Ring opening of pyridines: the pseudo-cis and pseudo-trans isomers of tetra-n-butyl­ammonium 4-nitro-5-oxo-2-pentenenitrilate

The reaction of 2-chloro-5-nitro­pyridine with two equivalents of base produces the title carbanion as an inter­mediate in a ring-opening/ring-closing reaction. The crystal structures of the tetra-n-butyl­ammonium salts of the inter­mediates, C₁₆H₃₆N⁺·C₅H₃N₂O₃^-, revealed that pseudo-cis and pseudo-trans isomers are possible. One crystal structure displayed a mixture of the two isomers with approximately 90% pseudo-cis geometry and confirms the structure predicted by the S_N(ANRORC) mechanism. The pseudo-cis inter­mediate undergoes a slow isomerization over a period of months to the pseudo-trans isomer, which does not have the appropriate geometry for the subsequent ring-closing reaction. The structure of the pure pseudo-trans isomer is also reported. In both isomers, the negative charge is highly delocalized, but relatively small differences in C-C bond distances indicate a system of conjugated double bonds with the nitro group bearing the negative charge. The packing of the two unit cells is very similar and largely determined by the inter­actions between the planar carbanion and the bulky tetra­hedral cation.

S1. Comment

During the 1980 s, Reinheimer et al. (1980, 1984) investigated the reaction of 2-chloro-5-nitropyridine with an excess of sodium hydroxide in dimethyl sulfoxide/water solutions. Using visible spectroscopy, in addition to ¹H and ¹³C NMR, they were able to show that a relatively stable intermediate was formed. They proposed that the pseudo-cis isomer, (I), would enable the intermediate to undergo the second part of the reaction sequence, namely ring closure. This reaction sequence was named by van???? or Van der Plas (1978) as the S_N(ANRORC) process (addition of the nucleophile, ring opening and ring closure) [scheme 1].

If only two equivalents of hydroxide were used, the intermediate formed from 2-chloro-5-nitropyridine was reasonably stable in the reaction medium. However, over a period of months we observed that the intermediate either slowly isomerized or decomposed to formate. We followed these transformations using ¹H NMR spectroscopy. In contrast, 2-chloro-3-nitropyridine in the presence of two equivalents of sodium hydroxide forms a pseudo-cis intermediate that, during work-up, readily isomerizes to a pseudo-trans intermediate, (III). The structures of both of the intermediates from 2-chloro-3-nitropyridine were determined using NMR and X-ray crystallography (Haynes & Pett, 2007).

The dramatic difference between the isomerization rates of intermediates from two very similar starting materials prompted us to continue our investigations with the intermediates from 2-chloro-5-nitropyridine. In order to verify our assumptions concerning the structures of the two intermediates, we conducted crystallization experiments with samples containing predominantly one isomer or the other, as indicated by the ¹H NMR spectra.

One sample (as the tetra-n-butylammonium salt) gave disordered monoclinic crystals that were found to consist of a mixture of mainly the pseudo-cis isomer, (I), with a small but significant amount of the pseudo-trans isomer, (II) (Fig. 1a). Several crystals from different crystallization attempts were analyzed, resulting in all cases in similar pseudo-cis to pseudo-trans ratios. For the data set used here, the ratio refined to 91.7 (3) to 8.3 (3)% in favor of the pseudo-cis isomer [scheme 2].

The X-ray crystallographic study using the crystals isolated from a sample that was stable in solution for eight months (again as the tetra-n-butylammonium salt) showed that these crystals were made up only of carbanions in the pseudo-trans geometry, (II) (Fig. 1b). This pure isomer also crystallized with the same monoclinic space group, P2₁/n, and with an almost identical unit cell volume. The two monoclinic cells have comparable unit cell axes and β angles, but the positions of the glide planes differ. Thus, the designation of the unit cell axes is different; a, b and c in the (I/II) mixed crystal are converted into c, a and b in the crystal of pure (II).

The type of packing in the two different cells is very similar (Fig. 2), with layers of the planar carbanions alternating with the tetra-n-butylammonium cations. The orientation of the ions and their orientation with respect to each other is the same in both cells; only the separation between the ions varies slightly between the two structures. The largest difference is observed for the closest distance of the O atoms of adjacent nitro groups, which is 5.6827 (18) Å in (II) and 5.821 (3) Å in (I/II) [the symmetry operator relating the adjacent molecules is (-x + 1, -y + 1, -z + 1)].

Within the layers, the carbanions are arranged in loosely connected dimers. In both pseudo-trans (II) and disordered (I/II), the nitrile groups are arranged in such a way that the N atom interacts with atom H20 of the neighboring anion to form a very weak intermolecular hydrogen bond (Fig. 3). For the pseudo-cis isomer, (I), the interaction is slightly weaker, with a C20···N3 distance of 3.519 (4) Å. For the pseudo-trans geometry, in both types of crystals, the hydrogen bond is slightly strengthened, and the C···N distances are 3.39 (4) and 3.348 (2) Å in the structures of (I/II) and (II), respectively (see Tables 1 and 2 for the hydrogen-bonding parameters.) However, even this slightly shorter hydrogen bond is not unusually strong. A search of the Cambridge Structural Database for nitrile dimers connected via similar hydrogen bonds revealed 58 compounds with both hydrogen bonds equal to or shorter than 2.8 Å (Version ?; Allen, 2002).

In the pseudo-trans geometry, atom H20 also forms an intramolecular hydrogen bond with the aldehyde atom O3, thus possibly stabilizing the pseudo-trans geometry slightly as compared with the pseudo-cis isomer (Tables 1 and 2, and Fig. 3). Nevertheless, all the hydrogen-bonding interactions seem to be rather weak and are probably not a significant directing force towards the overall packing mode. It seems more likely that the packing is determined by the electrostatic interactions between the alternating layers of carbanions and tetra-n-butylammonium cations.

