Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102018255/ln1152sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270102018255/ln1152Isup2.hkl |
CCDC reference: 199443
Ethyl oximinobenzoylacetate was prepared by the dropwise addition of an acetic acid solution (8 ml) of ethyl benzoylacetate (5 ml, 0.0025 mol) to aqueous sodium nitrite (3.00 g, 0.0044 mol, in 20 ml water) and then stirring for 72 h at 293 K. A mixture of acetylacetone (2.50 g, 0.0025 mol), Zn dust (5.00 g, 0.00724 mol) and glacial acetic acid (35 ml) were placed in a 500 ml round-bottomed flask fitted with a reflux condenser and a silica guard tube. After the dissolution of all reactants, the oxime (ethyl oximinobenzoylacetate) was added slowly. The mixture was stirred and heated under reflux for 4 h. The hot reaction mixture was decanted from the zinc sludge before zinc acetate or a new compound could crystallize. To promote precipitation of the pyrrole, several volumes of water were added slowly to the reaction. After a few hours, the product was filtered off, washed thorougly with water and recrystallized from hot n-hexane. Compound (I) was obtained in 14% yield (m.p. 326–328 K). Spectroscopic analysis: IR (ν, cm-1): 1523 (aromatic C—C), 1662 (C═O), 2965 (aromatic C—H), 3508 (N—H); 1H NMR (CDCl3, δ, p.p.m.): 1.00 (t, 3H, CH3—CH2O, J = 7.00 Hz), 1.82 (s, 3H, position 4 COCH3), 2.58 (s, 3H, position 5 CH3), 4.09 (q, 2H, O—CH2—CH3, J = 7.25 Hz), 7.37 (m, 5H, position 3 aromatic H), 10.0 (sl, 1H, NH).
The methyl H atoms were constrained to an ideal geometry, with C—H distances of 0.96 Å and Uiso(H)= 1.5Ueq(C), but were allowed to rotate freely about the C—C bonds. All remaining H atoms were placed in geometrically idealized positions, with C—H distances in the range 0.93–0.97 Å and N—H distances of 0.86 Å, and constrained to ride on their parent atoms with Uiso(H) = 1.2Ueq(parent atom), with the exception of the H atoms on the water molecule, the positions and atomic displacement parameters of which were refined freely. Examination of the crystal structure with PLATON (Spek, 2002) showed that there are no solvent-accessible voids in the crystal lattice.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.
C16H17NO3·H2O | F(000) = 616 |
Mr = 289.32 | Dx = 1.244 Mg m−3 |
Monoclinic, P21/c | Cu Kα radiation, λ = 1.54180 Å |
a = 8.9102 (4) Å | Cell parameters from 25 reflections |
b = 17.1911 (10) Å | θ = 18.9–35.4° |
c = 10.4861 (10) Å | µ = 0.74 mm−1 |
β = 105.859 (8)° | T = 293 K |
V = 1545.08 (19) Å3 | Prism, yellow |
Z = 4 | 0.46 × 0.27 × 0.18 mm |
