N-(2,6-Diisopropyl­phen­yl)formamide

Jackson M Chitanda; J Wilson Quail; Stephen R Foley

doi:10.1107/S1600536808024811

. 2008 Aug 9;64(Pt 9):o1728. doi: 10.1107/S1600536808024811

N-(2,6-Diisopropylphenyl)formamide

Jackson M Chitanda ^a, J Wilson Quail ^b, Stephen R Foley ^a,^*

PMCID: PMC2960669 PMID: 21201711

Abstract

The title compound, C₁₃H₁₉NO, exhibits a non-planar structure in which the 2,6-diisopropylphenyl ring is tilted at a dihedral angle of 77.4 (1)° with respect to the formamide group. This is the largest dihedral angle known among structurally characterized formamides. The molecules are linked via N—H⋯O hydrogen bonds, forming infinite chains which run along the b-axis directions.

Related literature

For related literature, see: Boeyens et al. (1988 ▶); Ferguson et al. (1998 ▶); Gowda et al. (2000 ▶); Krishnamurthy (1982 ▶); LaPlanche & Rogers (1964 ▶); Omondi et al. (2005 ▶); Cerecetto et al. (2004 ▶); Chitanda et al. (2008 ▶).

Experimental

Crystal data

C₁₃H₁₉NO
M _r = 205.29
Monoclinic,
a = 8.9581 (15) Å
b = 8.7684 (15) Å
c = 15.840 (6) Å
β = 105.381 (10)°
V = 1199.6 (5) Å³
Z = 4
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 173 (2) K
0.25 × 0.05 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: none
7758 measured reflections
2365 independent reflections
1556 reflections with I > 2σ(I)
R _int = 0.070

Refinement

R[F ² > 2σ(F ²)] = 0.054
wR(F ²) = 0.128
S = 1.05
2365 reflections
140 parameters
H-atom parameters constrained
Δρ_max = 0.15 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ▶); data reduction: DENZO (Otwinowski & Minor, 1997 ▶) and SCALEPACK; 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: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808024811/bv2100sup1.cif

e-64-o1728-sup1.cif^{(16.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808024811/bv2100Isup2.hkl

e-64-o1728-Isup2.hkl^{(116.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1⋯O1ⁱ	0.88	2.04	2.910 (2)	171

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Symmetry code: (i) Inline graphic .

Acknowledgments

Financial assistance for this project was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) for an operating grant to SRF, and by the Canadian Government through the Commonwealth Scholarship fund for JMC.

supplementary crystallographic information

Comment

As part of the ongoing research in our laboratory directed at the synthesis substituted iminoisoindolines (Chitanda et al., 2008), the title compound was obtained as a by-product and then purposefully synthesized in 92% yield. N-(2,6-diisopropylphenyl)formamide has been previously reported (Krishnamurthy, 1982), however no X-ray structure nor NMR data has been previously published. We have now determined the single-crystal X-ray structure of the title compound, (I).

The ¹H NMR (CDCl₃) spectra of I is a mixture of two carbon-nitrogen bond rotomers, where the ratio of the major rotomer to the minor rotomer is about 2:1. Upon crystallization however, the solid state structure shows exclusive formation of the cisoidal rotomer. As shown in Figure 1, the carbonyl group on the formamide moiety is positioned almost perpendicular to the plane of the aromatic ring, and is oriented cis to the aromatic group about the carbon-nitrogen bond. The dihedral angle between the plane of the aromatic ring and that formed by the N—C=O moiety is 77.4 (1)°, which is considerably larger than the corresponding angle in previously structurally characterized aryl-substituted formamides (Figure 3). This is attributed to the presence of the bulky isopropyl groups on the ortho positions of the phenyl ring which increases torsional strain between the two planes defining the dihedral angle. For example, in the less bulky analogue, N-(4-methoxyphenyl)formamide, the dihedral angle is only 8.0 (3)° (Figure 3, Cerecetto et al., 2004). The two isomers of the title compound arise due to hindered rotation about the amidic bond (LaPlanche et al., 1964). (I) crystallizes in the monoclinic space group P21/c. The molecules of (I) are linked to form infinite chains which run along the b axis direction via N—H···O hydrogen bonds (details in Table 3).

Experimental

The refined procedure for the synthesis of (I) is as follows: A solution of 2,6-diisopropyl aniline (4.695 g, 26.5 mmol s) and formic acid (7.314 g, 159.0 mmol, 6eq.) in chloroform (20 ml) was refluxed with continuous stirring for 16 hrs. The colour of the solution changed from yellow to green to colorless over the course of the reaction. The solvent and excess formic acid were removed under vacuum to yield the title compound as a white solid. Needle-like single crystals suitable for X-ray analysis were obtained from slow evaporation of a chloroform solution (5.00 g, 92%). 1H-NMR (CDCl₃, p.p.m.): Two rotomers observed in 2:1 ratio. Major Rotomer: δ 1.19 (d, J = 6.9 Hz, 12H, –CH(CH3)2), δ 3.08 (septet, J = 6.9 Hz, 2H, –CH(CH₃)₂) δ 6.64 (s(br), 1H, –NH–), δ 7.17 (m, 2H, aromatic), δ 7.30 (m, 1H, aromatic), δ 8.47 (s, 1H, –C(H)=O). ¹³C-NMR (CDCl₃, p.p.m.): δ 23.74 (CH(CH3)2), d 28.9 (–CH(CH3)2), d 123.6, δ 128.7, δ 129.9, δ 146.2, δ 161.0 (–C(H)=O). Minor Rotomer: δ 1.20 (d, J = 6.9 Hz, 12H, –CH(CH₃)₂), δ 3.20 (septet, J = 6.9 Hz, 2H, –CH(CH₃)₂) δ 7.02 (d, J = 11.2 Hz, 1H, –NH–), δ 7.19 (m, 2H, aromatic), δ 7.30 (m, 1H, aromatic), δ 8.0 (d, J = 11.2 Hz, 1H, –C(H)=O). ¹³C-NMR (CDCl₃, p.p.m.), Major Rotomer: δ 23.77 (–CH(CH₃)₂), δ 28.6 (–CH(CH₃)₂), δ 123.9, δ 129.0, δ 130.4, δ 146.9, δ 165.9 (–C(H)=O). ESI-MS (m/z): calcd. for C13H19NO; 205.1467, 206.1545 [M+H]⁺; found; 206.1546 [M+H]⁺.