1-Methyl­pyrrole-2,5-dicarbaldehyde

The solid-state structure of the title compound, C₇H₇NO₂, is reported. The crystal packing is shaped mainly through carbon­yl–carbonyl inter­actions on the one hand, and C—H...n(O) hydrogen bonds and π(CO)...π inter­actions on the other.

Key indicators

• Single-crystal X-ray study
• T = 291 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.038
• wR factor = 0.107
• Data-to-parameter ratio = 7.0

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT089_ALERT_3_C Poor Data / Parameter Ratio (Zmax .LT. 18) .....       7.03
PLAT166_ALERT_4_C S.U's Given on Coordinates for calc-flagged ....        H7A
PLAT166_ALERT_4_C S.U's Given on Coordinates for calc-flagged ....        H7B
PLAT166_ALERT_4_C S.U's Given on Coordinates for calc-flagged ....        H7C

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           25.30
           From the CIF: _reflns_number_total                766
           Count of symmetry unique reflns          765
           Completeness (_total/calc)            100.13%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured         1
           Fraction of Friedel pairs measured     0.001
           Are heavy atom types Z>Si present         no

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   4 ALERT type 4 Improvement, methodology, query or suggestion

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S1. Comment

1-Methyl-2,5-pyrroledicarbaldehyde, (I) (Fig. 1), has been a sought after intermediate, especially for the synthesis of organic semiconductor materials (Berlin et al., 1987; Cadamuro et al., 1993, 1996; Van Der Looy et al., 1997) but also for biologically active compounds and several macrocycles (Cadamuro et al., 1993, 1996).

The structure crystallizes in the chiral space group P2₁2₁2₁ with no mirror symmetry present in the molecule or the structure. As a consequence, the two carbaldehyde moieties are surrounded in a different manner.

The crystal can be rationalized by stacks of individual molecules along the (100) direction (Fig. 2) and by planes in the (001) direction consisting of stacked ribbons running along the (110) and (110) directions (Fig. 3). Between the stacks of individual molecules along the (100) direction, the stabilizing interactions are type II carbonyl–carbonyl interactions, as described by Allen et al. (1998). These are situated around the twofold screw axis and involve the carbonyl group C6=O6: C6···O6ⁱ 3.318 (3) Å [symmetry code (i) −1/2 + x, 1/2 − y, −z] and O6)···C6ⁱ 3.067 (3) Å. They are shown in Fig. 2 by the orange dotted lines. Perpendicular to the direction of these carbonyl–carbonyl contacts, the stacks display a short contact between the C atom of a methyl group and the O atom of a carbonyl group, viz. N1—C7···O6ⁱⁱ 3.157 (3) Å, 179.06 (16)° [symmetry code (ii) 1/2 + x, −1/2 − y, −z]. This contact is shown in Fig. 2 by the cyan dotted lines.

The remaining contacts involve the other carbonyl group C5=O5 and interact either within the aforementioned ribbons, such as the weak hydrogen bond C3—H3···O5ⁱⁱⁱ 2.48 (3) Å, D—A 3.417 (3) Å, 170 (2)° [symmetry code (iii) −1 + x, 1 + y, z] (cyan dotted lines in Fig. 3), or inbetween the ribbons, such as C4···C5^iv 3.394 (4) Å [symm. code (iv) −1 + x, y, z] (orange dotted lines in Fig. 3), forming the planes mentioned above. The latter contact is the expression of a typical π(CO)···π contact, in this case given by CgA···O5^iv—C5^iv 3.598 (2) Å, 3.316 Å perp., 72.26 (17)°, where CgA indicates the centroid of the pyrrole ring and `perp.' indicates the perpendicular distance of O5 to the plane of the pyrrole ring.

In conclusion, (I) displays a chiral structure which is completely dominated by interactions concerning the two different carbonyl groups: one of them is involved in carbonyl-carbonyl dipolar interactions, the other in π(CO)···π contacts and CH···n(O) hydrogen bonds. This is in contrast with the derivative which lacks the N-methyl group (Adams et al., 1986), which has an achiral Pn structure in which the crystal symmetry does not coincide with the molecular symmetry. Unsurprisingly, the network in the latter structure consists of hydrogen-bonded layers involving the H atoms of the aldehyde group and the aromatic ring as well as those on the N atom. Yet, the On atoms of the carbonyl groups always act as acceptors. In addition, π–π interactions exist between the layers.

S2. Experimental

All starting materials were obtained from Acros and used as received. Benzene was dried over 3 A molecular sieves prior to use. ¹H and ¹³C NMR spectra were recorded on a Varian Unity-400 apparatus.