Enraf-Nonius CAD-4 diffractometer | 2726 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.035 |
Graphite monochromator | θmax = 72.5°, θmin = 5.1° |
ω/2θ scans | h = −11→11 |
Absorption correction: ψ scan (North et al., 1968) | k = 0→21 |
Tmin = 0.853, Tmax = 0.876 | l = −12→12 |
6215 measured reflections | 3 standard reflections every 180 min |
3048 independent reflections | intensity decay: 2% |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.040 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.110 | w = 1/[σ2(Fo2) + (0.0573P)2 + 0.2709P] where P = (Fo2 + 2Fc2)/3 |
S = 1.05 | (Δ/σ)max < 0.001 |
3048 reflections | Δρmax = 0.19 e Å−3 |
202 parameters | Δρmin = −0.20 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0073 (7) |
C16H17NO3·H2O | V = 1545.08 (19) Å3 |
Mr = 289.32 | Z = 4 |
Monoclinic, P21/c | Cu Kα radiation |
a = 8.9102 (4) Å | µ = 0.74 mm−1 |
b = 17.1911 (10) Å | T = 293 K |
c = 10.4861 (10) Å | 0.46 × 0.27 × 0.18 mm |
β = 105.859 (8)° |
Enraf-Nonius CAD-4 diffractometer | 2726 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.035 |
Tmin = 0.853, Tmax = 0.876 | 3 standard reflections every 180 min |
6215 measured reflections | intensity decay: 2% |
3048 independent reflections |
R[F2 > 2σ(F2)] = 0.040 | 0 restraints |
wR(F2) = 0.110 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | Δρmax = 0.19 e Å−3 |
3048 reflections | Δρmin = −0.20 e Å−3 |
202 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.88133 (11) | 0.10408 (7) | 0.27806 (10) | 0.0642 (3) | |
O2 | 0.68385 (11) | 0.15273 (6) | 0.11791 (11) | 0.0640 (3) | |
O3 | 0.23843 (13) | −0.08282 (8) | 0.35097 (12) | 0.0782 (4) | |
O4 | 0.03477 (11) | 0.09003 (7) | 0.55991 (12) | 0.0597 (3) | |
H41 | −0.004 (3) | 0.0874 (12) | 0.475 (2) | 0.092 (7)* | |
H42 | −0.051 (3) | 0.0841 (13) | 0.592 (2) | 0.101 (7)* | |
N1 | 0.67574 (12) | −0.00578 (6) | 0.33766 (10) | 0.0442 (3) | |
H1 | 0.7715 | −0.0164 | 0.3771 | 0.053* | |
C2 | 0.62729 (14) | 0.05404 (7) | 0.24752 (11) | 0.0417 (3) | |
C3 | 0.46600 (13) | 0.05257 (7) | 0.20471 (11) | 0.0394 (3) | |
C4 | 0.41710 (14) | −0.01037 (7) | 0.27367 (11) | 0.0420 (3) | |
C5 | 0.55279 (14) | −0.04469 (7) | 0.35483 (12) | 0.0433 (3) | |
C17 | 0.57321 (17) | −0.11363 (8) | 0.44444 (14) | 0.0566 (4) | |
H17A | 0.6822 | −0.1213 | 0.4867 | 0.085* | |
H17B | 0.5317 | −0.1590 | 0.3936 | 0.085* | |
H17C | 0.5189 | −0.1050 | 0.5106 | 0.085* | |
C15 | 0.26013 (15) | −0.03836 (8) | 0.26662 (13) | 0.0496 (3) | |
C16 | 0.12506 (17) | −0.01554 (11) | 0.15351 (18) | 0.0731 (5) | |
