[4-(Tri­fluoro­methyl)­phenyl]­aceto­nitrile

The crystal structure of the title compound, C₉H₆F₃N, at 123 K contains mol­ecules linked together via several C—H...F and C—H...N contacts, the strongest of which are 2.58 and 2.65 Å, respectively. Apparently, an F atom in the CF₃ group is able to compete with a cyano N atom for aromatic H atoms but is less prone to interact with the more acidic methyl­ene H atoms. The Ph–CH₂CN torsion angle is −6.4 (2)° and the planar phenyl ring exhibits a typical deformation of the endo angles at the ipso-C atoms, due to the difference in the electron-withdrawing power of the CF₃ and CH₂CN substituents.

S1. Comment

The molecular structure of 4-(trifluoromethyl)benzonitrile, (I) (Boitsov et al., 2002), has revealed that the molecules are closely packed due to several intermolecular F···H and N···H contacts. A comparison between the F···H contacts (2.50 Å), the N···H contacts (2.56 and 2.59 Å) and the sum of the van der Waals radii (2.67 Å for F···H and 2.75 Å for N···H) indicated that one of the F atoms, located close to the phenyl-ring plane, could readily compete with the cyano N atoms for the H atoms, even though the N···H distances are shorter than in either benzonitrile (2.67 Å; Fauvet et al., 1978) or 1,4-(dicyano)benzene (2.61 Å; Colapietro et al., 1984). The F···H interactions (Desiraju & Steiner, 1999) in (I), however, were not sufficiently strong to significantly alter any of the structural parameters of the C—CF₃ fragment (Schultz et al., 1981; Kovacs et al., 1996) of the molecule but is the probable cause for the fairly high melting point of the compound compared with that of 4-methylbenzonitrile. Furthermore, the close packing of 4-(trifluoromethyl)benzonitrile, (I), gives rise to a relatively high crystal density of 1.550 Mg m^-3.

It has been suggested that the strength of F···H interactions may be related to both the acidity of the H atom involved (Thalladi et al., 1998) and the hybridization of the C atom to which it is bonded (Desiraju & Steiner, 1999). We report herein the molecular structure of [4-(trifluoromethyl)phenyl]acetonitrile, (II), a compound which contains H atoms linked to both sp²– and sp³-hybridized C atoms. This compound melts at 321 K, significantly higher than [4-(methyl)phenyl]acetonitrile (293 K).

It is clear that the packing structure (Fig. 2) does not resemble reported structures of aryl cyanides which are based upon parallel layers linked together by antiparallel contacts between neighbouring cyano groups (Colapietro et al., 1984) nor on CH₂···Ar(H···π), CN···Ar (Bond et al., 2001) or Ar···Ar interactions. Molecules of (II) are linked together through four unique contacts (see Table 2) from which three are clearly shorter than the sum of the van der Waals radii (2.67 Å for F···H and 2.75 Å for N···H; Bondi, 1964), F1···H6, N···H7A and N···H3, the fourth F1···H7B being a borderline contact, 2.67 Å. The relatively small intermolecular bond angles, 123–146°, are typical for these types of hydrogen-bond interactions, as presented in scatterplots of H···F distances versus C—H···F angles by Thalladi et al. (1998).

The N···H7A intermolecular contacts connect the molecules into columns along [010] and the N···H3 contacts join two molecules related by an inversion centre. These are further connected via F1···H6 and possibly also F1···H7B contacts into sheets propagating along [101]. As in the structure of 4-(trifluoromethyl)benzonitrile (Boitsov et al., 2002), the N atom participates in bifurcated intermolecular hydrogen-bond interactions. It seems that an F atom (F1) is able to compete with the cyano N atom for the aromatic H atoms but does not favour interactions with the more acidic methylene H atoms (Bordwell, 1988). The shortest distances between the sheets are by F2···H3(x, -1 + y, z) and F3···H6(1/2 + x, 1/2 - y, 1/2 + z) of 2.74 and 2.72 Å, respectively. There are no overlaps between the rings in the crystal and the shortest distance between rings is C5···H5(1/2 - x, 1/2 + y, 1/2 - z) of 2.89 Å [ΣvdW(C+H) is 2.90 Å], with the two rings related by an angle of about 99°, as measured over H5—C5···H5.

All bond lengths and angles listed in Table 1 are in principle as expected. The endo angles C2—C1—C6 and C3—C4—C5 reflect the difference in electron-withdrawing power of the substituents CF₃ and CH₂CN (Colapietro et al., 1984), cf. the Hammett σ_p values of -0.54 (CF₃) and \sim0.2 (CH₂CN), the latter derived from -0.66 (CN) assuming a transmission coefficient of \sim0.3 for a CH₂ group (Hine, 1962).

