1.2.4- Trioxolane, conformation

The 1,2,4-trioxolane ring prefers a half-chair conformation (131) the C—O—C portion of the ring forms the reference plane, and alkyl substituents prefer the equatorial positions. 

Trioxolane, 3-methyl-conformation, 6, 854 dipole moments, 6, 858 microwave spectra, 6, 855, 858... 

The gas-phase dipole moment of 1,2,3-trioxolane was determined to be 3.43 D from microwave spectroscopic studies <88JA799l>. This compares with calculated values of 3.90 D and 4.03 D using SCF and MP2 methods, respectively <89JA2497>. The dipole moment of 1,3,2-dioxathiolane 2-oxide has been measured as 3.65 D <49DOK(69)4i> and 3.74 D <6IJA2105> (both in benzene), and that of 1,3,2-dioxathiolane 2,2-dioxide has been determined to be 5.64 D (in dioxane) <68JHC289>. These results are consistent with the compounds adopting nonplanar conformations. 

Ab initio calculations have been carried out on several simple 1,2,4-trioxolanes in conjunction with other experimental methods, notably microwave spectroscopy, in order to provide additional insight into the conformations arising from experiments (Section 4.16.3.2). 

Compound 0—0 Bond length (A) C—0—C Bond angle n Trioxolane conformation Ref... 

Table 2 Structural parameters and conformations of 1,2,4-trioxolane rings obtained from x-ray diffraction compared with data for 1,2,4-trioxolane from electron diffraction. ...

Figure 1 Selected bond distances (A) and representations of the conformations of 1,2,4-trioxolanes and 1,2,4-...

The photoelectron spectra of 1,2,4-trioxolane and 1,2,4-trithiolane were in good agreement with theoretical calculations which assumed a half-chair conformation as a starting point. 1,2,4-Trithiolane gave the following characteristic vertical ionization potentials (eV) 8.72 ( (SS)), 9.10 ( (SS) — n(S)), 10.99 (n" (SS)-I- (S)), and 11.06 ((t(CS)) <76CJC146> (see also Section 4.16.2 for energy calculations). 

Structural, conformational, and energetic properties of cyclopentane and 1,2,4-trioxolane were... 

Substituents can play important roles in determining conformation. It is clear from microwave analysis of fiuorinated and alkoxy substituted 1,2,4-trioxolanes, where the substituents are mostly axial and C—O bonds in the rings are shorter, that the anomeric effect is dominant (Section... 

The rotational spectra of 3-methoxy-l,2,4-trioxolane (281) and 15 isotopomers containing H, and 0 point to a preferred conformation for both the ring and the methyl group and to other structural features. The C(3) atom is bonded to three oxygen atoms, for which the C—OMe bond distance is short (137.7 pm) as compared to C—(141.1 pm)... 

Electron diffraction measurements of gaseous 1,2,4-trioxolane point to either a C2 symmetry, as depicted at the bottom of Appendix A, or a Cj symmetry, corresponding to an envelope conformation. However, consideration of steric interactions favors the twisted chair conformation (288c) for the molecule. Table 5 presents the structural parameters derived from electron diffraction, assuming that both C—O distances are equal and that the H atoms are symmetrically placed with respect of the neighboring atoms. Assumptions on the vibrational amplitudes of the ring bonds do not affect the calculated values of Table 5, except for the H—C—H angle . ... 

The ozonide of 2,3-diphenyl-2-bomene can be prepared by photosensitized addition of oxygen to the corresponding epoxide (313), as shown in equation 103. The structure of product 314 was determined by single-crystal XRD crystallographic analysis. It should be pointed out that both 302 and 314 have Oe envelope conformation for the 1,2,4-trioxolane... 

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