Quantum yield aldehydes

Autooxidation. Liquid-phase oxidation of hydrocarbons, alcohols, and aldehydes by oxygen produces chemiluminescence in quantum yields of 10 to 10 ° ein/mol (128—130). Although the efficiency is low, the chemiluminescent reaction is important because it provides an easy tool for study of the kinetics and properties of autooxidation reactions including industrially important processes (128,131). The light is derived from combination of peroxyl radicals (132), which are primarily responsible for the propagation and termination of the autooxidation chain reaction. The chemiluminescent termination step for secondary peroxy radicals is as follows ... 

The reported quantum yields of the long-chain aldehydes in the luminescence reaction catalyzed by P. fischeri luciferase are 0.1 for dodecanal with the standard I (Lee, 1972) 0.13 for decanal with the standard I (McCapra and Hysert, 1973) and 0.15-0.16 for decanal, dodecanal and tetradecanal with the standard III (Shimomura et al., 1972). Thus, the quantum yield of long-chain aldehydes in the bacterial bioluminescence reaction appears to be in the range of 0.10-0.16. 

When an excess amount of luciferin was preincubated with H2O2 before the addition of luciferase, the quantum yields of luciferase and the luciferin-H202 adduct were found to be 0.63 and 0.03, respectively (Rudie et al., 1981). The aldehyde group of luciferin is probably converted into the corresponding acid in the luminescence reaction, although it has not been experimentally confirmed. 

Quantula (Dyakia), 180, 334 Quantum yield, xvi, 361, 362 aequorin, 104, 106, 110 aldehydes in bacterial bioluminescence, 36, 41 Chaetopterus photoprotein, 224 coelenterazine, 85, 143, 149 Cypridina luciferin, 69-71 definition, xvi, 361 Diplocardia bioluminescence, 242 firefly luciferin, 12 fluorescent compound F, 73 Latia luciferin, 190 pholasin, 197 PMs, 286... 

Table 4.8. Some Photodecarbonylation Quantum Yields for a-Aryl Aldehydes...

Benzimidazolyl-iminocoumarins react with aromatic aldehydes to give the benzimidazopyrimidinocoumarins, which are of interest as dyes because of their fluorescence with high quantum yields (Equation 117) <2002CHE1518, 2004CHE334>. 

The quantum yields are about 10 4 with the aldehydes and 10 3 with the ketones 93 and 94. The respective acridones were found to be the emitters when potassium hydroxide was used as base in the oxidation of 92 and 95 and t-butoxide, in the oxidation of the ketones 93 and 94. 

The quantum yields for oxetane formation have not been determined in every case, and only a few relative rate constants are known. The reactivities of singlet and triplet states of alkyl ketones are very nearly equal in attack on electron rich olefins. 72> However, acetone singlets are about an order of magnitude more reactive in nucleophilic attack on electron-deficient olefins. 61 > Oxetane formation is competitive with a-cleavage, hydrogen abstraction and energy-transfer reactions 60 64> so the absolute rates must be reasonably high. Aryl aldehydes and ketones add to olefins with lower quantum yields, 66> and 3n-n states are particularly unreactive. 76>... 

The ratio of the rate constants of these reactions depends on the energy of photon absorbed by the aldehyde molecule. The values of the quantum yield for acetaldehyde are the following [205] ... 

Many aromatic aldehydes and ketones (e.g. benzophenone, anthrone, 1- and 2-naphthaldehyde) have a low-lying n-n excited state and thus exhibit low fluorescence quantum yields, as explained above. The dominant de-excitation pathway is intersystem crossing (whose efficiency has been found to be close to 1 for benzophenone). 

Table IV summarizes the pertinent characteristics of some of the naphthyl carbonyl compounds. All of these compounds emit from a it,7T triplet very similar to that of naphthalene. Those that have been studied are resistant to photoreduction in isopropyl alcohol and photocycloaddition with 2-methyl-2-butene25 and isobutylene.17 Significant oxetane formation was, however, observed with the aldehydes, albeit with only moderate efficiency (quantum yield approximately one-tenth that of benzaldehyde).25...

