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organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoIUCrDATA
ISSN: 2414-3146
Volume 4| Part 12| December 2019| x191629
https://doi.org/10.1107/S2414314619016298

1,1,3,3-Tetra­ethyl-5-nitro­isoindoline

CROSSMARK_Color_square_no_text.svg
Lukas Tapmeyer,a Maurice Beskea and Jörn Plackmeyerb*

aInstitut für Anorganische und Analytische Chemie, Goethe-Universität, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main, Germany, and bInstitut für Physikalische und Theoretische Chemie, Goethe-Universität, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main, Germany
*Correspondence e-mail: jp@prisner.de

Edited by C. Rizzoli, Universita degli Studi di Parma, Italy (Received 19 November 2019; accepted 3 December 2019; online 17 December 2019)

The title compound, C16H24N2O2, previously obtained as a yellow oil, exhibits a rather low melting point close to room temperature 297–298 K). In the mol­ecule, the isoindoline ring system is approximately planar and coplanar to the nitro group, forming a dihedral angle of 5.63 (15)°. In the crystal, only weak N—H⋯O and C—H⋯π inter­actions are observed, linking mol­ecules into chains parallel to the [101] direction.

CCDC reference: 1969794

Similar articles
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[Scheme 3D1]
Chemical scheme
[Scheme 1]

Structure description

1,1,3,3-Tetra­ethyl-5-nitro­isoindoline is a precursor in the synthesis of 1,1,3,3-tetra­ethyl­isoindolin-5-iso­thio­cyanate-2-oxyl, which in turn is a versatile reduction-resistant spin label for RNA (Saha et al., 2015[Saha, S., Jagtap, A. P. & Sigurdsson, S. Th. (2015). Chem. Commun. 51, 13142-13145.]). The atomic connectivity of the title compound has been established by NMR spectroscopy and confirmed by several analytical methods (Haugland et al., 2016[Haugland, M. M., El-Sagheer, A. H., Porter, R. J., Peña, J., Brown, T., Anderson, E. A. & Lovett, J. E. (2016). J. Am. Chem. Soc. 138, 9069-9072.]) but its crystal structure remained unknown, mainly due to its low melting point of 297–298 K (Tönjes et al., 1964[Tönjes, H., Heidenbluth, K. & Scheffler, R. (1964). J. Prakt. Chem. 26, 218-224.]).

The title compound (Fig. 1[link]) crystallizes in the monoclinic space group P21/n with one mol­ecule in the asymmetric unit. The isoindoline ring system is approximately planar [r.m.s deviation of the nine fitted atoms = 0.0542 Å; maximum deviation 0.1005 (14) Å for atom N2] and forms a dihedral angle of 5.63 (15)° with the plane through the nitro group. In the crystal structure, each N—H group links via a weak hydrogen bond (Table 1[link]) to the O—N group of an adjacent mol­ecule. Centrosymmetrically related chains are further connected by weak C—H⋯π inter­actions (Table 1[link]), forming chains parallel to [101]. Other inter­actions such as π–π stacking are not observed, which could be explained by the sterically demanding ethyl groups. This lack of strong inter­molecular inter­actions may account for the low melting point of the substance.

Table 1
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the C3A/C4/C5/C6/C7/C7A benzene ring.
D—H⋯A D—H H⋯A D⋯A D—H⋯A
N2—H2⋯O81i 0.865 (15) 2.634 (16) 3.4860 (18) 168.4 (16)
C11—H11B⋯Cg1ii 0.99 2.91 3.7552 (18) 144
Symmetry codes: (i) x+1, y, z+1; (ii) -x+1, -y+1, -z+1.
[Figure 1]
Figure 1
The mol­ecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

A search of the Cambridge Structural Database (CSD, version 5.40, update August 2019; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) for lengths of hydrogen bonds has been performed with a search fragment of a twofold carbon-bound N—H donor to a carbon-bound NO2 acceptor (Fig. 2[link]). The mean length of (C–)2N—H⋯O(–NOR) hydrogen bonds in deposited structures was found to be 2.28 (19) Å. This renders the H2⋯O81 length of 2.634 (16) Å found in the title compound a rather long but plausible peculiarity. Since the position of the H atom was freely refined against X-ray data, the H⋯O distance as well as the (still plausible) N—H distance is not fully trustworthy. The mean donor–acceptor distance for hydrogen bonds was found to be 2.96 (8) Å with a maximum of 3.07 Å. This confirms the value of 3.4860 (18) Å found for N2⋯O81 to be rather long.

