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N-Phenyl­formamide, C7H7NO, crystallizes with two mol­ecules in the asymmetric unit which have different conformations of the formyl­amino group, one being cis and the other trans. This is the first example of an aryl­formamide crystal containing both conformational isomers and it may thus be considered a cocrystal of the two conformers. The two mol­ecules in the unit cell are linked through N—H...O hydrogen bonding to two other mol­ecules, thereby forming hydrogen-bonded tetra­mers within the crystal structure.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270108002746/gd3183sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270108002746/gd3183Isup2.hkl
Contains datablock I

CCDC reference: 682820

Comment top

The study of the title compound, (I), has attracted considerable interest in recent years. However, no crystallographic studies on N-phenylformamide have been reported previously. Previous studies of the compound have been largely theoretical (Moreno et al., 2006; Moisan & Danneberg, 2003; Kobko & Danneberg, 2003; Vargas et al., 2001; Bock et al., 1996; Manea et al., 1997), including density functional theory (DFT) studies (Doerksen et al., 2004), and experimental investigations on resonant two-photon ionization spectroscopy (Federov & Cable, 2000) and laser-induced fluorescence excitation (Dickinson et al., 1999). The study of (I) has also been improtant as a model for the understanding of the structure, folding and stability of proteins. This understanding has typically been gained from an interpretation of IR, Raman or NMR spectra of model systems such as formamide (the most simple representative of this class of compounds), N-alkyl- or N-phenylamide–water clusters, either isolated in a matrix or dispersed in an aqueous solution (Dickinson et al., 1999). The solution NMR spectrum of a powdered sample of (I) in CDCl3 showed equal concentrations of both cis and trans isomers which is in agreement with the dynamic solution behaviour of amide systems reported previously (Siddall et al., 1968, and references therein; Omondi et al., 2005).

N-Phenylformamide crystallizes with two molecules in the asymmetric unit (Fig. 1). One of the molecules adopts a cis conformation, while the other shows a trans conformation. The formation of a cocrystal of the two conformations is unusual as N-phenylformamides and N-phenylthioamides usually crystallize as only one of these isomers (Omondi, 2007; Omondi et al., 2005), even though both conformers exist in solution. The two conformers show similar bond lengths and angles that compare well to those of related compounds in the literature. The N11—C17 and O11—C17 bond lengths are, as expected for conjugated π-systems, in the regions of 1.33 and 1.22 Å respectively. Both molecules adopt the almost planar geometry that would be preferred in order to extend π-conjugation from the ring system to the formamide group. This, in turn, shortens the N11—C11 single-bond length. The shortening of this bond is, however, not very significant. A notable difference between the two conformers is in the angle between the plane defined by the phenyl ring (C11–C16 or C21—C26) and the plane defined by the formamide group (C11—N11—C17—O11 or C21—N21—C27—O21). In the cis isomer, the angle between the two mean planes is approximately equal to zero, whereas in the trans isomer the formamide group is slightly out of the plane of the phenyl ring by about 9.1 (1)°. This angle varies in related compounds, such as acetanilide, and also in the calculated structures of the cis and trans isomers of N-phenylformamide. The gas-phase conformation of the trans isomer is reported to be nonplanar (Manea et al., 1997), in contrast to what is observed here in the crystalline phase.

The two molecules in the unit cell have a dihedral angle of 19.07 (6)° between their mean planes. Each molecule of a particular conformation (cis or trans) is related to its nearest neighbor of the same conformation through a glide plane.

Each molecule is connected to another molecule of a different conformation through N—H···O hydrogen bonding, resulting in a tetrameric arrangement, with graph-set R44(16), such that each tetramer contains two molecules of each conformation. Due to the nearly planar backbone of the molecule, the hydrogen bonds are almost linear, with N—H···O angles of 178 and 176° for the cis and trans conformers, respectively. The intramolecular N···O distances are slightly shorter than those in acetanilide and other related acetamides, such as paracetamol (2.894–2.967 Å; Wasserman et al., 1985; Johnson et al., 1995), all of which adopt only the trans conformation in the solid state.

