Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100020448/bm1441sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270100020448/bm1441IIsup2.hkl |
CCDC reference: 169933
H atoms on C were placed geometrically and the H atom on O was located in a difference Fourier synthesis. C—H distances were fixed at 1.00 Å and the O—H distance was fixed at 0.96 Å. A common Uiso parameter for all H atoms converged at 0.046 (2) Å2. Query - not methyl H.
1-Heterosubstituted 2-nitroethylene derivatives undergo polyprotonations in trifluoromethanesulfonic acid that lead to loss of water and formation of hydroxynitrilium ions, or O-protonated nitrile oxides, which are fairly electrophilic (Coustard, 1995, 1996, 1999). In this medium, 1-methyl-2-nitromethylenepyrrolidine, (I), also undergoes this transformation, leading to the corresponding hydroxynitrilium ion (scheme), which reacts with benzene to afford a stable dication observable either by 1H or 13C NMR spectroscopy. Quenching with water affords the title compound, (II), which is stable in acidic or neutral aqueous solution. In basic solution, deprotonation of the OH oxime group leads to formation of a conjugated nitroso derivative which dimerizes readily to give a mixture of isomers. In compound (II), the presence of a trifluoromethanesulfonate anion, phenyl ring and oxime (or hydroxyimino) group was expected from 1H and 13NMR data (Coustard, 1999). However, the configuration of the oxime is important from a mechanistic point of view and needed to be confirmed. The unusual behavior of this salt also prompted us to undertake the present X-ray crystallographic analysis. \sch
Most of the cation is nearly planar (Fig. 1), but the aromatic ring lies out of the plane, with a C12—C7—C6—N6 torsion angle of 72.2 (2)°. The maximum deviation of the atoms defining the least-squares mean plane through O6, N6, C6, C5, N1 and C13 is observed for C6 and N6, with respective values of -0.116 Å and 0.098 Å. The atoms of the five-membered ring C5/N1/C2/C3/C4 are also approximately coplanar, with maximum deviations from the least-squares mean plane of -0.114 Å for C4 and 0.135 Å for C3.
The O6—N6—C6—C7 torsion angle of -5.0 (2)° indicates a E-configured oxime group; the adjacent C6—C5 bond adopts an s-trans conformation [N1—C5—C6—N6 - 170.2 (3)°]. Such an oxime configuration has also been reported for products resulting from hydroxynitrilium ion trapping (Cousson & Coustard, 1998, 1999).
Conjugation of the N6—C6—C5—N1 double-bond system allows delocalization of the positive charge and accounts for the lengthening of both the C6—C5 single bond [1.469 (2) Å, compared with the expected value for a single bond in a dienic conjugated system of 1.455 (11) Å; Allen et al., 1987] and the C6—N6 double bond [1.290 (2) Å, compared with the expected value in an unconjugated oxime of 1.280 (13) Å; Allen et al., 1987].
The relatively short distance of 2.651 (2) Å between atom O1 of the trifluoromethanesulfonate anion and the oxime oxygen O6 implies a hydrogen bond involving H6 [H6···O1 1.69 and O6···O1 2.651 (2) Å, and O6—H6···O1 177°].
The O3i···N2 and O3i···C5 distances [symmetry code: (i) 1 - x, 1/2 + y, 1/2 - z] of 2.855 (2) and 2.873 (2) Å, respectively, are shorter than expected, the sum of the relevant van der Waals sums (Bondi, 1964) being 3.07 and 3.22 Å. A search of the Cambridge Structural Database (Allen & Kennard, 1993; October 2000 Version) for the fragment F3C—SO3···N═C indicates that about half the 25 or so occurrences have generally similar distances to those above. In the present case, the short distances may result from the formation of some kind of π-adduct between the π-electrons of the C═N double bond and the O3 atom of the trifluoromethanesulfonate anion. In agreement with this hypothesis is the fact that the O3i atom is almost equidistant from N2 and C5, and the dihedral angle between the N2/O3i/C5 and N1/C2/C3/C4/C5 planes is 97.54°, indicating that they are almost perpendicular.
