Crystal structure of 4,5-di­methyl-1,3-dioxol-2-one

The planar title compound 4,5-dimethyl-1,3-dioxol-2-one, C₅H₆O₃, 1, crystallizes with its mol­ecular C₂ axis coincident with a crystallographic mirror plane in space group P2₁/m. In the plane defined by the b axis and an ac face diagonal, anti­parallel linear strands of 1, formed by simple translation, associate to form sheets with close H⋯H and O⋯O inter­molecular contacts. Between the sheets, parallel strands of 1 place the carbonyl O atom near the five-membered ring centroid of a neighboring mol­ecule with close O⋯O and O⋯C contacts.

1. Chemical context

4,5-Dimethyl-1,3-dioxol-2-one, 1 (Fig. 1 and scheme), is a simple derivative of vinyl­ene carbonate, 2a, that has attracted recent attention as a key component of non-aqueous electrolyte blends for advanced Li ion batteries (Park et al., 2021; Liu et al., 2017; Kotani & Kadota, 2016; Xu et al., 2010). Its 4-chloro­methyl and 4-bromo­methyl derivatives, 3, have significance in the pharmaceutical industry as building elements in the preparation of antibiotics such as prulifloxacin (Cao et al., 2013), cefuroxime variants (Webber, 1987), and ampicillin (Sakamoto et al., 1984; Xiao, 2004). In principle, by analogy to the usefulness that the related 4,5-dimethyl-1,3-di­thiol-2-one, 4a, enjoys as a masked form of the di­methyl­dithiol­ene ligand (Chandrasekaran et al., 2009), 1 could function as a protected form of the dimethyldioxolene(2−) ligand, 5, that is liberated by straightforward base hydrolysis.

Figure 1 Displacement ellipsoid plot (50% probability) of 4,5-dimethyl-1,3-dioxol-2-one (1) with non-H atom labeling.

Although a few coordination complexes with the di­methyl­dioxolene ligand are known, they have been prepared by oxidative addition of the corresponding α-diketone to a low-valent metal precursor (Chisholm et al., 1983) or by an obscure route involving the reductive coupling of CO(g) with methyl ligands (Hofmann et al., 1985). This context of demonstrated usefulness and unrealized, but plausible, possibility for 1 persuaded us to undertake a study of its utility as a dioxolene ligand precursor. In an early research stage, serendipitously obtained diffraction-quality crystals of 1 provided an opportunity for characterization by X-ray diffraction, details of which are reported herein.

2. Structural commentary

Compound 1 crystallizes in the monoclinic space group P2₁/m upon a crystallographic mirror plane that coincides with the carbonyl bond (Fig. 1).

3. Supra­molecular features

Mol­ecules of 1 are aligned as one-dimensional strands by simple translation along one of the diagonals of the ac face of the unit cell (Fig. 2). The C=O oxygen atom of 1 forms close contacts of 2.53 Å with the hydrogen atoms from each of the methyl groups of the mol­ecule aligned before or behind (Table 1), at a distance that approaches the sum of the van der Waals radii of the elements (Batsanov, 2001). These strands are further organized into two-dimensional sheets through side-by-side placement but with an alternating orientation of the polarized, carbonyl end of the mol­ecules (Fig. 2). The b axis defines the 2nd dimension of these sheets. Between strands within these sheets, inter­atomic H⋯H separations are 2.89 and 3.05 Å, while nearest O⋯O distances between rings are 3.3962 (13) Å. Fig. 3 presents a perspective of these sheets that is approximately along the b axis of the cell such that the close stacking between them is visible.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3A⋯O1^i	0.98	2.53	3.4976 (13)	171
Symmetry code: (i) .

Figure 2 Packing diagram for 4,5-dimethyl-1,3-dioxol-2-one (1) illustrating the sheetlike arrangement in the plane defined by the b axis and an ac face diagonal. Displacement ellipsoids are at the 50% level, and closest inter­molecular contacts are indicated.

Figure 3 Cell packing diagram of 1 with a view along the b axis of the cell. Displacement ellipsoids are drawn at the 50% level, and all H atoms are omitted for clarity.

