Synthesis, crystal structure and Hirshfeld surface analysis of (E)-benzo[d][1,3]dioxole-5-carbaldehyde oxime

The asymmetric unit of the title compound consists of two independent molecules differing slightly in conformation and in their intermolecular interactions in the solid.

The asymmetric unit of the title molecule, C 8 H 7 NO 3 , consists of two molecules differing slightly in conformation and in their intermolecular interactions in the solid. The dihedral angle between the benzene and dioxolane rings is 0.20 (7) in one molecule and 0.31 (7) in the other. In the crystal, the two molecules are linked into dimers through pairwise O-HÁ Á ÁN hydrogen bonds, with these units being formed into stacks by two different sets of aromatic -stacking interactions. The stacks are connected by C-HÁ Á ÁO hydrogen bonds. A Hirshfeld surface analysis indicates that the most significant contacts in the crystal packing are HÁ Á ÁO/OÁ Á ÁH (36.7%), HÁ Á ÁH (32.2%) and CÁ Á ÁH/HÁ Á ÁC (12.7%).

Chemical context
Oxime compounds containing an R 2 C N-OH functional group have been studied for many years because of their important role as acetylcholinesterase reactivators and their utility as therapeutic agents for various diseases (Musilek et al., 2011;Canario et al., 2018). Various oximes have been identified in plants as biosynthetic intermediates and can facilitate a range of processes associated with plant growth and development (Sørensen et al., 2018). Oximes also have a wide range of biological activities, such as human immunodeficiency virus (HIV) agents that can inhibit HIV protease (Komai et al., 1997) and can act as anti-inflammatories (Li et al., 2018;Kwon et al., 2014). The introduction of an oxime group into an appropriate chemical backbone is a reasonable approach for the preparation of cytotoxic agents and many oxime derivatives have been reported to have therapeutic activity for cancer (Canario et al., 2018;Shen et al., 2015) and neurodegenerative disorders (Avrahami et al., 2013;Yuskaitis et al., 2009).
As part of our studies in this area, we now describe the synthesis, structure and Hirshfeld surface analysis of the title compound (I).

Structural commentary
The asymmetric unit ( Fig. 1) consists of two independent molecules differing slightly in the orientation of some hydrogen atoms. The benzodioxolane portion of the molecule containing O1 is planar to within 0.0171 (12) Å (r.m.s. deviation of the fitted atoms = 0.0091 Å ) with C7 deviating by 0.0171 (12) Å from one side of the mean plane and O1 by 0.0170 (10) Å from the other, indicating a slight twist in the dioxolane ring. The corresponding portion of the second molecule containing O4 is planar to within 0.0041 (11) Å (r.m.s. deviation of the fitted atoms = 0.0030 Å ), indicating a conformational difference, albeit small, between the two molecules. The overlay fit of inverted molecule 2 on molecule 1 is shown in Fig. 2 with the weighted r.m.s. fit of the 12 non-H atoms being 0.036 Å and showing the major differences to be in the hydrogen-atom positions. The C6-C1-C8-N1 and C1-C8-N1-O3 torsion angles are, respectively, 3.9 (2) and À179.96 (11) , indicating the side chain to be nearly coplanar with the benzodioxolane unit. The corresponding torsion angles in the second molecule are virtually the same as above. The two molecules are connected into dimers through O3-H3AÁ Á ÁN2 and O6-H6AÁ Á ÁN1 hydrogen bonds (Table 1 and Fig. 1), generating R 2 2 (6) loops.

Figure 3
View of the packing seen along the a-axis direction with O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and -stacking interactions depicted, respectively, by light blue, black and orange dashed lines.

Figure 1
The asymmetric unit with 50% probability ellipsoids. The O-HÁ Á ÁN hydrogen bonds are depicted by dashed lines.

Figure 2
A least-squares overlay of the two independent molecules [inverted O4 molecule (red) on O1 molecule (black)].

Figure 4
View of the packing seen along the [101] direction. Intermolecular interactions are depicted as in Fig. 3.

Database survey
A search using CCDC ConQuest of the Cambridge Structural Database (CSD, Version 5.44, updated to April 2023; Groom et al., 2016) using the title molecule with all hydrogen atoms deleted gave 26 hits. Most of these contain the search fragment as part of a larger, often polycyclic molecule, but three are considered similar to (I). These are N-

Hirshfeld surface analysis
The Hirshfeld surface analysis was performed with Crystal Explorer (Version 21.5; Spackman et al., 2021). Fig. 5 shows views of the d norm surfaces for the two molecules in the asymmetric unit plotted over the limits from À0.63 to 1.18 a.u for molecule 1 and À0.63 to 1.07 a.u for molecule 2. The O-HÁ Á ÁN hydrogen bonds, which generate the dimers are indicated by the bright-red spots in Fig. 5(a) and 5(b), respectively.

Special details
Experimental. The diffraction data were obtained from 3 sets of 400 frames, each of width 0.5° in ω, collected at φ = 0.00, 90.00 and 180.00° and 2 sets of 800 frames, each of width 0.45° in φ, collected at ω = -30.00 and 210.00°. The scan time was 20 sec/frame. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.99 Å) while those attached to oxygen were placed in locations derived from a difference map and their coordinates adjusted to give O-H = 0.87 Å. All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms.