Crystal structure of (E)-furan-2-carbaldehyde O-benzoyloxime

In the title oxime ester, the benzoate and furan rings are almost coplanar, making a dihedral angle of 11.68 (9)°. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming chains along the a-axis direction.


Structural commentary
The molecular structure of the title compound is shown in Fig. 1. An intramolecular short contact (C8-H8Á Á ÁO2) is present (Table 1), which may prevent the -COO group from tilting, since the twist angle between the -C6/O2/O3 unit and the benzene ring (C7-C12) is only 2. 79 (16) . This also might be the reason why the molecule is almost planar. The dihedral angle between the furan (O1/C1-C4) ring and the benzene ring is 11.68 (9) . The C6-O2 and C6 O3 distances of 1.352 (2) and 1.195 (2) Å , respectively, are typical values for single and double C-O bonds. This overall geometry is very similar to that observed for E-benzaldehyde O-benzoyloxime (Altinbas et al., 2004). Within the five-membered furan ring, the interatomic O1-C1 and O1-C4 distances of 1.369 (2) and 1.367 (2) Å , respectively, are typical values for O-Csp 2 bonds. The short C4-C3 and C1-C2 bond lengths of 1.324 (4) and 1.347 (3) Å , respectively, and the stretched C2-C3 bond distance of 1.408 (2) Å are typical values observed for double C C and single C-C bonds, respectively. The -C5/N1/O2 group is twisted by 4.40 (13) with respect to the furan ring. The N1-O2 distance of 1.444 (1) Å is only slightly longer than reported in other oxime compounds (Wetherington & Moncrief, 1973), whereas the C N-O angle of 106.73 (11) is slightly smaller.

Database survey
A search of the Cambridge Structural Database (Version 5.38, update May 2017; Groom et al., 2016) for the substructure furan-2-carbaldehyde oxime gave 20 hits, while for substructure formaldehyde O-benzoyloxime there were 24 hits. The O-N distances vary from ca 1.38 to 1.45 Å , while the N C distances vary from ca 1.25 to 1.32 Å . In the title compound, these distances are N1-O2 = 1.444 (1) Å and N1 C5 is 1.270 (2) Å , within the limits observed. In the majority of the formaldehyde O-benzoyloxime structures, the dihedral angle between the plane of the -COO group and the benzene ring is <10 . In the title compound, this dihedral angle is 2.79 (16) .

Figure 2
A view along the b axis of the crystal packing of the title compound. The C-HÁ Á ÁO hydrogen bonds, linking molecules to form chains along [100], are shown as dashed lines [see Table 1; only H atom H5 (grey ball) has been included].

Figure 3
A view along the a axis of the crystal packing of the title compound. The offsetinteractions are shown as blue double arrows, and only H atom H5 (grey ball) has been included.

Figure 1
View of the molecular structure of the title compound, with the atom labelling and 50% probability displacement ellipsoids. Preparation of the O-benzoyl ester of furanaldoxime: Benzoyl chloride (5.01 mmol) was added dropwise under stirring to 4.55 mmol of furanaldoxime. Since the reaction was vigorous and exothermic the mixture was placed in an ice bath for 30 min. The reaction mixture was then quenched in icewater, and then extracted with EtOAc. The organic layer was separated and washed with 1M NaOH solution to remove the benzoic acid and HCl that had formed as by products. The EtOAc layer was passed through anhydrous Na 2 SO 4 and dried in vacuo to give the title compound as a light-brown solid (0.9806 g).  147.65, 145.28, 134.35, 129.77, 129.48, 128.52, 119.14, 113.07.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The H atoms were located from difference-Fourier maps and freely refined.