2-Chloro-4,6-di­methoxy-1,3,5-triazine

The mol­ecules of 2-chloro-4,6-di­methoxy-1,3,5-triazine, C₅H₆ClN₃O₂, lie on a crystallographic mirror plane. There is a close contact of 3.180 (3) Å between one of the methyl C atoms and the N atom of a neighboring mol­ecule. Differential scanning calorimetry measurements show that methyl rearrangement does not take place in the solid state, despite the close proximity of the methyl group to the N atom.

S1. Comment

2-Chloro-4,6-dimethoxy-1,3,5-triazine, (I), has been examined for its ability to undergo methyl rearrangement in the solid or liquid-state (Kaftory & Handelsman-Benory, 1994; Handelsman-Benory at al., 2000; Greenberg at al. 2001; Kaftory at al., 2001; Kaftory, 2002). Therefore, we have investigated the structure and thermal behavior of 2,4-dimethoxy-6-chloro-1,3,5-triazine. 2,4-Dimethoxy-6-chloro-1,3,5-triazine crystallizes in the orthorhombic crystal system, in space group Pbcm (Fig. 1). Based on their work on s-triazine derivatives, Glowka & Iwanicka (1989a, 1989b) concluded that the endocyclic bond angles at all N atoms are less than 120°, while those at the C atoms are larger than 120°, irrespective of their hybridization. The molecular geometry of (I) has the same characteristics; the endocyclic bond angles at the N atoms lie in the range 126.9 (2)–128.7 (3)° and those at the C atoms lie in the range 111.9 (2)–112.8 (2)°. The steric effects are best observed by the differences between outer-ring bond angles at the C atoms. Those bond angles at the side of the methyl group are larger [119.6 (2) and 120.0 (2)°] than the other outer-ring bond angles [113.5 (2) and 112.7 (2)°]. Since the substituent on atom C1 is symmetric with respect to atoms N1 and N2 the outer bond angles at atom C1 are practically equal [115.4 (2) and 115.9 (2)°].

The molecules lie on a crystallographic mirror plane. Succesive layers along the c axis are shifted by 1.720 (3) Å relative to one another, parallel to the b axis. As a result, the overlap between two molecules (shown in Fig. 2) is such that parallel columns of Cl atoms are formed, the interatomic distance between the Cl atoms of two neighboring columns being 3.972 (3) Å. The molecules within a layer are arranged in rows along the b axis (Fig. 1), so that a methyl group of one molecule is close [3.180 (3) Å] to an N atom of the second molecule in the same row. This short contact and the O—C···N angle of 177.5 (2)° are the ideal geometry that is expected for methyl rearrangement to take place in the solid state, as described in the references mentioned above. Similar geometry was found in 2-(p-trideuteromethoxyphenyl)-5-trideuteromethoxy-1,3,4-oxadiazole that undergoes methyl rearrangement in the solid state [Dessolin et al. (1992)] where the distance between the methyl C atom and the N atom is 2.992 Å and the O—C···N bond angle is 164.9°. However, the DSC thermograph of I (Fig. 3) indicates that in this compound the methyl rearrangement does not take place in the solid state. The first endothermic peak at 354 K with ΔH = 17.5 kJ mol⁻¹ is attributed to the melting of the compound. The ripples at higher temperature are the result of spillage of the melt, and the exothermic peak at 512 K is assigned to a methyl rearrangement in the liquid state. The melting temperature of (I) is lower (354 K) than the expected temperature of topochemically assisted methyl rearrangement in the solid state (373 K) of closely related compounds, as shown by Kaftory & Handelsman- Benory (1994), Handelsman-Benory at al. (2000) and Kaftory (2002); therefore, methyl rearrangement in the solid state of (I) does not take place.

Scheme 1

Figures 1–3

Crystal data

S2. Experimental

2,4-Dimethoxy-6-chloro-1,3,5-triazine (I) was prepared according to the procedure of Cronin et al. (1996) and crystallized from a 1:1 mixture of chloroform and n-heptane.

S3. Refinement

During refinement, H atoms were constrained to ride on their parent atoms. The methyl H atoms are disordered over two sites with equal occupancies.

Computing details

Data collection: Collect (Nonius, 2000); cell refinement: DENZO–SMN (Otwinowski & Minor 1997); data reduction: DENZO–SMN (Otwinowski & Minor 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997).

Figures

	Fig. 1. A layer of molecules of (I), showing the short distances between methyl C and N atoms of neighbouring molecules (the two sets of the disordered methyl H atoms are shown). Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.
	Fig. 2. An overlap diagram, viewed along the c axis. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.
	Fig. 3. A DSC (diferential scanning calorimetry) thermogram of a 5.8 mg sample of (I), measured at a heating rate of 10° min^−1.