Related literature top

For related literature, see: Bock et al. (1996); Dickinson et al. (1999); Doerksen et al. (2004); Federov & Cable (2000); Johnson et al. (1995); Kobko & Danneberg (2003); Manea et al. (1997); Moreno et al. (2006); Omondi (2007); Omondi et al. (2005); Siddall, Stewart & Marston (1968); Ugi et al. (1965); Vargas et al. (2001); Wasserman et al. (1985).

Experimental top

N-Phenylformamide was synthesized according to the procedure of Ugi et al. (1965). Commercially available aniline (Aldrich, purity > 95%) was heated in a tenfold excess of formic acid for a period of 15 h at 363 K. The excess formic acid was removed under vacuum to give a brown liquid which was treated with dilute hydrochloric acid (0.1 M HCl) and ethyl acetate. The organic layer was separated from the aqueous layer, dried over magnesium sulfate and distilled under vacuum. An off-white solid was obtained in good yield. The first suitable single crystals of N-phenylformamide were obtained by crystallization from ethyl acetate on work-up of the reaction mixture. Only subsequent to their growth, which took almost one year, was it possible to grow the same crystals (as established by X-ray powder diffraction) from various solvents by slow evaporation (chloroform, ethanol, dichloromethane, ethyl acetate, dimethyl sulfoxide and tetrahydrofuran). The powder was recrystallized from a variety of solvents giving crystals suitable for single-crystal X-ray diffraction studies. 1H NMR (DMSO): δ 7.02, 7.22, 7.47 (m; cis and trans, para, meta and ortho Ar—H; trans, NH), 8.37 (d, trans, CHO, JH—H = 1.13 Hz), 8.70 (d, cis, CHO, JH—H = 11.38), 8.46 (s, broad, cis, NH).

Refinement top

H atoms were positioned geometrically and allowed to ride on their respective parent atoms, with bond lengths of 0.95 (CH) and 0.88 Å (NH), and isotropic displacement parameters 1.2 times Ueq of the parent atom.

