Analogy with photochemistry

Polycarbonates can be included in this category. In fact, the bisphenol A-based polycarbonates are one of the most deeply studied classes of polymers in relation to its photochemical stability. To date, it is well established that the photochemical processes occurring in these polymers are wavelength dependent [226-230]. When photolyzed with > 300 nm, several radical and oxidative reactions take place, whereas with < 300 nm, the PFR as shown in Scheme 76 becomes important. Analogous dual photochemistry has been shown recently for trimethylclohexane-polycarbonate [231]. 

Unsubstimted spiropyrans similarly exhibit rapid ring-opening photochemistry to the spiro-oxazines also via a singlet state. One transient state has been identified also in polar solvents. This was assigned as 5i, but by analogy with the spiro-oxazines, this may be similar to X that was proposed by many workers. Photochemical ring closure appears to be inefficient and we often observe non-... 

As mechanistic hypothesis it was proposed (9-11) that the excited platinum complex undergoes homolytic Pt Cl cleavage affording a Ptm intermediate and an adsorbed chlorine atom (Scheme 1), by analogy with the known photochemistry of hexachloroplatinate in homogeneous solution (23,31). Electron injection from the platinum(III) complex into the titania conduction band reforms PtIv. Thus, the... 

Phosphorus tribromide, 426 Photochemical rearrangement, of 4-hydroxy-thiazolium innersalt, 375 Photochemistry, mass spectra fragmentation analogy with, of 2-imino-4-thia-zolines, 27... 

First, we can ask a relative question Is interfacial electrochemistry simply a special aspect of reaction kinetics, somewhat analogous to photochemistry In photochemistry, one might say, one studies the effect of energy packets (photons) striking molecules in electrochemistry, one studies the effect of striking molecules dissolved in solution with electrons emitted from electrically charged conductors. 

Couture showed that methyl- and dimethylthiophene on irradiation in a primary amine gave pyrroles and proposed a mechanism where the first step is the formation of a thioketone or a thioaldehyde by analogy with furan photochemistry (Scheme 2).7... 

This effect is known variously as self-absorption, thickness effect or overabsorption. An analogous effect in photochemistry is known as saturation of the action spectrum. The first term is somewhat of a misnomer because it suggests that the problem has to do with re-absorption of the fluorescence radiation, by analogy with certain effects in optical spectroscopy. Actually, the absorption of the fluorescence is independent of the incident energy, hence does not contribute to any non-linearity. What is important is that the penetration depth for the incident radiation depends on the quantity one wants to measure. 

Therefore, by analogy with the term initiator in thermal polymerizations, the dye is also usually presented as a photoinitiator (PI), i.e. a substance that absorbs light and participates in the photoinitiation of a polymerization reaction. In die sense of photochemistry [TUR 90], however, it can also play the true role of a photosensitizer (PS) in some specific reactions. Sometimes, there is an apparent ambiguity with the words photoinitiator and photosensitizer in papers dealing with... 

Studies of the photochemistry of 2-methylbutanal and its mixtures with iodine have been reported for excitation at one wavelength, 313 nm (Gruver and Calvert, 1956, 1958). By analogy with the other aldehydes, the following primary processes are expected to occur ... 

We are not aware of any studies of the photochemistry of the OH-substituted polycyclic aromatic hydrocarbons, but by analogy with the photochemistry of the simple substituted phenols discussed in this section, we would expect photodissociation by process (I) to be significant at the wavelengths of sunlight available within the troposphere ... 

The literature of mechanistic aromatic photochemistry has produced a number of examples of [4 + 4]-photocycloadditions. The photodimerization of anthracene and its derivatives is one of the earliest known photochemical reactions of any type97. More recently, naphthalenes98, 2-pyridones" and 2-aminopyridinium salts100 have all been shown to undergo analogous head-to-tail [4 + 4]-photodimerization. Moreover, crossed [4+4]-photocycloaddition products can be obtained in some cases101. Acyclic 1,3-dienes, cyclohexadienes and furan can form [4 + 4]-cycloadducts 211-214 with a variety of aromatic partners (Scheme 48). 

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