In conclusion, compound (II) may be considered as resulting from O-protonation of the nitroso group of α-(N-methyl-1-azacyclopent-1-en-2-yl)-α-nitrosotoluene by trifluoromethanesulfonic acid. The oxime group thus formed is E-configured, in agreement with an electrophilic aromatic substitution mechanism involving the C ≡N of the transient hydroxynitrilium ion (Hegarty et al., 1980; Nguyen et al., 1991).
Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Nonius, 1998); cell refinement: DENZO; data reduction: DENZO; program(s) used to solve structure: SHELXS86 (Sheldrick, 1986); program(s) used to refine structure: CRYSTALS (Watkin, Prout, Carruthers & Betteridge, 1996); molecular graphics: CAMERON (Watkin, Prout & Pearce, 1996); software used to prepare material for publication: CRYSTALS.
Fig. 1. The molecular view of (II) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radii. |
C12H15N2O+·CF3SO3− | Dx = 1.511 Mg m−3 |
Mr = 352.33 | Melting point = 386.5–389 K |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 11.7643 (5) Å | Cell parameters from 11326 reflections |
b = 8.2154 (4) Å | θ = 1–28° |
c = 16.5207 (6) Å | µ = 0.26 mm−1 |
β = 104.10 (2)° | T = 120 K |
V = 1548.6 Å3 | Plate, colourless |
Z = 4 | 0.25 × 0.20 × 0.10 mm |
F(000) = 728.77 |
Nonius KappaCCD area-detector diffractometer | Rint = 0.036 |
Graphite monochromator | θmax = 28°, θmin = 1° |
φ rotation scans with 2° steps | h = −15→15 |
11326 measured reflections | k = −9→10 |
3595 independent reflections | l = −21→19 |
2749 reflections with I > 3σ(I) |
Refinement on F | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.044 | H-atom parameters constrained |
wR(F2) = 0.054 | Chebychev polynomial with 3 parameters, 0.683, 0.650 and 0.343 (Carruthers & Watkin, 1979) |
S = 1.03 | (Δ/σ)max = 0.001 |
2749 reflections | Δρmax = 0.67 e Å−3 |
209 parameters | Δρmin = −0.49 e Å−3 |
C12H15N2O+·CF3SO3− | V = 1548.6 Å3 |
Mr = 352.33 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 11.7643 (5) Å | µ = 0.26 mm−1 |
b = 8.2154 (4) Å | T = 120 K |
c = 16.5207 (6) Å | 0.25 × 0.20 × 0.10 mm |
β = 104.10 (2)° |
Nonius KappaCCD area-detector diffractometer | 2749 reflections with I > 3σ(I) |
11326 measured reflections | Rint = 0.036 |
3595 independent reflections |
R[F2 > 2σ(F2)] = 0.044 | 209 parameters |
wR(F2) = 0.054 | H-atom parameters constrained |
S = 1.03 | Δρmax = 0.67 e Å−3 |
2749 reflections | Δρmin = −0.49 e Å−3 |
x | y | z | Uiso*/Ueq | ||
