Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807045539/dn2230sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807045539/dn2230Isup2.hkl |
CCDC reference: 663794
The synthesis was carried out according to a published procedure (Banares et al., 1989). Ethyl-α-ketocyclopentylcarboxylate (two equivalents) was added to a solution of ethylenediamine (one equivalent) in dry ethanol. After standing for several hours, the ethanol was partially removed until precipitation commenced. The title compound was isolated in good yield. Crystals suitable for X-ray analysis were obtained directly from the reaction mixture.
The hydrogen atoms of the two amine groups at N1 and N2 were located by difference Fourier synthesis and refined isotropically. All other hydrogen atoms wereintroduced in calculated positions and treated as riding on their parent atoms with C—H= 0.98 Å (methyl) or 0.99 Å (methylene) and with Uiso(H) = 1.5Ueq(C).
There is only one crystal structure reported in the literature containing N,N'-ethylenediamine ligand with a cycloalkene residue, as revealed by a search in the Version 5.27 of the Cambridge Structural Database (Allen, 2002). In this case, the ligand shows a perfectly staggered conformation in the solid state, with a torsion angle of 180° (Fernández-G et al., 1993). The structure of the title compound is shown in Figure 1. Molecules are linked by two diffenerent N—H···O hydrogen bonds involving most of potential donors, generating sheets parallel to the (110) plane, as shown in Fig. 2. The coordination geometry around the N atoms is perhaps best described as trigonal planar, with C11–N1–H1N1, C1–N1–H1N1 and C11–N1–C1 angles of 118 (2), 115 (2) and 125.5 (2)°, and with C3–N2–H1N2, C2–N2–H1N2 and C3–N2–C2 angles of 116 (2), 117 (2) and 125.2 (2)°, respectively. In contrast to the cyclohexylen subsituted N,N'-ethylenediamine ligand (Fernández-G et al., 1993), (I) has no centre of symmetry and with a N1–C1–C2–N2 dihedral of -67.93° it displays a partially eclipsed conformation.
For related structure, see: Fernández-G et al. (1993); Banares et al. (1989); Allen (2002).
Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1990); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).
C18H28N2O4 | V = 899.17 (11) Å3 |
Mr = 336.42 | Z = 2 |
Triclinic, P1 | F(000) = 364 |
Hall symbol: -P1 | Dx = 1.243 Mg m−3 |
a = 7.2622 (4) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 10.5603 (9) Å | µ = 0.09 mm−1 |
c = 11.9036 (9) Å | T = 183 K |
α = 92.908 (4)° | Prism, colourless |
β = 95.723 (5)° | 0.03 × 0.03 × 0.02 mm |
γ = 97.278 (5)° |
Nonius KappaCCD diffractometer | 2742 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.026 |
Graphite monochromator | θmax = 27.4°, θmin = 2.5° |
φ and ω scans | h = −9→9 |
6086 measured reflections | k = −13→12 |
