In the title compound, C
13H
13NO
2, there is polarization of π-electron density from the amine N atom to the acceptor carbonyl groups: as a result, the molecule exists predominantly in an azomethino-1,3-diketone tautomeric form. There is crystallographic evidence that the phenyl ring, although roughly coplanar with the rest of the molecule, is deconjugated with the adjacent π system of the molecule. The cyclohexane ring adopts an unsymmetrical half-chair conformation and converts between two inversion-related conformers. The molecule is stabilized by an intramolecular hydrogen bond, while the intermolecular packing is dominated by a number of short C—H
O contacts.
Supporting information
CCDC reference: 237935
The title compound, (I), was synthesized by a three-component reaction of equimolar amounts of aniline, triethyl orthoformate and cyclohexane- 1,3-dione in ethanol under reflux according to Wolfbeis & Ziegler (1976), as described in detail by Marko et al. (2004). The product (m.p. 434 K) was recrystallized from ethanol to give single crystals suitable for X-ray analysis.
The disorder of the cyclohexane ring was modelled by resolving the positions of atoms C5, C6 and O1 into two components (C5/C5', C6/C6', and O1/O1') and using a total of 35 restraints on corresponding bond distances and anisotropic displacement parameters [a combination of DFIX and SIMU options in SHELXL97 (Sheldrick, 1997)]. The refined occupancies for the unprimed (major) and primed (minor) sites were 58.2 (6) and 41.8 (6)%, respectively. H atoms were refined with fixed geometry, riding on their carrier atoms, with Uiso(H) set to 1.2Ueq of the parent atom.
Data collection: XSCANS (Siemens, 1991); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLUTON (Spek, 1992); software used to prepare material for publication: SHELXL97.
2-(phenylaminomethylidene)cyclohexane-1,3-dione
top
Crystal data top
C13H13NO2 | F(000) = 228 |
Mr = 215.24 | Dx = 1.298 Mg m−3 |
Triclinic, P1 | Melting point: 434 K |
a = 5.678 (2) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 8.424 (3) Å | Cell parameters from 20 reflections |
c = 12.404 (5) Å | θ = 7–20° |
α = 100.17 (3)° | µ = 0.09 mm−1 |
β = 93.85 (3)° | T = 293 K |
γ = 107.96 (4)° | Prism, colourless |
V = 550.8 (4) Å3 | 0.30 × 0.20 × 0.15 mm |
Z = 2 | |
Data collection top
Siemens P4 diffractometer | Rint = 0.037 |
Radiation source: fine-focus sealed tube | θmax = 30.0°, θmin = 1.7° |
Graphite monochromator | h = −1→7 |
ω/2θ scans | k = −11→11 |
