6-Chloro-2-oxindole: X-ray and DFT-calculated study

The mol­ecule of the title compound (systematic name: 6-chloro­indolin-2-one), C₈H₆ClNO, is almost planar, with a dihedral angle of 1.13 (9)° between the planes of the constituent pyrrolidine and benzene rings. Centrosymmetric dimers are formed in the crystal structure by N—H...O hydrogen bonds, and these dimers are additionally linked by Cl...Cl and C—H...O inter­actions. Density functional theory (DFT) calculations at the B3LYP/6-31 G(d,p) level of theory were used to optimize the mol­ecular structure and the geometry was best reproduced by optimization of two inter­acting mol­ecules. The bond orders in the mol­ecule, estimated using the natural bond orbitals (NBO) formalism, are consistent with the observed bond lengths. In particular, the contribution of the lone pair of electrons on the N atom to the N—C bond in the N—C=O group is revealed. The measured IR spectrum of the compound shows a red shift of the N—H stretching frequency compared with the free molecule, due to the formation of the hydrogen bonds.

S1. Comment

The structure determination of 6-chloro-2-oxindole, (I), is part of a series of structure determinations of indole derivatives (Hachuła et al., 2008, 2012). There is considerable chemical interest in the development of oxindole derivatives because the heterocyclic ring of oxindole (indolin-2-one) is the basic nucleus of a number of alkaloids (e.g. vincatine, mitraphylline, herbaline, crassanine and voachalotin) and of many natural and/or synthetic compounds exhibiting biological and pharmacological activity (Crumeyrolle-Arias et al., 2004; England et al., 2007; Fatima et al., 2007; Galliford & Scheidt, 2007; Peddibhotla, 2009; Midoh et al., 2010). Our interest in the compound comes from investigations of the IR spectra and hydrogen bonding in oxindole (Lipkowski et al., 1995; Hachuła et al., 2012) and in indole derivatives such as indole-3-carboxaldehyde and 3-acetylindole (Flakus et al., 2011; Flakus & Hachuła, 2012).

The molecule of (I) (Fig. 1) is essentially planar (r.m.s. deviation 0.0149 Å for all non-H atoms). The dihedral angle between the planes defined by the constituent pyrrolidine and benzene rings is 1.13 (9)°. By comparison, this angle is 4.22° in indole-3-carboxaldehyde (Ng, 2007) and 0.29° in indole-3-carboxylic acid (Smith et al., 2003). The N1—C1 and N1—C8 bond lengths [1.4006 (17) and 1.3572 (18) Å, respectively] differ from the corresponding mean values of 1.419 and 1.331 Å reported for the γ-lactams (Allen et al., 1987). Comparable asymmetric bonding patterns are found in similar structures [e.g. 3-methylindolin-2-one (Lipkowski et al., 1995), 3,3-dimethylindolin-2-one (Lipkowski et al., 1995), 3,3-dichloroindolin-2-one (Zukerman-Schpector et al., 1993), 2,3-indolinedione (Bocelli & Grenier-Loustalot, 1982) and 5-hydroxyindolin-2-one (Wei et al., 2004)] and in other indole derivatives [e.g. indole-3-carboxaldehyde (Ng, 2007), 3-acetylindole (Hachuła et al., 2008), 3-acetyl-1-methoxyindole (Acheson et al., 1980), indole-3-carboxylic acid (Smith et al., 2003) and indole-3-acetic acid (Karle et al., 1964)]. This is consistent with electron delocalization from the N atom towards the carbonyl group. The C8═ O1 bond length [1.2312 (17) Å] is comparable with the mean value of 1.232 Å reported for the γ-lactams (Nerskov-Lauritsen et al., 1985). Natural bond orbital (NBO) analysis (Foster & Weinhold, 1980) of the electronic structure [Table 1; showing calculations for a single molecule (A) and for a hydrogen-bonded molecular pair (B)] confirms that the electrons of the lone pair on atom N1 contribute to the electronic density of the N1—C8 bond, lending it a partial double-bond character.