3981 independent reflections | l = −15→15 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.062 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.178 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.01 | w = 1/[σ2(Fo2) + (0.0888P)2 + 0.3965P] where P = (Fo2 + 2Fc2)/3 |
3981 reflections | (Δ/σ)max < 0.001 |
227 parameters | Δρmax = 0.63 e Å−3 |
0 restraints | Δρmin = −0.38 e Å−3 |
C18H28N2O4 | γ = 97.278 (5)° |
Mr = 336.42 | V = 899.17 (11) Å3 |
Triclinic, P1 | Z = 2 |
a = 7.2622 (4) Å | Mo Kα radiation |
b = 10.5603 (9) Å | µ = 0.09 mm−1 |
c = 11.9036 (9) Å | T = 183 K |
α = 92.908 (4)° | 0.03 × 0.03 × 0.02 mm |
β = 95.723 (5)° |
Nonius KappaCCD diffractometer | 2742 reflections with I > 2σ(I) |
6086 measured reflections | Rint = 0.026 |
3981 independent reflections |
R[F2 > 2σ(F2)] = 0.062 | 0 restraints |
wR(F2) = 0.178 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.01 | Δρmax = 0.63 e Å−3 |
3981 reflections | Δρmin = −0.38 e Å−3 |
227 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.0548 (2) | 0.54795 (15) | 0.64357 (12) | 0.0394 (4) | |
O2 | 0.1410 (2) | 0.58230 (16) | 0.83181 (12) | 0.0427 (4) | |
O3 | 0.4505 (2) | −0.04109 (16) | 0.63702 (14) | 0.0432 (4) | |
O4 | 0.3582 (2) | −0.07723 (17) | 0.80960 (14) | 0.0455 (4) | |
N1 | 0.2322 (3) | 0.11600 (17) | 0.50903 (16) | 0.0350 (4) | |
N2 | 0.2955 (3) | 0.40689 (17) | 0.52720 (14) | 0.0312 (4) | |
C1 | 0.2004 (3) | 0.1990 (2) | 0.41747 (18) | 0.0359 (5) | |
H1A | 0.0697 | 0.2174 | 0.4128 | 0.043* | |
H1B | 0.2180 | 0.1539 | 0.3451 | 0.043* | |
C2 | 0.3316 (3) | 0.3252 (2) | 0.43306 (17) | 0.0333 (5) | |
H2A | 0.4621 | 0.3065 | 0.4451 | 0.040* | |
H2B | 0.3183 | 0.3713 | 0.3629 | 0.040* | |
C3 | 0.3759 (3) | 0.40687 (18) | 0.63412 (17) | 0.0289 (4) | |
C4 | 0.5496 (3) | 0.3452 (2) | 0.66374 (18) | 0.0346 (5) | |
H4A | 0.6602 | 0.3943 | 0.6368 | 0.042* | |
H4B | 0.5350 | 0.2562 | 0.6305 | 0.042* | |
C5 | 0.5669 (4) | 0.3486 (3) | 0.7932 (2) | 0.0467 (6) | |
H5A | 0.6994 | 0.3691 | 0.8246 | 0.056* | |
H5B | 0.5168 | 0.2646 | 0.8187 | 0.056* | |
C6 | 0.4537 (3) | 0.4526 (2) | 0.83228 (19) | 0.0405 (5) | |
H6A | 0.3841 | 0.4256 | 0.8963 | 0.049* | |
H6B | 0.5356 | 0.5339 | 0.8553 | 0.049* | |
C7 | 0.3224 (3) | 0.46606 (19) | 0.72838 (17) | 0.0309 (5) | |
C8 | 0.1630 (3) | 0.5333 (2) | 0.72661 (18) | 0.0327 (5) | |
C9 | −0.0083 (4) | 0.6581 (3) | 0.8407 (2) | 0.0553 (7) | |
H9A | −0.1290 | 0.6082 | 0.8098 | 0.066* | |
H9B | 0.0124 | 0.7355 | 0.7977 | 0.066* | |
C10 | −0.0100 (6) | 0.6945 (5) | 0.9631 (3) | 0.1147 (18) | |
H10A | −0.1145 | 0.7429 | 0.9731 | 0.172* | |
H10B | 0.1076 | 0.7476 | 0.9916 | 0.172* | |
H10C | −0.0244 | 0.6171 | 1.0052 | 0.172* | |
C11 | 0.1436 (3) | 0.11193 (19) | 0.60260 (18) | 0.0321 (5) | |
C12 | −0.0269 (3) | 0.1780 (2) | 0.6155 (2) | 0.0382 (5) | |
H12A | −0.1329 | 0.1401 | 0.5602 | 0.046* | |
H12B | −0.0001 | 0.2706 | 0.6046 | 0.046* | |
C13 | −0.0699 (4) | 0.1559 (3) | 0.7355 (3) | 0.0665 (9) | |
H13A | −0.2024 | 0.1194 | 0.7355 | 0.080* | |
H13B | −0.0483 | 0.2380 | 0.7818 | 0.080* | |
