1,2-Dioxetanes thermal generation

Adam W, Saha-Moller CR, Schonberger A (1996) Photooxidation of 8-oxo-7,8-dihydro-2 -deoxy-guanosine by thermally generated triplet-excited ketones from 3-(hydroxymethyl)-3,4,4,-tri-methyl-1,2-dioxetane and comparison with type I and type II photosensitizers. J Am Chem Soc 118 9233-9238... 

In this regard, clear chemical and spectroscopic evidence for the disproportionation of the intermediate radical cations, photochemically and/or thermally generated, were achieved on 2,3-diphenyl-5,6-dihydro-1,4-dioxin, and derivatives 22a - c [90, 111, 57-159]. In fact, the 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one (TBCHD)-sensitized photooxygenation of 22a affords the corresponding 1,2-ethanedioldibenzoate, 67, the cleavage product of the intermediate 1,2-dioxetane, 24a, together with minor amounts of 4a,8a-diphenyl-2,3,4a,6,7,8a-hexahydro-p-dioxino[2,3-b]-p-dioxin 68 [158] ... 

The dark initiation of the photosensitized degradation of a styrene-methyl isopropenyl ketone copolymer by thermally generated 7i(3iwr ) acetone using the tetramethyl-l,2-dioxetan dissociation reaction has been studied.217 The reaction... 

Dloxetanes. Simple dioxetanes (3) decompose thermally near or below room temperature to generate excited states of carbonyl products... 

The contemporary trends of dioxetane chemistry include a number of fundamental and applied aspects. The fundamental aspects encompass the stereoselective synthesis and the transformations of novel chiral dioxetanes, as well as the mechanistic studies on the thermal, electron-transfer-induced and catalytic dioxetane decomposition. The emphasis lies on the elucidation of the excited-state generation in these chemiluminescent processes. 

A wealth of experimental data on the thermal dioxetane decomposition and the excited-state generation in the thermolysis process has been comprehensively surveyed in previous reviews". During the last decade, computational elucidation of the thermal cleavage received major attention and in the present subsection we consider the relevant smd-ies. Computations on the dioxetane thermolysis were conducted by both ab initio and semiempiricaP methods at different levels of sophistication. 

A less usual method for the generation of starting dienones is thermal rearrangement of fulvene-l,2-dioxetanes 139a,b, leading to 2//-pyrans (140a,b).182... 

Further detailed information on the reactive excited states of p. -unsaturated ketones has been acquired with (3a-c). Inefficient intersystem crossing from the singlet to the triplet state precedes population of Tz(.n,Tt ) from which the 1,3-acyl shift, induced by Norrish type I cleavage, occurs more readily than internal conversion to Ti Ti has been estimated to lie within 8 W mol of the acetone triplet (335 kJ mol ). That the 1,3-acyl shift is coupled not only with singlet-state but also Tz-state reactivity has been unequivocally shown by two methods. Thermal decomposition of a dioxetane, a derivative of (3a), generates predominantly the T2 state from which the 1,3-acyl shift product is formed concurrently with the ODPM products (4a) and (5a) via A photo-CIDNP study has independently demon-... 

Fig. 3. Generation of chemiluminescence by thermal decomposition of substituted dioxetanes.

T24. Turro, N. J., and Lechtken, P., Thermal decomposition of tetramethyl-l,2-dioxetane. Selective and efficient chemelectronic generation of triplet acetone. J. Am. Chem. Soc. 94, 2886-2888 (1972). 

Various mechanisms have been advanced for generation of muconaldehyde [19-21], For example, one postulate is that singlet oxygen reacts with benzene to form the dioxetane 15 [4,24]. This intermediate is unlikely, however, on a number of grounds [16]. First, there is simply no precedent for reaction of benzene itself in a symmetry-forbidden 2, + n2, thermal reaction with singlet oxygen [16]. Second,... 

Luminescence due to the decomposition of tetramethyl-1,2-dioxetane in benzene yielded a maximum value for wavelength of 430-440 mvi. This is similar to the spectrum of luminescence obtained by Kopecky (1969) for the thermal decomposition of 3,3,4-trimethyl-l,2-dioxetane with a maximum emission of 430-440 mji. Decomposition of these transient 1,2-dioxetanes form the electronically excited carbonyl compounds acetone and acetone/acetaldehyde, respectively. By excitation of acetone and acetaldehyde either singly, or as a 50% mixture of each with O2 generated from KO2, we obtained identical photon interference data placing the maximum emission around 435 my. 

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