7-Chloro-3,6-di­methyl-1H-indene-2-carb­aldehyde

In the crystal structure of C₁₂H₁₁ClO, the (planar) mol­ecules give rise to a parallel packing. A model crystal obtained by semi-empirical and packing-energy calculations is consistent with the observed structure.

S1. Comment

The Vilsmeier reaction has proven to be a versatile tool in achieving different synthetic transformations, ranging from the normal introduction of a formyl group into an activated aromatic nucleus to the access of different ring systems (Marson & Giles, 1994). The reaction between carvone (I) and the Vilsmeier reagent (N,N-dimethylformamide and POCl₃, denoted VR in the reaction scheme) gave the expected product (II) along with a product (III), whose structure, initially not clarified by spectroscopic methods, has been determined by X-ray diffraction (this work). \sch

The ORTEP diagram (Johnson, 1976) of compound (III) is shown in Fig. 1. Bond lengths and bond angles are in the normal range and even in good agreement with those of compounds having the same frame of fused rings, as retrieved from the Cambridge Structural Database (Version 5.18; Allen & Kennard, 1993). The C2═C3 and C2—C10 bond lengths are, respectively, fairly longer and shorter than the reported reference values (Allen et al., 1987), indicating a tendency to π-delocalization. The orientation of the C12 methyl group is probably conditioned by two H···Cl intramolecular contacts, both slightly shorter than the sum of van der Waals radii (Pauling, 1960). (We are grateful to a referee for calling our attention on this point.)

Considering the non-hydrogen atoms, the molecule adopts a planar conformation with a maximum deviation of 0.047 (2) Å (atom O1) from the mean plane. In the crystal, the molecules are in a parallel arrangement, in planes approximately normal to the x axis.

The geometry of the isolated molecule of the title compound has been investigated by simple semi-empirical molecular orbital calculations. A starting model (with m symmetry) was generated using a graphical interface (program SPARTAN; Wavefunction, 1998) and its geometry fully optimized at the AM1 level (Dewar et al., 1985). The calculated C2═C3 and C2—C10 bond lengths (1.368 and 1.455 Å, respectively) do confirm the corresponding observed trend. The atomic charges were calculated with the method of the best-fit to the electrostatic potential. This subject has been reviewed by Williams (1991); the validity of its extension to semi-empirical wavefunctions has been assessed by Ferenczy et al. (1990). Some of the resulting net charges are here reported: Cl −0.02, C12 − 0.26, C11 − 0.22, C2 − 0.23, C10 0.53, O1 − 0.46, H10 0.00, the values for other H atoms ranging between 0.09 and 0.12 a.u. The molecular dipole moment (4.02 D) is oriented parallel to the C═O vector.

In order to study the most favoured molecular arrangement in a crystal structure and to calculate its packing energy, the program PROMET (Gavezzotti, 1991, 1998) was used, starting from the Cartesian coordinates and the atomic charges of the AM1-optimized molecule. The search was performed for molecular orientations and translations within the (standard) space group Cc, giving rise to a total of 6624 optimized structures. The solution of lowest energy corresponded to a parallel stacking of the molecules, with a packing energy of −113.2 kJ mol⁻¹ and a packing coefficient C_K = 0.78 (Kitaigorodski, 1961). [Please put the following sentence into a Footnote: As a comparison, in the actual crystal the value of C_K is 0.76, having re-normalized the C—H bond lengths to 1.10 Å.] The unit-cell parameters of the model crystal, referred back to the Ia space group, resulted in a = 7.086, b = 19.541, c = 7.387 Å, β = 105.21°, V = 987.10 ų. The corresponding crystal coordinates of the oriented and displaced molecule were used for a short least-squares refinement. After four isotropic cycles (SHELXL97), the R1 factor was 0.1212 for all 2289 data.

In the crystal, no remarkably short intermolecular contacts have been found. Considering the couples of molecules facing each other (1 and 2; 3 and 4, see Fig. 2), the phenyl rings lie on planes a/2 away, with an in-plane shift of 1.70 Å along y. This parallel-displaced geometry is similar to that calculated for a low-energy arrangement of the benzene dimer, stabilized by `π-π' interactions (Hobza et al., 1994; distance between molecular planes, R = 3.5 Å; parallel shift R2 = 1.6 Å).