H16A | 0.0400 | −0.0508 | 0.1481 | 0.110* | |
H16B | 0.1554 | −0.0175 | 0.0725 | 0.110* | |
H16C | 0.0930 | 0.0364 | 0.1673 | 0.110* | |
C9 | 0.36512 (13) | 0.10835 (7) | 0.11089 (11) | 0.0389 (3) | |
C10 | 0.34435 (17) | 0.10208 (8) | −0.02454 (12) | 0.0524 (3) | |
H10 | 0.3966 | 0.0634 | −0.0573 | 0.063* | |
C11 | 0.24661 (18) | 0.15282 (9) | −0.11168 (14) | 0.0595 (4) | |
H11 | 0.2325 | 0.1475 | −0.2025 | 0.071* | |
C12 | 0.17039 (15) | 0.21107 (8) | −0.06446 (14) | 0.0534 (3) | |
H12 | 0.1050 | 0.2452 | −0.1230 | 0.064* | |
C13 | 0.19144 (15) | 0.21853 (7) | 0.06983 (14) | 0.0517 (3) | |
H13 | 0.1403 | 0.2579 | 0.1021 | 0.062* | |
C14 | 0.28840 (15) | 0.16766 (7) | 0.15739 (13) | 0.0471 (3) | |
H14 | 0.3022 | 0.1733 | 0.2481 | 0.057* | |
C6 | 0.74409 (14) | 0.10513 (7) | 0.21830 (12) | 0.0460 (3) | |
C7 | 0.7887 (2) | 0.20652 (11) | 0.07913 (19) | 0.0771 (5) | |
H7A | 0.8862 | 0.1808 | 0.0812 | 0.092* | |
H7B | 0.8111 | 0.2503 | 0.1397 | 0.092* | |
C8 | 0.7114 (3) | 0.23353 (12) | −0.0563 (2) | 0.0897 (6) | |
H8A | 0.6911 | 0.1899 | −0.1156 | 0.135* | |
H8B | 0.7780 | 0.2698 | −0.0842 | 0.135* | |
H8C | 0.6147 | 0.2585 | −0.0573 | 0.135* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0413 (5) | 0.0833 (7) | 0.0640 (6) | −0.0005 (5) | 0.0077 (4) | 0.0147 (5) |
O2 | 0.0489 (5) | 0.0709 (6) | 0.0672 (6) | −0.0063 (5) | 0.0073 (4) | 0.0263 (5) |
O3 | 0.0551 (6) | 0.0989 (9) | 0.0827 (8) | −0.0022 (6) | 0.0225 (5) | 0.0347 (7) |
O4 | 0.0433 (5) | 0.0716 (7) | 0.0590 (6) | 0.0002 (4) | 0.0049 (5) | 0.0073 (5) |
N1 | 0.0397 (5) | 0.0475 (6) | 0.0423 (5) | 0.0077 (4) | 0.0060 (4) | 0.0041 (4) |
C2 | 0.0424 (6) | 0.0426 (6) | 0.0384 (6) | 0.0044 (5) | 0.0083 (4) | 0.0022 (5) |
C3 | 0.0416 (6) | 0.0403 (6) | 0.0354 (5) | 0.0048 (4) | 0.0090 (4) | −0.0017 (4) |
C4 | 0.0425 (6) | 0.0425 (6) | 0.0405 (6) | 0.0057 (5) | 0.0106 (5) | 0.0012 (5) |
C5 | 0.0458 (6) | 0.0430 (6) | 0.0404 (6) | 0.0055 (5) | 0.0107 (5) | 0.0017 (5) |
C17 | 0.0603 (8) | 0.0518 (7) | 0.0562 (8) | 0.0097 (6) | 0.0137 (6) | 0.0139 (6) |
C15 | 0.0469 (7) | 0.0493 (7) | 0.0536 (7) | 0.0027 (5) | 0.0154 (6) | 0.0032 (6) |
C16 | 0.0452 (8) | 0.0785 (11) | 0.0855 (11) | −0.0087 (7) | 0.0008 (7) | 0.0216 (9) |
C9 | 0.0374 (6) | 0.0391 (6) | 0.0386 (6) | 0.0015 (4) | 0.0076 (4) | 0.0011 (4) |
C10 | 0.0593 (8) | 0.0549 (7) | 0.0407 (6) | 0.0134 (6) | 0.0099 (5) | −0.0025 (5) |
C11 | 0.0678 (9) | 0.0661 (9) | 0.0393 (6) | 0.0086 (7) | 0.0056 (6) | 0.0054 (6) |
C12 | 0.0477 (7) | 0.0488 (7) | 0.0568 (8) | 0.0035 (6) | 0.0025 (6) | 0.0135 (6) |