2-Chloro-4,6-dimethoxy-1,3,5-triazine

Crystal data

C5H6ClN3O2	Z = 4
Mr = 175.58	F(000) = 360
Orthorhomic, Pbcm	Dx = 1.546 Mg m^−3
Hall symbol: -P 2c 2b	Mo Kα radiation, λ = 0.71073 Å
a = 7.743 (1) Å	Cell parameters from 1249 reflections
b = 14.940 (3) Å	θ = 2.6–25.0°
c = 6.523 (1) Å	µ = 0.46 mm^−1
α = 90°	T = 293 K
β = 90°	Plate, colorless
γ = 90°	0.32 × 0.20 × 0.12 mm
V = 754.6 (2) Å^3

Data collection

Nonius KappaCCD diffractometer	493 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.030
Graphite monochromator	θmax = 25.0°, θmin = 2.6°
Detector resolution: 95 pixels mm^-1	h = −9→9
ϕ scans	k = −17→17
1249 measured reflections	l = −7→7
726 independent reflections

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)] = 0.031	H-atom parameters constrained
wR(F^2) = 0.075	w = 1/[σ^2(Fo^2) + (0.0431P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.89	(Δ/σ)max < 0.001
726 reflections	Δρmax = 0.15 e Å^−3
70 parameters	Δρmin = −0.14 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: 0.016 (4)

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	Occ. (<1)
Cl	0.32694 (9)	0.17414 (5)	0.2500	0.0629 (3)
O1	−0.1782 (2)	0.36094 (12)	0.2500	0.0531 (5)
O2	−0.2652 (2)	0.06174 (12)	0.2500	0.0524 (5)
N1	0.0130 (3)	0.11433 (14)	0.2500	0.0436 (6)
N2	0.0514 (3)	0.27225 (15)	0.2500	0.0447 (6)
N3	−0.2325 (3)	0.21017 (14)	0.2500	0.0432 (6)
C1	0.1054 (4)	0.1889 (2)	0.2500	0.0432 (7)
C2	−0.1214 (4)	0.27744 (18)	0.2500	0.0411 (7)
C3	−0.1551 (4)	0.13012 (18)	0.2500	0.0409 (6)
C4	−0.3624 (4)	0.3752 (2)	0.2500	0.0587 (9)
H4A	−0.4091	0.3580	0.3806	0.088*	0.50
H4B	−0.4144	0.3396	0.1440	0.088*	0.50
H4C	−0.3863	0.4373	0.2254	0.088*	0.50
C5	−0.1928 (4)	−0.02792 (18)	0.2500	0.0643 (8)
H5A	−0.1483	−0.0415	0.3838	0.096*	0.50
H5B	−0.1012	−0.0313	0.1512	0.096*	0.50
H5C	−0.2813	−0.0703	0.2150	0.096*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl	0.0359 (4)	0.0743 (6)	0.0784 (5)	−0.0003 (4)	0.000	0.000
O1	0.0521 (13)	0.0433 (12)	0.0640 (11)	0.0020 (10)	0.000	0.000
O2	0.0404 (11)	0.0442 (12)	0.0726 (12)	−0.0039 (9)	0.000	0.000
N1	0.0367 (14)	0.0477 (15)	0.0464 (11)	−0.0003 (12)	0.000	0.000
N2	0.0424 (16)	0.0457 (16)	0.0459 (13)	−0.0022 (11)	0.000	0.000
N3	0.0413 (14)	0.0412 (15)	0.0473 (12)	0.0005 (11)	0.000	0.000
C1	0.0395 (16)	0.056 (2)	0.0340 (14)	−0.0010 (15)	0.000	0.000
C2	0.0484 (19)	0.0398 (18)	0.0351 (14)	0.0017 (14)	0.000	0.000
C3	0.0419 (17)	0.0464 (17)	0.0343 (13)	−0.0029 (15)	0.000	0.000
C4	0.050 (2)	0.060 (2)	0.0664 (18)	0.0109 (16)	0.000	0.000
C5	0.058 (2)	0.0400 (19)	0.095 (2)	0.0004 (17)	0.000	0.000

Geometric parameters (Å, º)

Cl—C1	1.729 (3)	N3—C2	1.323 (3)
O1—C2	1.323 (3)	N3—C3	1.338 (3)
O1—C4	1.442 (3)	C4—H4A	0.9600
O2—C3	1.331 (3)	C4—H4B	0.9600
O2—C5	1.452 (3)	C4—H4C	0.9600
N1—C3	1.323 (3)	C5—H5A	0.9600
N1—C1	1.324 (3)	C5—H5B	0.9600
N2—C1	1.314 (3)	C5—H5C	0.9600
N2—C2	1.340 (3)
C2—O1—C4	117.9 (2)	O2—C3—N3	113.5 (2)
C3—O2—C5	117.5 (2)	O1—C4—H4A	109.5
C3—N1—C1	112.4 (2)	O1—C4—H4B	109.5
C1—N2—C2	111.9 (2)	H4A—C4—H4B	109.5
C2—N3—C3	112.8 (2)	O1—C4—H4C	109.5
N2—C1—N1	128.7 (3)	H4A—C4—H4C	109.5
N2—C1—Cl	115.9 (2)	H4B—C4—H4C	109.5
N1—C1—Cl	115.4 (2)	O2—C5—H5A	109.5
N3—C2—O1	120.0 (2)	O2—C5—H5B	109.5
N3—C2—N2	127.2 (2)	H5A—C5—H5B	109.5
O1—C2—N2	112.7 (2)	O2—C5—H5C	109.5
N1—C3—O2	119.6 (2)	H5A—C5—H5C	109.5
N1—C3—N3	126.9 (2)	H5B—C5—H5C	109.5
C2—N2—C1—N1	0.0	C1—N2—C2—N3	0.0
C2—N2—C1—Cl	180.0	C1—N2—C2—O1	180.0
C3—N1—C1—N2	0.0	C1—N1—C3—O2	180.0
C3—N1—C1—Cl	180.0	C1—N1—C3—N3	0.0
C3—N3—C2—O1	180.0	C5—O2—C3—N1	0.0
C3—N3—C2—N2	0.0	C5—O2—C3—N3	180.0
C4—O1—C2—N3	0.0	C2—N3—C3—N1	0.0
C4—O1—C2—N2	180.0	C2—N3—C3—O2	180.0