S1 | 0.23655 (4) | 0.77001 (6) | 0.07596 (3) | 0.0293 | |
O1 | 0.30177 (11) | 0.92007 (15) | 0.07503 (8) | 0.0288 | |
O2 | 0.15339 (18) | 0.7745 (3) | 0.12625 (12) | 0.0590 | |
O3 | 0.30712 (14) | 0.62638 (18) | 0.08194 (11) | 0.0458 | |
O6 | 0.52897 (11) | 0.89981 (18) | 0.14656 (8) | 0.0325 | |
N1 | 0.68740 (13) | 0.77957 (18) | 0.42736 (9) | 0.0234 | |
N6 | 0.52186 (13) | 0.88205 (19) | 0.22798 (9) | 0.0265 | |
C2 | 0.64478 (17) | 0.7695 (2) | 0.50482 (11) | 0.0292 | |
C3 | 0.51219 (17) | 0.7596 (2) | 0.47273 (11) | 0.0306 | |
C4 | 0.48847 (16) | 0.8280 (2) | 0.38356 (11) | 0.0287 | |
C5 | 0.60483 (15) | 0.8092 (2) | 0.3618 (1) | 0.0235 | |
C6 | 0.61798 (15) | 0.8287 (2) | 0.2761 (1) | 0.0236 | |
C7 | 0.72305 (14) | 0.7776 (2) | 0.2472 (1) | 0.0237 | |
C8 | 0.74806 (15) | 0.6124 (2) | 0.24575 (11) | 0.0271 | |
C9 | 0.84465 (17) | 0.5598 (3) | 0.21780 (12) | 0.0324 | |
C10 | 0.91529 (16) | 0.6732 (3) | 0.19139 (12) | 0.0359 | |
C11 | 0.89034 (17) | 0.8379 (3) | 0.19271 (12) | 0.0355 | |
C12 | 0.79380 (16) | 0.8913 (2) | 0.22050 (12) | 0.0317 | |
C13 | 0.81448 (15) | 0.7725 (2) | 0.43582 (11) | 0.0281 | |
C14 | 0.14536 (18) | 0.7633 (3) | −0.03011 (14) | 0.0382 | |
F1 | 0.07281 (12) | 0.88976 (18) | −0.0453 (1) | 0.0582 | |
F2 | 0.21115 (14) | 0.7675 (2) | −0.08562 (9) | 0.0593 | |
F3 | 0.08090 (12) | 0.62762 (17) | −0.0437 (1) | 0.0540 | |
H6 | 0.4472 | 0.9100 | 0.1196 | 0.0530 (19)* | |
H21 | 0.6679 | 0.8691 | 0.5400 | 0.0476 (19)* | |
H22 | 0.6760 | 0.6708 | 0.5378 | 0.0476 (19)* | |
H31 | 0.4719 | 0.8276 | 0.5078 | 0.0476 (19)* | |
H32 | 0.4843 | 0.6448 | 0.4721 | 0.0476 (19)* | |
H41 | 0.4645 | 0.9453 | 0.3818 | 0.0476 (19)* | |
H42 | 0.4257 | 0.7642 | 0.3443 | 0.0476 (19)* | |
H81 | 0.6966 | 0.5324 | 0.2651 | 0.0476 (19)* | |
H91 | 0.8629 | 0.4410 | 0.2166 | 0.0476 (19)* | |
H101 | 0.9845 | 0.6357 | 0.1710 | 0.0476 (19)* | |
H111 | 0.9428 | 0.9197 | 0.1748 | 0.0476 (19)* | |
H121 | 0.7748 | 1.0098 | 0.2206 | 0.0476 (19)* | |
H131 | 0.8378 | 0.8546 | 0.4017 | 0.0527 (19)* | |
H132 | 0.8456 | 0.8017 | 0.4921 | 0.0527 (19)* | |
H133 | 0.8347 | 0.6633 | 0.4217 | 0.0527 (19)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.0316 (2) | 0.0255 (2) | 0.0333 (2) | −0.00125 (17) | 0.01289 (17) | 0.00211 (17) |
O1 | 0.0290 (6) | 0.0213 (6) | 0.0353 (6) | 0.0004 (5) | 0.0065 (5) | 0.0013 (5) |
O2 | 0.0624 (11) | 0.0712 (12) | 0.0574 (11) | −0.0149 (9) | 0.0417 (9) | −0.0076 (9) |