4085 measured reflections | l = −17→17 |
3188 independent reflections | 3 standard reflections every 97 reflections |
1818 reflections with I > 2σ(I) | intensity decay: 2% |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.065 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.199 | H-atom parameters constrained |
S = 1.05 | w = 1/[σ2(Fo2) + (0.0636P)2 + 0.2041P] where P = (Fo2 + 2Fc2)/3 |
3188 reflections | (Δ/σ)max = 0.001 |
178 parameters | Δρmax = 0.21 e Å−3 |
35 restraints | Δρmin = −0.17 e Å−3 |
Crystal data top
C13H13NO2 | γ = 107.96 (4)° |
Mr = 215.24 | V = 550.8 (4) Å3 |
Triclinic, P1 | Z = 2 |
a = 5.678 (2) Å | Mo Kα radiation |
b = 8.424 (3) Å | µ = 0.09 mm−1 |
c = 12.404 (5) Å | T = 293 K |
α = 100.17 (3)° | 0.30 × 0.20 × 0.15 mm |
β = 93.85 (3)° | |
Data collection top
Siemens P4 diffractometer | Rint = 0.037 |
4085 measured reflections | 3 standard reflections every 97 reflections |
3188 independent reflections | intensity decay: 2% |
1818 reflections with I > 2σ(I) | |
Refinement top
R[F2 > 2σ(F2)] = 0.065 | 35 restraints |
wR(F2) = 0.199 | H-atom parameters constrained |
S = 1.05 | Δρmax = 0.21 e Å−3 |
3188 reflections | Δρmin = −0.17 e Å−3 |
178 parameters | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
C1 | 0.4552 (4) | 0.6907 (4) | 0.56698 (19) | 0.0723 (8) | |
C2 | 0.4521 (4) | 0.6600 (3) | 0.67881 (16) | 0.0500 (5) | |
C3 | 0.6640 (4) | 0.7432 (3) | 0.76235 (17) | 0.0529 (5) | |
C4 | 0.8945 (4) | 0.8666 (3) | 0.73295 (19) | 0.0659 (7) | |
H4A | 0.8927 | 0.9820 | 0.7577 | 0.079* | 0.582 (6) |
H4B | 1.0412 | 0.8566 | 0.7722 | 0.079* | 0.582 (6) |
H4C | 1.0171 | 0.8094 | 0.7185 | 0.079* | 0.418 (6) |
H4D | 0.9666 | 0.9613 | 0.7953 | 0.079* | 0.418 (6) |
C5 | 0.9149 (7) | 0.8370 (7) | 0.6109 (3) | 0.0702 (14) | 0.582 (6) |
H5A | 0.9426 | 0.7288 | 0.5874 | 0.084* | 0.582 (6) |
H5B | 1.0558 | 0.9267 | 0.5961 | 0.084* | 0.582 (6) |
C6 | 0.6762 (11) | 0.8356 (12) | 0.5469 (6) | 0.076 (3) | 0.582 (6) |
H6A | 0.6917 | 0.8204 | 0.4686 | 0.091* | 0.582 (6) |
H6B | 0.6486 | 0.9438 | 0.5704 | 0.091* | 0.582 (6) |
C5' | 0.8372 (12) | 0.9349 (7) | 0.6320 (4) | 0.0721 (18) | 0.418 (6) |
H5'1 | 0.7313 | 1.0045 | 0.6491 | 0.086* | 0.418 (6) |
H5'2 | 0.9913 | 1.0061 | 0.6124 | 0.086* | 0.418 (6) |
C6' | 0.7070 (16) | 0.7887 (16) | 0.5356 (6) | 0.074 (3) | 0.418 (6) |
H6'1 | 0.8070 | 0.7143 | 0.5208 | 0.089* | 0.418 (6) |
H6'2 | 0.6824 | 0.8321 | 0.4698 | 0.089* | 0.418 (6) |
C7 | 0.2363 (4) | 0.5429 (3) | 0.70021 (16) | 0.0501 (5) | |