C13 | 0.0497 (7) | 0.0420 (6) | 0.0626 (8) | 0.0085 (5) | 0.0140 (6) | 0.0019 (5) |
C14 | 0.0509 (7) | 0.0468 (7) | 0.0436 (6) | 0.0072 (5) | 0.0131 (5) | −0.0001 (5) |
C6 | 0.0433 (6) | 0.0500 (7) | 0.0436 (6) | 0.0029 (5) | 0.0100 (5) | 0.0005 (5) |
C7 | 0.0715 (10) | 0.0791 (11) | 0.0816 (11) | −0.0177 (9) | 0.0227 (8) | 0.0229 (9) |
C8 | 0.1153 (16) | 0.0819 (12) | 0.0797 (12) | 0.0005 (11) | 0.0398 (11) | 0.0248 (10) |
O1—C6 | 1.2122 (16) | C16—H16A | 0.9600 |
O2—C6 | 1.3255 (15) | C16—H16B | 0.9600 |
O2—C7 | 1.4492 (18) | C16—H16C | 0.9600 |
O3—C15 | 1.2238 (17) | C9—C10 | 1.3854 (17) |
O4—H41 | 0.87 (2) | C9—C14 | 1.3881 (17) |
O4—H42 | 0.92 (2) | C10—C11 | 1.3855 (18) |
N1—C5 | 1.3371 (16) | C10—H10 | 0.9300 |
N1—C2 | 1.3836 (15) | C11—C12 | 1.376 (2) |
N1—H1 | 0.8600 | C11—H11 | 0.9300 |
C2—C3 | 1.3838 (16) | C12—C13 | 1.375 (2) |
C2—C6 | 1.4569 (18) | C12—H12 | 0.9300 |
C3—C4 | 1.4337 (17) | C13—C14 | 1.3859 (18) |
C3—C9 | 1.4873 (15) | C13—H13 | 0.9300 |
C4—C5 | 1.4043 (16) | C14—H14 | 0.9300 |
C4—C15 | 1.4617 (18) | C7—C8 | 1.474 (3) |
C5—C17 | 1.4923 (17) | C7—H7A | 0.9700 |
C17—H17A | 0.9600 | C7—H7B | 0.9700 |
C17—H17B | 0.9600 | C8—H8A | 0.9600 |
C17—H17C | 0.9600 | C8—H8B | 0.9600 |
C15—C16 | 1.493 (2) | C8—H8C | 0.9600 |
C6—O2—C7 | 117.69 (12) | C10—C9—C3 | 121.01 (10) |
H41—O4—H42 | 103.6 (19) | C14—C9—C3 | 120.52 (10) |
C5—N1—C2 | 110.47 (10) | C9—C10—C11 | 120.72 (12) |
C5—N1—H1 | 124.8 | C9—C10—H10 | 119.6 |
C2—N1—H1 | 124.8 | C11—C10—H10 | 119.6 |
N1—C2—C3 | 108.09 (10) | C12—C11—C10 | 120.27 (13) |
N1—C2—C6 | 118.96 (11) | C12—C11—H11 | 119.9 |
C3—C2—C6 | 132.93 (11) | C10—C11—H11 | 119.9 |
C2—C3—C4 | 106.38 (10) | C13—C12—C11 | 119.60 (12) |
C2—C3—C9 | 126.09 (11) | C13—C12—H12 | 120.2 |
C4—C3—C9 | 127.46 (10) | C11—C12—H12 | 120.2 |
C5—C4—C3 | 107.02 (11) | C12—C13—C14 | 120.37 (12) |
C5—C4—C15 | 123.08 (11) | C12—C13—H13 | 119.8 |
C3—C4—C15 | 129.89 (11) | C14—C13—H13 | 119.8 |
N1—C5—C4 | 108.04 (11) | C13—C14—C9 | 120.56 (12) |
N1—C5—C17 | 121.24 (11) | C13—C14—H14 | 119.7 |
C4—C5—C17 | 130.68 (12) | C9—C14—H14 | 119.7 |
C5—C17—H17A | 109.5 | O1—C6—O2 | 123.51 (12) |
C5—C17—H17B | 109.5 | O1—C6—C2 | 124.06 (12) |
H17A—C17—H17B | 109.5 | O2—C6—C2 | 112.43 (11) |
C5—C17—H17C | 109.5 | O2—C7—C8 | 107.72 (15) |
H17A—C17—H17C | 109.5 | O2—C7—H7A | 110.2 |
H17B—C17—H17C | 109.5 | C8—C7—H7A | 110.2 |
O3—C15—C4 | 120.47 (12) | O2—C7—H7B | 110.2 |
O3—C15—C16 | 119.08 (13) | C8—C7—H7B | 110.2 |
C4—C15—C16 | 120.41 (12) | H7A—C7—H7B | 108.5 |
C15—C16—H16A | 109.5 | C7—C8—H8A | 109.5 |
C15—C16—H16B | 109.5 | C7—C8—H8B | 109.5 |