C14 | 0.0571 (3) | 0.0636 (2) | 0.7851 (2) | 0.0405 (5) | |
H14A | 0.1269 | 0.1001 | 0.8576 | 0.049* | |
H14B | −0.0158 | −0.0192 | 0.7979 | 0.049* | |
C15 | 0.1879 (3) | 0.0473 (2) | 0.69595 (18) | 0.0337 (5) | |
C16 | 0.3416 (3) | −0.0251 (2) | 0.70755 (18) | 0.0351 (5) | |
C17 | 0.5103 (4) | −0.1500 (3) | 0.8320 (2) | 0.0519 (7) | |
H17A | 0.6303 | −0.0979 | 0.8223 | 0.062* | |
H17B | 0.4946 | −0.2272 | 0.7794 | 0.062* | |
C18 | 0.5081 (6) | −0.1870 (4) | 0.9510 (3) | 0.0802 (10) | |
H18A | 0.6131 | −0.2344 | 0.9708 | 0.120* | |
H18B | 0.3906 | −0.2411 | 0.9587 | 0.120* | |
H18C | 0.5192 | −0.1099 | 1.0019 | 0.120* | |
H1N1 | 0.328 (4) | 0.078 (3) | 0.507 (2) | 0.047 (7)* | |
H1N2 | 0.195 (4) | 0.440 (3) | 0.518 (2) | 0.049 (7)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0418 (9) | 0.0456 (9) | 0.0326 (8) | 0.0212 (7) | −0.0044 (7) | −0.0017 (7) |
O2 | 0.0425 (9) | 0.0581 (10) | 0.0312 (8) | 0.0258 (8) | 0.0008 (7) | −0.0043 (7) |
O3 | 0.0447 (9) | 0.0448 (9) | 0.0456 (9) | 0.0215 (7) | 0.0105 (7) | 0.0078 (7) |
O4 | 0.0471 (9) | 0.0554 (10) | 0.0398 (9) | 0.0243 (8) | 0.0076 (7) | 0.0094 (8) |
N1 | 0.0373 (10) | 0.0286 (9) | 0.0410 (10) | 0.0133 (8) | 0.0039 (8) | −0.0003 (8) |
N2 | 0.0338 (9) | 0.0308 (9) | 0.0303 (9) | 0.0133 (8) | 0.0005 (7) | −0.0015 (7) |
C1 | 0.0427 (12) | 0.0332 (11) | 0.0321 (11) | 0.0131 (9) | −0.0027 (9) | −0.0031 (9) |
C2 | 0.0391 (11) | 0.0331 (11) | 0.0294 (10) | 0.0126 (9) | 0.0029 (9) | 0.0000 (8) |
C3 | 0.0294 (10) | 0.0238 (9) | 0.0336 (11) | 0.0063 (8) | −0.0002 (8) | 0.0028 (8) |
C4 | 0.0330 (11) | 0.0327 (11) | 0.0390 (12) | 0.0125 (9) | −0.0011 (9) | 0.0000 (9) |
C5 | 0.0507 (14) | 0.0527 (14) | 0.0392 (13) | 0.0273 (12) | −0.0071 (11) | −0.0015 (11) |
C6 | 0.0400 (12) | 0.0476 (13) | 0.0352 (12) | 0.0188 (10) | −0.0033 (9) | −0.0021 (10) |
C7 | 0.0332 (10) | 0.0295 (10) | 0.0302 (10) | 0.0087 (8) | −0.0015 (8) | 0.0007 (8) |
C8 | 0.0355 (11) | 0.0327 (11) | 0.0304 (10) | 0.0083 (9) | 0.0022 (9) | −0.0005 (8) |
C9 | 0.0505 (15) | 0.081 (2) | 0.0395 (13) | 0.0388 (14) | 0.0015 (11) | −0.0127 (13) |
C10 | 0.104 (3) | 0.204 (5) | 0.0504 (19) | 0.099 (3) | 0.0024 (18) | −0.032 (2) |
C11 | 0.0314 (10) | 0.0230 (9) | 0.0409 (12) | 0.0053 (8) | 0.0016 (9) | −0.0069 (8) |
C12 | 0.0336 (11) | 0.0303 (11) | 0.0514 (14) | 0.0100 (9) | 0.0026 (10) | −0.0028 (10) |
C13 | 0.0704 (18) | 0.0708 (19) | 0.075 (2) | 0.0453 (16) | 0.0351 (16) | 0.0245 (16) |
C14 | 0.0396 (12) | 0.0420 (13) | 0.0413 (13) | 0.0120 (10) | 0.0057 (10) | −0.0035 (10) |
C15 | 0.0326 (10) | 0.0312 (11) | 0.0376 (11) | 0.0073 (9) | 0.0039 (9) | −0.0033 (9) |
C16 | 0.0356 (11) | 0.0342 (11) | 0.0369 (12) | 0.0105 (9) | 0.0037 (9) | 0.0008 (9) |
C17 | 0.0528 (15) | 0.0580 (16) | 0.0511 (15) | 0.0280 (13) | 0.0047 (12) | 0.0150 (12) |
C18 | 0.096 (3) | 0.081 (2) | 0.067 (2) | 0.028 (2) | −0.0014 (18) | 0.0152 (18) |
O1—C8 | 1.229 (2) | C6—H6B | 0.9900 |
O2—C8 | 1.362 (3) | C7—C8 | 1.432 (3) |
O2—C9 | 1.436 (3) | C9—C10 | 1.491 (4) |