[Figure 2]
Figure 2
Search fragment for relevant hydrogen bonds in the CSD.

Synthesis and crystallization

The title compound was synthesized in-house, using a modified literature procedure (Haugland et al., 2016[Haugland, M. M., El-Sagheer, A. H., Porter, R. J., Peña, J., Brown, T., Anderson, E. A. & Lovett, J. E. (2016). J. Am. Chem. Soc. 138, 9069-9072.]) as follows: to a solution of 1,1,3,3-tetra­ethyl­isoindoline (2.192 g, 9.47 mmol) in 21.9 ml sulfuric acid (95%), 21.9 ml of fuming nitric acid (100%) was added dropwise. During the addition, the reaction flask was cooled with ice/sodium chloride in order to hold the reaction temperature between −5 and 0°C (inter­nal temperature control). The onset of the reaction was accompanied by a strong rise of temperature. After complete addition of nitric acid, the yellow solution was stirred at 0°C for 60 min. The cold reaction mixture was poured carefully into a cooled beaker containing 30 g of sodium hydroxide and 300 ml of ice/water. The pH of the resulting pale-yellow suspension was adjusted to 10 by the addition of more sodium hydroxide and the solution was stirred for 15 min. The aqueous solution was extracted four times with 100–150 ml of di­chloro­methane. The combined organic phases were washed with brine and dried over Na2SO4. After removing the solvent, the yellow residue was purified by means of column chromatography (alumina, 4% H2O, 3×28 cm) with hexa­nes/ethyl acetate (95:5 v/v). The product was obtained as a yellow oil. Yield: 2.583 g (9.34 mmol, 98.7%). Crystals were obtained after storing the product at 277 K for 48 h. Several good-looking, yellow crystals could then be picked from the yellow oil. NMR analysis of the measured crystal confirmed its chemical identity with the yellow oil.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link].

Table 2
Experimental details

Crystal data
Chemical formula C16H24N2O2
Mr 276.37
Crystal system, space group Monoclinic, P21/n
Temperature (K) 173
a, b, c (Å) 9.0277 (6), 19.9356 (13), 9.4811 (7)
β (°) 116.169 (2)
V (Å3) 1531.43 (18)
Z 4
Radiation type Cu Kα
μ (mm−1) 0.63
Crystal size (mm) 1.20 × 0.60 × 0.60
 
Data collection
Diffractometer Siemens Bruker three circle
Absorption correction Multi-scan (SADABS; Bruker, 2015[Bruker (2015). APEX3, SAINT and SADABS. Madison, Wisconsin: Bruker AXS Inc.])
Tmin, Tmax 0.568, 0.753
No. of measured, independent and observed [I > 2σ(I)] reflections 32894, 2769, 2699
Rint 0.053
(sin θ/λ)max (Å−1) 0.608
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.051, 0.134, 1.09
No. of reflections 2769
No. of parameters 185
H-atom treatment H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3) 0.38, −0.25
Computer programs: APEX3 and SAINT (Bruker, 2015[Bruker (2015). APEX3, SAINT and SADABS. Madison, Wisconsin: Bruker AXS Inc.]), SHELXT (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2018/3 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), Mercury (Macrae et al., 2006[Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453-457.]), ORTEP-3 for Windows (Farrugia, 2012[Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849-854.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Structural data

CCDC reference: 1969794

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314619016298/rz4034sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314619016298/rz4034Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314619016298/rz4034Isup3.cml

checkCIF report


Computing details top

Data collection: APEX3 (Bruker, 2015); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2006) and ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: publCIF (Westrip, 2010).

