Strong overcrowding in dimethyl 2-(dimethyl­amino)terephthalate

The mol­ecular structure of the title compound, C₁₂H₁₅NO₄, has several features related to steric hindrance due to the ester and dimethyl­amine groups being located ortho with respect to one another. In particular, the carbonyl group of the ester is not coplanar with the ring, the amine N atom is in a pyramidal arrangement [the N atom is 0.2161 (12) Å from the three C atoms to which it is bonded] and the C atom of the adjacent ester group lies 0.3784 (14) Å out of the plane of the aromatic ring. The deformations found in the X-ray structure have been confirmed by ab initio quantum mechanical calculations.

S1. Comment

The title compound, (I), has been prepared as an electron-rich intermediate in the synthesis of new polymeric materials for electronics and photonics. In many of these systems, π conjugation between electron-rich and electron-poor moieties along the polymer chain is required (Dhanabalan et al., 2001).

The determination of the X-ray structure of (I) was undertaken on the basis of the presumed effects of steric overcrowding due to the location of the ester and dimethylamine groups ortho to one another; these effects could affect the planarity of the molecule and hence the π conjugation and performance of the derived compounds.

In terephthalic or benzoic acid derivatives, the carbonyl group is generally found to be coplanar with the phenyl ring (Centore et al., 1991; Centore & Tuzi, 1998). Deviations from coplanarity are observed as a result of steric overcrowding, e.g. for 2,6-disubstituted benzoic acids (Anca et al., 1967; Florencio & Smith, 1970).

Of the two carbonyl groups of (I), C9/O3 is essentially coplanar with the ring, as expected, while C2/O1, located ortho to the dimethylamine group, is not. The torsion of the carbonyl group does not fully relax the steric overcrowding, because of the contact between atom O1 and one of the H atoms bonded to atom C11. The dimethylamine group is also involved in the pattern of deformations.

In the absence of steric overcrowding, N,N-dialkyl groups are often found to be essentially coplanar with phenyl rings, and the geometry about the N atom is trigonal–planar, the sp²-hybridization favouring interaction of the lone pair with the π electrons of the ring (Centore et al., 1997, 2002; Centore & Tuzi, 2001; Castaldo et al., 2002). In (I), the N atom is in a pyramidal configuration [the sum of the valence angles around N1 is 353.3 (1)°]. Moreover, the disposition of the dimethylamine group is not symmetric with respect to the phenyl ring. In fact, the methyl group not involved in the close contact (C12) is essentially coplanar with the phenyl ring [0.133 (3) Å below the mean plane], while the other is not [0.874 (3) Å below the mean plane]. On the other hand, atom O1 lies 1.176 (3) Å above the mean plane of the phenyl ring.

An additional structural evidence probably still related to the steric overcrowding is the out-of-plane deformation of carbonyl atom C2. Actually, the phenyl ring is planar within 0.039 (1) Å, and atom C2 lies 0.378 (2) Å above the mean plane of the phenyl ring. It is worth noticing that the same type of deformation is not observed for atom N1, probably because of the π–π interaction between the N atom and the phenyl ring.

In summary, all of the deformations described above drive the nonbonded distance O1···C11 to 2.950 (2) Å.

We have searched the Cambridge Structural Database (CSD; Version 5.29; Allen, 2002) for compounds having an N,N-dimethylamine and a COO group ortho to one another. Out of the four hits found (refcodes CUNJEA, DOZDAX, ISOGOM and XERCOM), two are significant in this context (see Table 2). In one case (refcode CUNJEA; Swisher et al., 1984) the pattern of deformations is very similar to the present one. In the other (refcode ISOGOM; Davies et al., 2004) the pattern is different. In fact, the N atom has a trigonal–planar geometry, with the plane twisted with respect to the phenyl ring (by about 20°); a higher twist of the carbonyl group is observed and the carbonyl C atom is essentially coplanar with the phenyl ring. The different pattern observed in ISOGOM is probably due to the nitro group being in the para position with respect to the dimethylamine group (push–pull effect).

In view of the different deformations found in the X-ray structures, we have performed a theoretical quantum mechanical calculation of the gas phase molecular structure of (I) in order to verify the equilibrium geometry of the isolated molecule.

The gas phase equilibrium geometry of (I) has been computed by using Density Functional Theory, using the hybrid B3LYP exchange- correlation functional and the standard 6-31++G^** basis set. All computations have been performed using the GAUSSIAN03 package (Frisch et al., 2003).