O3 | 0.0441 (8) | 0.0224 (7) | 0.0671 (11) | 0.0039 (6) | 0.0059 (7) | 0.0073 (7) |
O6 | 0.0313 (7) | 0.0468 (8) | 0.0202 (6) | 0.0044 (6) | 0.0080 (5) | 0.0040 (5) |
N1 | 0.0266 (7) | 0.0211 (6) | 0.0233 (6) | −0.0005 (5) | 0.0072 (5) | −0.0006 (5) |
N6 | 0.0305 (7) | 0.0298 (7) | 0.0209 (6) | 0.0020 (6) | 0.0096 (5) | 0.0015 (5) |
C2 | 0.0337 (9) | 0.0339 (9) | 0.0216 (7) | 0.0026 (7) | 0.0098 (6) | 0.0012 (7) |
C3 | 0.0330 (9) | 0.036 (1) | 0.0260 (8) | 0.0011 (7) | 0.0131 (7) | 0.0019 (7) |
C4 | 0.0282 (8) | 0.0348 (9) | 0.0247 (8) | 0.0016 (7) | 0.0094 (6) | 0.0007 (7) |
C5 | 0.0266 (8) | 0.0215 (8) | 0.0234 (8) | −0.0010 (6) | 0.0080 (6) | −0.0006 (6) |
C6 | 0.0267 (8) | 0.0222 (8) | 0.0231 (8) | −0.0019 (6) | 0.0086 (6) | 0.0003 (6) |
C7 | 0.0231 (7) | 0.0289 (8) | 0.0195 (7) | −0.0018 (6) | 0.0061 (6) | −0.0009 (6) |
C8 | 0.0277 (8) | 0.0280 (9) | 0.0269 (8) | −0.0017 (7) | 0.0093 (6) | −0.0002 (7) |
C9 | 0.0301 (9) | 0.036 (1) | 0.0329 (9) | 0.0048 (8) | 0.0109 (7) | −0.0026 (7) |
C10 | 0.0251 (8) | 0.0541 (12) | 0.0305 (9) | 0.0023 (8) | 0.0103 (7) | −0.0016 (8) |
C11 | 0.0271 (9) | 0.0485 (12) | 0.0327 (9) | −0.0081 (8) | 0.0103 (7) | 0.0064 (8) |
C12 | 0.0305 (9) | 0.033 (1) | 0.0313 (9) | −0.0047 (7) | 0.0081 (7) | 0.0057 (7) |
C13 | 0.0247 (8) | 0.0300 (9) | 0.0285 (8) | −0.0015 (7) | 0.0043 (6) | −0.0009 (7) |
C14 | 0.0314 (9) | 0.0365 (11) | 0.0456 (11) | −0.0041 (8) | 0.0070 (8) | −0.0023 (8) |
F1 | 0.0392 (7) | 0.0469 (8) | 0.077 (1) | 0.0051 (6) | −0.0072 (7) | 0.0094 (7) |
F2 | 0.0608 (9) | 0.0840 (12) | 0.0356 (7) | −0.0165 (8) | 0.0164 (6) | −0.0107 (7) |
F3 | 0.0407 (7) | 0.0431 (8) | 0.072 (1) | −0.0138 (6) | 0.0023 (6) | −0.0118 (7) |
S1—O1 | 1.4541 (13) | C5—C6 | 1.469 (2) |
S1—O2 | 1.4300 (16) | C6—C7 | 1.490 (2) |
S1—O3 | 1.4323 (15) | C7—C8 | 1.390 (3) |
S1—C14 | 1.819 (2) | C7—C12 | 1.392 (2) |
O6—N6 | 1.3757 (18) | C8—C9 | 1.396 (3) |
O6—H6 | 0.96 | C8—H81 | 1.00 |
N1—C2 | 1.486 (2) | C9—C10 | 1.388 (3) |
N1—C5 | 1.290 (2) | C9—H91 | 1.00 |
N1—C13 | 1.468 (2) | C10—C11 | 1.386 (3) |
N6—C6 | 1.290 (2) | C10—H101 | 1.00 |
C2—C3 | 1.522 (3) | C11—C12 | 1.395 (3) |
C2—H21 | 1.00 | C11—H111 | 1.00 |
C2—H22 | 1.00 | C12—H121 | 1.00 |
C3—C4 | 1.537 (2) | C13—H131 | 0.96 |
C3—H31 | 1.00 | C13—H132 | 0.94 |
C3—H32 | 1.00 | C13—H133 | 0.97 |
C4—C5 | 1.506 (2) | C14—F1 | 1.329 (3) |
C4—H41 | 1.00 | C14—F2 | 1.337 (3) |
C4—H42 | 1.00 | C14—F3 | 1.336 (2) |
O1—S1—O2 | 114.9 (1) | N6—C6—C7 | 124.66 (15) |
O1—S1—O3 | 113.62 (9) | C5—C6—C7 | 124.65 (15) |