The phenyl ring is planar within experimental error and is otherwise symmetrical with respect to the bond lengths and angles. The C—F1 bond, involved in a weak intermolecular interaction with H6, and possibly also H7B, is slightly longer than F2—C9 and F3—C9; cf. the suggested elongation of one of the C—F bonds in 2-(trifluoromethyl)phenol (Kovacs et al., 1996). Furthermore, the F1—C9—C4 bond angle is smaller than those of F2—C9—C4 and F3—C9—C4. The two exo bond angles around C1 are distinctly different, indicating the effect of the proximity of the CH₂CN group to the plane of the ring, the C2—C1—C7—C8 torsion angle is -6.4 (2)°. [The Cambridge Structural Database (Version 5.21; Allen & Kennard, 1993) contains presently some 30 crystal structures of arylacetonitriles; however, no particular range of torsion angles seems to be favoured.] Similarly, the two exo angles around C4 differ, likely due to F3 being closer to the plane of the ring than F2. The distances (Å) of the non-aromatic atoms from the plane of the phenyl ring are: F1 - 1.284 (2), F2 0.686 (2), F3 0.429 (2), C7 0.054 (2), C8 - 0.055 (2), C9 - 0.031 (2) and N -0.150 (3) Å. The pertinent torsion angles are given in Table 1.

S2. Experimental

[4-(Trifluoromethyl)phenyl]acetonitrile (Aldrich, 98%) was dissolved in a minimum volume of diethyl ether at room temperature. Hexane was then added and the diethyl ether removed by evaporation. After filtration, the solution was left at room temperature overnight for crystallization. The solid was washed with cold hexane and dried. Crystals suitable for crystallographic study were obtained by slow crystallization from cyclohexane at room temperature (m.p. 321–322 K).

S3. Refinement

The H atoms were treated as riding, with C—H(CH) and C—H(CH₂) distances of 0.95 and 0.99 Å, respectively. The isotropic displacement parameters of the H atoms were fixed at 1.2U_eq of their parent atoms. The maximum residual peak is located on the C4—C5 bond, 0.68 Å from C4.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 2001b); molecular graphics: SHELXTL/PC (Sheldrick, 2001a); software used to prepare material for publication: SHELXTL/PC and PLATON (Spek, 2001).

Figures

Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level.

Fig. 2. The packing structure of (I) with a [101] sheet centred around the inversion centre at (1/2,1,0). The weak F1···H7B contacts have been included. H atoms (H2 and H5) not participating in hydrogen bonding have been omitted. Atoms labelled with the suffix A lie at positions (1 - x, 2 - y, -z), B at (x, 1 + y, z), C at (1/2 - x, 1/2 + y, 1/2 - z), D at (1/2 - x, -1/2 + y, 1/2 - z), E at (1 - x, 1 - y, -z), F(1/2 + x, 5/2 - y, -1/2 + z) and G at (1/2 + x, 3/2 - y, -1/2 + z).

[4-(trifluoromethyl)phenyl]acetonitrile

Crystal data

C9H6F3N	F(000) = 376
Mr = 185.15	Dx = 1.535 Mg m^−3
Monoclinic, P21/n	Melting point: 48-49° C K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 11.9085 (15) Å	Cell parameters from 4798 reflections
b = 5.5168 (7) Å	θ = 2.3–28.2°
c = 12.2376 (15) Å	µ = 0.14 mm^−1
β = 94.67 (3)°	T = 123 K
V = 801.30 (17) Å^3	Needle, colourless
Z = 4	0.55 × 0.12 × 0.10 mm

Data collection

Bruker AXS SMART 2K CCD diffractometer	1984 independent reflections
Radiation source: normal-focus sealed tube	1541 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.044
ω scans	θmax = 28.3°, θmin = 2.3°
Absorption correction: numerical (SHELXTL/PC; Sheldrick 2001a)	h = −15→15
Tmin = 0.937, Tmax = 0.991	k = −7→7
11234 measured reflections	l = −16→16