There is a good agreement between the experimental and the computed molecular geometry (see Table 3); the bond lengths do not differ by more than 0.016 Å and the bond angles differ by a maximum of 1.6°. The three main structural effects related to the steric overcrowding, i.e. the torsion angle of the carbonyl group around C2—C3, the deformation of the dimethylamine group and the out-of-plane displacement of atom C2, are found also in the calculated geometry.

The UV–VIS characterization of (I) in chloroform solution shows the HOMO–LUMO band centered at λ_max = 350 nm, with a tail in the visible region, responsible for the yellow colour of (I). By exciting the compound at 350 nm, emission at 425 nm is observed (blue fluorescence). The measured quantum yield is 0.091.

Related literature

For related literature, see: Allen (2002); Anca et al. (1967); Castaldo et al. (2002); Centore & Tuzi (1998, 2001); Centore et al. (1991, 1997, 2002); Davies et al. (2004); Dhanabalan et al. (2001); Florencio & Smith (1970); Frisch et al. (2003); Lakowicz (1999); Swisher et al. (1984).

S2. Experimental

2-Aminoterephthalic acid (10 g, 55 mmol), methyliodide (62.5 g, 440 mmol), potassium carbonate (30.4 g) and 58 ml N,N-dimethylformamide were stirred at room temperature for 4 d in a round-bottomed flask equipped with a condenser connected to air through a CaCl₂ trap. The inorganic solid was then filtered off and the solution was poured into 200 ml of water at 273–278 K with stirring. Within some minutes a pasty solid formed. The solution was filtered, the solid was dissolved in chloroform and anhydrified over sodium sulfate, and the excess chloroform was distilled off. A yellow oil of (I) was finally obtained, which crystallized after several days (m.p. 322 K). Crystals of (I) suitable for structure determination were obtained by slow evaporation of a dichloromethane solution at room temperature. ¹H NMR (200 MHz, 298 K, CDCl₃): δ 2.89 (s, 6H, NCH₃), 3.91 (s, 6H, OCH₃), 7.45 (d, 1H, J₁ = 8.0 Hz, J₂ = 1.2 Hz, Ph), 7.598 (s, 1H, Ph), 7.66 (d, 1H, J₁ = 8.0 Hz, Ph).

S3. Refinement

H atoms were positioned stereochemically and constrained using a riding model, with U_iso(H) set at 1.2U_eq of the carrier atom for ring H atoms or 1.5U_eq of the carrier atom for methyl H atoms. For H atoms of methyl groups, the conformation was defined on the basis of difference maps. The H atoms of the two ester methyl groups and methylamine group (C11) are disordered over two sites rotated by 60° with respect to each other.

Computing details

Data collection: COLLECT (Nonius, 1999); cell refinement: DIRAX/LSQ (Duisenberg et al., 2000); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 50% probability level. Only one position is shown for H atoms of disordered methyl groups.

dimethyl 2-(dimethylamino)terephthalate

Crystal data

C12H15NO4	F(000) = 252
Mr = 237.25	Dx = 1.352 Mg m^−3
Triclinic, P1	Melting point: 322 K
a = 7.7120 (7) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.9190 (8) Å	Cell parameters from 180 reflections
c = 9.989 (3) Å	θ = 4.7–26.3°
α = 74.624 (14)°	µ = 0.10 mm^−1
β = 82.576 (16)°	T = 173 K
γ = 85.663 (9)°	Prism, yellow
V = 582.7 (2) Å^3	0.38 × 0.33 × 0.28 mm
Z = 2

Data collection

Bruker–Nonius KappaCCD diffractometer	2622 independent reflections
Radiation source: normal focus sealed tube	1977 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
Detector resolution: 9 pixels mm^-1	θmax = 27.5°, θmin = 3.2°
CCD rotation images, thick slices scans	h = −9→10
Absorption correction: multi-scan SADABS (Bruker–Nonius, 2002)	k = −10→8
Tmin = 0.952, Tmax = 0.972	l = −12→12
8647 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0514P)^2 + 0.1249P] where P = (Fo^2 + 2Fc^2)/3
2622 reflections	(Δ/σ)max < 0.001
158 parameters	Δρmax = 0.25 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

Special details

Experimental. The absorption and emission spectrum of (I) has been recorded in chloroform solution, using a modular spectro-fluorimeter, with monochromators and light source from Acton Research. The fluorescence quantum yield has been measured by comparison with a quinine sulfate standard solution (0.1 M H2SO4 in water). Both the sample and the standard have been excited at 350?nm. The solvent Raman emission at ca 390?nm has been subtracted from the emission spectrum in the range 380–400?nm. The sample quantum yield Q is 0.091 and has been obtained by the expression (Lakowicz, 1999) Q=QR×(I/IR)×(ODR/OD)×(n/nR)2 in which Q is the quantum yield, I is the integrated intensity, OD is the optical density and n the refractive index. The subscript R refers to the reference fluorophore of known quantum yield (QR=0.577, Lakowicz, 1999).