O2—S1—O3 | 116.65 (12) | C6—C7—C8 | 118.43 (15) |
O1—S1—C14 | 101.80 (9) | C6—C7—C12 | 121.29 (16) |
O2—S1—C14 | 103.54 (12) | C8—C7—C12 | 120.26 (16) |
O3—S1—C14 | 103.7 (1) | C7—C8—C9 | 120.08 (17) |
N6—O6—H6 | 100 | C7—C8—H81 | 119 |
C2—N1—C5 | 113.00 (14) | C9—C8—H81 | 121 |
C2—N1—C13 | 117.72 (14) | C8—C9—C10 | 119.59 (18) |
C5—N1—C13 | 128.93 (15) | C8—C9—H91 | 120 |
O6—N6—C6 | 112.70 (14) | C10—C9—H91 | 120 |
N1—C2—C3 | 103.60 (14) | C9—C10—C11 | 120.36 (17) |
N1—C2—H21 | 111 | C9—C10—H101 | 120 |
C3—C2—H21 | 111 | C11—C10—H101 | 120 |
N1—C2—H22 | 111 | C10—C11—C12 | 120.29 (18) |
C3—C2—H22 | 111 | C10—C11—H111 | 120 |
H21—C2—H22 | 110 | C12—C11—H111 | 120 |
C2—C3—C4 | 104.22 (14) | C7—C12—C11 | 119.41 (18) |
C2—C3—H31 | 111 | C7—C12—H121 | 120 |
C4—C3—H31 | 110 | C11—C12—H121 | 120 |
C2—C3—H32 | 111 | N1—C13—H131 | 110 |
C4—C3—H32 | 111 | N1—C13—H132 | 103 |
H31—C3—H32 | 109 | H131—C13—H132 | 108 |
C3—C4—C5 | 103.19 (14) | N1—C13—H133 | 109 |
C3—C4—H41 | 111 | H131—C13—H133 | 113 |
C5—C4—H41 | 111 | H132—C13—H133 | 114 |
C3—C4—H42 | 111 | S1—C14—F1 | 111.06 (15) |
C5—C4—H42 | 111 | S1—C14—F2 | 110.85 (14) |
H41—C4—H42 | 109 | F1—C14—F2 | 107.60 (19) |
N1—C5—C4 | 111.17 (15) | S1—C14—F3 | 111.39 (15) |
N1—C5—C6 | 126.52 (16) | F1—C14—F3 | 107.96 (16) |
C4—C5—C6 | 122.29 (15) | F2—C14—F3 | 107.83 (18) |
N6—C6—C5 | 110.41 (15) | ||
C12—C7—C6—N6 | 72.0 (2) | N1—C5—C6—N6 | 170.0 (2) |
O6—N6—C6—C7 | −4.9 (2) |
Experimental details
Crystal data | |
Chemical formula | C12H15N2O+·CF3SO3− |
Mr | 352.33 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 120 |
a, b, c (Å) | 11.7643 (5), 8.2154 (4), 16.5207 (6) |
β (°) | 104.10 (2) |
V (Å3) | 1548.6 |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.26 |
Crystal size (mm) | 0.25 × 0.20 × 0.10 |
Data collection | |
Diffractometer | Nonius KappaCCD area-detector |
Absorption correction | – |
No. of measured, independent and observed [I > 3σ(I)] reflections | 11326, 3595, 2749 |
Rint | 0.036 |
(sin θ/λ)max (Å−1) | 0.661 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.054, 1.03 |
No. of reflections | 2749 |
No. of parameters | 209 |
No. of restraints | ? |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.67, −0.49 |
Computer programs: DENZO (Otwinowski & Minor, 1997) and COLLECT (Nonius, 1998), DENZO, SHELXS86 (Sheldrick, 1986), CRYSTALS (Watkin, Prout, Carruthers & Betteridge, 1996), CAMERON (Watkin, Prout & Pearce, 1996), CRYSTALS.