1,1,3,3-Tetraethyl-5-nitroisoindoline top
Crystal data top
C16H24N2O2Dx = 1.199 Mg m−3
Mr = 276.37Melting point: 297 K
Monoclinic, P21/nCu Kα radiation, λ = 1.54178 Å
a = 9.0277 (6) ÅCell parameters from 130 reflections
b = 19.9356 (13) Åθ = 2.4–67.7°
c = 9.4811 (7) ŵ = 0.63 mm−1
β = 116.169 (2)°T = 173 K
V = 1531.43 (18) Å3Elongated block, pale yellow
Z = 41.20 × 0.60 × 0.60 mm
F(000) = 600
Data collection top
Siemens Bruker three circle
diffractometer		2699 reflections with I > 2σ(I)
Radiation source: Incoatec microfocus tube, X-Ray microfocus tubeRint = 0.053
ω and Phi scansθmax = 69.7°, θmin = 4.4°
Absorption correction: multi-scan
(SADABS; Bruker, 2015)		h = −10→10
Tmin = 0.568, Tmax = 0.753k = −24→24
32894 measured reflectionsl = −10→11
2769 independent reflections
Refinement top
Refinement on F2Hydrogen site location: mixed
Least-squares matrix: fullH atoms treated by a mixture of independent and constrained refinement
R[F2 > 2σ(F2)] = 0.051 w = 1/[σ2(Fo2) + (0.0661P)2 + 0.6801P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.134(Δ/σ)max < 0.001
S = 1.09Δρmax = 0.38 e Å−3
2769 reflectionsΔρmin = −0.25 e Å−3
185 parametersExtinction correction: SHELXL-2018/3 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.034 (2)
Special details top

