2-Formyl­benzonitrile

The title compound, C₈H₅NO, has an intra­molecular O...CN contact involving an O...C distance of 2.797 (2) Å and a C—C—N bond angle of 174.5 (2)°, both indicative of a weak nucleophilic attack of the aldehyde O atom on the electrophilic C atom in the nitrile group. Calculations at the B3LYP density functional level using the 6–31G* basis set support this inter­pretation; natural bond-order analysis indicates an n_O1 → π delocalization energy of 6.3 kJ mol⁻¹. Similar results were obtained from density functional calculations on three related mol­ecules. The 2-formyl­benzonitrile mol­ecules pack in sheets as a consequence of C—H...N and C—H...O hydrogen bonds.

S1. Comment

In three o-nitrobenzonitrile derivatives (5-chloro-, 6-chloro- and 6-methyl-) there are weak electrophilic nucleophilic (or Lewis acid–base) interactions between a nitro O atom and the nitrile C atom (Britton & Cramer, 1996). This situation is shown by a short O···C distance and a bending of the C—CN group away from the interacting O atom. The study of o-cyanobenzaldehyde reported here was undertaken to see whether the same (expected) interaction occurred.

The atoms labelling and displacement ellipsoids are shown in Fig. 1, which also shows the O···C interaction. The O1···C7 distance is 2.797 (2) Å, which can be compared with the van der Waals distance of 3.22 (Bondi, 1964; Rowland & Taylor, 1996). The C1—C7—N1 angle is 174.5 (2)° and the CN group bends away from atom O1. This is similar to the results in the o-nitrobenzonitriles except that the O···C distance is about 0.2 Å longer in the aldehyde. This difference is reasonable since the aldehyde O atom has no formal change, while the nitro O atom has a formal change of −1/2. The other bond angles and distances in the molecule are normal.

The molecules pack in sheets parallel to (102) (Fig. 2). The molecules are tilted by 7.8 (1)° with respect to the sheets. There are three weak C—H···X interactions with H···X distances less than 2.70 Å. These interactions give rise to three different rings as can be seen in Fig. 2. Using graph-set notation (Etter, 1990; Bernstein et al., 1995) there is an R₂²(10) ring involving two H6 atoms, an R₃³(10) ring involving atoms H3, H6 and H5, and an R₄⁴(22) ring involving two H3 and two H5 atoms. The geometric data for these interactions are given in Table 1.

The Cambridge Structure Database (Allen, 2002) contains three additional structures with short O···CN interactions, viz. 2-cyanobenzophenone, (II) (Preut et al., 1992), 9-oxo-1-thioxanthenecarbonitrile, (III) (Abboud et al., 1990), and 5-cyano-7-methoxy,2,2-dimethyl-4-oxo-chroman-6-yl acetate, (IV) (Clegg, 2003). These are shown in Fig. 3. Relevant experimental data for these compounds are given in Table 2, where they are compared with electronic structure calculations.

To provide further insight into interactions between the potentially interacting carbonyl and nitrile groups in (I)–(IV), electronic structure calculations were carried out at the density functional level (Cramer, 2004) using the 6–31G* basis set (Hehre et al., 1986) and the hybrid B3LYP functional (Becke, 1988; Lee et al., 1988; Becke, 1993; Stephens et al., 1994). All structures were fully optimized without the imposition of any symmetry constraints. The optimized densities were employed in the computation of interatomic bond orders according to the scheme of Mayer (1983). In addition, the energetic stabilization associated with the n_O1 → π*_CN interaction was quantified by second-order perturbation theory in the natural bond orbital (NBO) basis (Reed et al., 1988). CM3 partial atomic charges (Winget et al., 2002) were also examined but charges on the nitrile N atoms in (I)–(IV) varied negligibly.

Although the calculated gas-phase and experimental solid-state structures should not be expected to match completely, key trends in the two sets of structures are manifest. Most noteworthy is the increasing deviation of the nitrile N atom from collinearity with the nitrile C atom and the ipso C atom of the aromatic ring as the distance between the carbonyl O and the nitrile C atoms decreases. If the carbon–oxygen interaction were purely repulsive, the nitrile group would be expected to be displaced away from the O atom, but that does not require bending at the nitrile C atom.

