1.3- Dipoles ozone

Nowadays a broad range of different 1,3-dipoles, ozone, azides ° and diazoalkanes on the one hand as well as dipoles like nitrones, nitro compounds, carbonyl ylides, nitrile oxides, nitrile imines and ylides on the other hand, are well-established. The addition of these 1,3-dipoles to an alkene is one of the most frequently used cycloaddition reactions in organic synthesis. ... 

Using modern analytical methods, a number of transient intermediates and byproducts could be verified [19, 20]. The first step in the mechanism of ozonolysis is the 1,3-dipolar cycloaddition of the dipole ozone to the double bond of OA. A 1,2,3-trioxolane is formed, the unstable primary ozonide or molozonide. The primary ozonide collapses in a 1,3 dipolar cycloreversion to a carbonyl compound and a carbonyl oxide, the so-called Criegee zwitterion. Since OA is substituted with two diverse groups at the double bond, two different opportunities exist for the formation of carbonyl compound and carbonyl oxide. Again, a 1,3-dipolar cycloaddition of these intermediates leads to three different pairs of 1,2,4-trioxolane derivatives (cisltram), the secondary ozonides, which are more stable than the primary ones. Their oxidative cleavage results in AA and PA. 

Freon-12, CCI2F2, was used as a coolant in refrigerators until it was suspected to he a cause of ozone depletion. Determine the molecular shape of CCI2F2 and discuss the possibility that the molecule will be a dipole. 

C3Hj C(HS. 03, liq, bp 70° at 0.5 mm, d 1.1361 at 20°, d 1-5132 at 20°. Can be prepd by ozonization of allylbenzene using the method of Harries (Ref 1 for oconization of org compds. A detailed description of its prepn is given by Ryffel(Ref 3). Briner et al (Ref 4) detd the following props of allylbenzeneozonide soly in benz, Raman spectra, UV absorption spectra, dielectric constants and dipole moments Note According to Dr H. Walter of PicArs this ozonide is an explosive... 

In electrophilic oxygenation with ozone in superacidic media or in dry ozonation over silica gel, protonated ozone, namely, +C>3H, was suggested to be the de facto electrophile. These reactions are fundamentally different from conventional ozonations with O3, which is a highly dipolar molecule. In 03H+ the dipole is removed by protonation. Cacace and Sporenza were able to directly identify +C>3H in the gas phase and also measure the proton affinity of ozone.107... 

Ozone is a symmetrical 1,3-dipole with both ends equally nucleophilic and equally electrophilic . 

Fig. 2.3 shows the core structures of the most important 1,3-dipoles, and what they are all called. As with dienes, they can have electron-donating or withdrawing substituents attached at any of the atoms with a hydrogen atom in the core structure, and these modify the reactivity and selectivity that the dipoles show for different dipolarophiles. Some of the dipoles are stable compounds like ozone and diazomethane, or, suitably substituted, like azides, nitrones, and nitrile oxides. Others, like the ylids, imines, and carbonyl oxides, are reactive intermediates that have to be made in situ. Fig. 2.4 shows some examples of some common 1,3-dipolar cycloadditions, and Fig. 2.5 illustrates two of the many ways in which unstable dipoles can be prepared. 

Ozonium Ion (H03+). Ozone is a resonance hybrid of canonical structures 50a-50d.135 Ozone does in fact act as a 1,3-dipole—that is, either as an electrophile or a nucleophile. The electrophilic nature of ozone has been recognized for a long time in its reactions with alkenes, alkynes, arenes, amines, phosphines,... 

Since ozone is a strong 1,3-dipole,635 or at least has a strong polarizability (even if a singlet biradical structure is also feasible), it is expected to be readily protonated in superacids, in manner analogous to its alkylation by alkylcarbenium ions. Protonated ozone HC>3+, once formed, should have a much higher affinity (i.e., be a more powerful electrophile) for cr-donor single bonds in alkanes than neutral ozone. 

The extreme forms of resonance structures in ozone molecules can be represented as shown in Figure 4.7. This structure illustrates that the ozone molecule has two types of dipoles, which can serve as electrophilic and nucleophilic agents, respectively. In organic solvents, the following three reactions can be observed ... 

Ozone is a symmetrical bent molecule with a central positively charged oxygen atom and two terminal oxygen atoms that share a negative charge. It is a 1,3-dipole and does typical 1,3-dipolar cycloadditions with alkenes. 

The Ta <— So transition moments to particular spin sublevels for the three lowest triplet states of the ozone molecule, 3B2,3 A2 and 3B, were calculated by the MCQR method in ref. [70] using CASSCF wave functions. Table 7 recapitulates results for electric dipole radiative activity of different S-T transitions in ozone [70]. The type of information gained form this kind of spin-orbit response calculations are viz. transition electric dipole moments and oscillator strengths for each spin sublevel T , their polarization directions (7), radiative lifetimes (r ) and excitation energies (En). The most prominent features of the Chappuis band are reproduced in calculations, which simulate the photodynamics of ozone visible absorption [78, 79]. Because the CM (M2) state cannot be responsible for the Wulf bands, the only other candidates ought to... 

The structure of ozone 21, after a long period of uncertainty, is now probably as indicated, with a bond angle of 126° and a bond length 1.26 A ozone has a dipole moment of 0.49 D. The following four configurations contribute so that the O—O distance lies between those of a single and of a double bond (1.46 A and 1.10 A). 

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