H7 | 0.1048 | 0.4931 | 0.6432 | 0.060* | |
C8 | −0.0070 (4) | 0.3819 (2) | 0.82497 (15) | 0.0473 (5) | |
C9 | −0.2384 (4) | 0.3293 (3) | 0.76301 (18) | 0.0583 (6) | |
H9 | −0.2597 | 0.3667 | 0.6980 | 0.070* | |
C10 | −0.4390 (4) | 0.2194 (3) | 0.7994 (2) | 0.0696 (7) | |
H10 | −0.5958 | 0.1827 | 0.7579 | 0.084* | |
C11 | −0.4101 (5) | 0.1638 (3) | 0.8957 (2) | 0.0701 (7) | |
H11 | −0.5463 | 0.0914 | 0.9198 | 0.084* | |
C12 | −0.1784 (5) | 0.2165 (3) | 0.95562 (19) | 0.0661 (7) | |
H12 | −0.1575 | 0.1780 | 1.0203 | 0.079* | |
C13 | 0.0245 (4) | 0.3256 (3) | 0.92158 (17) | 0.0568 (6) | |
H13 | 0.1811 | 0.3611 | 0.9631 | 0.068* | |
N1 | 0.2070 (3) | 0.4985 (2) | 0.79583 (13) | 0.0528 (5) | |
H1 | 0.3320 | 0.5454 | 0.8469 | 0.063* | |
O1 | 0.2915 (10) | 0.5952 (8) | 0.4895 (5) | 0.0732 (17) | 0.582 (6) |
O1' | 0.2559 (14) | 0.6629 (13) | 0.5050 (8) | 0.084 (3) | 0.418 (6) |
O2 | 0.6626 (3) | 0.7175 (2) | 0.85724 (13) | 0.0793 (6) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
C1 | 0.0476 (12) | 0.103 (2) | 0.0540 (13) | −0.0041 (12) | 0.0032 (10) | 0.0375 (13) |
C2 | 0.0424 (10) | 0.0585 (12) | 0.0431 (10) | 0.0030 (9) | 0.0057 (8) | 0.0193 (9) |
C3 | 0.0490 (11) | 0.0537 (12) | 0.0494 (11) | 0.0050 (9) | 0.0038 (9) | 0.0157 (9) |
C4 | 0.0491 (12) | 0.0681 (15) | 0.0622 (13) | −0.0064 (11) | 0.0021 (10) | 0.0140 (11) |
C5 | 0.054 (2) | 0.072 (3) | 0.069 (2) | −0.007 (2) | 0.0148 (18) | 0.022 (2) |
C6 | 0.060 (3) | 0.100 (5) | 0.064 (3) | 0.004 (3) | 0.014 (2) | 0.043 (3) |
C5' | 0.067 (3) | 0.059 (3) | 0.071 (3) | −0.013 (3) | 0.020 (3) | 0.020 (3) |
C6' | 0.058 (3) | 0.096 (6) | 0.060 (3) | −0.001 (4) | 0.018 (3) | 0.036 (3) |
C7 | 0.0432 (10) | 0.0597 (12) | 0.0420 (10) | 0.0052 (9) | 0.0044 (8) | 0.0181 (9) |
C8 | 0.0461 (10) | 0.0485 (11) | 0.0434 (10) | 0.0054 (8) | 0.0106 (8) | 0.0163 (8) |
C9 | 0.0505 (12) | 0.0721 (14) | 0.0523 (11) | 0.0098 (10) | 0.0086 (9) | 0.0306 (11) |
C10 | 0.0459 (12) | 0.0837 (17) | 0.0737 (15) | 0.0039 (11) | 0.0071 (11) | 0.0336 (13) |
C11 | 0.0621 (14) | 0.0747 (16) | 0.0695 (15) | 0.0028 (12) | 0.0219 (12) | 0.0350 (13) |
C12 | 0.0761 (16) | 0.0682 (14) | 0.0515 (12) | 0.0093 (12) | 0.0136 (11) | 0.0296 (11) |
C13 | 0.0577 (12) | 0.0626 (13) | 0.0441 (10) | 0.0063 (10) | 0.0038 (9) | 0.0202 (9) |
N1 | 0.0447 (9) | 0.0604 (11) | 0.0440 (9) | −0.0004 (8) | 0.0020 (7) | 0.0198 (8) |
O1 | 0.0527 (19) | 0.106 (4) | 0.048 (2) | 0.002 (2) | 0.0017 (15) | 0.029 (3) |
O1' | 0.061 (3) | 0.120 (6) | 0.055 (3) | −0.003 (3) | −0.006 (3) | 0.043 (4) |