S2. Experimental

Compound (III) was crystallized from cyclohexane.

S3. Refinement

Within the θ range explored, a whole set of h,k,±l reflections was measured, along with all their Friedel opposites. The absorption effects were corrected, according to the recommendations by Jones (1984). The final value and s.u. obtained for the Flack (1983) parameter assure that a polar dispersion error (Ueki et al., 1966; Cruickshank & McDonald, 1967) has been avoided. The methyl H atoms were located by means of circular difference syntheses and refined as idealized rigid groups; for each methyl group a general U_iso was also refined. All other H atoms were determined with difference syntheses and refined isotropically without constraints.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CADABS (local software); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976) and PLUTO (Motherwell & Clegg, 1978); software used to prepare material for publication: PARST (Nardelli, 1983, 1995) and PARSTCIF (Nardelli, 1991).

Figures

	Fig. 1. Compound (III) with numbering scheme of atoms. Displacement ellipsoids are drawn at 0.40 level of probability. H atoms are spheres of arbitrary size.
	Fig. 2. The crystal packing viewed along the z axis (PLUTO; Motherwell & Clegg, 1978). Equivalent positions: (i) = x, y, z; (ii) = x + 1/2, −y, z; (iii) = x + 1/2, y + 1/2, z + 1/2; (iv) = x, −y + 1/2, z + 1/2.

7-Chloro-3,6-dimethyl-1H-indene-2-carbaldehyde

Crystal data

C12H11ClO	Dx = 1.367 Mg m^−3
Mr = 206.7	Melting point: 438 K
Monoclinic, Ia	Mo Kα radiation, λ = 0.7107 Å
a = 7.146 (2) Å	Cell parameters from 25 reflections
b = 19.751 (4) Å	θ = 17.3–20.7°
c = 7.408 (1) Å	µ = 0.34 mm^−1
β = 106.12 (2)°	T = 294 K
V = 1004.5 (4) Å^3	Trapezoidal irregular prism, light yellow
Z = 4.0	0.52 × 0.44 × 0.28 mm
F(000) = 432.0

Data collection

Enraf-Nonius CAD-4 diffractometer	2140 reflections with Fo > 4 σ(Fo)
Radiation source: fine-focus sealed tube	Rint = 0.004
Graphite monochromator	θmax = 27.5°, θmin = 3.0°
ω–2θ scan mode	h = 0→9
Absorption correction: ψ scan (North et al., 1968)	k = 0→25
Tmin = 0.698, Tmax = 0.909	l = −9→9
2300 measured reflections	2 standard reflections every 150 min
2289 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.095	w = 1/[σ^2(Fo^2) + (0.0723P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.002
2289 reflections	Δρmax = 0.38 e Å^−3
151 parameters	Δρmin = −0.30 e Å^−3
2 restraints	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.03 (5)

Special details

Refinement. The structure was solved and refined in space group Ia; the full-matrix refinement proceeded smoothly, all final correlation factors being smaller than 0.55. A l l atomic displacement parameters have usual values.