H16A—C16—H16B | 109.5 | H8A—C8—H8B | 109.5 |
C15—C16—H16C | 109.5 | C7—C8—H8C | 109.5 |
H16A—C16—H16C | 109.5 | H8A—C8—H8C | 109.5 |
H16B—C16—H16C | 109.5 | H8B—C8—H8C | 109.5 |
C10—C9—C14 | 118.47 (11) | ||
C5—N1—C2—C3 | −0.50 (14) | C2—C3—C9—C10 | 78.88 (16) |
C5—N1—C2—C6 | 178.03 (11) | C4—C3—C9—C10 | −104.56 (15) |
N1—C2—C3—C4 | 0.61 (13) | C2—C3—C9—C14 | −101.68 (14) |
C6—C2—C3—C4 | −177.64 (13) | C4—C3—C9—C14 | 74.87 (16) |
N1—C2—C3—C9 | 177.76 (10) | C14—C9—C10—C11 | −1.4 (2) |
C6—C2—C3—C9 | −0.5 (2) | C3—C9—C10—C11 | 178.09 (13) |
C2—C3—C4—C5 | −0.51 (13) | C9—C10—C11—C12 | 1.0 (2) |
C9—C3—C4—C5 | −177.61 (11) | C10—C11—C12—C13 | −0.2 (2) |
C2—C3—C4—C15 | −179.91 (12) | C11—C12—C13—C14 | −0.2 (2) |
C9—C3—C4—C15 | 3.0 (2) | C12—C13—C14—C9 | −0.2 (2) |
C2—N1—C5—C4 | 0.17 (14) | C10—C9—C14—C13 | 1.00 (19) |
C2—N1—C5—C17 | 178.24 (11) | C3—C9—C14—C13 | −178.45 (12) |
C3—C4—C5—N1 | 0.22 (13) | C7—O2—C6—O1 | −0.5 (2) |
C15—C4—C5—N1 | 179.67 (11) | C7—O2—C6—C2 | −179.95 (14) |
C3—C4—C5—C17 | −177.61 (13) | N1—C2—C6—O1 | −8.06 (19) |
C15—C4—C5—C17 | 1.8 (2) | C3—C2—C6—O1 | 170.04 (14) |
C5—C4—C15—O3 | 15.1 (2) | N1—C2—C6—O2 | 171.40 (11) |
C3—C4—C15—O3 | −165.61 (14) | C3—C2—C6—O2 | −10.5 (2) |
C5—C4—C15—C16 | −162.52 (14) | C6—O2—C7—C8 | 161.41 (15) |
C3—C4—C15—C16 | 16.8 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O4i | 0.86 | 2.10 | 2.8966 (14) | 155 |
O4—H42···O3ii | 0.92 (2) | 1.92 (2) | 2.8386 (16) | 173 (2) |
O4—H41···O1iii | 0.87 (2) | 2.06 (2) | 2.9077 (16) | 167 (2) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x, −y, −z+1; (iii) x−1, y, z. |
Experimental details
Crystal data | |
Chemical formula | C16H17NO3·H2O |
Mr | 289.32 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 293 |
a, b, c (Å) | 8.9102 (4), 17.1911 (10), 10.4861 (10) |
β (°) | 105.859 (8) |
V (Å3) | 1545.08 (19) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 0.74 |
Crystal size (mm) | 0.46 × 0.27 × 0.18 |
Data collection | |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | ψ scan (North et al., 1968) |
Tmin, Tmax | 0.853, 0.876 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6215, 3048, 2726 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.618 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.040, 0.110, 1.05 |
No. of reflections | 3048 |
No. of parameters | 202 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.19, −0.20 |
Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, HELENA (Spek, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEPII (Johnson, 1976), SHELXL97.