O2 | 0.0673 (11) | 0.0951 (13) | 0.0519 (9) | −0.0111 (9) | −0.0091 (7) | 0.0287 (9) |
Geometric parameters (Å, º) top
C1—O1 | 1.257 (5) | C5'—C6' | 1.515 (7) |
C1—O1' | 1.258 (7) | C5'—H5'1 | 0.9700 |
C1—C2 | 1.455 (3) | C5'—H5'2 | 0.9700 |
C1—C6 | 1.527 (6) | C6'—H6'1 | 0.9700 |
C1—C6' | 1.529 (8) | C6'—H6'2 | 0.9700 |
C2—C7 | 1.391 (3) | C7—N1 | 1.311 (2) |
C2—C3 | 1.438 (3) | C7—H7 | 0.9300 |
C3—O2 | 1.234 (2) | C8—C9 | 1.378 (3) |
C3—C4 | 1.512 (3) | C8—C13 | 1.385 (3) |
C4—C5 | 1.508 (4) | C8—N1 | 1.421 (2) |
C4—C5' | 1.523 (5) | C9—C10 | 1.387 (3) |
C4—H4A | 0.9700 | C9—H9 | 0.9300 |
C4—H4B | 0.9700 | C10—C11 | 1.376 (3) |
C4—H4C | 0.9700 | C10—H10 | 0.9300 |
C4—H4D | 0.9700 | C11—C12 | 1.368 (3) |
C5—C6 | 1.520 (6) | C11—H11 | 0.9300 |
C5—H5A | 0.9700 | C12—C13 | 1.378 (3) |
C5—H5B | 0.9700 | C12—H12 | 0.9300 |
C6—H6A | 0.9700 | C13—H13 | 0.9300 |
C6—H6B | 0.9700 | N1—H1 | 0.8600 |
| | | |
O1—C1—C2 | 121.2 (4) | C6'—C5'—C4 | 110.2 (6) |
O1'—C1—C2 | 121.3 (5) | C6'—C5'—H5'1 | 109.6 |
O1—C1—C6 | 121.8 (4) | C4—C5'—H5'1 | 109.6 |
O1'—C1—C6 | 114.5 (6) | C6'—C5'—H5'2 | 109.6 |
C2—C1—C6 | 116.9 (3) | C4—C5'—H5'2 | 109.6 |
O1'—C1—C6' | 120.6 (6) | H5'1—C5'—H5'2 | 108.1 |
C2—C1—C6' | 117.1 (4) | C5'—C6'—C1 | 107.4 (6) |
C7—C2—C3 | 121.58 (17) | C5'—C6'—H6'1 | 110.2 |
C7—C2—C1 | 116.70 (18) | C1—C6'—H6'1 | 110.2 |
C3—C2—C1 | 121.69 (18) | C5'—C6'—H6'2 | 110.2 |
O2—C3—C2 | 121.99 (19) | C1—C6'—H6'2 | 110.2 |
O2—C3—C4 | 119.13 (19) | H6'1—C6'—H6'2 | 108.5 |
C2—C3—C4 | 118.88 (18) | N1—C7—C2 | 124.01 (18) |
C5—C4—C3 | 113.4 (2) | N1—C7—H7 | 118.0 |
C3—C4—C5' | 112.2 (3) | C2—C7—H7 | 118.0 |
C5—C4—H4A | 108.9 | C9—C8—C13 | 120.53 (18) |
C3—C4—H4A | 108.9 | C9—C8—N1 | 122.59 (17) |
C5—C4—H4B | 108.9 | C13—C8—N1 | 116.86 (18) |
C3—C4—H4B | 108.9 | C8—C9—C10 | 118.8 (2) |
H4A—C4—H4B | 107.7 | C8—C9—H9 | 120.6 |
C3—C4—H4C | 109.2 | C10—C9—H9 | 120.6 |
C5'—C4—H4C | 109.2 | C11—C10—C9 | 121.1 (2) |
C3—C4—H4D | 109.2 | C11—C10—H10 | 119.4 |
C5'—C4—H4D | 109.2 | C9—C10—H10 | 119.4 |
H4C—C4—H4D | 107.9 | C12—C11—C10 | 119.2 (2) |
C4—C5—C6 | 109.8 (5) | C12—C11—H11 | 120.4 |
C4—C5—H5A | 109.7 | C10—C11—H11 | 120.4 |
C6—C5—H5A | 109.7 | C11—C12—C13 | 121.0 (2) |
C4—C5—H5B | 109.7 | C11—C12—H12 | 119.5 |
C6—C5—H5B | 109.7 | C13—C12—H12 | 119.5 |
H5A—C5—H5B | 108.2 | C12—C13—C8 | 119.4 (2) |
C5—C6—C1 | 109.8 (5) | C12—C13—H13 | 120.3 |
C5—C6—H6A | 109.7 | C8—C13—H13 | 120.3 |
C1—C6—H6A | 109.7 | C7—N1—C8 | 127.64 (17) |
C5—C6—H6B | 109.7 | C7—N1—H1 | 116.2 |
