Vibrational spectra and structure of cyclopropane-d1 and dicyclopropyl ketone

Towards the identification of molecular constituents associated with the surfaces of isoprene-derived secondary organic aerosol (SOA) particles

“…While the SFG responses observed from epoxides 3 and 4 between 3050 and 3020 cm −1 are weak, they are likely to indicate the presence of the single methylene group attached to the strained epoxide ring structure in these compounds: previous SFG studies have shown that as the number of carbon atoms in a cyclic hydrocarbon decreases, and the C-C single bonds become increasingly strained, the vibrational frequencies of the methylene symmetric stretches shift beyond 3000 cm −1 (Buchbinder et al, 2011). Furthermore, the IR spectra of bromocyclopropane (Diallo and Waters, 1988), cyclopropane-d 1 (Diallo and Waters, 1988), cyclopropane-1,1-d 2 (Keeports and Eggers, 1984), cyclopropane 1,1,2,2-d 4 (Keeports and Eggers, 1984), and cyclopropane (Diallo and Waters, 1988;Spiekermann et al, 1980) all show vibrational responses beyond 3000 cm −1 . Similar frequency shifts have been observed for epoxide-containing molecules, both due to the strain of the three-membered ring and the proximity to the oxygen atom (Henbest et al, 1957).…”

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 overwhelming spectral evidence that a second conformer is present in the fluid phases, but the relative intensities of the observed bands from this rotamer indicates that it is a minor component. However it should be noted that bands previously reported at 728, 1418, 1460 and 1672 cm À1 as probably arising from a second conformer 12,13 were not observed as distinct bands in the spectra of the xenon solutions.…”

“…In order to obtain the conformational stability of dicyclopropyl ketone, a vibrational assignment needs to be made for the predominant conformer as well as the minor form to ensure that the vibrational fundamentals of one rotamer are not contributing to the intensity of the fundamentals of the other. In the earlier vibrational studies, [11][12][13] the Raman lines initially reported 11 at 534, 728 and 877 cm À1 from the spectrum of the liquid were subsequently assigned 12 to the second conformer and later a second C=O stretch at 1672 cm À1 was assigned to the minor form. By utilizing vibrational data from the sample dissolved in liquid xenon at low temperature with much narrower band contours than those from the gas, it is possible to identify many more bands than from either the spectra of the pure liquid or gas (Fig.…”

“…Also these authors 12 considered six possible structures, with four of the six having at least one of the cyclopropyl rings in the gauche configuration with the other two the cis-cis form of the major component and the trans-trans form, which is expected to be so sterically hindered that it will not exist. Another vibrational study 13 followed shortly thereafter and these authors tentatively identified the minor component as the cis-trans conformer on the basis of the 1672 cm À1 shoulder on the C=O stretch of the major cis-cis conformer which has a frequency of 1685 cm À1 . These authors 13 also pointed out the significant difference in the assignments of the two C-C ring stretches as well as the symmetric ring deformation in the two earlier studies.…”

“…Another vibrational study 13 followed shortly thereafter and these authors tentatively identified the minor component as the cis-trans conformer on the basis of the 1672 cm À1 shoulder on the C=O stretch of the major cis-cis conformer which has a frequency of 1685 cm À1 . These authors 13 also pointed out the significant difference in the assignments of the two C-C ring stretches as well as the symmetric ring deformation in the two earlier studies. 11,12 Thus, there still remain several questions concerning the vibrational assignment as well as the conformation of the minor component of dicyclopropyl ketone.…”