The C—C bonds in carbanions (I), (II) and (III) are shorter than standard single bonds, indicating considerable delocalization of the negative charge over each anion (Table 3). However, the C19—C20 distances in all three anions are significantly shorter than the other C—C bonds and almost as short as a standard double bond. Also, the C18—N2 distances in the nitro group are shorter than a single C—N bond, while the N2—O1 and N2—O2 distances are longer than an N═O double bond. The bond distances in these three carbanions exhibit a conjugated system of double bonds, revealing that the electron distribution is clearly directed by the nitro group, the most powerful electron withdrawing substituent in the anions. Thus, the structures coincide with what we would expect from the electronegativities of the atoms.

Related literature

For related literature, see: Allen (2002); Haynes & Pett (2007); Reinheimer et al. (1980, 1984); Van der Plas (1978).

S2. Experimental

The original samples of the intermediates as their sodium salts were prepared by following the directions of Reinheimer et al. (1980, 1984). Because of what appeared to be oxidation of the intermediate, one reaction of 2-chloro-5-nitropyridine with sodium hydroxide was carried out in a nitrogen atmosphere. Interestingly, the intermediate formed was (II). That reaction provided the sample of (II) that was used for the crystal structure determination. To produce crystalline material suitable for the vapor diffusion process, tetra-n-butylammonium bromide was added to an aqueous or water/dimethyl sulfoxide solution of the sodium salt. After freeze-drying to remove solvent(s), the tetra-n-butylammonium salt of the intermediate was separated from inorganic salts by extraction with acetone. Evaporation of the acetone gave a solid suitable for crystallization. ¹H NMR: pseudo-cis (I) (D₂O/D₆DMSO): δ 9.75, 6.97, 5.23; pseudo-trans (II) (D₂O/D₆DMSO): δ 9.80, 7.37, 6.20. Suitable crystals of the tetra-n-butylammonium salts of the mixture of both intermediates were grown by vapor diffusion of hexanes into dichloromethane solutions of the intermediates.

S3. Refinement

The crystals grown from the original sample exhibit a disorder of the major pseudo-cis intermediate, (I), with a minor presence of the pseudo-trans isomer, (II). The data of several crystals were collected (only the best data set is reported here) and all structures exhibited similar pseudo-cis to pseudo-trans ratios [0.917 (3) to 0.083 (3) for the reported example]. The bond distances within the minor component were restrained to be the same as those of the major component (within a standard deviation of 0.02 Å), and the anisotropic displacement parameters of the minor component atoms were set to be the same as those of the major isomer. Atom C19, which by itself is not disordered, was included in the disorder but the major and minor component atoms were set to have the same coordinates and anisotropic displacement parameters, thus allowing us to add H19 and H19B in calculated positions rather than refining their positions using constraints. In both structures, all H atoms were placed in calculated positions with C—H distances of 0.98, 0.99 and 0.95 Å for methyl, methylene and alkene H atoms, respectively, and were refined with an isotropic displacement parameter of 1.5 (methyl) or 1.2 (methylene, alkene) times U_eq of the adjacent C atom. Methyl H atoms were allowed to rotate to best fit the experimental electron density.

Computing details

For both compounds, data collection: SMART (Bruker, 1997); cell refinement: SAINT-Plus (Bruker, 2003); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. Displacement ellipsoid diagrams at the 50% probability level of the molecular structures of (a) the pseudo-cis/pseudo-trans mixture, (I/II), showing both components, viz. pseudo-cis intermediate (I) and the pseudo-trans intermediate (II) (B labels), in the disordered structure, and (b) the pure pseudo-trans intermediate, (II).
	Fig. 2. A packing view of the crystal structures with 50% probability displacement ellipsoids, showing the layered nature of the two structures: (a) the disordered structure of the pseudo-cis/pseudo-trans mixture, (I/II), showing both components, and (b) the pure pseudo-trans intermediate, (II).
	Fig. 3. A packing view of the crystal structures: (a) the disordered structure of the mixture showing both the main pseudo-cis intermediate, (I), and the minor pseudo-trans intermediate, (II), and (b) the pure pseudo-trans intermediate, (II). Displacement ellipsoids are drawn at the 50% probability level.

(I_II) tetra-n-butylammonium 4-nitro-5-oxo-2-pentenenitrilate

Crystal data

C16H36N^+·C5H3N2O3^−	F(000) = 840
Mr = 381.55	Dx = 1.158 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 12.2793 (16) Å	Cell parameters from 6428 reflections
b = 9.7588 (12) Å	θ = 2.7–30.6°
c = 18.422 (2) Å	µ = 0.08 mm^−1
β = 97.444 (2)°	T = 100 K
V = 2189.0 (5) Å^3	Block, colourless
Z = 4	0.6 × 0.4 × 0.25 mm

Data collection

Bruker SMART APEX CCD diffractometer	5406 independent reflections
Radiation source: fine-focus sealed tube	4323 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.047
ω scans	θmax = 28.3°, θmin = 1.9°
Absorption correction: multi-scan (SADABS in SAINT-Plus; Bruker, 2003)	h = −16→16
Tmin = 0.848, Tmax = 0.981	k = −13→13
21198 measured reflections	l = −24→23