C1—C6—H6B | 109.7 | C8—N1—H1 | 116.2 |
H6A—C6—H6B | 108.2 | | |
| | | |
O1—C1—C2—C7 | −12.2 (5) | O1'—C1—C6—C5 | −169.9 (8) |
O1'—C1—C2—C7 | 23.8 (7) | C2—C1—C6—C5 | 39.6 (9) |
C6—C1—C2—C7 | 172.1 (5) | C4—C5'—C6'—C1 | 64.4 (10) |
C6'—C1—C2—C7 | −167.5 (7) | O1'—C1—C6'—C5' | 126.3 (9) |
O1—C1—C2—C3 | 166.2 (4) | C2—C1—C6'—C5' | −42.6 (11) |
O1'—C1—C2—C3 | −157.8 (6) | C3—C2—C7—N1 | −0.1 (4) |
C6—C1—C2—C3 | −9.5 (6) | C1—C2—C7—N1 | 178.3 (2) |
C6'—C1—C2—C3 | 10.9 (7) | C13—C8—C9—C10 | 0.2 (4) |
C7—C2—C3—O2 | −1.6 (4) | N1—C8—C9—C10 | −178.0 (2) |
C1—C2—C3—O2 | −179.9 (3) | C8—C9—C10—C11 | 0.3 (4) |
C7—C2—C3—C4 | 178.8 (2) | C9—C10—C11—C12 | −0.8 (4) |
C1—C2—C3—C4 | 0.5 (4) | C10—C11—C12—C13 | 0.8 (4) |
O2—C3—C4—C5 | 157.5 (3) | C11—C12—C13—C8 | −0.3 (4) |
C2—C3—C4—C5 | −22.9 (4) | C9—C8—C13—C12 | −0.2 (4) |
O2—C3—C4—C5' | −158.3 (4) | N1—C8—C13—C12 | 178.1 (2) |
C2—C3—C4—C5' | 21.3 (4) | C2—C7—N1—C8 | 179.2 (2) |
C3—C4—C5—C6 | 53.4 (6) | C9—C8—N1—C7 | −16.2 (4) |
C4—C5—C6—C1 | −61.3 (8) | C13—C8—N1—C7 | 165.6 (2) |
O1—C1—C6—C5 | −136.0 (6) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2 | 0.86 | 1.97 | 2.641 (3) | 134 |
C7—H7···O1 | 0.93 | 2.41 | 2.749 (8) | 102 |
C7—H7···O1′ | 0.93 | 2.46 | 2.780 (10) | 100 |
C5—H5A···O1′i | 0.97 | 2.27 | 3.006 (11) | 132 |
C6′—H6′1···O1ii | 0.97 | 2.47 | 3.196 (16) | 131 |
C7—H7···O1iii | 0.93 | 2.52 | 3.436 (6) | 167 |
C7—H7···O1′iii | 0.93 | 2.51 | 3.434 (8) | 175 |
C9—H9···O1iii | 0.93 | 2.41 | 3.317 (8) | 166 |
C9—H9···O1′iii | 0.93 | 2.49 | 3.332 (11) | 151 |
Symmetry codes: (i) x+1, y, z; (ii) −x+1, −y+1, −z+1; (iii) −x, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | C13H13NO2 |
Mr | 215.24 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 293 |
a, b, c (Å) | 5.678 (2), 8.424 (3), 12.404 (5) |
α, β, γ (°) | 100.17 (3), 93.85 (3), 107.96 (4) |
V (Å3) | 550.8 (4) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.30 × 0.20 × 0.15 |
|
Data collection |
Diffractometer | Siemens P4 diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4085, 3188, 1818 |
Rint | 0.037 |
(sin θ/λ)max (Å−1) | 0.703 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.065, 0.199, 1.05 |
No. of reflections | 3188 |
No. of parameters | 178 |
No. of restraints | 35 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.21, −0.17 |
Selected geometric parameters (Å, º) topC1—O1 | 1.257 (5) | C5—C6 | 1.520 (6) |
C1—O1' | 1.258 (7) | C7—N1 | 1.311 (2) |
C1—C2 | 1.455 (3) | C8—C9 | 1.378 (3) |
C1—C6 | 1.527 (6) | C8—C13 | 1.385 (3) |