An alternative description of the third dimension of the packing is that the one-dimensional strands noted above translate as a whole along the a axis of the cell with an offset that places the carbonyl oxygen atom of one mol­ecule of one strand near the five-membered ring centroid of a neighboring mol­ecule (Fig. 4). In contrast to the intrasheet strands depicted in Fig. 2, which are anti­parallel, the neighboring intersheet strands are all oriented in the same direction. The closest inter­molecular C⋯C and C⋯O contacts between these parallel strands are the C_c⋯C_o separation of 3.3413 (16) Å, the O_c⋯C_c spacing of 3.3452 (18) Å, and the O_r⋯C_o distance of 3.3742 (13) Å (c = carbonyl, o = olefin, r = ring). It is likely that the electrostatic inter­actions of polarized bonds, e.g., placement of the negative end of the ^δ(–)O=C^δ(+) carbonyl dipole above the positive end of the same bond in the sheet below, exert a decisive role in guiding the organization and spacing of one mol­ecular plane over another. An end-on view of these sheets in space-filling presentation mode emphasizes the packing efficiency imposed by these cumulative inter­molecular inter­actions (Fig. 5).

Figure 4 View of the cell packing arrangement in 1 depicting the closest inter­molecular contacts between linear strands extending in the direction of a diagonal to the ac face. Displacement ellipsoids are at the 50% level.

Figure 5 Space-filling plot of the unit-cell packing in 1 as viewed along the length of the linear strands, which are orthogonal to the paper plane.

4. Database survey

Of the relatively few vinyl­ene carbonates that have been structurally characterized, only 1 and the parent compound 2a (Cser, 1974) are simple, symmetrically substituted variants. All other structurally identified compounds bearing this moiety are more complex organic mol­ecules that have been prepared and studied as angiotensin II receptor blockers (Yanagisawa et al., 1996; Dams et al., 2015; Zhang et al., 2017). Despite its ostensible similarity to 1, compound 2a crystallizes in a rather different fashion. Although arranged into extended sheets, which also contain the b axis, mol­ecules of 2a are not organized into discernible linear strands but instead are twisted relative to their neighbors so as to accommodate multiple C—H⋯O hydrogen-bonding inter­actions (Fig. 6). A glide plane, rather than simple translation, relates one mol­ecule of 2a to another in the horizontal direction (Fig. 6). As their different space groups would necessitate, the packing arrangements for vinyl­ene tri­thio­carbonate (2b, CSD refcode LAGMUC; Mereiter & Rosenau, 2005) and vinyl­ene tris­elenolate (2c, SELOLS; Lyubovskaya et al., 1976) contrast greatly with 2a. The former reveals linear strands of mol­ecules arranged in sheets with a parallel orientation of all strands. Inter­molecular π–π stacking inter­actions appear to be the decisive packing force between sheets. The latter, when viewed along the b axis of the cell, reveals a herringbone-like pattern in the arrangement of mol­ecules.

Figure 6 Ball and stick representation of the sheetlike arrangement in 2a, where mol­ecules (left-to-right) are related by a glide-plane operation rather than simple translation. Closest inter­molecular contacts are illustrated.

Compounds similar to 1 with methyl substituents at the 4 and 5 positions of the ring include 4a, already noted, and the all-sulfur form, 4b (DMTHTN; Smith & Luss, 1980). Compound 4b occurs in the same space group (No. 62, Pnma) as 2c with a qualitatively similar packing arrangement that differs in having the herringbone pattern visible when viewed along the cell's a axis. Compound 4a crystallizes in P2₁/c on a general position with similar generalities of description pertinent to its packing pattern as found for 2a. However, adjacent strands of 4b that are generated by the glide plane operation are slightly out of plane relative to one another. The selenium analogue (6) of 1 and 4a has not been characterized crystallographically but is a target of current study in our laboratory.

5. Synthesis and crystallization

The sample of 4,5-dimethyl-1,3-dioxol-2-one used in this study was purchased from AK Scientific, Inc. and recrystallized by evaporation of a MeOH solution from a test tube at room temperature.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms are added in calculated positions and refined with isotropic displacement parameters that are approximately 1.5 times those of the carbon atom to which they are attached. The C—H distances are fixed at 0.98 Å.

Table 2
Experimental details

Crystal data
Chemical formula	C5H6O3
Mr	114.10
Crystal system, space group	Monoclinic, P21/m
Temperature (K)	100
a, b, c (Å)	3.8283 (10), 10.972 (2), 6.1096 (10)
β (°)	93.523 (2)
V (Å^3)	256.15 (10)
Z	2
Radiation type	Mo Kα
μ (mm^−1)	0.12
Crystal size (mm)	0.27 × 0.21 × 0.16
Data collection
Diffractometer	Bruker SMART APEX
Absorption correction	Multi-scan (SADABS; Krause et al., 2015)
Tmin, Tmax	0.967, 0.980
No. of measured, independent and observed [I > 2σ(I)] reflections	2310, 636, 617
Rint	0.027
(sin θ/λ)max (Å^−1)	0.667
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.030, 0.077, 1.10
No. of reflections	636
No. of parameters	42
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å^−3)	0.30, −0.21
Computer programs: SMART (Bruker, 2000), SAINT-Plus (Bruker, 2004), SHELXT (Sheldrick, 2015a), SHELXL (Sheldrick, 2015b), and SHELXTL (Sheldrick, 2008).

