Propyl from photolysis

The quantum yields and G values of H2 elimination for a larger group of alkanes are eolleeted in Table 4 the values were mostly determined by using Eq. (10). Because in the photolysis and radiolysis of the -alkanes shown in the table various kinds of radicals are produced simultaneously (e.g., -propyl and ec-propyl from propane), the weighted averages of several k /kc values were used in Eq. (10). The ratios can be determined by suppressing the radiolytic alkene and dimer yields in the presence of radical scavenger (e.g., I2) ... 

Lipscher and Rscher used di-/-propyl ketone photolysis to generate /-propyl radicals (166). As with the other ketones, the mechanism for /-propyl radical formation involves a-cleavage from the triplet state followed by activated decarbonylation of 2-methylpropanoyl radicals, with/og A (s ) = 14.0 0.5, E, = 13.0 0.5 kcal/mol (166). At T> 35 C the decarbonylation is sufficiently fast to allow clean bimolecular self-reaction, monitored by ESR, of the /-propyl radicals to give coupling and disproportionation products (Eq. 59). Below this temperature the longer lifetime of the 2-methylpropanoyl radicals introduces... 

Preparative Photolysis. The preparative photolysis of an aqueous solution (pH=8.5) of AETSAPPE (2.5 M) was conducted in a 1-inch diameter quartz test tube in a Rayonet Reactor (Southern New England Radiation Co.) fitted with 254 nm lamps. Within two hours the solution gelled and the reaction was terminated. Upon acidification the solution cleared, and the product could be re-precipitated by addition of base. This indicates loss of the thiosulfate functionality. The product was dissolved in dilute HC1, precipitated with acetone, and filtered. This process was repeated three times, and the final precipitate was washed with water. The product (20 to 30 mg) was dried in vacuo for 24 hours and stored in a dessicator until use. Comparison of the13 C NMR spectrum of the product with the starting AETSAPPE 13C NMR spectrum clearly shows that the thiosulfate methylene peak shifted upfield, from 39 ppm to 35 ppm. The complete 13 C NMR and IR analysis of the product were consistent with the disulfide product. Further, elemental analysis of the product confirmed that the product was the desired disulfide product 2-amino (2-hydroxy 3-(phenyl ether) propyl) ethyl disulfide (AHPEPED) Expected C 58.39, H 7.08, N 6.20, S 14.18 actual C 58.26, H 7.22, N 6.06, S 14.28. 

Preparative photolysis of AETSAPPE (0.25 M aqueous solution) at 254 nm (Rayonet reactor) resulted in the formation of the disulfide product 2-amino(2-hydroxy-3-(phenyl ether) propyl) ether disulfide (AHPEPED) as the primary photoproduct Photolysis of AETSAPPE at 254 nm (isolated line of medium pressure mercury lamp) resulted in rapid initial loss of starting material accompanied by formation (analyzed by HPLC) of AHPEPED (Figure 12a and 12b) (Scheme IV). Similar results were obtained for photolysis- at 280 nm. Quantum yields for disappearance of AETSAPPE and formation of AHPEPED at 254 nm and 280 nm are given in Table I. The photolytic decomposition of AETSAPPE in water was also accomplished by sensitization ( x =366 nm) with (4-benzoylbenzyl) trimethylammonium chloride (BTC), a water soluble benzophenone type triplet sensitizer. The quantum yield for the sensitized disappearance (Table I) is comparable to the results for direct photolysis (unfortunately, due to experimental complications we did not measure the quantum yield for AHPEPED formation). These results indicate that direct photolysis of AETSAPPE probably proceeds from a triplet state. 

FIGURE 4.22 Experimental values of the photolysis rate constant, kp, for (a) ethyl nitrate and (b) n-propyl nitrate as a function of zenith angle compared to calculated values shown by the solid lines. Different symbols represent different measurement days (adapted from Luke et al., 1989). 

An improved synthesis7 of aldosterone acetate lb was based on the readily available dienone 30. Conversion to the nitrite and photolysis affords the oxime 31 with no attack on C19. On warming in iso-propyl alcohol this oxime 31, cyclized smoothly to the nitrone 32 with the loss of water. This nitrone is at the right oxidation level to rearrange to the 21-acetoxyimine. The overall yield of nitrone from 30 was 55%. 

Thermal decomposition of butane involves the unimolecular decomposition of sec- and n-butyl radicals as chain carrier steps, but little quantitative information can be obtained from the work. The best estimation of the A factor for the thermal decomposition of butyl radical is based on the high-temperature photolysis of 2-methylbutanal and has the value, log A — 15.32.64 Corresponding values for w-propyl radicals2 were 15.3655 and 13.9.62 In view of the complexity of these experimental systems, these compare reasonably with the value of 14.35 in Table XX. 