S1—O1 | 1.4541 (13) | C5—C6 | 1.469 (2) |
S1—O2 | 1.4300 (16) | C6—C7 | 1.490 (2) |
S1—O3 | 1.4323 (15) | C7—C8 | 1.390 (3) |
S1—C14 | 1.819 (2) | C7—C12 | 1.392 (2) |
O6—N6 | 1.3757 (18) | C8—C9 | 1.396 (3) |
N1—C2 | 1.486 (2) | C9—C10 | 1.388 (3) |
N1—C5 | 1.290 (2) | C10—C11 | 1.386 (3) |
N1—C13 | 1.468 (2) | C11—C12 | 1.395 (3) |
N6—C6 | 1.290 (2) | C14—F1 | 1.329 (3) |
C2—C3 | 1.522 (3) | C14—F2 | 1.337 (3) |
C3—C4 | 1.537 (2) | C14—F3 | 1.336 (2) |
C4—C5 | 1.506 (2) | ||
O1—S1—O2 | 114.9 (1) | N6—C6—C7 | 124.66 (15) |
O1—S1—O3 | 113.62 (9) | C5—C6—C7 | 124.65 (15) |
O2—S1—O3 | 116.65 (12) | C6—C7—C8 | 118.43 (15) |
O1—S1—C14 | 101.80 (9) | C6—C7—C12 | 121.29 (16) |
O2—S1—C14 | 103.54 (12) | C8—C7—C12 | 120.26 (16) |
O3—S1—C14 | 103.7 (1) | C7—C8—C9 | 120.08 (17) |
C2—N1—C5 | 113.00 (14) | C8—C9—C10 | 119.59 (18) |
C2—N1—C13 | 117.72 (14) | C9—C10—C11 | 120.36 (17) |
C5—N1—C13 | 128.93 (15) | C10—C11—C12 | 120.29 (18) |
O6—N6—C6 | 112.70 (14) | C7—C12—C11 | 119.41 (18) |
N1—C2—C3 | 103.60 (14) | S1—C14—F1 | 111.06 (15) |
C2—C3—C4 | 104.22 (14) | S1—C14—F2 | 110.85 (14) |
C3—C4—C5 | 103.19 (14) | F1—C14—F2 | 107.60 (19) |
N1—C5—C4 | 111.17 (15) | S1—C14—F3 | 111.39 (15) |
N1—C5—C6 | 126.52 (16) | F1—C14—F3 | 107.96 (16) |
C4—C5—C6 | 122.29 (15) | F2—C14—F3 | 107.83 (18) |
N6—C6—C5 | 110.41 (15) | ||
C12—C7—C6—N6 | 72.0 (2) | N1—C5—C6—N6 | 170.0 (2) |
O6—N6—C6—C7 | −4.9 (2) |
1-Heterosubstituted 2-nitroethylene derivatives undergo polyprotonations in trifluoromethanesulfonic acid that lead to loss of water and formation of hydroxynitrilium ions, or O-protonated nitrile oxides, which are fairly electrophilic (Coustard, 1995, 1996, 1999). In this medium, 1-methyl-2-nitromethylenepyrrolidine, (I), also undergoes this transformation, leading to the corresponding hydroxynitrilium ion (scheme), which reacts with benzene to afford a stable dication observable either by 1H or 13C NMR spectroscopy. Quenching with water affords the title compound, (II), which is stable in acidic or neutral aqueous solution. In basic solution, deprotonation of the OH oxime group leads to formation of a conjugated nitroso derivative which dimerizes readily to give a mixture of isomers. In compound (II), the presence of a trifluoromethanesulfonate anion, phenyl ring and oxime (or hydroxyimino) group was expected from 1H and 13NMR data (Coustard, 1999). However, the configuration of the oxime is important from a mechanistic point of view and needed to be confirmed. The unusual behavior of this salt also prompted us to undertake the present X-ray crystallographic analysis. \sch