N-methyl-2,5-pyrroledicarbaldehyde (I) was prepared starting from N-methyl-2,5-bis(hydroxymethyl)pyrrole (II). For the synthesis of the latter N-methylpyrrole (22 ml, 0.255 mol), ground paraformaldehyde (16.1 g, 0.536 mol), potassium carbonate (0.2 g, 0.0015 mol) and water (5 ml) were mixed together and heated under a nitrogen atmosphere to 323–333 K until all the paraformaldehyde had dissolved. The reaction mixture was then cooled in a waterbath until completion of the exothermic process (ca 30 min.). The mixture was subsequently reheated to 353 K for 3 h. To remove water, N-methylpyrrole and N-methyl-2-(hydroxymethyl)pyrrole from the resulting crude reaction mixture, it was distilled in vacuo (1–2 m mH g/323 K). The remaining impure precipitate was then recrystallized from propanol (10–15 ml) and washed with a small amount of chloroform. Overnight cooling of the filtrate yielded an additional fraction of (II). The yield was 22.7 g (65%) of an off-white powder [m.p. 386–387 K (uncorrected) in accordance with the literature (Chelintzev & Maksorov, 1916; Severin & Ipach, 1975)]. (II) should be refrigerated to prevent oxidation. ¹H NMR (CDCl₃, 400 MHz, TMS): δ 3.71 (s, 3H, CH₃), 4.60 (d, 4H, J = 2.6 Hz, CH₂), 6.40 (s, 2H, H3 and H4), 7.26 (s, 2H, OH). ¹³C NMR (CDCl₃, 100 MHz, TMS): δ 30.6 (CH₃), 57.1 (CH₂), 132 (C2 and C5), 107.7 (C3 and C4).

N-methyl-2,5-pyrroledicarbaldehyde (I) was prepared by refluxing a mixture consisting of (II) (7.7 g, 0.055 mol), dry benzene (300 ml) and precipitated active manganese dioxide (25.0 g, 0.287 mol) for 6 h and subsequently stirring at room temperature for 24 h. The precipitate was filtered off and washed carefully with 1,4-dioxane or tetrahydrofurane. The impure dark-brown crystals were sublimed under reduced pressure (typically for 6 h at 0.1 m mH g/338 K) (Severin & Ipach, 1975). (I) was collected in a yield of 3.0 g (40%) as light-yellow crystals [m.p. 370 K (uncorrected); lit. 368–369 K (Cresp & Sargent, 1972; Cresp & Sargent,1973; Severin & Ipach, 1975)]. The NMR data of (I) are identical to those of Loader et al. (1982) [¹H NMR] and Cadamuro et al. (1993) [¹³C NMR].

S3. Refinement

All H atoms were located in a difference density map and left free to refine [C—H = 0.90 (3)–0.99 (3) Å], except the methyl H atoms, for which a common distance was refined and the group was twisted so that it coincides with the maxima in the Fourier difference map (AFIX 138).

Computing details

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Mercury (Bruno et al., 2002) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: PLATON (Spek, 2003) and WinGX (Farrugia, 1999).

Figures

	Fig. 1. View of (1), including the numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are numbered according to the C atom they are substituted on.
	Fig. 2. View of the structure quasi along the a axis. For details, see text.
	Fig. 3. View of the structure along the bc cell diagonal. For details, see Comment.

1-Methylpyrrole-2,5-dicarbaldehyde

Crystal data

C7H7NO2	Dx = 1.355 Mg m^−3
Mr = 137.14	Melting point: 370 K
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 25 reflections
a = 4.650 (1) Å	θ = 5.7–19.7°
b = 6.457 (1) Å	µ = 0.10 mm^−1
c = 22.386 (4) Å	T = 291 K
V = 672.1 (2) Å^3	Prism, light yellow
Z = 4	0.4 × 0.3 × 0.2 mm
F(000) = 288

Data collection

Enraf–Nonius Mach3 diffractometer	Rint = 0.032
Radiation source: fine-focus sealed tube	θmax = 25.3°, θmin = 1.8°
Graphite monochromator	h = 0→5
ω/2θ scans	k = 0→7
1499 measured reflections	l = −26→26
766 independent reflections	3 standard reflections every 60 min
652 reflections with I > 2σ(I)	intensity decay: 21%

