2,2,2-Trinitro­ethanol

2,2,2-Trinitro­ethanol, C₂H₃N₃O₇, at 100 (2) K has Z′ = 2 in the space group P2₁/c. The structure displays intra­molecular O—H...O hydrogen bonds, as well as inter­molecular O—H...O and C—H...O hydrogen bonding; the O—H...O hydrogen bonds, forming R₄⁴(8) rings, and dipolar nitro–nitro inter­actions account for the high density of 1.839 Mg m⁻³.

S1. Comment

2,2,2-Trinitroethanol, (I), with three nitro groups bonded to the same C atom, is a valuable intermediate in the preparation of energetic materials. However, the structure of (I)in the solid state has not been investigated. Only a hypothesis about the intra- and intermolecular hydrogen bonding, based on IR spectroscopy data, has been made (Ungnade & Kissinger, 1963). Our X-ray investigation shows intra- and intermolecular O—H···O hydrogen bonding as well as nonclassical C—H···O hydrogen bonding.

The asymmetric unit of (I) (Fig. 1) consists of two crystallographically independent trinitroethanol molecules. These two moieties display a very similar molecular geometry with a propeller-type orientation of the nitro groups (D₃) bonded to the β-C atom. In both molecules, the conformation of the substituents of the α- and β-C atoms is found to be staggered, and intramolecular O—H···O hydrogen bonding does occur (O1—H1···O3 and O8—H8···O13). The C—N bonds joining the three nitro groups to the β-C atom [range 1.5150 (18)–1.5197 (18) Å; Table 1] are significantly longer than the normal C—N bond distance of 1.47 Å (Shannon, 1976), as was observed previously in the determination of the crystal structure of N,N'-bis-(β,β,β-trinitroethyl)urea (Lind, 1970). A comparison of the geometrical trends for the bonding of the three nitro groups to one C atom in (I) with those in N,N'-bis-(β,β,β-trinitroethyl)urea reported by Lind again shows good agreement, taking into account that the measurement of Lind was undertaken at 296 K, whereas our experiment was run at 100 K. The independent N—C—N bond angles are smaller [range 105.90 (10)–108.43 (10)°] than the tetrahedral value, whereas the corresponding N—C—C bond angles are greater [range 110.18 (11)–113.42 (12)°] than the tetrahedral value. The three independent nitro groups of each molecule are identical in structure within the limits of error and display common geometric parameters such as N—O distances [range 1.2079 (18)–1.2181 (18) Å], O—N—O bond angles [range 126.96 (14)–127.91 (15)°] and O—N—C bond angles [range 113.63 (12)–118.64 (12)°]. In turn, the arrangement of the C—N and N—O bonds is coplanar, with the sums of the three bond angles around one N atom being 360° within the limits of error.

The extended structure of (I) involves secondary interactions in terms of intermolecular O—H···O hydrogen bonding, intermolecular C—H···O hydrogen bonding and dipolar nitro group interactions. The circular O—H···O hydrogen bonding between the hydroxyl groups of four trinitroethanol molecules results in four-membered homodromic rings (O1—H1···O8—H8···O1ⁱ—H1ⁱ···O8ⁱ—H8ⁱ; symmetry code as in Table 2). The structure that can be observed along the crystallographic a axis shows a stacking of these rings. Every ring is surrounded by four neighbouring rings, whereby two of the four molecules of trinitroethanol that form such a ring interconnect the central ring to the surrounding rings via C3—H3B···O14ⁱⁱ hydrogen bonding (Table 2 and Fig. 2). The close approach of O atoms found in the extended structure of (I) suggests the possibility of dipolar nitro group interactions, in analogy to a variety of noncovalent interactions, such as halogen···O_nitro (Allen et al., 1997), halogen···O=C (Lommerse et al., 1996) and carbonyl interactions (Allen et al., 1998). Short intermolecular O···O distances with values substantially less than 3.04 Å, the sum of the van der Waals radii for O (1.52 Å; Bondi, 1964), were investigated to that effect. Dipolar nitro group interactions were accepted for N···O contacts shorter than 3.17 Å. The value of 3.17 Å was chosen as the sum of the van der Waals radii of nitrogen and oxygen (Bondi, 1964) plus a tolerance value of 0.1 Å. Given these values, two dipolar nitro group contacts were identified. Those two interactions were found for the N₂O₄O₅ nitro group interacting with the N₅O₁₁O₁₂ nitro group in one case and with itself in the other, leading to O···O distances with values of 2.8519 (18) Å (O5···O12) and 2.8251 (15) Å (O4···O4). The corresponding values for the N···O contacts are 3.1184 (17) Å (O5···N5) and 3.1234 (16) Å (O4···N2) [symmetry codes for these interactions?]. Fig. 3 displays the symmetric interaction of the two N₂O₄O₅ nitro groups.