The presence of substantial repulsion is certainly supported by other geometric parameters. For instance, as the OCCC dihedral angle is reduced, the CCO angle increases to maintain separation from the nitrile C atom. In the case of o-cyanobenzaldehyde, where conjugation evidently favors coplanarity of all of the exocyclic functionality, the CCO bond angle increases to 125.3°.

Analysis of the B3LYP densities provides in each case some support for an incipient nucleophilic interaction between the carbonyl O atom and nitrile C atom. That interaction is not sufficient to lead to any significant Mayer bond order developing between the two atoms. Instead, NBO analysis suggests that there is a stabilization associated with an n_O1 → π*_CN interaction that increases steadily with decreasing O—C distance and concomitant decreasing C—C—N angles. The bending of the nitrile group facilitates this delocalization by increasing the amplitude of the π* orbital on the side of the bond adjacent to the carbonyl O atom. This effect does lead to a small reduction in the C—N Mayer bond order as the bond angle increasingly deviates from linearity.

S2. Experimental

The compound was obtained from Aldrich. The crystal used for diffraction was grown from chloroform.

S3. Refinement

H atoms were introduced at calculated positions, with C—H distances of 0.95 Å, and refined using a riding model [U_iso(H) = 1.2U_eq(C)].

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXLTL; molecular graphics: SHELXLTL; software used to prepare material for publication: SHELXLTL.

Figures

	Fig. 1. o-Cyanobenzaldehyde. Displacement ellipsoids are shown at the 50% probability level. The O···C—N interaction is shown as a dashed line.
	Fig. 2. A view normal to (102). C—H···N and C—H···O interactions are shown as dashed lines.
	Fig. 3. (Top) Compound (II), 2-cyanobenzophenone. (Center) Compound (III), 9-oxo-1-thioxanthenecarbonitrile. (Bottom) Compound (IV), 5-cyano-7-methoxy-2,2-dimethyl-4-oxo-chroman-6-yl acetate. Intramolecular O···C interactions are shown as dashed lines.

2-Formylbenzonitrile

Crystal data

C8H5NO	F(000) = 272
Mr = 131.13	Dx = 1.374 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1810 reflections
a = 3.7889 (9) Å	θ = 2.3–24.3°
b = 15.580 (4) Å	µ = 0.09 mm^−1
c = 10.759 (3) Å	T = 173 K
β = 93.73 (3)°	Needle, colorless
V = 633.8 (3) Å^3	0.50 × 0.05 × 0.05 mm
Z = 4

Data collection

Siemens SMART area-detector diffractometer	974 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.041
Graphite monochromator	θmax = 25.0°, θmin = 2.3°
ω scans	h = −4→4
3166 measured reflections	k = −18→15
1115 independent reflections	l = −12→12

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.101	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.038P)^2 + 0.26P] where P = (Fo^2 + 2Fc^2)/3
1115 reflections	(Δ/σ)max = 0.001
91 parameters	Δρmax = 0.15 e Å^−3
0 restraints	Δρmin = −0.17 e Å^−3

