Acet­amidoxime

The oxime of acet­amide, viz. N-hydroxy­ethanimid­amide, C₂H₆N₂O, has a complex hydrogen-bonding arrangement in its crystal structure, featuring one strong O—H...N hydrogen bond together with weaker hydrogen bonding involving the amide groups. Conjugation effects lead to atypical distances and angles.

S1. Comment

The molecular structure of acetamidoxime, (I), is shown in Fig. 1. The molecular geometry has somewhat atypical distances and angles, which can be explained by a contribution from a resonance form that places partial double-bond character in the C1—N2 bond. The C1—N1 and N1—O1 distances are longer than average, having values of 1.295 (2) and 1.442 (2) Å, respectively, whereas the C1—N2 distance is 1.346 (2) Å. In addition, the C=N—O angle [109.37 (13)°] is more acute than comparable angles in other oxime structures (Chertanova et al., 1994). For a more exact comparison, the structure of N,N-dimethylacetamidoxime (Bright et al., 1973) differs only in the replacement of NH₂ by N(CH₃)₂, yet the C=N and N—O distances are shorter [1.284 (2) and 1.430 (2) Å, respectively], while the C—N(CH₃)₂ distance is longer [1.367 (3) Å] and the C=N—O angle is 111.8 (2)°. Excluding the methyl H atoms, the entire molecule of (I) is planar. Based on unit weights, the RMS deviation is 0.069 Å.

The major form of hydrogen bonding in the structure of (I), depicted in Fig. 2, is between the O—H donor and oxime N acceptor, as is commonly found. It consists of a unidirectional interaction along a screw axis of the structure in the c direction. The N···O distance is longer than average [2.804 (2) Å; Chertanova et al., 1994]. Weaker hydrogen bonds are apparent for each of the amide H atoms; atom H2A participates in an intramolecular hydrogen bond, while atom H2B participates in a hydrogen bond to the oxime O acceptor.

S2. Experimental

The title compound was synthesized, as described by Sahbari & Russell (2000, 2001), from acetamide and hydroxylamine. Hygroscopic crystals were obtained from recrystallization in perfluorocyclohexane.

S3. Refinement

Molecule (I) crystallized in the chiral space group P2₁2₁2₁, but the absolute structure was indeterminate since only light atoms were present. Merging Friedel pairs reduces the reflections/parameters ratio from 9.15 to 6.92, but the reliability of the structure does not change, being based more on the quality of data than their number. H atoms on atoms N2 and O1 were refined freely, while H atoms on atom C2 were refined using a riding model, with C—H distances of 0.98 Å and U_iso(H) values of 1.5U_eq(C2).

Computing details

Data collection: P3-PC (Siemens, 1994); cell refinement: P3-PC; data reduction: XDISK (Siemens, 1994); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b); molecular graphics: XP in SHELXTL (Sheldrick, 1994); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A view of the hydrogen-bonding scheme. [Symmetry codes: (i) x − 1/2,1/2 − y,1 − z; (ii) 1 − x,1/2 + y,3/2 − z.]

N-hydroxyethanimidamide

Crystal data

C2H6N2O	F(000) = 160
Mr = 74.09	Dx = 1.311 Mg m^−3
Orthorhombic, P212121	Cu Kα radiation, λ = 1.54178 Å
Hall symbol: P 2ac 2ab	Cell parameters from 50 reflections
a = 5.0422 (14) Å	θ = 7.3–29.9°
b = 8.016 (3) Å	µ = 0.89 mm^−1
c = 9.284 (3) Å	T = 130 K
V = 375.2 (2) Å^3	Parallelepiped, colorless
Z = 4	0.50 × 0.26 × 0.25 mm

Data collection

Syntex P21 diffractometer	Rint = 0.013
Radiation source: normal-focus sealed tube	θmax = 66.7°, θmin = 7.3°
Graphite monochromator	h = −2→6
2θ–ω scans	k = 0→9
886 measured reflections	l = 0→11
415 independent reflections	2 standard reflections every 198 reflections
413 reflections with I > 2σ(I)	intensity decay: <0.1%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.072	w = 1/[σ^2(Fo^2) + (0.0415P)^2 + 0.0757P] where P = (Fo^2 + 2Fc^2)/3
S = 1.26	(Δ/σ)max = 0.008
415 reflections	Δρmax = 0.15 e Å^−3
60 parameters	Δρmin = −0.17 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.056 (6)

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	0.1742 (3)	0.31633 (15)	0.63878 (13)	0.0201 (4)
H	0.072 (6)	0.252 (4)	0.580 (3)	0.060 (9)*
N1	0.3723 (3)	0.38656 (16)	0.54462 (15)	0.0181 (4)
N2	0.4119 (4)	0.5737 (2)	0.73681 (18)	0.0246 (5)
H2A	0.274 (6)	0.526 (3)	0.783 (3)	0.046 (8)*
H2B	0.520 (5)	0.650 (3)	0.772 (3)	0.035 (7)*
C1	0.4825 (4)	0.51323 (19)	0.60715 (18)	0.0165 (4)
C2	0.7054 (4)	0.5974 (2)	0.5305 (2)	0.0246 (5)
H2C	0.8737	0.5672	0.5764	0.037*
H2D	0.6812	0.7186	0.5352	0.037*
H2E	0.7077	0.5617	0.4296	0.037*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0223 (7)	0.0188 (6)	0.0193 (6)	−0.0038 (6)	0.0000 (6)	0.0008 (5)
N1	0.0186 (8)	0.0171 (7)	0.0185 (7)	0.0006 (7)	0.0015 (7)	−0.0003 (6)
N2	0.0303 (9)	0.0240 (8)	0.0195 (8)	−0.0068 (8)	0.0003 (8)	−0.0061 (7)
C1	0.0175 (8)	0.0146 (8)	0.0173 (8)	0.0039 (7)	−0.0025 (7)	0.0020 (7)
C2	0.0224 (11)	0.0211 (8)	0.0305 (10)	−0.0003 (9)	0.0029 (9)	0.0015 (8)

Geometric parameters (Å, º)

O1—N1	1.4418 (19)	N2—H2B	0.88 (3)
O1—H	0.91 (3)	C1—C2	1.491 (3)
N1—C1	1.295 (2)	C2—H2C	0.9800
N2—C1	1.346 (2)	C2—H2D	0.9800
N2—H2A	0.90 (3)	C2—H2E	0.9800
N1—O1—H	104.4 (17)	N2—C1—C2	117.59 (16)
C1—N1—O1	109.37 (13)	C1—C2—H2C	109.5
C1—N2—H2A	118.6 (17)	C1—C2—H2D	109.5
C1—N2—H2B	114.9 (17)	H2C—C2—H2D	109.5
H2A—N2—H2B	126 (2)	C1—C2—H2E	109.5
N1—C1—N2	124.75 (17)	H2C—C2—H2E	109.5
N1—C1—C2	117.65 (16)	H2D—C2—H2E	109.5
O1—N1—C1—N2	−3.1 (2)	O1—N1—C1—C2	176.37 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H···N1^i	0.91 (3)	1.89 (3)	2.804 (2)	178 (3)
N2—H2A···O1	0.90 (3)	2.21 (3)	2.554 (2)	102 (2)
N2—H2B···O1^ii	0.88 (3)	2.20 (3)	3.078 (2)	173 (2)

Symmetry codes: (i) x−1/2, −y+1/2, −z+1; (ii) −x+1, y+1/2, −z+3/2.