O1—C6 | 1.2122 (16) | N1—C2 | 1.3836 (15) |
O2—C6 | 1.3255 (15) | C2—C6 | 1.4569 (18) |
N1—C5 | 1.3371 (16) | C4—C15 | 1.4617 (18) |
C5—N1—C2 | 110.47 (10) | C2—C3—C4 | 106.38 (10) |
N1—C2—C3 | 108.09 (10) | C5—C4—C3 | 107.02 (11) |
N1—C2—C6 | 118.96 (11) | ||
C3—C4—C5—N1 | 0.22 (13) | C2—C3—C9—C10 | 78.88 (16) |
C5—C4—C15—O3 | 15.1 (2) | C4—C3—C9—C10 | −104.56 (15) |
C3—C4—C15—O3 | −165.61 (14) | C2—C3—C9—C14 | −101.68 (14) |
C5—C4—C15—C16 | −162.52 (14) | C6—O2—C7—C8 | 161.41 (15) |
C3—C4—C15—C16 | 16.8 (2) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O4i | 0.86 | 2.10 | 2.8966 (14) | 155 |
O4—H42···O3ii | 0.92 (2) | 1.92 (2) | 2.8386 (16) | 173 (2) |
O4—H41···O1iii | 0.87 (2) | 2.06 (2) | 2.9077 (16) | 167 (2) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x, −y, −z+1; (iii) x−1, y, z. |
Pyrroles are important compounds in many fields of research, from materials to pharmaceutical sciences. They are percursors of porphyrins and related macrocycles (Baltazzi & Krimen, 1963; Chadwick, 1990) and are also suitable for the assembly of Langmuir-Blodgett films when substituted with amphiphilic chains (Ramos Silva et al., 2002a). In the pharmaceutical sciences, 2-(alkoxycarbonyl)pyrrole derivatives have attracted much interest, as they display a broad spectrum of biological activities, including analgesic, spasmolytic and even anti-HIV-1 activity (Artico et al., 1996; Gribble, 1996). Some pyrrole alkaloid derivatives show anticancer properties because of their DNA-cleaving capabilities (Furstner et al., 2002). Following our work on the synthesis and structure determination of several substituted pyrroles (Paixão et al., 2002; Ramos Silva et al., 2000, 2002a,b), which are intended for incorporation at the β-pyrrole ring of porphyrins, the title compound, (I), was synthesized and an X-ray diffraction study was undertaken to clarify the conformation of the molecule. The results are presented here. \sch
The weighted average of the absolute torsion angles of the pyrrole ring of (I) is 0.42 (6)°, indicating that the heterocyclic ring is almost perfectly planar. The internal ring angles range from 106.38 (10) to 110.47 (10)°, showing a small distortion from C2v symmetry. The acetyl group at C4 and the ethoxycarbonyl group at C2 influence the π-electron distribution within the pyrrole ring, which results in a shortening of the C4—C15 and C2—C6 bond distances with respect to the usual value found for Csp2—Caryl bonds [1.483 (15) Å; Allen et al., 1987]. The same effect accounts for the asymmetric nature of the two N—C bonds within the heterocyclic ring [usual average value 1.372 (16) Å; Allen et al., 1987].
