N-(2,3,5,6-Tetrafluoropyridin-4-yl)formamide

In the title compound, the Cp—N—C—O (p = pyridine) grouping has an anti conformation.


Structure description
The title compound, N-(2,3,5,6-tetrafluoropyridin-4-yl)formamide, (I), contains a perfluorinated pyridine heterocycle and a formamide group para to the pyridine N atom. These groups have shown utility in independent biochemical applications. For example, fluoroaromatic compounds are used in positron emission tomography (Hashizume et al., 1996) and pyridine rings can act as the bioisosteres of amides (Sun et al., 2019). The structure reported here combines these components and could be of interest for biochemical applications. A search of the CCDC shows no structures that contain a pyridine ring functionalized with a formamide group in the 4-position (Groom et al., 2016).
The crystal structure of (I) represents the first example of a perfluorinated pyridine ring with a formamide functional group (Fig. 1). The amide bond lengths for (I) are 1.218 (3) Å and 1.366 (3) Å for the C O and C-N bonds, respectively, which are in good agreement with the corresponding bonds in the related compounds N-phenylformamide (Omondi et al., 2014), N-(2,6-difluorophenyl)formamide (Omondi et al., 2009b), and N-(2,6-dibromophenyl)formamide (Omondi et al., 2009a). As observed in other structures, the amide bond lengths for (I) are consistent with little to no N C/C-O bond resonance contribution. The formamide group and pyridine ring in (I) are somewhat twisted with a dihedral angle of 13.21 (5) . This is similar to N-phenyl-data reports formamide (Omondi et al., 2014) (dihedral angle between the benzene ring and formamide groups = 10.5 ) but in contrast to N-(2,6-difluorophenyl)formamide (Omondi et al., 2009b) and N-(2,6-dibromophenyl)formamide (Omondi et al., 2009a) where the equivalent dihedral angles are 58.4 and 83.2 , respectively. The latter structures indicate that the steric effects likely increase from H to F to Br; however, this large deviation from planarity is not observed in (I). Furthermore, the torsion angle of 179.0 (2) for C3-N2-C6-O1 in (I) indicates a near anti-conformation, but in structures with a benzene ring, the carbonyl-benzene conformation is syn regardless of aromatic substituents (Omondi et al., 2009a(Omondi et al., ,b, 2014. Taken together, these indicate that the pyridine ring is playing a role in the structure beyond the sterics of the aromatic ring substituents. The pyridyl related compounds N-(3,5-dichloro-2-pyridyl)formamide (Resinger et al., 2005) and formyl(2-pyridyl)amine (Bock et al., 1996) also show an anti-conformation for the carbonyl and pyridine ring as well as near coplanarity of the functional groups as observed for the title compound.
In the extended structure of (I) the molecules are linked by N-HÁ Á ÁO hydrogen bonds with a bond angle of 171 (3) ( Table 1), which suggests evidence of intermediate-strong hydrogen bonding (Arunan et al., 2011). The hydrogen bonding generates chains of molecules propagating along the b-axis direction in the extended structure ( Fig. 2) with adjacent molecules in the chain related by 2 1 screw axis symmetry. Neighboring sets of chains form an L shape through a nearly orthogonal (84 ) orientation of the pyridine rings in each chain (Fig. 3). This brings about short contacts between the pyridyl nitrogen atoms and the systems of these orthogonal pyridine rings (NÁ Á Ácentroid = 3.502 Å ; shortest NÁ Á ÁC = 3.032 Å ). Table 1 Hydrogen-bond geometry (Å , ). (3) 171 (3) Symmetry code: (i) Àx; y À 1 2 ; Àz þ 3 2 .

Figure 2
Intermolecular hydrogen bonding forming a chain propagating along the b-axis direction where hydrogen bonds are represented with dashed lines.

Figure 3
Extended structure as viewed looking down the b-axis showing the Lshape that is formed by the orthogonal pyridine rings of neighboring chains.

Figure 1
Displacement ellipsoid perspective view (50% probability) for the title structure showing the atom-numbering scheme.

Refinement
Crystal data, data collection, and structure refinement details are summarized in Table 2.

N-(2,3,5,6-Tetrafluoropyridin-4-yl)formamide
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.