Most of the cation is nearly planar (Fig. 1), but the aromatic ring lies out of the plane, with a C12—C7—C6—N6 torsion angle of 72.2 (2)°. The maximum deviation of the atoms defining the least-squares mean plane through O6, N6, C6, C5, N1 and C13 is observed for C6 and N6, with respective values of -0.116 Å and 0.098 Å. The atoms of the five-membered ring C5/N1/C2/C3/C4 are also approximately coplanar, with maximum deviations from the least-squares mean plane of -0.114 Å for C4 and 0.135 Å for C3.
The O6—N6—C6—C7 torsion angle of -5.0 (2)° indicates a E-configured oxime group; the adjacent C6—C5 bond adopts an s-trans conformation [N1—C5—C6—N6 - 170.2 (3)°]. Such an oxime configuration has also been reported for products resulting from hydroxynitrilium ion trapping (Cousson & Coustard, 1998, 1999).
Conjugation of the N6—C6—C5—N1 double-bond system allows delocalization of the positive charge and accounts for the lengthening of both the C6—C5 single bond [1.469 (2) Å, compared with the expected value for a single bond in a dienic conjugated system of 1.455 (11) Å; Allen et al., 1987] and the C6—N6 double bond [1.290 (2) Å, compared with the expected value in an unconjugated oxime of 1.280 (13) Å; Allen et al., 1987].
The relatively short distance of 2.651 (2) Å between atom O1 of the trifluoromethanesulfonate anion and the oxime oxygen O6 implies a hydrogen bond involving H6 [H6···O1 1.69 and O6···O1 2.651 (2) Å, and O6—H6···O1 177°].
The O3i···N2 and O3i···C5 distances [symmetry code: (i) 1 - x, 1/2 + y, 1/2 - z] of 2.855 (2) and 2.873 (2) Å, respectively, are shorter than expected, the sum of the relevant van der Waals sums (Bondi, 1964) being 3.07 and 3.22 Å. A search of the Cambridge Structural Database (Allen & Kennard, 1993; October 2000 Version) for the fragment F3C—SO3···N═C indicates that about half the 25 or so occurrences have generally similar distances to those above. In the present case, the short distances may result from the formation of some kind of π-adduct between the π-electrons of the C═N double bond and the O3 atom of the trifluoromethanesulfonate anion. In agreement with this hypothesis is the fact that the O3i atom is almost equidistant from N2 and C5, and the dihedral angle between the N2/O3i/C5 and N1/C2/C3/C4/C5 planes is 97.54°, indicating that they are almost perpendicular.
In conclusion, compound (II) may be considered as resulting from O-protonation of the nitroso group of α-(N-methyl-1-azacyclopent-1-en-2-yl)-α-nitrosotoluene by trifluoromethanesulfonic acid. The oxime group thus formed is E-configured, in agreement with an electrophilic aromatic substitution mechanism involving the C ≡N of the transient hydroxynitrilium ion (Hegarty et al., 1980; Nguyen et al., 1991).