In the structure of (I), the molecules form dimers across inversion centres through two N—H···O hydrogen bonds (Fig. 2 and Table 2), forming an R₂²(8) graph-set motif (Etter et al., 1990; Bernstein et al., 1995; Motherwell et al., 1999). According to the hydrogen-bonding classification provided by Steiner (2002) and Desiraju & Steiner (1999), these are medium-strength electrostatic interactions. Neighbouring dimers interact through C4—H4···O1ⁱⁱ contacts [symmetry code: (ii) x + 1, -y + 1/2, z - 1/2], Cl···Cl interactions [C3—Cl1···Cl1ⁱ = 3.4378 (6) Å and 170.87 (5)°; symmetry code: (iii) -x + 2, -y + 1, -z] and stacking interactions [interplanar separation of 3.33 (1) Å]. According to the classification of Pedireddi et al. (1994), the Cl···Cl contacts are type I in nature, having equal C—Cl···Cl angles.

The experimental values of the bond lengths and angles are in good agreement with those obtained from density functional theory (DFT) calculations (Table 3). The DFT calculations were obtained for both a single molecule (A) and a hydrogen-bonded dimer (B), comprising two molecules of (I) linked through N1—H1···O1 hydrogen bonds. The largest differences between the calculated and experimental values for a single molecule are 0.0332 Å for the bond lengths and 2.0° for the bond angles, while the corresponding values for the hydrogen-bonded dimer are 0.0122 Å and 0.75°. The better agreement in the latter case could be considered as an indication that the intermolecular interactions slightly influence the molecular geometry of (I). The total energy for the geometry-optimized single molecule is -3.918 × 10 ^-15 J and the calculated dipole moment is 1.1904 D. The dipole vector lies in the molecular plane and is oriented approximately along the axis passing through atoms C1 and C4 (Fig. 1). In the structure, the molecular dipoles are arranged antiparallel to each other. The calculated total energy of the two intermolecular hydrogen bonds, corrected for basis set superposition error (BSSE) using a standard procedure (Boys & Bernardi, 1970), is -81.568 kJ mol^-1. The calculated hydrogen-bond geometry [N—H = 1.031 Å, H···O = 1.823 Å, N···O = 2.847 Å and N—H···O = 171.98°] also corresponds well with the experimental data.

In the measured IR spectrum of (I), an intense and broad band in the region 3400–2400 cm^-1 can be assigned to the ν_N—H stretching mode of the N—H group involved in hydrogen bonding. In the IR spectrum derived from the DFT calculations, this band is observed at 3295 cm^-1. The shift in the N—H stretch to lower frequency (red shift) compared with the expected non-hydrogen-bonded value of 3451 cm^-1 is associated with hydrogen bonding and a lengthening of the N—H bond (Schuster et al., 1976; Schuster & Mikenda, 1999; Jeffrey, 1997). The extent of the shift, Δν_s, is related to important chemical and physical properties, such as hydrogen-bond energy and interatomic distances. For medium-strength hydrogen bonds, the X—H···A distance ranges from 2.5 to 3.2 Å [X—H ca 1.5–2.2 Å and X—H···A 130–180°], Δν_s is expected to be 10–25% and the hydrogen-bond energy lies in the range 4–15 kcal mol^-1 (ca 15–60 kJ mol^-1; Jeffrey, 1997). Thus, the N—H···O hydrogen bonds in (I) are confirmed to be medium-strength. The geometric parameters of (I) are comparable with those of the N—H···O bond occurring in oxindole form II [N···O = 2.833 (2) and 2.857 (2) Å; Hachuła et al., 2012].