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)] = 0.038	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.107	H atoms treated by a mixture of independent and constrained refinement
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0701P)^2 + 0.0615P] where P = (Fo^2 + 2Fc^2)/3
766 reflections	(Δ/σ)max < 0.001
109 parameters	Δρmax = 0.16 e Å^−3
0 restraints	Δρmin = −0.14 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
O6	0.6125 (5)	0.0711 (3)	0.01315 (8)	0.0714 (6)
C4	0.8443 (5)	0.1555 (3)	0.10499 (9)	0.0454 (5)
N1	1.0208 (4)	−0.0097 (2)	0.11338 (7)	0.0439 (5)
C1	1.1625 (5)	0.0190 (3)	0.16646 (9)	0.0461 (5)
C2	1.0708 (6)	0.2034 (4)	0.19095 (10)	0.0538 (6)
C6	0.6496 (6)	0.1870 (5)	0.05518 (10)	0.0575 (6)
C3	0.8729 (6)	0.2887 (4)	0.15297 (10)	0.0521 (6)
O5	1.4762 (5)	−0.2716 (3)	0.17326 (10)	0.0828 (7)
C5	1.3801 (6)	−0.1129 (5)	0.19272 (12)	0.0590 (7)
C7	1.0498 (7)	−0.1891 (4)	0.07389 (11)	0.0633 (7)
H7A	0.872 (3)	−0.246 (2)	0.0672 (7)	0.095*
H7B	1.167 (4)	−0.285 (2)	0.0914 (5)	0.095*
H7C	1.128 (4)	−0.1480 (10)	0.0383 (7)	0.095*
H3	0.781 (7)	0.420 (4)	0.1572 (11)	0.064 (8)*
H2	1.146 (6)	0.264 (4)	0.2235 (11)	0.049 (6)*
H6	0.566 (5)	0.322 (4)	0.0589 (9)	0.043 (6)*
H5	1.447 (7)	−0.052 (5)	0.2312 (13)	0.077 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O6	0.0777 (13)	0.0826 (13)	0.0540 (9)	−0.0049 (12)	−0.0106 (9)	−0.0054 (9)
C4	0.0459 (12)	0.0476 (12)	0.0426 (11)	0.0004 (10)	0.0048 (10)	0.0028 (9)
N1	0.0499 (10)	0.0429 (9)	0.0389 (8)	0.0017 (10)	0.0067 (8)	−0.0007 (8)
C1	0.0427 (11)	0.0538 (13)	0.0417 (10)	0.0017 (11)	0.0042 (9)	0.0021 (9)
C2	0.0540 (14)	0.0604 (14)	0.0469 (12)	−0.0008 (13)	−0.0006 (11)	−0.0112 (11)
C6	0.0597 (15)	0.0631 (16)	0.0497 (13)	0.0020 (15)	−0.0014 (11)	0.0077 (12)
C3	0.0542 (14)	0.0487 (13)	0.0534 (12)	0.0044 (13)	0.0064 (11)	−0.0044 (10)
O5	0.0874 (15)	0.0788 (13)	0.0824 (13)	0.0343 (13)	0.0044 (11)	0.0087 (11)
C5	0.0523 (14)	0.0669 (16)	0.0578 (15)	0.0105 (14)	0.0050 (13)	0.0104 (12)
C7	0.0773 (18)	0.0523 (13)	0.0602 (13)	0.0043 (15)	0.0059 (14)	−0.0139 (12)

Geometric parameters (Å, º)

O6—C6	1.214 (3)	C2—H2	0.90 (2)
C4—N1	1.359 (3)	C6—H6	0.96 (2)
C4—C3	1.383 (3)	C3—H3	0.96 (3)
C4—C6	1.451 (3)	O5—C5	1.200 (3)
N1—C1	1.372 (3)	C5—H5	1.00 (3)
N1—C7	1.463 (3)	C7—H7A	0.9153
C1—C2	1.379 (3)	C7—H7B	0.9153
C1—C5	1.447 (3)	C7—H7C	0.9153
C2—C3	1.369 (4)
N1—C4—C3	108.85 (19)	C4—C6—H6	108.3 (13)
N1—C4—C6	126.4 (2)	C2—C3—C4	107.3 (2)
C3—C4—C6	124.7 (2)	C2—C3—H3	126.7 (16)
C4—N1—C1	107.69 (17)	C4—C3—H3	125.9 (16)
C4—N1—C7	126.42 (19)	O5—C5—C1	128.0 (3)
C1—N1—C7	125.87 (19)	O5—C5—H5	122.5 (17)
N1—C1—C2	108.2 (2)	C1—C5—H5	109.6 (17)
N1—C1—C5	127.5 (2)	N1—C7—H7A	109.5
C2—C1—C5	124.3 (2)	N1—C7—H7B	109.5
C3—C2—C1	108.0 (2)	H7A—C7—H7B	109.5
C3—C2—H2	126.3 (15)	N1—C7—H7C	109.5
C1—C2—H2	125.3 (15)	H7A—C7—H7C	109.5
O6—C6—C4	126.7 (3)	H7B—C7—H7C	109.5
O6—C6—H6	124.8 (13)
C3—C4—N1—C1	−0.3 (2)	C5—C1—C2—C3	177.7 (2)
C6—C4—N1—C1	−178.6 (2)	N1—C4—C6—O6	0.2 (4)
C3—C4—N1—C7	178.2 (2)	C3—C4—C6—O6	−177.8 (3)
C6—C4—N1—C7	0.0 (4)	C1—C2—C3—C4	−0.1 (3)
C4—N1—C1—C2	0.2 (2)	N1—C4—C3—C2	0.3 (3)
C7—N1—C1—C2	−178.3 (2)	C6—C4—C3—C2	178.5 (2)
C4—N1—C1—C5	−177.5 (2)	N1—C1—C5—O5	−0.3 (4)
C7—N1—C1—C5	4.0 (4)	C2—C1—C5—O5	−177.7 (3)
N1—C1—C2—C3	−0.1 (3)