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)
O1	0.47151 (13)	0.20200 (14)	0.50560 (10)	0.0327 (3)
O2	0.22131 (13)	0.12717 (13)	0.44894 (9)	0.0298 (3)
O3	0.09094 (16)	−0.40205 (14)	1.13535 (10)	0.0397 (3)
O4	0.20049 (14)	−0.18755 (13)	1.20262 (9)	0.0316 (3)
N1	0.34854 (16)	0.29631 (14)	0.78190 (12)	0.0262 (3)
C1	0.2926 (2)	0.1799 (2)	0.30224 (14)	0.0337 (4)
H1A	0.3038	0.3073	0.2733	0.051*	0.776 (18)
H1B	0.2138	0.1463	0.2451	0.051*	0.776 (18)
H1C	0.4080	0.1217	0.2897	0.051*	0.776 (18)
H1D	0.3133	0.0762	0.2654	0.051*	0.224 (18)
H1E	0.4032	0.2372	0.2937	0.051*	0.224 (18)
H1F	0.2091	0.2618	0.2490	0.051*	0.224 (18)
C2	0.32830 (18)	0.14155 (17)	0.54078 (14)	0.0237 (3)
C3	0.25481 (17)	0.06346 (17)	0.68881 (13)	0.0217 (3)
C4	0.17405 (18)	−0.09610 (18)	0.71668 (14)	0.0245 (3)
H4	0.1443	−0.1349	0.6407	0.029*
C5	0.13578 (18)	−0.20008 (17)	0.85184 (13)	0.0242 (3)
H5	0.0804	−0.3081	0.8686	0.029*
C6	0.18083 (17)	−0.14146 (17)	0.96195 (13)	0.0217 (3)
C7	0.25243 (17)	0.02053 (17)	0.93814 (13)	0.0227 (3)
H7	0.2792	0.0584	1.0155	0.027*
C8	0.28683 (17)	0.13111 (17)	0.80168 (13)	0.0210 (3)
C9	0.15006 (18)	−0.25888 (17)	1.10732 (14)	0.0243 (3)
C10	0.1882 (2)	−0.2932 (2)	1.34595 (14)	0.0359 (4)
H10A	0.0682	−0.2842	1.3904	0.054*	0.689 (19)
H10B	0.2686	−0.2511	1.3971	0.054*	0.689 (19)
H10C	0.2197	−0.4159	1.3473	0.054*	0.689 (19)
H10D	0.3028	−0.3499	1.3661	0.054*	0.311 (19)
H10E	0.1023	−0.3831	1.3594	0.054*	0.311 (19)
H10F	0.1513	−0.2183	1.4092	0.054*	0.311 (19)
C11	0.2981 (2)	0.44154 (18)	0.66779 (15)	0.0333 (4)
H11A	0.2138	0.4023	0.6182	0.050*	0.781 (18)
H11B	0.4021	0.4821	0.6029	0.050*	0.781 (18)
H11C	0.2445	0.5379	0.7056	0.050*	0.781 (18)
H11D	0.3598	0.5459	0.6663	0.050*	0.219 (18)
H11E	0.1715	0.4661	0.6815	0.050*	0.219 (18)
H11F	0.3291	0.4103	0.5789	0.050*	0.219 (18)
C12	0.3864 (2)	0.3510 (2)	0.90307 (15)	0.0329 (3)
H12A	0.2765	0.3708	0.9591	0.049*
H12B	0.4498	0.4597	0.8717	0.049*
H12C	0.4584	0.2591	0.9599	0.049*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0339 (6)	0.0378 (6)	0.0277 (5)	−0.0114 (5)	0.0026 (4)	−0.0109 (4)
O2	0.0304 (6)	0.0390 (6)	0.0186 (5)	−0.0058 (4)	−0.0031 (4)	−0.0037 (4)
O3	0.0619 (8)	0.0289 (6)	0.0268 (5)	−0.0173 (5)	−0.0039 (5)	−0.0009 (4)
O4	0.0445 (6)	0.0306 (6)	0.0192 (5)	−0.0090 (5)	−0.0052 (4)	−0.0029 (4)
N1	0.0344 (7)	0.0213 (6)	0.0234 (6)	−0.0051 (5)	−0.0013 (5)	−0.0065 (4)
C1	0.0416 (9)	0.0403 (9)	0.0183 (7)	−0.0047 (7)	−0.0029 (6)	−0.0055 (6)
C2	0.0285 (7)	0.0209 (6)	0.0226 (7)	−0.0015 (6)	−0.0023 (5)	−0.0074 (5)
C3	0.0219 (7)	0.0218 (6)	0.0206 (6)	0.0010 (5)	−0.0017 (5)	−0.0047 (5)
C4	0.0268 (7)	0.0261 (7)	0.0228 (7)	−0.0016 (6)	−0.0038 (5)	−0.0094 (5)
C5	0.0265 (7)	0.0206 (6)	0.0257 (7)	−0.0036 (5)	−0.0011 (5)	−0.0063 (5)
C6	0.0217 (7)	0.0212 (6)	0.0210 (6)	0.0006 (5)	−0.0007 (5)	−0.0044 (5)
C7	0.0248 (7)	0.0234 (7)	0.0210 (6)	−0.0003 (5)	−0.0016 (5)	−0.0085 (5)
C8	0.0195 (6)	0.0202 (6)	0.0234 (6)	−0.0004 (5)	−0.0002 (5)	−0.0071 (5)
C9	0.0254 (7)	0.0236 (7)	0.0227 (7)	−0.0005 (6)	−0.0016 (5)	−0.0048 (5)
C10	0.0443 (9)	0.0412 (9)	0.0200 (7)	−0.0087 (7)	−0.0066 (6)	−0.0005 (6)
C11	0.0465 (9)	0.0222 (7)	0.0287 (7)	−0.0045 (6)	0.0021 (6)	−0.0043 (6)
C12	0.0413 (9)	0.0282 (7)	0.0325 (8)	−0.0106 (7)	−0.0028 (6)	−0.0120 (6)

