Conjugated cyclopropyls: the molecular structures and conformations of 1,1-dicyclopropylethene and dicyclopropyl ketone as studied by gas phase electron diffraction and ab initio calculations

Conformational stabilities of dicyclopropyl ketone determined from variable temperature infrared spectra of xenon solutions and ab initio calculationsElectronic supplementary information (ESI) available: Calculated energies, diagonal force constants, symmetry coordinates and calculated asymmetric torsional potential function. See http://www.rsc.org/suppdata/cp/b4/b400142g/

“…Thus, there is a significant amount this second conformer present at room temperature. From the electron diffraction investigation 14 of dicyclopropyl ketone it was estimated that 7 AE 3% of the molecules were in the cis-trans conformation, which, is nearly in agreement with our results if one uses their largest estimated value with our lowest value. It should be noted that none of the B3LYP predictions are close to predicting the experimental enthalpy difference between the two stable conformers, where the lowest predicted energy difference is 678 cm À1 with the 6-311þG(2df,2pd) basis set.…”

“…Of course, the C-H distances were not adjusted, nor were any of the angles except for the trigonal ring angles (Table 3). These parameters are compared to those reported from the electron diffraction study 14 and the major difference is for the C-C distance with the carbon bonded to the oxygen atom where this distance is shorter by 0.015 A ˚than the reported experimental value. Since it was not possible to simultaneously refine the unique C-C distance in the ring together with the other geometrical and vibrational parameters, it is not an independent parameter and appears to be too short by 0.006 A ˚.…”

“…16 The structural optimization for the two conformers were carried out with initial parameters taken from those reported from an electron diffraction study of dicyclopropyl ketone. 14 Several different basis sets starting with 6-31G(d) and increasing to 6-311þG(2d,2p) were employed at the level of restricted Hartree-Fock and/or Møller-Plesset perturbation theory to the second order (MP2) to obtain the energy differences between the two stable conformers (Table 1S). Density functional theory calculations were also carried out by the B3LYP method using the same basis sets as those used for the ab initio calculations.…”

“…Although ab initio calculations at the restricted Hartree-Fock (RHF) and with electron correlation by the perturbation method to second order (MP2) with only the rather small 6-31G(d) basis set 14 have been reported, we have carried out similar calculations with larger basis sets up to 6-311G-(2d,2p) as well as those with diffuse functions, i.e., 6-311þ G(2d,2p). We have found that there can be significant differences in the predicted stabilities of the c-C 3 H 5 CXO molecules with and without diffuse functions as well as those with the smaller 6-31G(d) basis set and the significantly larger ones at the MP2 level.…”

Synthesis and Characterization of Cyclopropylpolyketides: A Combined Experimental and Theoretical Study

“…It has been shown experimentally that dicyclopropyl ketone possesses one syn / syn and one syn / anti conformation 16. The syn / syn conformer (93 %) has two cyclopropyl rings pointing towards the oxygen atom of the carbonyl group; the syn / anti conformer (7 %) has one cyclopropyl ring pointing towards and one pointing away from the carbonyl group.…”