Related literature

For related literature, see: Allen et al. (1997, 1998); Bondi (1964); Feuer & Kucera (1960); Lind (1970); Lommerse et al. (1996); Marans & Zelinski (1950); Shannon (1976); Ungnade & Kissinger (1963).

S2. Experimental

Caution: Trinitroethanol is an energetic material. Proper protective measures (safety glasses, face shields, leather coat, earthening (equipment and person), Kevlar gloves and ear protectors) should be used when handling this material. Trinitroethanol (Marans & Zelinski, 1950) was prepared from the reaction of trinitromethane with formaldehyde (Feuer & Kucera, 1960). Multinuclear NMR spectroscopy data confirm the structure of the compound: ¹H NMR (acetone-d6, p.p.m.): δ 5.17 (2H, d, ³J = 5.6 Hz), 6.32 (1H, t, ³J = 5.6 Hz); ¹³C NMR (acetone-d6, p.p.m.): δ 63.1 (d, –CH₂), 127.5 [bs, –C(NO₂)₃]; ¹⁴N NMR (acetone-d6, p.p.m., nitromethane): δ -30.8 (–NO₂). The crystal growth was accomplished by sublimation of the solid at 298 K applying static low pressure (0.1 mbar), yielding colourless single crystals of rectangular habit.

S3. Refinement

H atoms were directly located in the crystallographic study using difference Fourier maps. All H-atom parameters were then refined, giving O—H distances of 0.804 (18) and 0.81 (2) Å, and C—H distances in the range 0.942 (18)–0.981 (17) Å.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED; program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: PLATON (Spek, 2003), SHELXL97, ORTEP-3, DIAMOND and publCIF (Westrip, 2007).

Figures

	Fig. 1. The asymmetric unit of trinitroethanol, together with the numbering scheme. Displacement ellipsoids are shown at the 50% probability level.
	Fig. 2. A representation of the structure of trinitroethanol, viewed along the a axis. Hydrogen bonding is indicated by dashed lines.
	Fig. 3. The interaction of the N2 and O4 atoms [N···O = 3.1234 (16) Å] obviously brings the O atoms into close proximity [O4···O4 = 2.8251 (15) Å]. [Symmetry code for these interactions?]

2,2,2-Trinitroethanol

Crystal data

C2H3N3O7	Z = 8
Mr = 181.07	F(000) = 736
Monoclinic, P21/c	Dx = 1.839 Mg m^−3
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 6.1242 (4) Å	µ = 0.19 mm^−1
b = 18.8223 (7) Å	T = 100 K
c = 11.7466 (4) Å	Rectangular block, colourless
β = 104.962 (3)°	0.44 × 0.19 × 0.10 mm
V = 1308.14 (11) Å^3

Data collection

Oxford Diffraction Xcalibur3 CCD diffractometer	2345 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.030
Graphite monochromator	θmax = 26.1°, θmin = 4.4°
ω scans	h = −7→7
13153 measured reflections	k = −23→23
2566 independent reflections	l = −14→14