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

	x	y	z	Uiso*/Ueq
Cl	0.36884 (9)	0.11600 (2)	0.79279 (8)	0.0528 (2)
O1	0.3884 (3)	−0.18294 (9)	0.8798 (2)	0.0590 (6)
C1	0.3474 (3)	−0.04515 (8)	0.7241 (2)	0.0354 (5)
C2	0.3109 (3)	−0.11074 (7)	0.6173 (2)	0.0357 (4)
C3	0.2481 (2)	−0.10016 (8)	0.4295 (2)	0.0356 (5)
C4	0.1791 (3)	0.00951 (9)	0.2304 (2)	0.0424 (6)
C5	0.1818 (3)	0.0797 (1)	0.2410 (3)	0.0479 (6)
C6	0.2408 (3)	0.11439 (8)	0.4112 (3)	0.0408 (6)
C7	0.2969 (2)	0.07580 (8)	0.5758 (2)	0.0372 (5)
C8	0.2949 (2)	0.00606 (8)	0.5699 (2)	0.0331 (5)
C9	0.2364 (2)	−0.02702 (8)	0.3967 (2)	0.0349 (4)
C10	0.3394 (3)	−0.1763 (1)	0.7102 (3)	0.0446 (7)
C11	0.1960 (3)	−0.1502 (1)	0.2743 (3)	0.0478 (6)
C12	0.2417 (4)	0.1903 (1)	0.4146 (4)	0.0600 (8)
H1A	0.263 (4)	−0.0426 (12)	0.796 (4)	0.045 (6)*
H1B	0.490 (4)	−0.0399 (11)	0.788 (4)	0.046 (6)*
H4	0.133 (4)	−0.0193 (14)	0.112 (4)	0.062 (7)*
H5	0.138 (4)	0.1051 (14)	0.130 (4)	0.059 (7)*
H10	0.319 (4)	−0.2159 (16)	0.627 (4)	0.076 (8)*
H11A	0.223	−0.195	0.325	0.065 (4)*
H11B	0.271	−0.142	0.188	0.065 (4)*
H11C	0.060	−0.146	0.210	0.065 (4)*
H12A	0.204	0.207	0.288	0.092 (6)*
H12B	0.370	0.206	0.478	0.092 (6)*
H12C	0.152	0.206	0.480	0.092 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl	0.0716 (3)	0.0390 (2)	0.0457 (2)	−0.0020 (2)	0.0129 (2)	−0.0110 (2)
O1	0.0890 (11)	0.0426 (8)	0.0434 (8)	0.0049 (7)	0.0152 (8)	0.0105 (6)
C1	0.0477 (9)	0.0288 (7)	0.0292 (6)	0.0024 (6)	0.0100 (6)	0.0000 (5)
C2	0.0442 (7)	0.0287 (7)	0.0348 (8)	0.0019 (6)	0.0119 (6)	−0.0006 (5)
C3	0.0416 (7)	0.0330 (7)	0.0330 (8)	0.0026 (6)	0.0117 (6)	−0.0017 (6)
C4	0.0529 (10)	0.0432 (9)	0.0298 (8)	0.0064 (7)	0.0096 (7)	0.0034 (6)
C5	0.0579 (11)	0.0459 (10)	0.0408 (9)	0.0102 (8)	0.0151 (8)	0.0153 (8)
C6	0.0459 (8)	0.0325 (8)	0.0466 (9)	0.0081 (7)	0.0171 (7)	0.0079 (7)
C7	0.0398 (7)	0.0357 (8)	0.0371 (8)	0.0028 (6)	0.0125 (6)	−0.0004 (6)
C8	0.0376 (7)	0.0327 (7)	0.0296 (8)	0.0039 (6)	0.0101 (6)	0.0021 (6)
C9	0.0395 (7)	0.0346 (7)	0.0314 (6)	0.0038 (6)	0.0114 (5)	0.0010 (6)
C10	0.0600 (11)	0.0315 (9)	0.0426 (10)	0.0030 (7)	0.0143 (8)	0.0051 (7)
C11	0.0632 (11)	0.0400 (9)	0.0388 (8)	0.0018 (8)	0.0118 (8)	−0.0104 (7)
C12	0.0823 (14)	0.0308 (9)	0.0715 (14)	0.0101 (9)	0.0289 (11)	0.0103 (9)

Geometric parameters (Å, º)