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. The H atom on nitrogen N2 was located in a difference Fourier map and refined freely with Uiso(H) = 1.2 Ueq(N). All other H atoms were treated as riding, with C–H = 0.96–0.98 Å, and with with Uiso(H) = 1.2 Ueq(C) or 1.5 Ueq(C) for methyl H atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.52355 (17)0.63396 (7)0.61223 (17)0.0270 (3)
N20.68275 (15)0.65271 (7)0.61351 (15)0.0293 (3)
H20.763 (2)0.6336 (10)0.692 (2)0.035*
C110.5343 (2)0.57151 (8)0.71234 (18)0.0329 (4)
H11A0.4214390.5597900.6965210.039*
H11B0.5760550.5335160.6728950.039*
C120.6438 (2)0.57893 (10)0.8882 (2)0.0420 (4)
H12A0.6428180.5369660.9416210.063*
H12B0.7569090.5891220.9061170.063*
H12C0.6019170.6154600.9298010.063*
C130.4529 (2)0.69406 (8)0.6662 (2)0.0360 (4)
H13A0.3487880.6798910.6682670.043*
H13B0.5318510.7060680.7749170.043*
C140.4189 (3)0.75591 (10)0.5640 (3)0.0530 (5)
H14A0.3746840.7914650.6059350.080*
H14B0.5217760.7712610.5633720.080*
H14C0.3383890.7450380.4565340.080*
C30.68746 (17)0.63829 (7)0.46225 (16)0.0256 (3)
C310.79690 (18)0.57636 (8)0.47844 (18)0.0311 (4)
H31A0.9078200.5849890.5648740.037*
H31B0.7497580.5375980.5100140.037*
C320.8174 (2)0.55661 (9)0.3331 (2)0.0385 (4)
H32A0.8886290.5170020.3565220.058*
H32B0.7090850.5462750.2470670.058*
H32C0.8676570.5938190.3021030.058*
C330.74827 (19)0.70079 (8)0.40784 (19)0.0326 (4)
H33A0.7399470.6922500.3017270.039*
H33B0.6747110.7389600.3995500.039*
C340.9256 (2)0.72039 (10)0.5175 (2)0.0448 (5)
H34A0.9564110.7603430.4762210.067*
H34B0.9345230.7300880.6222510.067*
H34C0.9998240.6833310.5243300.067*
C3A0.50770 (17)0.62372 (7)0.35502 (17)0.0251 (3)
C40.43042 (18)0.61567 (7)0.19321 (17)0.0277 (3)
H40.4894820.6208200.1321340.033*
C50.26335 (18)0.59978 (8)0.12360 (17)0.0300 (4)
C60.17277 (18)0.59141 (8)0.20808 (19)0.0334 (4)
H60.0597490.5788470.1568770.040*
C7A0.41760 (17)0.61856 (7)0.44111 (17)0.0263 (3)
C70.25063 (18)0.60177 (8)0.36886 (19)0.0322 (4)
H70.1908030.5974730.4294400.039*
N80.17901 (16)0.59159 (8)−0.04799 (16)0.0380 (4)
O810.03459 (17)0.57346 (10)−0.10830 (17)0.0695 (5)
O820.25620 (17)0.60204 (9)−0.12333 (14)0.0549 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0263 (7)0.0337 (8)0.0227 (7)−0.0013 (5)0.0123 (6)−0.0024 (6)
N20.0250 (6)0.0415 (7)0.0214 (6)−0.0035 (5)0.0102 (5)−0.0032 (5)
C110.0368 (8)0.0377 (8)0.0269 (8)−0.0023 (6)0.0167 (7)0.0001 (6)
C120.0455 (10)0.0532 (10)0.0280 (9)0.0019 (8)0.0168 (8)0.0047 (7)
C130.0369 (8)0.0407 (9)0.0345 (9)0.0017 (7)0.0195 (7)−0.0072 (7)
C140.0658 (13)0.0385 (9)0.0583 (12)0.0112 (9)0.0306 (11)−0.0021 (8)
C30.0233 (7)0.0316 (7)0.0215 (7)−0.0014 (5)0.0095 (6)−0.0014 (5)
C310.0264 (7)0.0371 (8)0.0264 (8)0.0036 (6)0.0085 (6)0.0002 (6)
C320.0313 (8)0.0490 (10)0.0366 (9)0.0061 (7)0.0162 (7)−0.0054 (7)
C330.0321 (8)0.0369 (8)0.0297 (8)−0.0049 (6)0.0144 (7)0.0008 (6)
C340.0388 (9)0.0504 (10)0.0442 (10)−0.0163 (8)0.0173 (8)−0.0043 (8)
C3A0.0241 (7)0.0269 (7)0.0236 (7)0.0010 (5)0.0100 (6)0.0007 (5)
C40.0257 (7)0.0340 (7)0.0240 (7)0.0014 (5)0.0114 (6)0.0011 (6)
C50.0264 (7)0.0365 (8)0.0223 (8)0.0037 (6)0.0064 (6)−0.0002 (6)
C60.0216 (7)0.0442 (9)0.0316 (8)−0.0001 (6)0.0091 (6)−0.0018 (6)
C7A0.0260 (7)0.0281 (7)0.0250 (8)0.0012 (5)0.0114 (6)−0.0004 (5)
C70.0256 (7)0.0427 (9)0.0310 (8)−0.0001 (6)0.0149 (6)−0.0009 (6)
N80.0282 (7)0.0529 (9)0.0256 (7)0.0028 (6)0.0053 (6)−0.0014 (6)
O810.0307 (7)0.1309 (15)0.0340 (7)−0.0130 (8)0.0026 (6)−0.0086 (8)