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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.092	All H-atom parameters refined
S = 1.13	w = 1/[σ^2(Fo^2) + (0.0478P)^2 + 0.19P] where P = (Fo^2 + 2Fc^2)/3
2566 reflections	(Δ/σ)max < 0.001
241 parameters	Δρmax = 0.21 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
O1	0.94856 (17)	0.50873 (6)	0.65952 (9)	0.0306 (2)
O7	0.7249 (2)	0.52193 (7)	0.96383 (9)	0.0444 (3)
O8	0.98458 (18)	0.39204 (5)	0.51176 (10)	0.0330 (3)
O4	0.37822 (18)	0.49841 (7)	0.58701 (9)	0.0436 (3)
O5	0.5593 (2)	0.59748 (6)	0.64030 (11)	0.0487 (3)
O6	0.42030 (19)	0.56930 (6)	0.85155 (11)	0.0444 (3)
O12	0.6094 (2)	0.26156 (7)	0.35581 (13)	0.0577 (4)
O11	0.6780 (2)	0.27685 (7)	0.54540 (13)	0.0554 (4)
O2	0.4273 (2)	0.41015 (7)	0.80177 (12)	0.0544 (4)
N3	0.5928 (2)	0.53496 (7)	0.86947 (11)	0.0305 (3)
O13	0.9989 (3)	0.31780 (7)	0.29317 (11)	0.0606 (4)
O9	1.2578 (2)	0.19336 (7)	0.58624 (12)	0.0539 (3)
O3	0.6921 (3)	0.38411 (6)	0.71691 (13)	0.0589 (4)
O10	0.9261 (2)	0.14714 (6)	0.51249 (12)	0.0528 (3)
O14	1.0882 (2)	0.20648 (7)	0.31610 (11)	0.0534 (3)
N5	0.7320 (2)	0.26878 (6)	0.45388 (13)	0.0368 (3)
N6	1.0275 (2)	0.26249 (7)	0.34772 (11)	0.0354 (3)
N4	1.0633 (2)	0.19535 (7)	0.52822 (12)	0.0364 (3)
N2	0.51551 (19)	0.53558 (7)	0.65338 (10)	0.0300 (3)
C3	1.1083 (3)	0.32899 (8)	0.54122 (13)	0.0294 (3)
C2	0.6582 (2)	0.50200 (7)	0.76524 (11)	0.0241 (3)
C1	0.9103 (2)	0.51155 (9)	0.77233 (12)	0.0285 (3)
C4	0.9858 (2)	0.26599 (7)	0.46923 (12)	0.0268 (3)
N1	0.5856 (2)	0.42467 (7)	0.76224 (11)	0.0358 (3)
H1A	0.987 (3)	0.4737 (9)	0.8252 (14)	0.029 (4)*
H3A	1.257 (3)	0.3310 (9)	0.5296 (15)	0.035 (4)*
H1B	0.950 (3)	0.5574 (9)	0.8028 (16)	0.035 (4)*
H3B	1.121 (3)	0.3183 (9)	0.6220 (15)	0.032 (4)*
H8	1.015 (3)	0.4105 (9)	0.4560 (16)	0.032 (5)*