O3—C16 | 1.229 (3) | C9—H9A | 0.9900 |
O4—C16 | 1.360 (3) | C9—H9B | 0.9900 |
O4—C17 | 1.435 (3) | C10—H10A | 0.9800 |
N1—C11 | 1.340 (3) | C10—H10B | 0.9800 |
N1—C1 | 1.452 (3) | C10—H10C | 0.9800 |
N1—H1N1 | 0.85 (3) | C11—C15 | 1.366 (3) |
N2—C3 | 1.346 (3) | C11—C12 | 1.514 (3) |
N2—C2 | 1.445 (3) | C12—C13 | 1.515 (4) |
N2—H1N2 | 0.85 (3) | C12—H12A | 0.9900 |
C1—C2 | 1.528 (3) | C12—H12B | 0.9900 |
C1—H1A | 0.9900 | C13—C14 | 1.526 (4) |
C1—H1B | 0.9900 | C13—H13A | 0.9900 |
C2—H2A | 0.9900 | C13—H13B | 0.9900 |
C2—H2B | 0.9900 | C14—C15 | 1.511 (3) |
C3—C7 | 1.371 (3) | C14—H14A | 0.9900 |
C3—C4 | 1.510 (3) | C14—H14B | 0.9900 |
C4—C5 | 1.531 (3) | C15—C16 | 1.430 (3) |
C4—H4A | 0.9900 | C17—C18 | 1.490 (4) |
C4—H4B | 0.9900 | C17—H17A | 0.9900 |
C5—C6 | 1.534 (3) | C17—H17B | 0.9900 |
C5—H5A | 0.9900 | C18—H18A | 0.9800 |
C5—H5B | 0.9900 | C18—H18B | 0.9800 |
C6—C7 | 1.509 (3) | C18—H18C | 0.9800 |
C6—H6A | 0.9900 | ||
C8—O2—C9 | 117.05 (17) | C10—C9—H9A | 110.3 |
C16—O4—C17 | 117.03 (18) | O2—C9—H9B | 110.3 |
C11—N1—C1 | 125.48 (19) | C10—C9—H9B | 110.3 |
C11—N1—H1N1 | 118.2 (18) | H9A—C9—H9B | 108.6 |
C1—N1—H1N1 | 115.3 (18) | C9—C10—H10A | 109.5 |
C3—N2—C2 | 125.21 (18) | C9—C10—H10B | 109.5 |
C3—N2—H1N2 | 116.6 (18) | H10A—C10—H10B | 109.5 |
C2—N2—H1N2 | 115.6 (18) | C9—C10—H10C | 109.5 |
N1—C1—C2 | 112.60 (17) | H10A—C10—H10C | 109.5 |
N1—C1—H1A | 109.1 | H10B—C10—H10C | 109.5 |
C2—C1—H1A | 109.1 | N1—C11—C15 | 126.27 (19) |
N1—C1—H1B | 109.1 | N1—C11—C12 | 122.7 (2) |
C2—C1—H1B | 109.1 | C15—C11—C12 | 111.01 (19) |
H1A—C1—H1B | 107.8 | C11—C12—C13 | 104.29 (19) |
N2—C2—C1 | 113.00 (18) | C11—C12—H12A | 110.9 |
N2—C2—H2A | 109.0 | C13—C12—H12A | 110.9 |
C1—C2—H2A | 109.0 | C11—C12—H12B | 110.9 |
N2—C2—H2B | 109.0 | C13—C12—H12B | 110.9 |
C1—C2—H2B | 109.0 | H12A—C12—H12B | 108.9 |
H2A—C2—H2B | 107.8 | C12—C13—C14 | 108.6 (2) |
N2—C3—C7 | 126.52 (19) | C12—C13—H13A | 110.0 |
N2—C3—C4 | 122.58 (18) | C14—C13—H13A | 110.0 |
C7—C3—C4 | 110.81 (18) | C12—C13—H13B | 110.0 |
C3—C4—C5 | 103.39 (17) | C14—C13—H13B | 110.0 |
C3—C4—H4A | 111.1 | H13A—C13—H13B | 108.4 |
C5—C4—H4A | 111.1 | C15—C14—C13 | 103.8 (2) |
C3—C4—H4B | 111.1 | C15—C14—H14A | 111.0 |
C5—C4—H4B | 111.1 | C13—C14—H14A | 111.0 |
H4A—C4—H4B | 109.0 | C15—C14—H14B | 111.0 |
C4—C5—C6 | 106.65 (18) | C13—C14—H14B | 111.0 |
C4—C5—H5A | 110.4 | H14A—C14—H14B | 109.0 |
C6—C5—H5A | 110.4 | C11—C15—C16 | 123.6 (2) |
C4—C5—H5B | 110.4 | C11—C15—C14 | 111.79 (19) |
C6—C5—H5B | 110.4 | C16—C15—C14 | 124.6 (2) |
H5A—C5—H5B | 108.6 | O3—C16—O4 | 121.46 (19) |
C7—C6—C5 | 103.00 (18) | O3—C16—C15 | 126.6 (2) |
C7—C6—H6A | 111.2 | O4—C16—C15 | 111.94 (18) |
C5—C6—H6A | 111.2 | O4—C17—C18 | 106.8 (2) |
C7—C6—H6B | 111.2 | O4—C17—H17A | 110.4 |
C5—C6—H6B | 111.2 | C18—C17—H17A | 110.4 |
H6A—C6—H6B | 109.1 | O4—C17—H17B | 110.4 |
C3—C7—C8 | 123.61 (19) | C18—C17—H17B | 110.4 |
C3—C7—C6 | 111.42 (18) | H17A—C17—H17B | 108.6 |