Related literature

For related literature, see: Acheson et al. (1980); Allen et al. (1987); Bernstein et al. (1995); Bocelli & Grenier-Loustalot (1982); Boys & Bernardi (1970); Crumeyrolle-Arias, Tournaire, Cane, Launay, Barritault & Medvedev (2004); Desiraju & Steiner (1999); England et al. (2007); Etter et al. (1990); Fatima et al. (2007); Flakus & Hachuła (2012); Flakus et al. (2011); Foster & Weinhold (1980); Frisch (2009); Galliford & Scheidt (2007); Glendening et al. (1993); Hachuła et al. (2008, 2012); Jeffrey (1997); Karle et al. (1964); Lipkowski et al. (1995); Midoh et al. (2010); Motherwell et al. (1999); Nerskov-Lauritsen, Burgi, Hofmann & Schmidt (1985); Ng (2007); Parr & Yang (1989); Peddibhotla (2009); Pedireddi et al. (1994); Schuster & Mikenda (1999); Schuster et al. (1976); Smith et al. (2003); Steiner (2002); Wei et al. (2004); Zukerman-Schpector, Pinto, da DaC, Silva & Barcellos (1993).

S2. Experimental

6-Chloro-2-oxindole (Sigma–Aldrich, 97% pure) was dissolved in acetone and left to evaporate under ambient conditions. Plate-shaped crystals of (I) appeared after a few days. Differential scanning calorimetry of the bulk showed only one sharp endothermic peak at 466.43 K, which corresponds to the melting process. Spectroscopic analysis: IR (KBr; ν, cm^-1): 1700 (s) (calculated 1800) ν_C═O; 1622–1002 (m) (calculated 1670–1092) ν_C═C and ν_C—C; 1333 (m) (calculated 1332) ν_C—N; 702 (m) (calculated 708) ν_C—Cl.

S3. Refinement

H atoms bound to C atoms were placed in idealized positions and refined as riding, with C—H = 0.95 Å and U_iso(H) = 1.2U_eq(C). Atom H1 of the NH group was located in a difference Fourier map and refined freely with an isotropic displacement parameter.

DFT calculations were carried out at the B3LYP/6-31 G(d,p) level using GAUSSIAN09 (Parr & Yang, 1989; Frisch et al., 2009), starting from the X-ray geometry. Natural bond orbital calculations (Foster & Weinhold, 1980) were carried out using the program NBO (Glendening et al., 1993) included in the GAUSSIAN09 package.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The molecular structure of (I), with displacement ellipsoids drawn at the 50% probability level.
	Fig. 2. The molecular packing, viewed along the a axis, showing dimers formed by N—H···O hydrogen bonds (solid lines), linked by C—H···O (thin dashed lines) and Cl···Cl interactions (thick dashed lines). H atoms not involved in hydrogen bonding have been omitted.

6-chloroindolin-2-one

Crystal data

C8H6ClNO	F(000) = 344
Mr = 167.59	Dx = 1.510 Mg m^−3
Monoclinic, P21/c	Melting point: 466 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 4.2475 (1) Å	Cell parameters from 6067 reflections
b = 12.3838 (2) Å	θ = 3.3–34.4°
c = 14.0372 (2) Å	µ = 0.45 mm^−1
β = 92.898 (2)°	T = 100 K
V = 737.42 (2) Å^3	Plate, colourless
Z = 4	0.60 × 0.46 × 0.16 mm

Data collection

Oxford Sapphire3 CCD area-detector diffractometer	1283 independent reflections
Radiation source: fine-focus sealed tube	1203 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
Detector resolution: 16.0328 pixels mm^-1	θmax = 25.1°, θmin = 3.3°
ω scans	h = −5→2
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006)	k = −14→14
Tmin = 0.775, Tmax = 0.932	l = −16→16
4675 measured reflections

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)] = 0.025	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.068	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ^2(Fo^2) + (0.038P)^2 + 0.345P] where P = (Fo^2 + 2Fc^2)/3
1283 reflections	(Δ/σ)max = 0.001
104 parameters	Δρmax = 0.21 e Å^−3
0 restraints	Δρmin = −0.25 e Å^−3

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.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

3.3241 (0.0007) x + 4.4223 (0.0044) y + 6.5930 (0.0018) z = 5.6248 (0.0013)

