Oxazole molecular structure

Figure 12.8.5 The molecular structure of oxazole. Figure 12.8.6 The molecular structure of biphenyl.

Figure 7.13. Molecular structures of N-Fmoc-protected oxazole (14) and thiazole (15) amino acids used as monomers of oligomer libraries.

Polymerization of terephthalic acid with 4,6-diamino-l,3-benzenediol via oxazole formation (Eq. 2-219) proceeds with a sharp and continuous decrease in reaction rate with increasing polymer molecular weight [Cotts and Berry, 1981]. Reaction becomes progressively more diffusion-controlled with increasing molecular size due to the increasing rigid-rod structure of the growing polymer. 

There have been several molecular orbital treatments of the structure and reactivity of oxazole these are summarized by Turchi and Dewar (75CRV389). Table 1 lists the a, it and net charge distributions calculated by the all-valence ab initio method, the net charges obtained by the MINDO/3 method and the bond lengths calculated by the latter method. 

The first published account of the mass spectrometry of isomeric di-phenyloxazoles was initiated in an attempt to establish the structure of a new oxazole alkaloid.283 A detailed study of the mass spectra of a variety of alkyl- and aryloxazoles was not reported until recently.284 286 The mass spectrum of oxazole itself is typical of an unsubstituted aromatic compound inasmuch as the molecular ion (m/e 69) constitutes the base peak. The major fragment ions occur at M — 1, M — 27 (M — HCN), M — 28 (M - H2CN and/or M - CO) and M - 29 (M - CHO).284... 

Oxazoles are extremely susceptible to the action of singlet molecular oxygen and behave as 1,3-dienes, as they do in the Diels-Alder reaction. The wide variety of reactions observed with singlet oxygen and oxazoles take place, not by diverse modes of attack of the excited oxygen species with the substrate, but rather by a multitude of paths that appear to be open for the decomposition of the intermediate peroxide or hydroperoxide. The secondary decompositions are highly dependent on the structure of the oxazole, the nature of the functional groups in the immediate environment of the newly formed peroxide, the solvent, temperature, and other conditions. 

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