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)] = 0.069	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.175	H-atom parameters constrained
S = 1.13	w = 1/[σ^2(Fo^2) + (0.0476P)^2 + 2.9417P] where P = (Fo^2 + 2Fc^2)/3
5406 reflections	(Δ/σ)max < 0.001
258 parameters	Δρmax = 0.46 e Å^−3
3 restraints	Δρmin = −0.22 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	Occ. (<1)
C1	0.66758 (17)	0.4305 (2)	0.51970 (11)	0.0177 (4)
H1A	0.6227	0.4714	0.5550	0.021*
H1B	0.6172	0.4070	0.4750	0.021*
C2	0.71834 (17)	0.2987 (2)	0.55253 (12)	0.0198 (4)
H2A	0.7618	0.3179	0.6006	0.024*
H2B	0.7680	0.2591	0.5198	0.024*
C3	0.62603 (18)	0.1977 (2)	0.56196 (12)	0.0225 (4)
H3A	0.5743	0.2410	0.5920	0.027*
H3B	0.5851	0.1767	0.5133	0.027*
C4	0.6689 (2)	0.0647 (2)	0.59833 (13)	0.0277 (5)
H4B	0.7051	0.0842	0.6478	0.042*
H4C	0.7216	0.0226	0.5695	0.042*
H4A	0.6074	0.0017	0.6011	0.042*
C5	0.82398 (17)	0.5857 (2)	0.56707 (11)	0.0180 (4)
H5A	0.8645	0.5051	0.5892	0.022*
H5B	0.8786	0.6499	0.5511	0.022*
C6	0.76742 (18)	0.6557 (2)	0.62561 (12)	0.0220 (4)
H6A	0.7154	0.5910	0.6442	0.026*
H6B	0.7250	0.7354	0.6041	0.026*
C7	0.85114 (18)	0.7034 (2)	0.68867 (12)	0.0244 (5)
H7B	0.9104	0.7548	0.6690	0.029*
H7A	0.8845	0.6226	0.7154	0.029*
C8	0.7982 (2)	0.7949 (2)	0.74164 (12)	0.0259 (5)
H8B	0.7385	0.7449	0.7604	0.039*
H8C	0.7687	0.8775	0.7160	0.039*
H8A	0.8534	0.8210	0.7826	0.039*
C9	0.67666 (17)	0.6553 (2)	0.46563 (11)	0.0174 (4)
H9A	0.6309	0.6200	0.4214	0.021*
H9B	0.6263	0.6836	0.5007	0.021*
C10	0.73768 (17)	0.7814 (2)	0.44421 (12)	0.0194 (4)
H10A	0.7813	0.7581	0.4043	0.023*
H10B	0.7887	0.8141	0.4867	0.023*
C11	0.65515 (18)	0.8942 (2)	0.41870 (12)	0.0205 (4)
H11A	0.6056	0.8616	0.3755	0.025*
H11B	0.6098	0.9141	0.4581	0.025*
C12	0.7123 (2)	1.0254 (2)	0.39888 (13)	0.0253 (5)
H12B	0.7546	1.0069	0.3584	0.038*
H12C	0.7618	1.0575	0.4415	0.038*
H12A	0.6570	1.0959	0.3840	0.038*
C13	0.82321 (17)	0.4830 (2)	0.44702 (11)	0.0185 (4)
H13A	0.8703	0.5588	0.4337	0.022*
H13B	0.8720	0.4131	0.4731	0.022*
C14	0.76606 (18)	0.4194 (2)	0.37688 (11)	0.0201 (4)
H14A	0.7269	0.4912	0.3458	0.024*
H14B	0.7116	0.3509	0.3887	0.024*
C15	0.85185 (19)	0.3506 (2)	0.33596 (13)	0.0257 (5)
H15A	0.9051	0.4205	0.3238	0.031*
H15B	0.8926	0.2819	0.3684	0.031*
C16	0.8011 (2)	0.2806 (2)	0.26595 (12)	0.0278 (5)
H16B	0.7615	0.3484	0.2333	0.042*
H16C	0.7499	0.2095	0.2778	0.042*
H16A	0.8592	0.2388	0.2416	0.042*
N1	0.74801 (14)	0.53846 (17)	0.49969 (9)	0.0167 (3)
C17	0.50529 (19)	0.8085 (2)	0.77333 (13)	0.0268 (5)
H17	0.5074	0.8763	0.7366	0.032*
C18	0.50457 (17)	0.6675 (2)	0.75225 (12)	0.0212 (4)
N2	0.50543 (15)	0.6390 (2)	0.67769 (10)	0.0243 (4)
O1	0.50716 (13)	0.51655 (17)	0.65574 (9)	0.0273 (4)
O2	0.50433 (15)	0.7341 (2)	0.63188 (10)	0.0343 (4)
O3	0.50335 (17)	0.84590 (19)	0.83661 (10)	0.0389 (5)
C19	0.50129 (18)	0.5527 (2)	0.79985 (13)	0.0237 (5)	0.917 (3)
H19	0.4973	0.4675	0.7746	0.028*	0.917 (3)