* -0.0097 (0.0007) Cl1 * 0.0006 (0.0010) N1 * -0.0264 (0.0009) O1 * 0.0112 (0.0011) C1 * 0.0225 (0.0010) C2 * -0.0025 (0.0011) C3 * -0.0181 (0.0011) C4 * -0.0041 (0.0010) C5 * 0.0068 (0.0011) C6 * 0.0247 (0.0011) C7 * -0.0050 (0.0011) C8

Rms deviation of fitted atoms = 0.0149

3.3538 (0.0014) x + 4.3195 (0.0062) y + 6.5174 (0.0067) z = 5.5896 (0.0018)

* -0.0071 (0.0009) C1 * 0.0074 (0.0009) C2 * -0.0015 (0.0009) C3 * -0.0048 (0.0009) C4 * 0.0055 (0.0009) C5 * 0.0005 (0.0009) C6

Rms deviation of fitted atoms = 0.0052

3.3075 (0.0017) x + 4.5066 (0.0073) y + 6.6126 (0.0080) z = 5.6636 (0.0031)

Angle to previous plane (with approximate esd) = 1.13 ( 0.09 )

* 0.0051 (0.0008) C1 * -0.0094 (0.0008) C6 * 0.0099 (0.0008) C7 * -0.0077 (0.0008) C8 * 0.0022 (0.0008) N1

Rms deviation of fitted atoms = 0.0075

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 > 2sigma(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
Cl1	0.86752 (9)	0.45746 (3)	0.10744 (2)	0.02315 (14)
O1	0.0776 (2)	0.37168 (8)	0.56074 (7)	0.0206 (2)
N1	0.2761 (3)	0.43530 (10)	0.42204 (8)	0.0152 (3)
H1	0.185 (4)	0.4949 (16)	0.4220 (12)	0.025 (4)*
C1	0.4698 (3)	0.39741 (11)	0.35143 (9)	0.0143 (3)
C2	0.5605 (3)	0.45152 (11)	0.27111 (9)	0.0158 (3)
H2	0.4979	0.5238	0.2577	0.019*
C3	0.7493 (3)	0.39346 (11)	0.21108 (9)	0.0168 (3)
C4	0.8478 (3)	0.28858 (11)	0.22936 (10)	0.0185 (3)
H4	0.9761	0.2519	0.1863	0.022*
C5	0.7555 (3)	0.23749 (11)	0.31230 (10)	0.0177 (3)
H5	0.8231	0.1659	0.3266	0.021*
C6	0.5653 (3)	0.29183 (11)	0.37342 (9)	0.0153 (3)
C7	0.4280 (3)	0.26059 (11)	0.46629 (10)	0.0170 (3)
H7A	0.5960	0.2458	0.5160	0.020*
H7B	0.2910	0.1962	0.4584	0.020*
C8	0.2381 (3)	0.36009 (11)	0.49083 (9)	0.0161 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0314 (2)	0.0229 (2)	0.0156 (2)	−0.00561 (14)	0.00590 (15)	−0.00066 (13)
O1	0.0260 (5)	0.0181 (5)	0.0182 (5)	−0.0005 (4)	0.0065 (4)	0.0020 (4)
N1	0.0174 (6)	0.0116 (6)	0.0168 (6)	0.0011 (5)	0.0021 (5)	0.0006 (5)
C1	0.0129 (6)	0.0143 (7)	0.0153 (7)	−0.0019 (5)	−0.0019 (5)	−0.0025 (5)
C2	0.0171 (7)	0.0138 (7)	0.0163 (7)	−0.0017 (5)	−0.0019 (5)	0.0000 (5)
C3	0.0175 (7)	0.0196 (7)	0.0131 (6)	−0.0053 (5)	−0.0002 (5)	−0.0015 (5)
C4	0.0179 (7)	0.0188 (7)	0.0189 (7)	−0.0016 (5)	0.0005 (5)	−0.0064 (5)
C5	0.0181 (7)	0.0132 (7)	0.0213 (7)	0.0004 (5)	−0.0030 (5)	−0.0032 (5)
C6	0.0142 (6)	0.0152 (7)	0.0159 (6)	−0.0032 (5)	−0.0033 (5)	−0.0003 (5)
C7	0.0190 (7)	0.0139 (7)	0.0179 (7)	−0.0009 (5)	−0.0008 (5)	0.0022 (5)
C8	0.0166 (6)	0.0152 (7)	0.0162 (7)	−0.0037 (5)	−0.0014 (5)	−0.0004 (5)