Atoms C15, C17 and C6 are approximately coplanar with the pyrrole ring and deviate by only -0.003 (2), -0.044 (2) and 0.046 (2) Å, respectively, from the least-squares plane of the pyrrole ring. On the other hand, atoms O1, O2 and O3 are tilted out of the ring plane by 0.219 (2), -0.137 (3) and 0.265 (3) Å, respectively. The angle between the least-squares planes of the phenyl and pyrrole rings is 76.93 (5)°. The ethoxycarbonyl group adopts an anti conformation with respect to the heterocyclic N atom. In this group, the C6—O2—C7—C8 torsion angle is 161.41 (15)°, which shows that atom C8 does not share the plane defined by atoms O1, C6, O2 and C7. The acetyl group is oriented so as to minimize the steric interaction between the C16 and C17 methyl groups.
Three strong hydrogen bonds link the molecules of (I) together into infinite one-dimensional chains and exhaust all donor sites of the substituted pyrrole and water molecules. Looking at the conventional hydrogen-bonding pattern, one can recognize the formation of chains and rings which can be characterized using Etter's graph-set analysis (Bernstein et al., 1995). At the basic binary level are centrosymmetric rings which can be described by the R44(14) motif and which involve the pyrrole N—H atom and one water H atom as donors, and the water and ethoxycarbonyl O atoms as acceptors. A larger ring is formed at the binary level when both of the water H atoms act as donors, thereby involving four molecules in the sequence water-substituted pyrrole-water-substituted pyrrole. This pattern has a graph-set motif of R44(20). Finally, chains with the motif C22(8) are formed by the N1—H1···O4i and O4—H42···O3ii hydrogen bonds [symmetry codes: (i) 1 - x, -y, 1 - z; (ii) -x, -y, 1 - z].
Two C—H···π intermolecular interactions can also be observed in (I), thereby exhausting the capacity of the pyrrole π electrons to act as acceptors. In one of the interactions, the phenyl atom C10 acts as the donor, while in the other, one of the methyl H atoms bonded to atom C17 is the donor. The H···Cg (Cg is the centroid of the pyrrole ring) distances are 2.842 and 2.902 Å, and the C—H···π angles are 147.31 and 150.60°, for the two types of bonds, respectively. The angles of approach of the H···Cg vector to the plane of the aromatic ring are 76.01 and 80.39°, respectively, and the perpendicular projections of the H atoms onto the pyrrole ring plane are 0.687 and 0.485 Å, respectively, from the centroid of the ring. In the former interaction, the H atom lies above the centre of the ring, with the C—H bond pointing towards a pyrrole ring C atom. This corresponds to a type III interaction, according to the classification of Malone et al. (1997). The latter interaction corresponds to a type I interaction, with the classical T-shaped geometry. It has been recognized that these weak C—H···π interactions play an appreciable role in determining the conformations of organic compounds (Umezawa et al., 1999).
To investigate the effect of these intermolecular interactions on the conformation of the molecule of (I), we have carried out an optimization of the geometry of the isolated molecule by ab initio quantum-mechanical molecular orbital Hartree-Fock (MO—HF) calculations using the computer program GAMESS (Schmidt et al., 1993). The atomic wavefunctions were expanded on a standard 3–21 G basis set. The optimization was conducted starting from the experimental crystal structure geometry without imposing any symmetry constraints on the molecule. Each self-consistent field calculation was iterated until a Δρ of less than 10-5 bohr-3 was achieved. The final equilibrium geometry at the minimum energy had a maximum gradient in the internal coordinates of 10-5 Hartree bohr-1 or Hartree rad-1. These results reproduce well the observed asymmetry in the pyrrole ring of (I). However, the minimum energy of the isolated molecule occurs for a geometry where the non-H substituent atoms are practically in the ring plane, except for the phenyl group, which lies perpendicular to the heterocyclic ring (C2—C3—C9—C14 88.9°; cf. Table 1). The twists observed in the solid state are therefore probably due to the hydrogen bonding with the water molecule and to the C—H···π intermolecular interactions.