C20	0.5026 (5)	0.5383 (4)	0.87301 (15)	0.0262 (7)	0.917 (3)
H20	0.4954	0.4462	0.8884	0.031*	0.917 (3)
C21	0.51271 (19)	0.6356 (3)	0.93144 (14)	0.0240 (5)	0.917 (3)
N3	0.51927 (18)	0.6968 (2)	0.98476 (12)	0.0290 (5)	0.917 (3)
C19B	0.50129 (18)	0.5527 (2)	0.79985 (13)	0.0237 (5)	0.083 (3)
H19B	0.4882	0.4648	0.7783	0.028*	0.083 (3)
C20B	0.516 (7)	0.561 (4)	0.8742 (10)	0.0262 (7)	0.083 (3)
H20B	0.5323	0.6467	0.8975	0.031*	0.083 (3)
C21B	0.506 (2)	0.440 (2)	0.9173 (14)	0.0240 (5)	0.083 (3)
N3B	0.494 (2)	0.341 (2)	0.9503 (13)	0.0290 (5)	0.083 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0183 (10)	0.0152 (9)	0.0199 (9)	−0.0024 (8)	0.0039 (7)	0.0002 (7)
C2	0.0213 (10)	0.0146 (9)	0.0235 (10)	−0.0009 (8)	0.0034 (8)	0.0014 (8)
C3	0.0258 (11)	0.0170 (10)	0.0250 (11)	−0.0033 (8)	0.0047 (8)	0.0021 (8)
C4	0.0367 (13)	0.0186 (11)	0.0282 (12)	−0.0045 (9)	0.0054 (9)	0.0032 (9)
C5	0.0175 (9)	0.0147 (9)	0.0209 (10)	−0.0005 (7)	−0.0001 (7)	0.0001 (8)
C6	0.0209 (10)	0.0216 (11)	0.0235 (10)	0.0001 (8)	0.0026 (8)	−0.0031 (8)
C7	0.0229 (11)	0.0255 (11)	0.0247 (11)	−0.0014 (9)	0.0025 (8)	−0.0023 (9)
C8	0.0302 (12)	0.0250 (11)	0.0223 (11)	−0.0007 (9)	0.0030 (9)	−0.0037 (9)
C9	0.0182 (9)	0.0118 (9)	0.0222 (10)	0.0013 (7)	0.0024 (7)	0.0015 (7)
C10	0.0202 (10)	0.0148 (9)	0.0234 (10)	0.0004 (8)	0.0039 (8)	0.0019 (8)
C11	0.0226 (10)	0.0154 (10)	0.0236 (10)	0.0024 (8)	0.0038 (8)	0.0010 (8)
C12	0.0311 (12)	0.0154 (10)	0.0306 (12)	0.0011 (9)	0.0081 (9)	0.0023 (9)
C13	0.0184 (10)	0.0150 (9)	0.0232 (10)	0.0023 (8)	0.0070 (8)	0.0007 (8)
C14	0.0223 (10)	0.0171 (10)	0.0215 (10)	0.0021 (8)	0.0054 (8)	0.0000 (8)
C15	0.0243 (11)	0.0230 (11)	0.0314 (12)	0.0033 (9)	0.0102 (9)	−0.0037 (9)
C16	0.0379 (13)	0.0243 (11)	0.0224 (11)	0.0048 (10)	0.0086 (9)	0.0005 (9)
N1	0.0171 (8)	0.0131 (8)	0.0202 (8)	0.0003 (6)	0.0037 (6)	0.0001 (6)
C17	0.0276 (12)	0.0184 (11)	0.0328 (12)	0.0019 (9)	−0.0018 (9)	−0.0011 (9)
C18	0.0182 (10)	0.0201 (10)	0.0251 (10)	−0.0005 (8)	0.0022 (8)	−0.0035 (8)
N2	0.0187 (9)	0.0264 (10)	0.0273 (10)	0.0022 (8)	0.0018 (7)	−0.0007 (8)
O1	0.0262 (8)	0.0287 (9)	0.0269 (8)	0.0030 (7)	0.0032 (6)	−0.0098 (7)
O2	0.0344 (10)	0.0357 (10)	0.0325 (9)	0.0041 (8)	0.0038 (7)	0.0058 (8)
O3	0.0561 (13)	0.0232 (9)	0.0356 (10)	0.0041 (8)	−0.0006 (9)	−0.0088 (8)
C19	0.0233 (11)	0.0177 (10)	0.0305 (11)	−0.0010 (8)	0.0052 (9)	−0.0057 (9)
C20	0.029 (2)	0.0205 (16)	0.0301 (12)	−0.0035 (14)	0.0070 (10)	−0.0040 (10)
C21	0.0182 (11)	0.0259 (12)	0.0287 (13)	−0.0014 (9)	0.0053 (9)	0.0002 (10)
N3	0.0256 (11)	0.0319 (12)	0.0298 (12)	−0.0029 (9)	0.0043 (9)	−0.0071 (9)
C19B	0.0233 (11)	0.0177 (10)	0.0305 (11)	−0.0010 (8)	0.0052 (9)	−0.0057 (9)
C20B	0.029 (2)	0.0205 (16)	0.0301 (12)	−0.0035 (14)	0.0070 (10)	−0.0040 (10)
C21B	0.0182 (11)	0.0259 (12)	0.0287 (13)	−0.0014 (9)	0.0053 (9)	0.0002 (10)
N3B	0.0256 (11)	0.0319 (12)	0.0298 (12)	−0.0029 (9)	0.0043 (9)	−0.0071 (9)