Geometric parameters (Å, º)

Cl1—C3	1.7523 (14)	C3—C4	1.385 (2)
Cl1—Cl1^i	3.4378 (6)	C4—C5	1.398 (2)
O1—C8	1.2312 (17)	C4—H4	0.950
N1—C8	1.3572 (18)	C5—C6	1.3827 (19)
N1—C1	1.4006 (17)	C5—H5	0.950
N1—H1	0.833 (19)	C6—C7	1.5053 (18)
C1—C2	1.3829 (19)	C7—C8	1.5219 (19)
C1—C6	1.3989 (19)	C7—H7A	0.990
C2—C3	1.3921 (19)	C7—H7B	0.990
C2—H2	0.950
C3—Cl1—Cl1^i	170.87 (5)	C6—C5—C4	119.58 (13)
C8—N1—C1	111.65 (12)	C6—C5—H5	120.2
C8—N1—H1	122.4 (12)	C4—C5—H5	120.2
C1—N1—H1	125.8 (12)	C5—C6—C1	119.34 (12)
C2—C1—C6	122.89 (12)	C5—C6—C7	132.56 (12)
C2—C1—N1	127.77 (12)	C1—C6—C7	108.10 (11)
C6—C1—N1	109.34 (12)	C6—C7—C8	102.77 (11)
C1—C2—C3	115.85 (12)	C6—C7—H7A	111.2
C1—C2—H2	122.1	C8—C7—H7A	111.2
C3—C2—H2	122.1	C6—C7—H7B	111.2
C4—C3—C2	123.38 (12)	C8—C7—H7B	111.2
C4—C3—Cl1	118.78 (10)	H7A—C7—H7B	109.1
C2—C3—Cl1	117.84 (11)	O1—C8—N1	125.29 (13)
C3—C4—C5	118.94 (12)	O1—C8—C7	126.59 (12)
C3—C4—H4	120.5	N1—C8—C7	108.12 (11)
C5—C4—H4	120.5
C8—N1—C1—C2	−179.82 (13)	C2—C1—C6—C5	−0.9 (2)
C8—N1—C1—C6	0.27 (15)	N1—C1—C6—C5	179.06 (11)
C6—C1—C2—C3	1.46 (19)	C2—C1—C6—C7	178.78 (12)
N1—C1—C2—C3	−178.43 (12)	N1—C1—C6—C7	−1.30 (14)
C1—C2—C3—C4	−0.9 (2)	C5—C6—C7—C8	−178.71 (14)
C1—C2—C3—Cl1	179.26 (9)	C1—C6—C7—C8	1.71 (14)
C2—C3—C4—C5	−0.2 (2)	C1—N1—C8—O1	−179.32 (12)
Cl1—C3—C4—C5	179.61 (10)	C1—N1—C8—C7	0.87 (15)
C3—C4—C5—C6	0.86 (19)	C6—C7—C8—O1	178.64 (13)
C4—C5—C6—C1	−0.36 (19)	C6—C7—C8—N1	−1.56 (14)
C4—C5—C6—C7	−179.90 (13)

Symmetry code: (i) −x+2, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1^ii	0.833 (19)	2.01 (2)	2.8399 (16)	170.4 (17)
C4—H4···O1^iii	0.95	2.39	3.2753 (16)	155

Symmetry codes: (ii) −x, −y+1, −z+1; (iii) x+1, −y+1/2, z−1/2.