Computing details top

Data collection: SMART-NT (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1999); data reduction: SAINT-Plus (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2003) and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. View of (I) down the a axis, showing N—H···O hydrogen-bonded tetramers (50% probability displacement ellipsoids).
N-Phenylformamide top
Crystal data top
C7H7NOF(000) = 1024
Mr = 121.14Dx = 1.285 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 2001 reflections
a = 31.177 (3) Åθ = 2.9–27.1°
b = 6.1229 (5) ŵ = 0.09 mm1
c = 14.3335 (12) ÅT = 173 K
β = 113.771 (2)°Block, pale green
V = 2504.1 (4) Å30.53 × 0.20 × 0.14 mm
Z = 16
Data collection top
Bruker SMART CCD area-detector
diffractometer
1953 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.026
Graphite monochromatorθmax = 27.0°, θmin = 1.4°
ϕ and ω scansh = 3939
7327 measured reflectionsk = 67
2732 independent reflectionsl = 189
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.040Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.110H-atom parameters constrained
S = 1.03 w = 1/[σ2(Fo2) + (0.0522P)2 + 0.7143P]
where P = (Fo2 + 2Fc2)/3
2732 reflections(Δ/σ)max < 0.001
163 parametersΔρmax = 0.19 e Å3
0 restraintsΔρmin = 0.18 e Å3
Crystal data top
C7H7NOV = 2504.1 (4) Å3
Mr = 121.14Z = 16
Monoclinic, C2/cMo Kα radiation
a = 31.177 (3) ŵ = 0.09 mm1
b = 6.1229 (5) ÅT = 173 K
c = 14.3335 (12) Å0.53 × 0.20 × 0.14 mm
β = 113.771 (2)°
Data collection top
Bruker SMART CCD area-detector
diffractometer
1953 reflections with I > 2σ(I)
7327 measured reflectionsRint = 0.026
2732 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0400 restraints
wR(F2) = 0.110H-atom parameters constrained
S = 1.03Δρmax = 0.19 e Å3
2732 reflectionsΔρmin = 0.18 e Å3
163 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C110.66832 (5)0.7492 (2)0.78636 (10)0.0299 (3)
C120.70000 (5)0.9093 (2)0.78800 (11)0.0377 (4)
H120.68901.04350.75340.045*
C130.74744 (5)0.8749 (3)0.83952 (12)0.0454 (4)
H130.76890.98530.83980.054*
C140.76399 (5)0.6826 (3)0.89039 (12)0.0470 (4)
H140.79670.66020.92680.056*
C150.73264 (6)0.5229 (3)0.88795 (13)0.0513 (4)
H150.74400.38920.92280.062*
C160.68483 (5)0.5527 (3)0.83581 (12)0.0438 (4)
H160.66360.43990.83400.053*
C170.58388 (5)0.6706 (3)0.72146 (12)0.0404 (4)
H170.58960.53060.75270.048*
N110.62025 (4)0.7959 (2)0.73282 (8)0.0331 (3)
H110.61360.92470.70320.040*
O110.54320 (4)0.7262 (2)0.67274 (9)0.0529 (3)
C210.57124 (5)1.5283 (2)0.46422 (10)0.0300 (3)
C220.54546 (5)1.6725 (3)0.38727 (11)0.0368 (3)
H220.51311.64660.34820.044*
C230.56680 (6)1.8534 (3)0.36752 (11)0.0451 (4)
H230.54911.95130.31450.054*
C240.61379 (6)1.8928 (3)0.42463 (11)0.0452 (4)
H240.62852.01820.41160.054*
C250.63909 (5)1.7487 (3)0.50050 (12)0.0425 (4)
H250.67141.77570.53970.051*
C260.61848 (5)1.5657 (2)0.52082 (11)0.0357 (3)
H260.63651.46670.57300.043*
C270.56217 (5)1.2025 (2)0.55652 (12)0.0405 (4)
H270.54131.08700.55380.049*
N210.54716 (4)1.34647 (19)0.48004 (9)0.0362 (3)
H210.51861.32520.43360.043*
O210.60001 (4)1.20441 (18)0.62962 (8)0.0472 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C110.0314 (7)0.0311 (7)0.0275 (6)0.0010 (6)0.0123 (5)0.0024 (6)
C120.0356 (7)0.0301 (8)0.0446 (8)0.0001 (6)0.0132 (6)0.0023 (6)
C130.0335 (8)0.0425 (9)0.0559 (9)0.0047 (7)0.0138 (7)0.0059 (8)
C140.0342 (8)0.0512 (10)0.0493 (9)0.0097 (7)0.0101 (7)0.0023 (8)
C150.0504 (9)0.0457 (10)0.0538 (10)0.0154 (8)0.0171 (8)0.0143 (8)
C160.0448 (9)0.0351 (9)0.0523 (9)0.0015 (7)0.0204 (7)0.0105 (7)
C170.0380 (8)0.0368 (8)0.0455 (8)0.0071 (7)0.0160 (7)0.0078 (7)
N110.0309 (6)0.0310 (6)0.0352 (6)0.0015 (5)0.0110 (5)0.0034 (5)
O110.0314 (5)0.0608 (8)0.0588 (7)0.0083 (5)0.0102 (5)0.0108 (6)
