one molecule and one of the nitro O atoms of another ( Figure 3). As a consequence of these interactions, the N-O bond that participates in the hydrogen bond is about 0.01 Å longer than the other N-O bond on each nitro group. Also, the relative shortness of the H···O interactions and the linearity of the N-H···O bonds (Table 1) clearly demonstrate that these are classic single-acceptor hydrogen bonds, unlike the three-center interactions found in many nitroaniline derivatives including N-methyl-4-nitroaniline (Panunto et al., 1987). The hydrogen bonding links the molecules into chains that run along the 101 direction with the decyl chains on adjacent molecules oriented up and down, with an angle between the chains of about 77°. To complete the two-dimensional layers, these molecular chains then stack along the b axis with the decyl tails interleaved in parallel fashion so as to maximize favorable non-bonded contacts.
The series of N-alkyl-4-nitroanilines where alkyl = propyl-octyl has been examined for potential optical second harmonic generation (SHG) behavior (Gangopadhyay et al., 1999). SHG effects require the absence of a center of inversion, although this condition alone does not guarantee activity. Physical measurements of this series showed that only the butyl compound is active, and single-crystal structure analyses of the propyl, butyl and pentyl derivatives confirmed that only the butyl crystallizes in an noncentrosymmetric space group. The authors report that poor crystal quality prevented structure determinations of the longer chain derivatives, however, our successful crystallization of the decyl compound demonstrates that at least some of these may be characterized. The N-H···O hydrogen bonding in (I) is very similar to that found in the shorter chain analogs in terms of involving only one of the nitro O atoms. The packing in (I) is subtly different. In the propyl and pentyl compounds, the molecules stack in one direction in identical orientation so that both the rings and chains are parallel and in supplementary materials sup-2 close contact. By contrast, in (I), the layers are staggered so that rings in adjacent layers are not directly over one another but rather have an alkyl chain in between. This indicates that the fully interleaved packing of the decyl chains within the layer, which is unique to (I), is more important than the π-π interactions between the rings in determining the overall packing.

Experimental
Anhydrous potassium carbonate (2.0811 g, 0.015 mol) and a solution of 4-nitrofluorobenzene (0.9993 g, 0.007 mol) in 8 ml of dimethyacetamide (DMAC) were combined in a three-necked 100 ml round-bottomed flask, fitted with a nitrogen inlet, a thermometer, a magnetic stirring bar, and a Dean-Stark trap fitted with a condenser. To the clear yellow solution, n-decylamine (1.1767 g, 0.0075 mol) dissolved in DMAC (5 ml) was added with stirring. Additional DMAC (8 ml) was used to wash the transfer container and this was added to the reaction mixture, followed by the addition of 20 ml of toluene.
The temperature of the reaction mixture was raised to 403 K, and the reaction was allowed to continue at this temperature for one hour. Water, the by-product of the reaction, was removed via azeotropic distillation with toluene. After the removal of water, toluene was removed via the Dean-Stark trap, and the temperature of the reaction mixture was allowed to rise to 433 K. The reaction was allowed to continue at this temperature for three hours, after which it was allowed to cool to room temperature and then diluted with 20 ml of dichloromethane. The resulting heterogeneous mixture was then filtered through celite at reduced pressure, and the solvents from the filtrate were removed under high vacuum to yield a bright orange liquid residue. This crude product was dissolved in trichloromethane (15 ml), transferred to a separatory funnel, and washed repeatedly with deionized water. The organic layer was collected, dried over anhydrous magnesium sulfate, filtered, and the filtrate was evaporated using a rotary evaporator to yield a bright yellow solid. Crystals suitable for X-ray diffraction were obtained by recrystallization from hexane. Yield 56%, m.p. 332-333 K. IR (KBr, ν > 1400 cm −1 ): 3353,3064,2952,2925,2850,1602,1541,1475,1466 63, 137.74, 129.69.111.11, 43.66, 32.09, 29.75, 29.54, 29.51, 29.36, 27.21, 22.89, 14.33. MS (M/Z) (% base peak), 278 (11.6), 151 (100), 105 (19.7).

Refinement
Upon evaluation of systematic absences and weaknesses, the space group was determined to be P2 1 /c with an additional pseudo-a glide perpendicular to the b axis. A partial structure solution was obtained by direct methods and revealed two crystallographically independent molecules in the asymmetric unit. The remaining non-hydrogen atoms were located with difference Fourier techniques and refined with anisotropic atomic displacement parameters. All hydrogen atoms could be located in the difference Fourier maps and refined isotropically. Fig. 1. The asymmetric unit of (I) showing two independent molecules with atom labels and 50% probability displacement ellipsoids for non-hydrogen atoms.   as large as those based on F, and R-factors based on ALL data will be even larger.