Geometric parameters (Å, º)

O1—C2	1.2095 (17)	C5—C6	1.3928 (19)
O1—C11	2.9492 (19)	C5—H5	0.9500
O2—C2	1.3419 (16)	C6—C7	1.3851 (19)
O2—C1	1.4579 (16)	C6—C9	1.5026 (18)
O3—C9	1.2035 (17)	C7—C8	1.4157 (18)
O4—C9	1.3381 (17)	C7—H7	0.9500
O4—C10	1.4494 (16)	C10—H10A	0.9800
N1—C8	1.3819 (17)	C10—H10B	0.9800
N1—C11	1.4577 (18)	C10—H10C	0.9800
N1—C12	1.4581 (18)	C10—H10D	0.9800
C1—H1A	0.9800	C10—H10E	0.9800
C1—H1B	0.9800	C10—H10F	0.9800
C1—H1C	0.9800	C11—H11A	0.9800
C1—H1D	0.9800	C11—H11B	0.9800
C1—H1E	0.9800	C11—H11C	0.9800
C1—H1F	0.9800	C11—H11D	0.9800
C2—C3	1.4971 (18)	C11—H11E	0.9800
C3—C4	1.3963 (19)	C11—H11F	0.9800
C3—C8	1.4253 (18)	C12—H12A	0.9800
C4—C5	1.3900 (19)	C12—H12B	0.9800
C4—H4	0.9500	C12—H12C	0.9800
C2—O1—C11	78.56 (9)	H10A—C10—H10B	109.5
C2—O2—C1	115.63 (11)	O4—C10—H10C	109.5
C9—O4—C10	117.26 (11)	H10A—C10—H10C	109.5
C8—N1—C11	120.81 (12)	H10B—C10—H10C	109.5
C8—N1—C12	118.93 (11)	O4—C10—H10D	109.5
C11—N1—C12	113.52 (11)	H10A—C10—H10D	141.1
O2—C1—H1A	109.5	H10B—C10—H10D	56.3
O2—C1—H1B	109.5	H10C—C10—H10D	56.3
H1A—C1—H1B	109.5	O4—C10—H10E	109.5
O2—C1—H1C	109.5	H10A—C10—H10E	56.3
H1A—C1—H1C	109.5	H10B—C10—H10E	141.1
H1B—C1—H1C	109.5	H10C—C10—H10E	56.3
O2—C1—H1D	109.5	H10D—C10—H10E	109.5
H1A—C1—H1D	141.1	O4—C10—H10F	109.5
H1B—C1—H1D	56.3	H10A—C10—H10F	56.3
H1C—C1—H1D	56.3	H10B—C10—H10F	56.3
O2—C1—H1E	109.5	H10C—C10—H10F	141.1
H1A—C1—H1E	56.3	H10D—C10—H10F	109.5
H1B—C1—H1E	141.1	H10E—C10—H10F	109.5
H1C—C1—H1E	56.3	N1—C11—O1	80.37 (8)
H1D—C1—H1E	109.5	N1—C11—H11A	109.5
O2—C1—H1F	109.5	O1—C11—H11A	69.4
H1A—C1—H1F	56.3	N1—C11—H11B	109.5
H1B—C1—H1F	56.3	O1—C11—H11B	62.4
H1C—C1—H1F	141.1	H11A—C11—H11B	109.5
H1D—C1—H1F	109.5	N1—C11—H11C	109.5
H1E—C1—H1F	109.5	O1—C11—H11C	169.4
O1—C2—O2	122.92 (12)	H11A—C11—H11C	109.5