C210.0319 (7)0.0278 (7)0.0312 (7)0.0006 (6)0.0137 (6)0.0031 (5)
C220.0346 (7)0.0380 (8)0.0340 (7)0.0005 (6)0.0098 (6)0.0003 (6)
C230.0528 (9)0.0395 (9)0.0379 (8)0.0014 (7)0.0129 (7)0.0084 (7)
C240.0531 (9)0.0406 (9)0.0435 (8)0.0122 (8)0.0210 (7)0.0037 (7)
C250.0347 (7)0.0473 (10)0.0435 (8)0.0091 (7)0.0137 (6)0.0018 (7)
C260.0311 (7)0.0358 (8)0.0382 (7)0.0005 (6)0.0119 (6)0.0031 (6)
C270.0382 (8)0.0310 (8)0.0484 (9)0.0049 (6)0.0133 (7)0.0039 (7)
N210.0281 (6)0.0331 (7)0.0406 (7)0.0050 (5)0.0066 (5)0.0022 (5)
O210.0424 (6)0.0397 (6)0.0478 (6)0.0048 (5)0.0060 (5)0.0114 (5)
Geometric parameters (Å, º) top
C11—C121.385 (2)C21—C261.3846 (18)
C11—C161.386 (2)C21—C221.3884 (19)
C11—N111.4103 (17)C21—N211.4114 (18)
C12—C131.377 (2)C22—C231.379 (2)
C12—H120.9500C22—H220.9500
C13—C141.371 (2)C23—C241.381 (2)
C13—H130.9500C23—H230.9500
C14—C151.373 (2)C24—C251.375 (2)
C14—H140.9500C24—H240.9500
C15—C161.384 (2)C25—C261.380 (2)
C15—H150.9500C25—H250.9500
C16—H160.9500C26—H260.9500
C17—O111.2239 (17)C27—O211.2219 (17)
C17—N111.3238 (18)C27—N211.3359 (19)
C17—H170.9500C27—H270.9500
N11—H110.8800N21—H210.8800
C12—C11—C16119.35 (13)C26—C21—C22119.90 (13)
C12—C11—N11117.40 (12)C26—C21—N21123.06 (12)
C16—C11—N11123.24 (13)C22—C21—N21117.03 (12)
C13—C12—C11120.35 (14)C23—C22—C21120.10 (13)
C13—C12—H12119.8C23—C22—H22120.0
C11—C12—H12119.8C21—C22—H22120.0
C14—C13—C12120.60 (15)C22—C23—C24120.18 (14)
C14—C13—H13119.7C22—C23—H23119.9
C12—C13—H13119.7C24—C23—H23119.9
C13—C14—C15119.10 (15)C25—C24—C23119.33 (15)
C13—C14—H14120.4C25—C24—H24120.3
C15—C14—H14120.4C23—C24—H24120.3
C14—C15—C16121.37 (15)C24—C25—C26121.35 (14)
C14—C15—H15119.3C24—C25—H25119.3
C16—C15—H15119.3C26—C25—H25119.3
C15—C16—C11119.20 (15)C25—C26—C21119.12 (13)
C15—C16—H16120.4C25—C26—H26120.4
C11—C16—H16120.4C21—C26—H26120.4
O11—C17—N11123.25 (15)O21—C27—N21126.51 (14)
O11—C17—H17118.4O21—C27—H27116.7
N11—C17—H17118.4N21—C27—H27116.7
C17—N11—C11128.26 (13)C27—N21—C21128.27 (12)
C17—N11—H11115.9C27—N21—H21115.9
C11—N11—H11115.9C21—N21—H21115.9
C16—C11—C12—C130.9 (2)C26—C21—C22—C230.3 (2)
N11—C11—C12—C13179.53 (13)N21—C21—C22—C23179.86 (14)
C11—C12—C13—C140.4 (2)C21—C22—C23—C240.5 (2)
C12—C13—C14—C151.0 (3)C22—C23—C24—C250.7 (3)
C13—C14—C15—C160.4 (3)C23—C24—C25—C260.1 (3)
C14—C15—C16—C111.0 (3)C24—C25—C26—C210.7 (2)
C12—C11—C16—C151.6 (2)C22—C21—C26—C250.9 (2)
N11—C11—C16—C15178.91 (14)N21—C21—C26—C25179.59 (14)
O11—C17—N11—C11179.64 (14)O21—C27—N21—C211.7 (3)
C12—C11—N11—C17179.39 (14)C26—C21—N21—C2710.2 (2)
C16—C11—N11—C171.1 (2)C22—C21—N21—C27170.34 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N11—H11···O210.881.972.8444 (16)176
N21—H21···O11i0.881.942.8206 (15)178
Symmetry code: (i) x+1, y+2, z+1.

Experimental details

Crystal data
Chemical formulaC7H7NO
Mr121.14
Crystal system, space groupMonoclinic, C2/c
Temperature (K)173
a, b, c (Å)31.177 (3), 6.1229 (5), 14.3335 (12)
β (°) 113.771 (2)
V3)2504.1 (4)
Z16
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.53 × 0.20 × 0.14
Data collection
DiffractometerBruker SMART CCD area-detector
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
7327, 2732, 1953
Rint0.026
(sin θ/λ)max1)0.639
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.040, 0.110, 1.03
No. of reflections2732
No. of parameters163
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.19, 0.18

Computer programs: SMART-NT (Bruker, 1998), SAINT-Plus (Bruker, 1999), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2003) and ORTEP-3 (Farrugia, 1997), WinGX (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N11—H11···O210.881.972.8444 (16)176.0
N21—H21···O11i0.881.942.8206 (15)177.6
Symmetry code: (i) x+1, y+2, z+1.
 

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