H1	0.944 (3)	0.4678 (11)	0.6369 (18)	0.048 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0334 (5)	0.0333 (6)	0.0292 (5)	−0.0023 (4)	0.0157 (4)	−0.0036 (4)
O7	0.0442 (7)	0.0655 (8)	0.0233 (6)	−0.0073 (6)	0.0081 (5)	−0.0018 (5)
O8	0.0405 (6)	0.0244 (5)	0.0373 (6)	−0.0007 (4)	0.0159 (5)	0.0003 (4)
O4	0.0287 (6)	0.0687 (8)	0.0303 (6)	−0.0041 (5)	0.0016 (5)	−0.0070 (5)
O5	0.0521 (7)	0.0381 (7)	0.0540 (7)	0.0081 (5)	0.0102 (6)	0.0151 (5)
O6	0.0345 (6)	0.0509 (7)	0.0529 (7)	0.0011 (5)	0.0205 (5)	−0.0132 (6)
O12	0.0366 (7)	0.0495 (8)	0.0756 (10)	0.0020 (6)	−0.0061 (7)	−0.0158 (7)
O11	0.0519 (7)	0.0513 (8)	0.0784 (9)	−0.0044 (6)	0.0448 (7)	−0.0042 (7)
O2	0.0616 (8)	0.0472 (7)	0.0640 (8)	−0.0239 (6)	0.0337 (7)	−0.0046 (6)
N3	0.0301 (6)	0.0343 (7)	0.0300 (7)	−0.0077 (5)	0.0129 (5)	−0.0054 (5)
O13	0.1044 (12)	0.0454 (7)	0.0348 (6)	−0.0130 (7)	0.0229 (7)	0.0057 (5)
O9	0.0470 (7)	0.0479 (7)	0.0607 (8)	0.0137 (6)	0.0029 (6)	0.0136 (6)
O3	0.0807 (10)	0.0295 (6)	0.0784 (10)	0.0010 (6)	0.0421 (8)	−0.0091 (6)
O10	0.0634 (8)	0.0268 (6)	0.0690 (9)	−0.0039 (6)	0.0188 (7)	0.0080 (6)
O14	0.0673 (8)	0.0561 (8)	0.0437 (7)	0.0093 (6)	0.0267 (6)	−0.0124 (6)
N5	0.0317 (7)	0.0244 (7)	0.0566 (9)	−0.0019 (5)	0.0154 (7)	−0.0035 (6)
N6	0.0416 (7)	0.0394 (8)	0.0271 (6)	−0.0061 (6)	0.0121 (6)	−0.0028 (5)
N4	0.0440 (8)	0.0294 (7)	0.0389 (7)	0.0056 (6)	0.0163 (6)	0.0039 (5)
N2	0.0247 (6)	0.0387 (7)	0.0271 (6)	0.0048 (5)	0.0074 (5)	0.0019 (5)
C3	0.0315 (8)	0.0297 (8)	0.0276 (8)	−0.0001 (6)	0.0089 (6)	−0.0001 (6)
C2	0.0260 (7)	0.0259 (7)	0.0209 (6)	−0.0019 (5)	0.0068 (5)	−0.0005 (5)
C1	0.0241 (7)	0.0374 (8)	0.0240 (7)	0.0002 (6)	0.0064 (6)	−0.0019 (6)
C4	0.0296 (7)	0.0252 (7)	0.0284 (7)	0.0011 (5)	0.0123 (6)	0.0017 (5)
N1	0.0439 (8)	0.0294 (7)	0.0357 (7)	−0.0058 (6)	0.0130 (6)	−0.0012 (5)