C8—C7—C6 | 124.96 (19) | C17—C18—H18A | 109.5 |
O1—C8—O2 | 121.69 (19) | C17—C18—H18B | 109.5 |
O1—C8—C7 | 126.8 (2) | H18A—C18—H18B | 109.5 |
O2—C8—C7 | 111.52 (18) | C17—C18—H18C | 109.5 |
O2—C9—C10 | 107.0 (2) | H18A—C18—H18C | 109.5 |
O2—C9—H9A | 110.3 | H18B—C18—H18C | 109.5 |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N1···O3 | 0.85 (3) | 2.23 (3) | 2.833 (2) | 128 (2) |
N1—H1N1···O3i | 0.85 (3) | 2.52 (3) | 3.175 (3) | 135 (2) |
N2—H1N2···O1 | 0.85 (3) | 2.23 (3) | 2.851 (2) | 130 (2) |
N2—H1N2···O1ii | 0.85 (3) | 2.53 (3) | 3.195 (2) | 136 (2) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x, −y+1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C18H28N2O4 |
Mr | 336.42 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 183 |
a, b, c (Å) | 7.2622 (4), 10.5603 (9), 11.9036 (9) |
α, β, γ (°) | 92.908 (4), 95.723 (5), 97.278 (5) |
V (Å3) | 899.17 (11) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.09 |
Crystal size (mm) | 0.03 × 0.03 × 0.02 |
Data collection | |
Diffractometer | Nonius KappaCCD |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6086, 3981, 2742 |
Rint | 0.026 |
(sin θ/λ)max (Å−1) | 0.648 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.062, 0.178, 1.01 |
No. of reflections | 3981 |
No. of parameters | 227 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.63, −0.38 |
Computer programs: COLLECT (Nonius, 1998), DENZO (Otwinowski & Minor, 1997), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), XP (Siemens, 1990).
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1N1···O3 | 0.85 (3) | 2.23 (3) | 2.833 (2) | 128 (2) |
N1—H1N1···O3i | 0.85 (3) | 2.52 (3) | 3.175 (3) | 135 (2) |
N2—H1N2···O1 | 0.85 (3) | 2.23 (3) | 2.851 (2) | 130 (2) |
N2—H1N2···O1ii | 0.85 (3) | 2.53 (3) | 3.195 (2) | 136 (2) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x, −y+1, −z+1. |
There is only one crystal structure reported in the literature containing N,N'-ethylenediamine ligand with a cycloalkene residue, as revealed by a search in the Version 5.27 of the Cambridge Structural Database (Allen, 2002). In this case, the ligand shows a perfectly staggered conformation in the solid state, with a torsion angle of 180° (Fernández-G et al., 1993). The structure of the title compound is shown in Figure 1. Molecules are linked by two diffenerent N—H···O hydrogen bonds involving most of potential donors, generating sheets parallel to the (110) plane, as shown in Fig. 2. The coordination geometry around the N atoms is perhaps best described as trigonal planar, with C11–N1–H1N1, C1–N1–H1N1 and C11–N1–C1 angles of 118 (2), 115 (2) and 125.5 (2)°, and with C3–N2–H1N2, C2–N2–H1N2 and C3–N2–C2 angles of 116 (2), 117 (2) and 125.2 (2)°, respectively. In contrast to the cyclohexylen subsituted N,N'-ethylenediamine ligand (Fernández-G et al., 1993), (I) has no centre of symmetry and with a N1–C1–C2–N2 dihedral of -67.93° it displays a partially eclipsed conformation.