Geometric parameters (Å, º)

C1—C2	1.520 (3)	C11—H11A	0.9900
C1—N1	1.522 (3)	C11—H11B	0.9900
C1—H1A	0.9900	C12—H12B	0.9800
C1—H1B	0.9900	C12—H12C	0.9800
C2—C3	1.529 (3)	C12—H12A	0.9800
C2—H2A	0.9900	C13—C14	1.520 (3)
C2—H2B	0.9900	C13—N1	1.523 (3)
C3—C4	1.523 (3)	C13—H13A	0.9900
C3—H3A	0.9900	C13—H13B	0.9900
C3—H3B	0.9900	C14—C15	1.528 (3)
C4—H4B	0.9800	C14—H14A	0.9900
C4—H4C	0.9800	C14—H14B	0.9900
C4—H4A	0.9800	C15—C16	1.520 (3)
C5—C6	1.518 (3)	C15—H15A	0.9900
C5—N1	1.524 (3)	C15—H15B	0.9900
C5—H5A	0.9900	C16—H16B	0.9800
C5—H5B	0.9900	C16—H16C	0.9800
C6—C7	1.521 (3)	C16—H16A	0.9800
C6—H6A	0.9900	C17—O3	1.225 (3)
C6—H6B	0.9900	C17—C18	1.429 (3)
C7—C8	1.529 (3)	C17—H17	0.9500
C7—H7B	0.9900	C18—N2	1.403 (3)
C7—H7A	0.9900	C18—C19	1.427 (3)
C8—H8B	0.9800	N2—O2	1.253 (3)
C8—H8C	0.9800	N2—O1	1.263 (3)
C8—H8A	0.9800	C19—C20	1.353 (4)
C9—C10	1.520 (3)	C19—H19	0.9500
C9—N1	1.522 (3)	C20—C21	1.428 (4)
C9—H9A	0.9900	C20—H20	0.9500
C9—H9B	0.9900	C21—N3	1.143 (3)
C10—C11	1.528 (3)	C20B—C21B	1.44 (2)
C10—H10A	0.9900	C20B—H20B	0.9500
C10—H10B	0.9900	C21B—N3B	1.163 (18)
C11—C12	1.527 (3)
C2—C1—N1	115.89 (17)	C12—C11—C10	111.75 (18)
C2—C1—H1A	108.3	C12—C11—H11A	109.3
N1—C1—H1A	108.3	C10—C11—H11A	109.3
C2—C1—H1B	108.3	C12—C11—H11B	109.3
N1—C1—H1B	108.3	C10—C11—H11B	109.3
H1A—C1—H1B	107.4	H11A—C11—H11B	107.9
C1—C2—C3	108.59 (17)	C11—C12—H12B	109.5
C1—C2—H2A	110.0	C11—C12—H12C	109.5
C3—C2—H2A	110.0	H12B—C12—H12C	109.5
C1—C2—H2B	110.0	C11—C12—H12A	109.5
C3—C2—H2B	110.0	H12B—C12—H12A	109.5
H2A—C2—H2B	108.4	H12C—C12—H12A	109.5
C4—C3—C2	112.38 (19)	C14—C13—N1	115.80 (17)
C4—C3—H3A	109.1	C14—C13—H13A	108.3
C2—C3—H3A	109.1	N1—C13—H13A	108.3
C4—C3—H3B	109.1	C14—C13—H13B	108.3
C2—C3—H3B	109.1	N1—C13—H13B	108.3
H3A—C3—H3B	107.9	H13A—C13—H13B	107.4
C3—C4—H4B	109.5	C13—C14—C15	109.07 (18)
C3—C4—H4C	109.5	C13—C14—H14A	109.9
H4B—C4—H4C	109.5	C15—C14—H14A	109.9
C3—C4—H4A	109.5	C13—C14—H14B	109.9
H4B—C4—H4A	109.5	C15—C14—H14B	109.9
H4C—C4—H4A	109.5	H14A—C14—H14B	108.3
C6—C5—N1	115.24 (17)	C16—C15—C14	112.53 (19)
C6—C5—H5A	108.5	C16—C15—H15A	109.1
N1—C5—H5A	108.5	C14—C15—H15A	109.1
C6—C5—H5B	108.5	C16—C15—H15B	109.1
N1—C5—H5B	108.5	C14—C15—H15B	109.1
H5A—C5—H5B	107.5	H15A—C15—H15B	107.8
C5—C6—C7	110.73 (18)	C15—C16—H16B	109.5
C5—C6—H6A	109.5	C15—C16—H16C	109.5
C7—C6—H6A	109.5	H16B—C16—H16C	109.5
C5—C6—H6B	109.5	C15—C16—H16A	109.5
C7—C6—H6B	109.5	H16B—C16—H16A	109.5
H6A—C6—H6B	108.1	H16C—C16—H16A	109.5
C6—C7—C8	111.41 (19)	C1—N1—C9	105.15 (15)
C6—C7—H7B	109.3	C1—N1—C13	111.98 (15)
C8—C7—H7B	109.3	C9—N1—C13	111.56 (15)
C6—C7—H7A	109.3	C1—N1—C5	111.12 (15)
C8—C7—H7A	109.3	C9—N1—C5	111.58 (15)
H7B—C7—H7A	108.0	C13—N1—C5	105.59 (15)
C7—C8—H8B	109.5	O3—C17—C18	123.1 (2)
C7—C8—H8C	109.5	O3—C17—H17	118.5
H8B—C8—H8C	109.5	C18—C17—H17	118.5
C7—C8—H8A	109.5	N2—C18—C19	116.78 (19)
H8B—C8—H8A	109.5	N2—C18—C17	117.1 (2)
H8C—C8—H8A	109.5	C19—C18—C17	126.1 (2)
C10—C9—N1	115.90 (17)	O2—N2—O1	118.96 (19)
C10—C9—H9A	108.3	O2—N2—C18	120.8 (2)
N1—C9—H9A	108.3	O1—N2—C18	120.24 (19)
C10—C9—H9B	108.3	C20—C19—C18	134.1 (2)
N1—C9—H9B	108.3	C20—C19—H19	113.0
H9A—C9—H9B	107.4	C18—C19—H19	113.0
C9—C10—C11	109.49 (17)	C19—C20—C21	132.1 (3)
C9—C10—H10A	109.8	C19—C20—H20	113.9
C11—C10—H10A	109.8	C21—C20—H20	113.9
C9—C10—H10B	109.8	N3—C21—C20	169.7 (3)
C11—C10—H10B	109.8	C21B—C20B—H20B	120.0
H10A—C10—H10B	108.2	N3B—C21B—C20B	177 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C20—H20···N3^i	0.95	2.75	3.519 (4)	139
C20B—H20B···N3B^i	0.95	2.87	3.39 (4)	116
C20B—H20B···O3	0.95	2.25	2.86 (4)	122

Symmetry code: (i) −x+1, −y+1, −z+2.