C2—C7 | 1.391 (3) | C8—N1 | 1.421 (2) |
C2—C3 | 1.438 (3) | C9—C10 | 1.387 (3) |
C3—O2 | 1.234 (2) | C10—C11 | 1.376 (3) |
C3—C4 | 1.512 (3) | C11—C12 | 1.368 (3) |
C4—C5 | 1.508 (4) | C12—C13 | 1.378 (3) |
| | | |
O1—C1—C2 | 121.2 (4) | O2—C3—C4 | 119.13 (19) |
O1—C1—C6 | 121.8 (4) | C2—C3—C4 | 118.88 (18) |
C2—C1—C6 | 116.9 (3) | C5—C4—C3 | 113.4 (2) |
C7—C2—C3 | 121.58 (17) | C4—C5—C6 | 109.8 (5) |
C7—C2—C1 | 116.70 (18) | C5—C6—C1 | 109.8 (5) |
C3—C2—C1 | 121.69 (18) | N1—C7—C2 | 124.01 (18) |
O2—C3—C2 | 121.99 (19) | C7—N1—C8 | 127.64 (17) |
| | | |
O1—C1—C2—C3 | 166.2 (4) | C3—C4—C5—C6 | 53.4 (6) |
C6—C1—C2—C3 | −9.5 (6) | C4—C5—C6—C1 | −61.3 (8) |
C7—C2—C3—O2 | −1.6 (4) | O1—C1—C6—C5 | −136.0 (6) |
C7—C2—C3—C4 | 178.8 (2) | C2—C1—C6—C5 | 39.6 (9) |
C1—C2—C3—C4 | 0.5 (4) | C3—C2—C7—N1 | −0.1 (4) |
O2—C3—C4—C5 | 157.5 (3) | C9—C8—N1—C7 | −16.2 (4) |
C2—C3—C4—C5 | −22.9 (4) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O2 | 0.86 | 1.97 | 2.641 (3) | 134 |
C7—H7···O1 | 0.93 | 2.41 | 2.749 (8) | 102 |
C7—H7···O1' | 0.93 | 2.46 | 2.780 (10) | 100 |
C5—H5A···O1'i | 0.97 | 2.27 | 3.006 (11) | 132 |
C6'—H6'1···O1ii | 0.97 | 2.47 | 3.196 (16) | 131 |
C7—H7···O1iii | 0.93 | 2.52 | 3.436 (6) | 167 |
C7—H7···O1'iii | 0.93 | 2.51 | 3.434 (8) | 175 |
C9—H9···O1iii | 0.93 | 2.41 | 3.317 (8) | 166 |
C9—H9···O1'iii | 0.93 | 2.49 | 3.332 (11) | 151 |
Symmetry codes: (i) x+1, y, z; (ii) −x+1, −y+1, −z+1; (iii) −x, −y+1, −z+1. |
Recently, as a part of our ongoing study on the structure–activity relationships of the biologically active compounds, we focused our attention to the title compound, (I), following reports that such derivatives exhibit photobleaching activity as assayed in tobacco (Nicotiana tabacum) cultured cells (Wang et al., 1997). It was shown that the chlorophyll and carotenoid contents of the cells treated with the cyclic dione disapeared within 24 h under light but not dark condition. However, the rapid onset of photobleaching activity did not result from inhibition of protoporphyrinogen oxidase, indicating that some other mechanism of action might operate, for example, electron transport between the drug molecule and the photosynthetic pigments. Thus, to shed some light on the molecular mechanism of action, we initiated a study of the π-electronic structure of the dione in both ground and photo-activated states by a combination of theoretical and experimental techniques. In this communication, we report on the crystal structure of (I).