O820.0455 (8)0.0941 (11)0.0257 (6)−0.0105 (7)0.0161 (6)−0.0053 (6)
Geometric parameters (Å, º) top
C1—N21.4799 (18)C31—H31B0.9900
C1—C7A1.5075 (19)C32—H32A0.9800
C1—C111.542 (2)C32—H32B0.9800
C1—C131.547 (2)C32—H32C0.9800
N2—C31.4815 (19)C33—C341.526 (2)
N2—H20.86 (2)C33—H33A0.9900
C11—C121.525 (2)C33—H33B0.9900
C11—H11A0.9900C34—H34A0.9800
C11—H11B0.9900C34—H34B0.9800
C12—H12A0.9800C34—H34C0.9800
C12—H12B0.9800C3A—C41.386 (2)
C12—H12C0.9800C3A—C7A1.387 (2)
C13—C141.513 (3)C4—C51.390 (2)
C13—H13A0.9900C4—H40.9500
C13—H13B0.9900C5—C61.384 (2)
C14—H14A0.9800C5—N81.470 (2)
C14—H14B0.9800C6—C71.384 (2)
C14—H14C0.9800C6—H60.9500
C3—C3A1.5153 (19)C7A—C71.394 (2)
C3—C331.540 (2)C7—H70.9500
C3—C311.546 (2)N8—O821.216 (2)
C31—C321.521 (2)N8—O811.225 (2)
C31—H31A0.9900
N2—C1—C7A102.31 (11)C32—C31—H31B108.2
N2—C1—C11113.68 (12)C3—C31—H31B108.2
C7A—C1—C11109.62 (12)H31A—C31—H31B107.3
N2—C1—C13110.01 (12)C31—C32—H32A109.5
C7A—C1—C13110.81 (12)C31—C32—H32B109.5
C11—C1—C13110.18 (12)H32A—C32—H32B109.5
C1—N2—C3112.66 (11)C31—C32—H32C109.5
C1—N2—H2110.0 (13)H32A—C32—H32C109.5
C3—N2—H2111.8 (13)H32B—C32—H32C109.5
C12—C11—C1115.41 (13)C34—C33—C3113.65 (13)
C12—C11—H11A108.4C34—C33—H33A108.8
C1—C11—H11A108.4C3—C33—H33A108.8
C12—C11—H11B108.4C34—C33—H33B108.8
C1—C11—H11B108.4C3—C33—H33B108.8
H11A—C11—H11B107.5H33A—C33—H33B107.7
C11—C12—H12A109.5C33—C34—H34A109.5
C11—C12—H12B109.5C33—C34—H34B109.5
H12A—C12—H12B109.5H34A—C34—H34B109.5
C11—C12—H12C109.5C33—C34—H34C109.5
H12A—C12—H12C109.5H34A—C34—H34C109.5
H12B—C12—H12C109.5H34B—C34—H34C109.5
C14—C13—C1114.59 (14)C4—C3A—C7A120.20 (13)
C14—C13—H13A108.6C4—C3A—C3129.19 (13)
C1—C13—H13A108.6C7A—C3A—C3110.60 (12)
C14—C13—H13B108.6C3A—C4—C5117.57 (14)
C1—C13—H13B108.6C3A—C4—H4121.2
H13A—C13—H13B107.6C5—C4—H4121.2
C13—C14—H14A109.5C6—C5—C4123.15 (14)
C13—C14—H14B109.5C6—C5—N8118.51 (13)
H14A—C14—H14B109.5C4—C5—N8118.34 (14)
C13—C14—H14C109.5C7—C6—C5118.47 (14)
H14A—C14—H14C109.5C7—C6—H6120.8
H14B—C14—H14C109.5C5—C6—H6120.8
N2—C3—C3A101.96 (11)C3A—C7A—C7121.09 (14)
N2—C3—C33109.51 (12)C3A—C7A—C1111.09 (12)
C3A—C3—C33111.40 (12)C7—C7A—C1127.82 (14)
N2—C3—C31110.41 (12)C6—C7—C7A119.41 (14)
C3A—C3—C31111.23 (12)C6—C7—H7120.3
C33—C3—C31111.90 (12)C7A—C7—H7120.3
C32—C31—C3116.40 (13)O82—N8—O81122.97 (15)
C32—C31—H31A108.2O82—N8—C5118.68 (13)
C3—C31—H31A108.2O81—N8—C5118.34 (15)
Hydrogen-bond geometry (Å, º) top
Cg1 is the centroid of the C3A/C4/C5/C6/C7/C7A benzene ring.
D—H···AD—HH···AD···AD—H···A
N2—H2···O81i0.865 (15)2.634 (16)3.4860 (18)168.4 (16)
C11—H11B···Cg1ii0.992.913.7552 (18)144
Symmetry codes: (i) x+1, y, z+1; (ii) −x+1, −y+1, −z+1.
 

Acknowledgements

We are grateful to Professor Dr Thomas Prisner and Professor Dr Martin U. Schmidt (both of Goethe-Universität) for giving us the opportunity to obtain and publish these results. We thank Professor M. U. Schmidt for fruitful discussions.

Funding information

JP is thankful for financial support by the DFG (Deutsche Forschungsgemeinschaft) (CRC902: Mol­ecular Principles of RNA-Based Regulations).

References

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 First citationFarrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854.  Web of Science CrossRef CAS IUCr Journals Google Scholar
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ISSN: 2414-3146
Volume 4| Part 12| December 2019| x191629
https://doi.org/10.1107/S2414314619016298
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