Supporting information

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SAINT-Plus (Bruker, 2004); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

4,5-Dimethyl-1,3-dioxol-2-one

Crystal data

C5H6O3	F(000) = 120
Mr = 114.10	Dx = 1.479 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
a = 3.8283 (10) Å	Cell parameters from 2113 reflections
b = 10.972 (2) Å	θ = 3.2–28.3°
c = 6.1096 (10) Å	µ = 0.12 mm^−1
β = 93.523 (2)°	T = 100 K
V = 256.15 (10) Å^3	Block, white
Z = 2	0.27 × 0.21 × 0.16 mm

Data collection

Bruker SMART APEX diffractometer	636 independent reflections
Radiation source: fine-focus sealed tube	617 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
π and ο scans	θmax = 28.3°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −4→4
Tmin = 0.967, Tmax = 0.980	k = −14→14
2310 measured reflections	l = −8→8

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.030	H-atom parameters constrained
wR(F^2) = 0.077	w = 1/[σ^2(Fo^2) + (0.0345P)^2 + 0.0767P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max < 0.001
636 reflections	Δρmax = 0.30 e Å^−3
42 parameters	Δρmin = −0.21 e Å^−3
0 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.22 (2)

Special details

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 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 > 2sigma(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.

Hydrogen atoms were added in calculated positions and refined with isotropic displacement parameters that are approximately 1.5 times those of the carbon atom to which they are attached. The C–H distances assumed were 0.98 Å.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.1654 (3)	0.250000	0.67266 (16)	0.0247 (3)
O2	−0.08340 (16)	0.35049 (6)	0.94742 (10)	0.0174 (2)
C1	0.0147 (3)	0.250000	0.8382 (2)	0.0177 (3)
C2	−0.2444 (2)	0.31041 (8)	1.13620 (13)	0.0156 (2)
C3	−0.3662 (2)	0.40519 (8)	1.28542 (15)	0.0190 (2)
H3A	−0.479500	0.366409	1.407001	0.028*
H3B	−0.534168	0.458611	1.204840	0.028*
H3C	−0.165882	0.453408	1.343402	0.028*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0293 (6)	0.0271 (5)	0.0186 (5)	0.000	0.0091 (4)	0.000
O2	0.0204 (4)	0.0160 (4)	0.0162 (4)	−0.0002 (2)	0.0045 (2)	0.0011 (2)
C1	0.0185 (6)	0.0176 (6)	0.0169 (6)	0.000	0.0008 (4)	0.000
C2	0.0145 (4)	0.0180 (5)	0.0145 (4)	−0.0006 (3)	0.0020 (3)	0.0009 (3)
C3	0.0206 (5)	0.0168 (4)	0.0199 (4)	0.0004 (3)	0.0044 (3)	−0.0027 (3)

Geometric parameters (Å, º)

O1—C1	1.1949 (16)	C2—C3	1.4773 (12)
O2—C1	1.3537 (10)	C3—H3A	0.9800
O2—C2	1.4110 (10)	C3—H3B	0.9800
C2—C2^i	1.3257 (18)	C3—H3C	0.9800
C1—O2—C2	107.30 (7)	C2—C3—H3A	109.5
O1—C1—O2^i	125.46 (5)	C2—C3—H3B	109.5
O1—C1—O2	125.46 (5)	H3A—C3—H3B	109.5
O2^i—C1—O2	109.07 (10)	C2—C3—H3C	109.5
C2^i—C2—O2	108.16 (4)	H3A—C3—H3C	109.5
C2^i—C2—C3	134.74 (5)	H3B—C3—H3C	109.5
O2—C2—C3	117.09 (7)
C2—O2—C1—O1	−178.43 (12)	C1—O2—C2—C2^i	−0.72 (8)
C2—O2—C1—O2^i	1.19 (12)	C1—O2—C2—C3	178.50 (8)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3A···O1^ii	0.98	2.53	3.4976 (13)	171

Symmetry code: (ii) x−1, y, z+1.