The molecular structure along with the atom-numbering scheme is shown in Fig. 1. As shown in the figure, atoms C5, C6 and O1 are disordered between two positions, denoted by unprimed (major site) and primed (minor site) labels, respectively. The disorder originates from two conformations of the cyclohexane ring, which are related by an inversion of the ring. A calculation of the least-squares planes has shown that the ring is puckered in such a manner that atoms C1, C2, C3 and C4 are coplanar to within experimental error [r.m.s.deviation = 0.002 (2) Å], while atoms C5 and C6 are unequally displaced from this plane on opposite sides, with out-of-plane displacements of −0.531 (7) and 0.227 (12) Å, respectively. The corresponding displacements of atoms C5' and C6' in the inverted conformation are 0.518 (9) and −0.264 (15) Å, respectively. Thus, the conformation of the two puckered rings can be described according to Duax et al. (1976) as intermediate between half-chair, with a local pseudo twofold axis along the mid-points of the C2—C3 and C5—C6 (or C5'—C6') bonds, and sofa, with a local pseudo mirror along the C2···C5 (or C2···C5') direction. The puckering parameters according to Cremer & Pople (1975) are Q = 0.499 (6) Å, θ = 50.8 (3)° and ϕ = −104.0 (7)° (calculated for the sequence C1/C2/C3/C4/C5/C6); the corresponding parameters for the inverted ring are Q = 0.525 (8) Å, θ = 128.7 (2)° and ϕ = 79.3 (7)° (sequence C1/C2/C3/C4/C5'/C6').
As noted above, the main purpose of this work was to establish the (π) electron ditribution within the π-electronic portion of the molecule. Firstly, as shown in Table 1, the the C7—N1—C8 valence angle is even larger than 120°, i.e. the amine N atom is sp2-hybridized, with the lone-pair electrons available for π-bonding. Secondly, as estimated from the bond-order–bond-length curves proposed by Burke-Laing & Laing (1976), the bond order of the N1—C7 single bond is even higher (ca 1.7) than that of the C2—C7 double bond (ca 1.5). Furthermore, the C1—C2 and C2—C3 bond distances are significantly shorter than the normal value of 1.487 Å reported for the C(sp2)-C(sp2) single bond (Shmueli et al., 1973). These findings, coupled with the lengthening of the two carbonyl bonds with respect to the range (1.20–1.22 Å) normally accepted for a C=O double bond, imply that there is an extensive π-electron delocalization from atom N1 to the carbonyl groups, leading to the development of negative charges on atoms O1 and O3. A similar pattern of bond lengths and angles has also been observed in other compounds containing the aminomethylene-1,3- diketone substructure (e.g. DeGarcia-Martin et al., 1987), as revealed by a search of the Cambridge Structural Database (Allen et al., 1983). Thus, the electronic structure of the title and related compounds can better be described by the azomethino-1,3-diketone rather than the aminomethylene tautomerism. That the lone-pair electrons on atom N1 are delocalized through conjugation with the methylene-1,3-diketone moiety rather than the adjacent phenyl ring is also seen in the N1—C8 bond distance [1.421 (2) Å], which is not significantly different from the value [1.425 (3) Å] reported for a pure N(sp2)-C(sp2) single bond (Adler at al., 1976). Even though the phenyl ring is deconjugated with the azomethino-1,3-diketone moiety, both fragments are roughly coplanar to one another; the C9—C8—N1—C7 torsion angle is −16.2 (4)°.
The charge distribution in the molecule can also be guessed from the formation of an intramolecular hydrogen bond between the N1—H1 donor and O2 acceptor (Table 2). Besides this hydrogen bond, there are several short intermolecular C—H···O contacts, which, on the basisi of their H···O distances, can be regarded as weak hydrogen-bonding interactions (Table 2; Taylor & Kennard, 1982).