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.2865 (4)	0.69998 (8)	0.88147 (12)	0.0395 (4)
N1	0.4433 (4)	0.87051 (10)	1.05357 (14)	0.0372 (4)
C1	0.1212 (4)	0.88277 (10)	0.83388 (14)	0.0251 (4)
C2	0.0145 (4)	0.81241 (10)	0.75790 (15)	0.0246 (4)
C3	−0.1618 (4)	0.82789 (11)	0.64310 (15)	0.0275 (4)
H3	−0.2372	0.7809	0.5917	0.033*
C4	−0.2293 (4)	0.91114 (11)	0.60254 (15)	0.0309 (4)
H4	−0.3470	0.9209	0.5231	0.037*
C5	−0.1256 (4)	0.97997 (11)	0.67752 (16)	0.0323 (4)
H5	−0.1739	1.0369	0.6497	0.039*
C6	0.0491 (4)	0.96605 (11)	0.79340 (15)	0.0295 (4)
H6	0.1192	1.0134	0.8449	0.035*
C7	0.3021 (4)	0.87205 (10)	0.95581 (15)	0.0280 (4)
C8	0.0904 (4)	0.72222 (11)	0.79371 (15)	0.0300 (4)
H8	−0.0231	0.6785	0.7443	0.036*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0500 (8)	0.0320 (7)	0.0352 (7)	0.0035 (6)	−0.0076 (6)	0.0019 (5)
N1	0.0423 (9)	0.0381 (9)	0.0304 (8)	0.0009 (7)	−0.0047 (7)	−0.0030 (7)
C1	0.0221 (8)	0.0288 (9)	0.0242 (8)	−0.0002 (7)	0.0007 (7)	0.0001 (7)
C2	0.0232 (8)	0.0256 (8)	0.0254 (8)	−0.0008 (7)	0.0042 (6)	−0.0008 (6)
C3	0.0269 (9)	0.0314 (9)	0.0242 (9)	−0.0025 (7)	0.0005 (7)	−0.0042 (7)
C4	0.0296 (9)	0.0373 (10)	0.0254 (9)	0.0012 (8)	−0.0018 (7)	0.0043 (7)
C5	0.0336 (9)	0.0274 (9)	0.0356 (10)	0.0018 (7)	−0.0010 (8)	0.0064 (8)
C6	0.0291 (9)	0.0272 (9)	0.0318 (9)	−0.0015 (7)	−0.0003 (7)	−0.0041 (7)
C7	0.0288 (9)	0.0260 (8)	0.0294 (9)	−0.0003 (7)	0.0030 (7)	−0.0021 (7)
C8	0.0333 (9)	0.0294 (9)	0.0274 (9)	−0.0018 (7)	0.0024 (7)	−0.0031 (7)

Geometric parameters (Å, º)

O1—C8	1.214 (2)	C3—H3	0.9500
N1—C7	1.149 (2)	C4—C5	1.383 (2)
C1—C6	1.390 (2)	C4—H4	0.9500
C1—C2	1.411 (2)	C5—C6	1.390 (2)
C1—C7	1.450 (2)	C5—H5	0.9500
C2—C3	1.387 (2)	C6—H6	0.9500
C2—C8	1.480 (2)	C8—H8	0.9500
C3—C4	1.387 (2)
C6—C1—C2	120.05 (14)	C3—C4—H4	119.9
C6—C1—C7	117.57 (14)	C4—C5—C6	120.18 (16)
C2—C1—C7	122.38 (15)	C4—C5—H5	119.9
C3—C2—C1	118.96 (15)	C6—C5—H5	119.9
C3—C2—C8	118.10 (14)	C5—C6—C1	119.94 (15)
C1—C2—C8	122.92 (15)	C5—C6—H6	120.0
C2—C3—C4	120.75 (15)	C1—C6—H6	120.0
C2—C3—H3	119.6	N1—C7—C1	174.54 (17)
C4—C3—H3	119.6	O1—C8—C2	124.91 (16)
C5—C4—C3	120.12 (15)	O1—C8—H8	117.5
C5—C4—H4	119.9	C2—C8—H8	117.5
C6—C1—C2—C3	0.0 (2)	C3—C4—C5—C6	0.5 (3)
C7—C1—C2—C3	179.10 (15)	C4—C5—C6—C1	0.3 (2)
C6—C1—C2—C8	178.42 (15)	C2—C1—C6—C5	−0.5 (2)
C7—C1—C2—C8	−2.5 (2)	C7—C1—C6—C5	−179.65 (15)
C1—C2—C3—C4	0.7 (2)	C3—C2—C8—O1	168.30 (16)
C8—C2—C3—C4	−177.73 (15)	C1—C2—C8—O1	−10.1 (3)
C2—C3—C4—C5	−1.0 (2)