Geometric parameters (Å, º)

C2—N1	1.5197 (18)	N5—O11	1.2128 (18)
C2—N2	1.5155 (17)	N5—O12	1.2093 (19)
C2—N3	1.5159 (17)	N6—O13	1.2113 (18)
C4—N4	1.5177 (18)	N6—O14	1.2079 (18)
C4—N5	1.5188 (19)	O1—C1	1.4050 (17)
C4—N6	1.5150 (18)	O1—H1	0.81 (2)
N1—O2	1.2094 (18)	O8—C3	1.4025 (18)
N1—O3	1.2130 (18)	O8—H8	0.804 (18)
N2—O4	1.2107 (16)	C3—C4	1.535 (2)
N2—O5	1.2141 (17)	C3—H3A	0.953 (18)
N3—O6	1.2094 (17)	C3—H3B	0.953 (17)
N3—O7	1.2168 (16)	C2—C1	1.5352 (19)
N4—O9	1.2103 (18)	C1—H1A	0.981 (17)
N4—O10	1.2181 (18)	C1—H1B	0.942 (18)
N1—C2—N2	106.24 (11)	O6—N3—C2	118.64 (12)
N1—C2—N3	105.90 (10)	O7—N3—C2	113.63 (12)
N2—C2—N3	108.43 (10)	O9—N4—C4	115.51 (13)
N4—C4—N5	105.94 (11)	O10—N4—C4	117.45 (13)
N4—C4—N6	106.44 (11)	O11—N5—C4	113.80 (13)
N5—C4—N6	107.81 (11)	O12—N5—C4	118.27 (13)
N1—C2—C1	113.42 (12)	O13—N6—C4	115.13 (13)
N2—C2—C1	110.18 (11)	O14—N6—C4	117.90 (13)
N3—C2—C1	112.35 (11)	C1—O1—H1	110.0 (14)
N4—C4—C3	111.98 (12)	C3—O8—H8	110.0 (12)
N5—C4—C3	112.24 (11)	O8—C3—C4	111.19 (12)
N6—C4—C3	112.04 (11)	O8—C3—H3A	113.9 (10)
O2—N1—O3	126.98 (14)	C4—C3—H3A	107.4 (10)
O4—N2—O5	127.78 (13)	O8—C3—H3B	108.8 (10)
O6—N3—O7	127.73 (13)	C4—C3—H3B	106.7 (10)
O9—N4—O10	127.04 (14)	H3A—C3—H3B	108.5 (14)
O11—N5—O12	127.91 (15)	O1—C1—C2	110.77 (11)
O13—N6—O14	126.96 (14)	O1—C1—H1A	113.6 (9)
O2—N1—C2	117.80 (12)	C2—C1—H1A	105.0 (9)
O3—N1—C2	115.20 (12)	O1—C1—H1B	107.6 (10)
O4—N2—C2	117.80 (12)	C2—C1—H1B	106.7 (10)
O5—N2—C2	114.40 (12)	H1A—C1—H1B	113.0 (14)
O4—N2—C2—N3	−112.76 (13)	O9—N4—C4—N6	91.77 (15)
O5—N2—C2—N3	69.13 (14)	O10—N4—C4—N6	−88.10 (15)
O4—N2—C2—N1	0.68 (15)	O9—N4—C4—N5	−153.65 (13)
O5—N2—C2—N1	−177.44 (12)	O10—N4—C4—N5	26.48 (17)
O4—N2—C2—C1	123.91 (13)	O9—N4—C4—C3	−30.99 (17)
O5—N2—C2—C1	−54.20 (15)	O10—N4—C4—C3	149.15 (13)
O6—N3—C2—N2	14.15 (16)	O12—N5—C4—N6	6.43 (17)
O7—N3—C2—N2	−166.79 (12)	O11—N5—C4—N6	−174.99 (12)
O6—N3—C2—N1	−99.51 (14)	O12—N5—C4—N4	−107.20 (15)
O7—N3—C2—N1	79.55 (14)	O11—N5—C4—N4	71.37 (15)
O6—N3—C2—C1	136.16 (13)	O12—N5—C4—C3	130.30 (14)
O7—N3—C2—C1	−44.78 (16)	O11—N5—C4—C3	−51.13 (16)
N2—C2—C1—O1	−34.29 (16)	O8—C3—C4—N6	82.05 (15)
N3—C2—C1—O1	−155.30 (12)	O8—C3—C4—N4	−158.43 (11)
N1—C2—C1—O1	84.64 (14)	O8—C3—C4—N5	−39.43 (16)
O14—N6—C4—N4	6.89 (17)	N2—C2—N1—O2	−87.09 (15)
O13—N6—C4—N4	−171.89 (14)	N3—C2—N1—O2	28.07 (17)
O14—N6—C4—N5	−106.41 (15)	C1—C2—N1—O2	151.73 (14)
O13—N6—C4—N5	74.81 (16)	N2—C2—N1—O3	91.18 (15)
O14—N6—C4—C3	129.61 (14)	N3—C2—N1—O3	−153.65 (13)
O13—N6—C4—C3	−49.18 (18)	C1—C2—N1—O3	−30.00 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3	0.81 (2)	2.55 (2)	2.9948 (17)	116.2 (16)
O1—H1···O8	0.81 (2)	2.11 (2)	2.8431 (15)	150.2 (19)
O8—H8···O13	0.804 (18)	2.572 (17)	2.9444 (17)	109.9 (14)
O8—H8···O1^i	0.804 (18)	2.089 (19)	2.8512 (15)	158.3 (16)
C3—H3B···O14^ii	0.953 (17)	2.385 (17)	3.3304 (19)	171.0 (13)

Symmetry codes: (i) −x+2, −y+1, −z+1; (ii) x, −y+1/2, z+1/2.