(II) tetra-n-butylammonium 4-nitro-5-oxo-2-pentenenitrilate

Crystal data

C16H36N^+·C5H3N2O3^−	F(000) = 840
Mr = 381.55	Dx = 1.157 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 9.7894 (9) Å	Cell parameters from 7740 reflections
b = 18.3872 (16) Å	θ = 2.5–30.5°
c = 12.2327 (11) Å	µ = 0.08 mm^−1
β = 95.894 (2)°	T = 100 K
V = 2190.2 (3) Å^3	Plate, yellow
Z = 4	0.73 × 0.59 × 0.10 mm

Data collection

Bruker SMART APEX CCD diffractometer	5402 independent reflections
Radiation source: fine-focus sealed tube	4809 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.033
ω scans	θmax = 28.3°, θmin = 2.0°
Absorption correction: multi-scan (SADABS in SAINT-Plus; Bruker, 2003)	h = −12→12
Tmin = 0.792, Tmax = 0.992	k = −24→24
18699 measured reflections	l = −16→16

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)] = 0.058	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.136	H-atom parameters constrained
S = 1.19	w = 1/[σ^2(Fo^2) + (0.046P)^2 + 1.24P] where P = (Fo^2 + 2Fc^2)/3
5402 reflections	(Δ/σ)max < 0.001
248 parameters	Δρmax = 0.40 e Å^−3
0 restraints	Δρmin = −0.18 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
C1	0.63204 (14)	0.54280 (8)	0.32202 (11)	0.0164 (3)
H1A	0.6031	0.5820	0.3702	0.020*
H1B	0.6666	0.5020	0.3700	0.020*
C2	0.74961 (15)	0.57108 (8)	0.26236 (12)	0.0183 (3)
H2A	0.7195	0.6144	0.2183	0.022*
H2B	0.7786	0.5333	0.2119	0.022*
C3	0.87024 (15)	0.59110 (8)	0.34724 (12)	0.0189 (3)
H3A	0.8392	0.6276	0.3988	0.023*
H3B	0.9001	0.5473	0.3902	0.023*
C4	0.99152 (16)	0.62164 (9)	0.29370 (14)	0.0248 (3)
H4A	1.0225	0.5857	0.2425	0.037*
H4B	1.0667	0.6326	0.3505	0.037*
H4C	0.9635	0.6662	0.2536	0.037*
C5	0.44491 (15)	0.57737 (8)	0.17477 (12)	0.0169 (3)
H5A	0.5166	0.5953	0.1300	0.020*
H5B	0.3698	0.5568	0.1237	0.020*
C6	0.38857 (15)	0.64184 (8)	0.23411 (12)	0.0187 (3)
H6A	0.4632	0.6642	0.2837	0.022*
H6B	0.3166	0.6249	0.2794	0.022*
C7	0.32799 (17)	0.69845 (8)	0.15138 (12)	0.0216 (3)
H7A	0.4032	0.7213	0.1153	0.026*
H7B	0.2659	0.6739	0.0939	0.026*
C8	0.24848 (16)	0.75733 (8)	0.20554 (13)	0.0227 (3)
H8A	0.1708	0.7353	0.2378	0.034*
H8B	0.2143	0.7933	0.1503	0.034*
H8C	0.3092	0.7813	0.2633	0.034*
C9	0.40544 (14)	0.49097 (8)	0.32781 (11)	0.0162 (3)
H9A	0.4496	0.4514	0.3736	0.019*
H9B	0.3888	0.5318	0.3776	0.019*
C10	0.26728 (15)	0.46365 (8)	0.27566 (12)	0.0187 (3)
H10A	0.2796	0.4184	0.2338	0.022*
H10B	0.2239	0.5006	0.2244	0.022*
C11	0.17640 (16)	0.44895 (8)	0.36777 (13)	0.0209 (3)
H11A	0.2244	0.4147	0.4211	0.025*
H11B	0.1625	0.4950	0.4070	0.025*
C12	0.03667 (16)	0.41727 (9)	0.32632 (15)	0.0262 (3)
H12A	−0.0108	0.4505	0.2724	0.039*
H12B	−0.0183	0.4109	0.3882	0.039*
H12C	0.0493	0.3700	0.2916	0.039*
C13	0.54293 (15)	0.45516 (8)	0.17377 (12)	0.0173 (3)
H13A	0.4571	0.4361	0.1341	0.021*
H13B	0.5991	0.4755	0.1183	0.021*
C14	0.62082 (16)	0.39207 (8)	0.23095 (12)	0.0212 (3)
H14A	0.5679	0.3725	0.2891	0.025*
H14B	0.7104	0.4095	0.2662	0.025*