O1—C2—C3	124.74 (12)	H11B—C11—H11C	109.5
O2—C2—C3	112.22 (11)	N1—C11—H11D	109.5
C4—C3—C8	119.69 (11)	O1—C11—H11D	117.6
C4—C3—C2	116.99 (11)	H11A—C11—H11D	141.1
C8—C3—C2	122.65 (11)	H11B—C11—H11D	56.3
C5—C4—C3	122.22 (12)	H11C—C11—H11D	56.3
C5—C4—H4	118.9	N1—C11—H11E	109.5
C3—C4—H4	118.9	O1—C11—H11E	125.1
C4—C5—C6	118.14 (12)	H11A—C11—H11E	56.3
C4—C5—H5	120.9	H11B—C11—H11E	141.1
C6—C5—H5	120.9	H11C—C11—H11E	56.3
C7—C6—C5	120.93 (12)	H11D—C11—H11E	109.5
C7—C6—C9	120.86 (12)	N1—C11—H11F	109.5
C5—C6—C9	118.21 (12)	O1—C11—H11F	29.4
C6—C7—C8	121.76 (12)	H11A—C11—H11F	56.3
C6—C7—H7	119.1	H11B—C11—H11F	56.3
C8—C7—H7	119.1	H11C—C11—H11F	141.1
N1—C8—C7	120.39 (11)	H11D—C11—H11F	109.5
N1—C8—C3	122.74 (11)	H11E—C11—H11F	109.5
C7—C8—C3	116.87 (12)	N1—C12—H12A	109.5
O3—C9—O4	123.56 (12)	N1—C12—H12B	109.5
O3—C9—C6	124.40 (12)	H12A—C12—H12B	109.5
O4—C9—C6	112.02 (11)	N1—C12—H12C	109.5
O4—C10—H10A	109.5	H12A—C12—H12C	109.5
O4—C10—H10B	109.5	H12B—C12—H12C	109.5
C11—O1—C2—O2	120.59 (13)	C11—N1—C8—C3	33.88 (19)
C11—O1—C2—C3	−63.86 (13)	C12—N1—C8—C3	−176.74 (13)
C1—O2—C2—O1	3.47 (19)	C6—C7—C8—N1	176.12 (12)
C1—O2—C2—C3	−172.58 (11)	C6—C7—C8—C3	−3.89 (19)
O1—C2—C3—C4	−134.11 (15)	C4—C3—C8—N1	−172.80 (12)
O2—C2—C3—C4	41.85 (16)	C2—C3—C8—N1	16.9 (2)
O1—C2—C3—C8	36.5 (2)	C4—C3—C8—C7	7.21 (19)
O2—C2—C3—C8	−147.57 (12)	C2—C3—C8—C7	−163.11 (12)
C8—C3—C4—C5	−5.4 (2)	C10—O4—C9—O3	2.4 (2)
C2—C3—C4—C5	165.49 (13)	C10—O4—C9—C6	−176.01 (12)
C3—C4—C5—C6	−0.2 (2)	C7—C6—C9—O3	−178.82 (14)
C4—C5—C6—C7	3.7 (2)	C5—C6—C9—O3	1.0 (2)
C4—C5—C6—C9	−176.17 (12)	C7—C6—C9—O4	−0.46 (18)
C5—C6—C7—C8	−1.6 (2)	C5—C6—C9—O4	179.41 (12)
C9—C6—C7—C8	178.28 (12)	C8—N1—C11—O1	−60.33 (12)
C11—N1—C8—C7	−146.13 (13)	C12—N1—C11—O1	148.76 (11)
C12—N1—C8—C7	3.25 (19)	C2—O1—C11—N1	81.04 (11)