Cl—C7	1.738 (2)	C5—C6	1.393 (3)
O1—C10	1.214 (2)	C5—H5	0.94 (3)
C1—C2	1.503 (2)	C6—C7	1.399 (3)
C1—C8	1.494 (2)	C6—C12	1.500 (3)
C1—H1A	0.91 (3)	C7—C8	1.378 (2)
C1—H1B	1.00 (2)	C8—C9	1.396 (2)
C2—C3	1.354 (2)	C10—H10	0.98 (3)
C2—C10	1.454 (3)	C11—H11A	0.96
C3—C9	1.463 (2)	C11—H11B	0.96
C3—C11	1.483 (3)	C11—H11C	0.96
C4—C5	1.389 (3)	C12—H12A	0.96
C4—C9	1.388 (2)	C12—H12B	0.96
C4—H4	1.02 (3)	C12—H12C	0.96
C2—C1—C8	102.2 (1)	C6—C7—C8	121.3 (2)
C2—C1—H1A	108 (2)	C1—C8—C7	130.9 (1)
C2—C1—H1B	110 (1)	C1—C8—C9	109.5 (1)
C8—C1—H1A	110 (2)	C7—C8—C9	119.7 (1)
C8—C1—H1B	107 (1)	C3—C9—C4	130.5 (2)
H1A—C1—H1B	118 (2)	C3—C9—C8	108.7 (1)
C1—C2—C3	111.6 (1)	C4—C9—C8	120.8 (2)
C1—C2—C10	122.5 (1)	O1—C10—C2	123.2 (2)
C3—C2—C10	125.9 (2)	O1—C10—H10	121 (2)
C2—C3—C9	108.1 (1)	C2—C10—H10	116 (2)
C2—C3—C11	129.3 (2)	C3—C11—H11A	109.5
C9—C3—C11	122.6 (2)	C3—C11—H11B	109.5
C5—C4—C9	118.2 (2)	C3—C11—H11C	109.5
C5—C4—H4	127 (2)	H11A—C11—H11B	109.5
C9—C4—H4	115 (1)	H11A—C11—H11C	109.5
C4—C5—C6	122.5 (2)	H11B—C11—H11C	109.5
C4—C5—H5	119 (2)	C6—C12—H12A	109.5
C6—C5—H5	118 (2)	C6—C12—H12B	109.5
C5—C6—C7	117.6 (2)	C6—C12—H12C	109.5
C5—C6—C12	120.4 (2)	H12A—C12—H12B	109.5
C7—C6—C12	122.1 (2)	H12A—C12—H12C	109.5
Cl—C7—C6	119.8 (1)	H12B—C12—H12C	109.5
Cl—C7—C8	118.9 (1)
C8—C1—C2—C3	0.4 (2)	C9—C4—C5—C6	0.5 (3)
C8—C1—C2—C10	−178.9 (2)	C9—C4—C5—H5	−177 (2)
H1A—C1—C2—C3	116 (2)	H4—C4—C5—C6	177 (2)
H1A—C1—C2—C10	−63 (2)	H4—C4—C5—H5	0 (3)
H1B—C1—C2—C3	−113 (2)	C5—C4—C9—C3	179.9 (2)
H1B—C1—C2—C10	67 (2)	C5—C4—C9—C8	0.1 (3)
C2—C1—C8—C7	179.9 (2)	H4—C4—C9—C3	2 (2)
C2—C1—C8—C9	−0.2 (2)	H4—C4—C9—C8	−177 (2)
H1A—C1—C8—C7	65 (2)	C4—C5—C6—C7	−0.7 (3)
H1A—C1—C8—C9	−115 (2)	C4—C5—C6—C12	179.8 (2)
H1B—C1—C8—C7	−64 (2)	H5—C5—C6—C7	177 (2)
H1B—C1—C8—C9	115 (2)	H5—C5—C6—C12	−3 (2)
C1—C2—C3—C9	−0.4 (2)	C5—C6—C7—Cl	−179.1 (1)
C1—C2—C3—C11	179.9 (2)	C5—C6—C7—C8	0.4 (3)
C10—C2—C3—C9	178.9 (2)	C12—C6—C7—Cl	0.4 (3)
C10—C2—C3—C11	−0.8 (3)	C12—C6—C7—C8	179.9 (2)
C1—C2—C10—O1	2.4 (3)	C5—C6—C12—H12A	−3
C1—C2—C10—H10	−176 (2)	C5—C6—C12—H12B	−123
C3—C2—C10—O1	−176.9 (2)	C5—C6—C12—H12C	117
C3—C2—C10—H10	5 (2)	C7—C6—C12—H12A	178
C2—C3—C9—C4	−179.5 (2)	C7—C6—C12—H12B	58
C2—C3—C9—C8	0.3 (2)	C7—C6—C12—H12C	−62
C11—C3—C9—C4	0.2 (3)	Cl—C7—C8—C1	−0.5 (3)
C11—C3—C9—C8	−180.0 (2)	Cl—C7—C8—C9	179.6 (1)
C2—C3—C11—H11A	−5	C6—C7—C8—C1	180.0 (2)
C2—C3—C11—H11B	−125	C6—C7—C8—C9	0.1 (3)
C2—C3—C11—H11C	115	C1—C8—C9—C3	−0.1 (2)
C9—C3—C11—H11A	176	C1—C8—C9—C4	179.8 (2)
C9—C3—C11—H11B	56	C7—C8—C9—C3	179.8 (2)
C9—C3—C11—H11C	−65	C7—C8—C9—C4	−0.3 (3)