C15	0.64426 (17)	0.33200 (8)	0.14898 (13)	0.0226 (3)
H15A	0.5575	0.3049	0.1308	0.027*
H15B	0.6704	0.3542	0.0804	0.027*
C16	0.75587 (17)	0.27925 (9)	0.19360 (15)	0.0268 (3)
H16A	0.8427	0.3055	0.2095	0.040*
H16B	0.7668	0.2413	0.1389	0.040*
H16C	0.7301	0.2569	0.2612	0.040*
N1	0.50602 (12)	0.51662 (6)	0.24910 (9)	0.0153 (2)
C17	0.20257 (17)	0.77034 (9)	0.50905 (13)	0.0254 (3)
H17	0.1375	0.7324	0.5134	0.030*
C18	0.34253 (16)	0.75045 (8)	0.50268 (12)	0.0203 (3)
C19	0.45254 (16)	0.80048 (8)	0.49434 (12)	0.0202 (3)
H19	0.5414	0.7803	0.4912	0.024*
N2	0.37436 (14)	0.67619 (7)	0.50370 (10)	0.0214 (3)
O1	0.49752 (12)	0.65604 (6)	0.50463 (9)	0.0251 (3)
O2	0.28071 (13)	0.62929 (6)	0.50371 (10)	0.0289 (3)
O3	0.16086 (12)	0.83358 (7)	0.50927 (11)	0.0317 (3)
C20	0.44254 (16)	0.87390 (8)	0.49049 (13)	0.0225 (3)
H20	0.3557	0.8965	0.4936	0.027*
C21	0.56115 (17)	0.91752 (9)	0.48180 (13)	0.0244 (3)
N3	0.65593 (16)	0.95393 (8)	0.47543 (13)	0.0312 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0139 (6)	0.0180 (7)	0.0169 (6)	−0.0007 (5)	−0.0006 (5)	−0.0018 (5)
C2	0.0161 (7)	0.0200 (7)	0.0189 (7)	−0.0029 (5)	0.0015 (5)	0.0007 (5)
C3	0.0158 (7)	0.0202 (7)	0.0203 (7)	−0.0012 (5)	−0.0003 (5)	−0.0001 (5)
C4	0.0174 (7)	0.0287 (8)	0.0281 (8)	−0.0041 (6)	0.0007 (6)	0.0028 (6)
C5	0.0168 (7)	0.0162 (7)	0.0174 (6)	0.0002 (5)	0.0001 (5)	0.0032 (5)
C6	0.0199 (7)	0.0170 (7)	0.0191 (7)	0.0007 (5)	0.0008 (5)	0.0012 (5)
C7	0.0257 (8)	0.0182 (7)	0.0204 (7)	0.0024 (6)	−0.0008 (6)	0.0023 (5)
C8	0.0245 (8)	0.0163 (7)	0.0271 (8)	0.0004 (6)	0.0019 (6)	0.0018 (6)
C9	0.0153 (7)	0.0165 (6)	0.0171 (6)	−0.0009 (5)	0.0035 (5)	0.0016 (5)
C10	0.0164 (7)	0.0189 (7)	0.0209 (7)	−0.0026 (5)	0.0020 (5)	0.0002 (5)
C11	0.0186 (7)	0.0210 (7)	0.0237 (7)	−0.0019 (6)	0.0051 (6)	0.0005 (6)
C12	0.0191 (8)	0.0246 (8)	0.0355 (9)	−0.0029 (6)	0.0063 (6)	−0.0024 (7)
C13	0.0176 (7)	0.0173 (7)	0.0171 (7)	0.0006 (5)	0.0017 (5)	−0.0027 (5)
C14	0.0244 (8)	0.0194 (7)	0.0198 (7)	0.0048 (6)	0.0017 (6)	−0.0011 (6)
C15	0.0255 (8)	0.0177 (7)	0.0246 (7)	−0.0008 (6)	0.0027 (6)	−0.0036 (6)
C16	0.0249 (8)	0.0190 (7)	0.0366 (9)	0.0011 (6)	0.0037 (7)	−0.0049 (6)
N1	0.0137 (6)	0.0157 (6)	0.0166 (6)	−0.0004 (4)	0.0014 (4)	−0.0003 (4)
C17	0.0218 (8)	0.0293 (8)	0.0248 (8)	−0.0013 (6)	0.0009 (6)	−0.0062 (6)
C18	0.0225 (8)	0.0205 (7)	0.0175 (7)	0.0023 (6)	−0.0005 (5)	−0.0021 (5)
C19	0.0202 (7)	0.0240 (7)	0.0163 (7)	0.0038 (6)	0.0011 (5)	−0.0015 (5)
N2	0.0275 (7)	0.0211 (6)	0.0150 (6)	0.0012 (5)	−0.0001 (5)	−0.0012 (5)
O1	0.0278 (6)	0.0212 (5)	0.0257 (6)	0.0073 (5)	0.0006 (5)	−0.0014 (4)
O2	0.0343 (7)	0.0237 (6)	0.0281 (6)	−0.0067 (5)	−0.0006 (5)	−0.0016 (5)
O3	0.0219 (6)	0.0317 (6)	0.0408 (7)	0.0068 (5)	−0.0006 (5)	−0.0092 (5)
C20	0.0208 (7)	0.0226 (7)	0.0238 (7)	0.0031 (6)	0.0010 (6)	−0.0011 (6)
C21	0.0269 (8)	0.0196 (7)	0.0265 (8)	0.0064 (6)	0.0015 (6)	0.0002 (6)
N3	0.0269 (8)	0.0227 (7)	0.0439 (9)	0.0023 (6)	0.0038 (6)	0.0027 (6)

Geometric parameters (Å, º)