However, as discussed in Chapter 4, the absorption spectrum of higher aldehydes cuts off at shorter wavelengths than formaldehyde. This, combined with higher quantum yields for radical production in the 290- to 340-nm range and the fact that HCHO produces 2H02 essentially immediately upon dissociation, makes the photolysis of aldehydes larger than formaldehyde less important at equal concentrations of the aldehydes. 

There is some contribution due to / -scission of the alkyl radical formed by the type I process, particularly in the MIPK and tBVK polymers. Loss of carbonyl occurs from photoreduction or the formation of cyclobutanol rings, and also from vaporization of the aldehyde formed by hydrogen abstraction by acyl radicals formed in the Norrish type I process. As demonstrated previously (2) the quantum yields for chain scission are lower in the solid phase than in solution. Rates of carbonyl loss are substantially different for the copolymers, being fastest for tBVK, slower for MIPK, and least efficient for MVK copolymers (Table I and Figure 1). 

The photolysis of camphor (XXII) in aqueous alcoholic solution (11) has been observed to lead to a-campholenic aldehyde (XXXII) and a second isomer with a ketonic function. The structure of the latter has been found (30) to be 1,2,2-trimethyl cyclopent-3-enyl methyl ketone (XXXIII). The quantum yields at 3130 A. for the formation of the two isomers and of carbon monoxide in five different solvents have been determined (Table IV). It is interesting that the sum of the quantum... 

For neat-liquid it has been established that the dehydrogenation represents almost completely the phenomena observed, since with ethanol and 1-propanol, 1.1 values were found for the ratios /(aldehyde + acetal), which is within the experimental errors, and the formation of CO2 molecules only amounted to 1 (ethanol) or 4 (1-propanol) of the aldehyde + acetal molecules (8). Depending upon the catalyst and the alcohol, quantum yields in the range 0.1-0.8 were found for the following alcohols whose order of reactivity was MeOH > EtOH > 1-PrOH, 2-PrOH, 1-BuOH... 

Vife have extensively studied (10) the photoinduced catalytic system (Figure 2) which is based upon the photochemical generation of cyanide ions from various cyanometa I lates, especially from octa-cyanomolybdate(IV) aod octacyanotungstate(IV) ions. Upon photolysis both compounds form cyanide ions with relatively high quantum yields. Cyanide Sons may act as a catalyst for the dimerizat ion of appropriate heterocyclic carb-2-aldehydes to enediols. Since this photocatalytic system has proved to operate also in solid layers, it may be used for an unconventional photographic process (11,12). 

The largest quantum yield obtained from the aldehyde oxidation of Equation 45 was seen with tolualdehyde using absolute diethyl formamide as a solvent (45). In this instance, the quantum yield is 6 x 10-3, which is about twentyfold less than obtained with the bacterial luciferase enzymes. 

Norrish has suggested that the low quantum yield is probably due to the complexity of the molecule. Decomposition cannot occur if there is a wide distribution of energy among the various parts of a complex molecule for then there is not a sufficient quantity left at the one particular bond where chemical disruption must occur. The probability that a fraction of the whole amount sufficient for chemical decomposition will reach the proper bond at the proper instant depends largely on the complexity of the molecule and the amount of energy introduced. With acetone this probability appears to be about 0.2 with crotonic aldehyde the probability is zero, for Blacet and Roof35 have shown that this substance does... 

The gas phase photooxidation of crotonaldehyde has been studied by Blacet and Volman.21 The product is crotonic acid, which condenses out of the system as soon as it is formed. The quantum yield of oxidation was found to increase steadily over the 3660-2380 A. wavelength range. At constant aldehyde pressure, the quantum yield was independent of oxygen pressure at 3130 and 2804 A. At 2537 A., however, the quantum yield increased rapidly with the oxygen pressure and a chain mechanism is likely. Addition of nitrogen at 2537 A. caused a marked decrease in the quantum yield indicating that excited molecules are involved. 

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