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.125	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0895P)^2] where P = (Fo^2 + 2Fc^2)/3
1984 reflections	(Δ/σ)max < 0.001
118 parameters	Δρmax = 0.47 e Å^−3
0 restraints	Δρmin = −0.34 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
F1	0.40753 (7)	0.35793 (17)	0.42576 (7)	0.0374 (3)
F2	0.47320 (7)	0.03793 (16)	0.35519 (7)	0.0364 (3)
F3	0.57378 (7)	0.36128 (17)	0.36928 (7)	0.0372 (3)
N	0.34142 (11)	0.9956 (2)	−0.15647 (10)	0.0331 (3)
C1	0.32420 (11)	0.5166 (2)	0.03198 (10)	0.0222 (3)
C2	0.41226 (11)	0.6452 (2)	0.08568 (11)	0.0254 (3)
H2	0.4400	0.7870	0.0530	0.030*
C3	0.46010 (11)	0.5677 (3)	0.18710 (11)	0.0251 (3)
H3	0.5203	0.6564	0.2237	0.030*
C4	0.41976 (10)	0.3612 (2)	0.23453 (10)	0.0220 (3)
C5	0.33092 (11)	0.2319 (3)	0.18199 (11)	0.0253 (3)
H5	0.3031	0.0904	0.2149	0.030*
C6	0.28337 (11)	0.3111 (2)	0.08131 (11)	0.0249 (3)
H6	0.2221	0.2241	0.0455	0.030*
C7	0.27086 (12)	0.5867 (3)	−0.08045 (11)	0.0267 (3)
H7A	0.2855	0.4560	−0.1328	0.032*
H7B	0.1883	0.5975	−0.0768	0.032*
C8	0.31094 (11)	0.8160 (3)	−0.12318 (11)	0.0249 (3)
C9	0.46882 (11)	0.2799 (3)	0.34483 (11)	0.0260 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
F1	0.0395 (5)	0.0510 (6)	0.0228 (4)	0.0123 (4)	0.0095 (4)	−0.0042 (4)
F2	0.0469 (6)	0.0293 (5)	0.0322 (5)	0.0068 (4)	−0.0019 (4)	0.0014 (4)
F3	0.0271 (5)	0.0504 (6)	0.0329 (5)	−0.0021 (4)	−0.0044 (4)	−0.0004 (4)
N	0.0391 (7)	0.0306 (7)	0.0299 (6)	−0.0019 (5)	0.0048 (5)	0.0015 (5)
C1	0.0217 (6)	0.0230 (7)	0.0222 (6)	0.0009 (5)	0.0049 (5)	−0.0024 (5)
C2	0.0265 (7)	0.0226 (7)	0.0275 (7)	−0.0035 (5)	0.0050 (5)	−0.0013 (5)
C3	0.0223 (6)	0.0260 (7)	0.0271 (7)	−0.0027 (5)	0.0015 (5)	−0.0063 (5)
C4	0.0209 (6)	0.0247 (7)	0.0210 (6)	0.0032 (5)	0.0054 (5)	−0.0041 (5)
C5	0.0253 (7)	0.0257 (7)	0.0256 (7)	−0.0036 (5)	0.0058 (5)	−0.0004 (5)
C6	0.0229 (7)	0.0267 (7)	0.0252 (7)	−0.0053 (5)	0.0031 (5)	−0.0032 (5)
C7	0.0289 (7)	0.0275 (7)	0.0238 (6)	−0.0047 (6)	0.0017 (5)	−0.0007 (5)
C8	0.0250 (7)	0.0289 (7)	0.0211 (6)	0.0020 (5)	0.0034 (5)	−0.0022 (5)
C9	0.0247 (7)	0.0292 (7)	0.0244 (7)	0.0026 (5)	0.0038 (5)	−0.0049 (5)

Geometric parameters (Å, º)

F1—C9	1.3478 (15)	C4—C9	1.4953 (18)
F2—C9	1.3416 (18)	C5—C6	1.3842 (19)
F3—C9	1.3388 (16)	C7—C8	1.4636 (19)
N—C8	1.1415 (18)	C2—H2	0.9500
C1—C2	1.3865 (18)	C3—H3	0.9500
C1—C6	1.3907 (18)	C5—H5	0.9500
C1—C7	1.5179 (19)	C6—H6	0.9500
C2—C3	1.3902 (19)	C7—H7A	0.9900
C3—C4	1.3824 (19)	C7—H7B	0.9900
C4—C5	1.3896 (18)
C2—C1—C6	119.28 (12)	F2—C9—C4	113.15 (11)
C2—C1—C7	122.93 (12)	F3—C9—C4	112.96 (12)
C6—C1—C7	117.78 (11)	C6—C5—H5	120.3
C1—C2—C3	120.32 (13)	C4—C5—H5	120.3
C4—C3—C2	119.81 (12)	C5—C6—H6	119.6
C3—C4—C5	120.43 (12)	C1—C6—H6	119.6
C3—C4—C9	120.17 (12)	C1—C2—H2	119.8
C5—C4—C9	119.36 (13)	C3—C2—H2	119.8
C6—C5—C4	119.37 (13)	C4—C3—H3	120.1
C5—C6—C1	120.78 (12)	C2—C3—H3	120.1
C8—C7—C1	114.81 (11)	C8—C7—H7A	108.6
N—C8—C7	179.49 (15)	C1—C7—H7A	108.6
F2—C9—F1	105.52 (12)	C8—C7—H7B	108.6
F3—C9—F1	106.28 (11)	C1—C7—H7B	108.6
F3—C9—F2	106.51 (11)	H7A—C7—H7B	107.5
F1—C9—C4	111.86 (11)
C6—C1—C2—C3	0.8 (2)	C7—C1—C6—C5	177.64 (12)
C7—C1—C2—C3	−177.94 (12)	C2—C1—C7—C8	−6.39 (19)
C1—C2—C3—C4	0.1 (2)	C6—C1—C7—C8	174.85 (12)
C2—C3—C4—C5	−0.7 (2)	C3—C4—C9—F1	96.13 (15)
C2—C3—C4—C9	−178.51 (12)	C3—C4—C9—F2	−144.86 (12)
C3—C4—C5—C6	0.3 (2)	C3—C4—C9—F3	−23.73 (17)
C9—C4—C5—C6	178.17 (12)	C5—C4—C9—F2	37.26 (16)
C4—C5—C6—C1	0.6 (2)	C5—C4—C9—F3	158.38 (12)
C2—C1—C6—C5	−1.2 (2)	C5—C4—C9—F1	−81.75 (16)