C1—C2	1.517 (2)	C10—H10B	0.9900
C1—N1	1.5243 (17)	C11—C12	1.525 (2)
C1—H1A	0.9900	C11—H11A	0.9900
C1—H1B	0.9900	C11—H11B	0.9900
C2—C3	1.5350 (19)	C12—H12A	0.9800
C2—H2A	0.9900	C12—H12B	0.9800
C2—H2B	0.9900	C12—H12C	0.9800
C3—C4	1.521 (2)	C13—C14	1.519 (2)
C3—H3A	0.9900	C13—N1	1.5248 (18)
C3—H3B	0.9900	C13—H13A	0.9900
C4—H4A	0.9800	C13—H13B	0.9900
C4—H4B	0.9800	C14—C15	1.525 (2)
C4—H4C	0.9800	C14—H14A	0.9900
C5—C6	1.523 (2)	C14—H14B	0.9900
C5—N1	1.5233 (17)	C15—C16	1.520 (2)
C5—H5A	0.9900	C15—H15A	0.9900
C5—H5B	0.9900	C15—H15B	0.9900
C6—C7	1.528 (2)	C16—H16A	0.9800
C6—H6A	0.9900	C16—H16B	0.9800
C6—H6B	0.9900	C16—H16C	0.9800
C7—C8	1.524 (2)	C17—O3	1.233 (2)
C7—H7A	0.9900	C17—C18	1.428 (2)
C7—H7B	0.9900	C17—H17	0.9500
C8—H8A	0.9800	C18—N2	1.400 (2)
C8—H8B	0.9800	C18—C19	1.428 (2)
C8—H8C	0.9800	C19—C20	1.354 (2)
C9—C10	1.5203 (19)	C19—H19	0.9500
C9—N1	1.5211 (18)	N2—O2	1.2586 (18)
C9—H9A	0.9900	N2—O1	1.2602 (18)
C9—H9B	0.9900	C20—C21	1.424 (2)
C10—C11	1.530 (2)	C20—H20	0.9500
C10—H10A	0.9900	C21—N3	1.153 (2)
C2—C1—N1	115.80 (11)	H10A—C10—H10B	108.4
C2—C1—H1A	108.3	C12—C11—C10	113.10 (13)
N1—C1—H1A	108.3	C12—C11—H11A	109.0
C2—C1—H1B	108.3	C10—C11—H11A	109.0
N1—C1—H1B	108.3	C12—C11—H11B	109.0
H1A—C1—H1B	107.4	C10—C11—H11B	109.0
C1—C2—C3	109.02 (12)	H11A—C11—H11B	107.8
C1—C2—H2A	109.9	C11—C12—H12A	109.5
C3—C2—H2A	109.9	C11—C12—H12B	109.5
C1—C2—H2B	109.9	H12A—C12—H12B	109.5
C3—C2—H2B	109.9	C11—C12—H12C	109.5
H2A—C2—H2B	108.3	H12A—C12—H12C	109.5
C4—C3—C2	112.18 (12)	H12B—C12—H12C	109.5
C4—C3—H3A	109.2	C14—C13—N1	115.26 (11)
C2—C3—H3A	109.2	C14—C13—H13A	108.5
C4—C3—H3B	109.2	N1—C13—H13A	108.5
C2—C3—H3B	109.2	C14—C13—H13B	108.5
H3A—C3—H3B	107.9	N1—C13—H13B	108.5
C3—C4—H4A	109.5	H13A—C13—H13B	107.5
C3—C4—H4B	109.5	C13—C14—C15	110.65 (12)
H4A—C4—H4B	109.5	C13—C14—H14A	109.5
C3—C4—H4C	109.5	C15—C14—H14A	109.5
H4A—C4—H4C	109.5	C13—C14—H14B	109.5
H4B—C4—H4C	109.5	C15—C14—H14B	109.5
C6—C5—N1	115.19 (11)	H14A—C14—H14B	108.1
C6—C5—H5A	108.5	C16—C15—C14	112.16 (13)
N1—C5—H5A	108.5	C16—C15—H15A	109.2
C6—C5—H5B	108.5	C14—C15—H15A	109.2
N1—C5—H5B	108.5	C16—C15—H15B	109.2
H5A—C5—H5B	107.5	C14—C15—H15B	109.2
C5—C6—C7	110.46 (12)	H15A—C15—H15B	107.9
C5—C6—H6A	109.6	C15—C16—H16A	109.5
C7—C6—H6A	109.6	C15—C16—H16B	109.5
C5—C6—H6B	109.6	H16A—C16—H16B	109.5
C7—C6—H6B	109.6	C15—C16—H16C	109.5
H6A—C6—H6B	108.1	H16A—C16—H16C	109.5
C8—C7—C6	112.13 (13)	H16B—C16—H16C	109.5
C8—C7—H7A	109.2	C9—N1—C5	111.42 (11)
C6—C7—H7A	109.2	C9—N1—C1	105.37 (10)
C8—C7—H7B	109.2	C5—N1—C1	111.25 (10)
C6—C7—H7B	109.2	C9—N1—C13	111.21 (11)
H7A—C7—H7B	107.9	C5—N1—C13	106.60 (10)
C7—C8—H8A	109.5	C1—N1—C13	111.10 (11)
C7—C8—H8B	109.5	O3—C17—C18	124.18 (16)
H8A—C8—H8B	109.5	O3—C17—H17	117.9
C7—C8—H8C	109.5	C18—C17—H17	117.9
H8A—C8—H8C	109.5	N2—C18—C17	117.60 (14)
H8B—C8—H8C	109.5	N2—C18—C19	117.39 (14)
C10—C9—N1	116.27 (11)	C17—C18—C19	125.01 (14)
C10—C9—H9A	108.2	C20—C19—C18	126.33 (15)
N1—C9—H9A	108.2	C20—C19—H19	116.8
C10—C9—H9B	108.2	C18—C19—H19	116.8
N1—C9—H9B	108.2	O2—N2—O1	119.66 (13)
H9A—C9—H9B	107.4	O2—N2—C18	120.44 (13)
C9—C10—C11	107.99 (12)	O1—N2—C18	119.90 (13)
C9—C10—H10A	110.1	C19—C20—C21	120.49 (15)
C11—C10—H10A	110.1	C19—C20—H20	119.8
C9—C10—H10B	110.1	C21—C20—H20	119.8
C11—C10—H10B	110.1	N3—C21—C20	178.74 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C20—H20···N3^i	0.95	2.78	3.348 (2)	119
C20—H20···O3	0.95	2.26	2.887 (2)	123

Symmetry code: (i) −x+1, −y+2, −z+1.