A study of chemically induced dynamic electron polarization, CIDEP (see Section 12.3.3) on F and G pairs of radicals formed under photolysis of a common termo- and photoinitiator 2,2 -azobis(2-methylpropionitrile) (AIBN) led to a tentative conclusion that initial spatial separation of 2-cyano-2-propyl radicals does not depend upon viscosity However, it is plausible that the diamagnetic dinitrogen molecule formed under photolysis of AIBN (and is invisible by ESR) separates further from a contact RP under photolysis in solvents of lower viscosity. The problem of initial spatial separation and mutual orientation ofradicals under photolysis still waits experimental elucidation. 

MO calculations have been carried out on the isomerization of cyclopropane to propene, and the MNDO method has been used to study the reaction pathway and to optimize the structure of reactant, transition structure, and product of the ring opening reaction of bicyclo[1.1.0]butane. Various methods have been employed to estimate the rate constants for ring opening of the 2-cyclopropyl-2-propyl radical. 1-Acceptor-1-sulfenyl-substituted 2-vinylcyclopropanes of the type (430) have been found to afford 6-sulfenyl-a,jS y, -unsaturated carboxylic esters and nitriles (431) upon treatment with acid, by a process which involves C(l)—C(2) bond fission and a novel 1,5-sulfenyl rearrangement (see Scheme 110). It has been shown that the benzophenone-sensitized photolysis of vinyl norcaradiene derivatives, such as 5-(2-methylprop-l-enyl)-3-oxatricyclo[4.4.0.0 ]deca-7,9-dien-4-ones (432), results in the regioselective cleavage of only one of the cyclopropyl c-bonds to afford isochroman-3-one derivatives (433). It has been reported that the major product obtained from the reaction of structurally diverse a-diazo ketones with an electron-rich alkene in the... 

The lack of laser action in the photolysis of isopropyl iodide raises intriguing questions. As Husain and Donovan point out, this does not necessarily indicate the absence of population inversion, since under the laser experimental conditions there could instead be an insufficient absolute concentration of I atoms. Spectroscopic studies show that excited iodine atoms are produced from isopropyl iodide photodissociation, but at lower relative concentrations than for n-propyl iodide under similar conditions. Since the two propyl iodides show similar I quenching rates, it would appear most likely that a decreased I /I ratio is the reason stimulated emission is not seen. The present experiments, unfortunately, cannot provide a more quantitative explanation. The distinct broadness of the isopropyl iodide distribution in fig. 2 indicates a departure from the methyl- ethyln-propyl trend, and might represent comparable amounts of P and I atom production, with overlapping translational energy distributions, at least when viewed with our present... 

A further [3 4- 2)-cycloaddition process takes place when imines react with 2-azaallenyl radical cations (23) derived from azirines by photolysis (Scheme 4.2.10) [31, 32]. Yields of (24) are variable, e.g. 2,4,5-triphenyl-1-propyl- (87%), 4-butyl-1,5-dipropyl- (40%), 4-phenyl-1,5-dipropyl- (35%),... 

A series of other halogenated compounds have been identihed in seawater, including ethyl iodide, propyl iodide, bromoiodomethane, chloro-iodomethane, and di-iodomethane (Carpenter et al., 2000 Klick and Abrahamsson, 1992). Little is known about their production mechanisms. Loss mechanisms are likely to include photolysis and reaction with chloride and hydroxide ions. Information is too limited to be used to derive global fluxes for these compounds, although the data available indicate that a reasonable case can be made that the iodine flux from these compounds is similar to that from CH3I. 

Bamford and Norrish observed that the free radical formation is the sole primary process in the photolysis of cyclohexanone, while step II is the major reaction occurring in the photolysis of 1-menthone. These results are rather difficult to interpret if reaction II occurs through a four-centred ring complex however, if a six-centred complex is involved, the consideration of the steric factors leads to a conclusion which is reconcilable with the results of Bamford andNorrish. The significance of steric factors (stereoelectronic requirements) appears from the fact that type II elimination is the major intramolecular path in the photolysis of ciy-2- -propyl-4-t-butyl cyclohexanone, while the photolysis of the tram compound yields the cis isomer as the major product The difference has been explained... 

Photolysis of 6-phenyl- and 6,7-diphenyl-4,5,6-triazaspiro[2.4]hept-4-ene la and lb dissolved in dichloromethane with filtered light (A > 295 nm) from a mercury lamp resulted in nitrogen expulsion and formation of the corresponding phenyl-substituted l-azaspiro[2.2]pentanes A similar reaction occurred when methyl 4,5-dihydro-l-(l-phenylcyclo-propyl)-l,2,3-triazole-4-carboxylate (3), obtained by treating methyl acrylate with 1-azido-l-phenylcyclopropane, was refluxed in toluene. 

Cyclopropanoxyl radicals were generated by thermal and photochemical decomposition of cyclopropyl nitrites.The nitrites were prepared from cyclopropanols and nitrosyl chloride in pyridine, and they decomposed at low temperatures often below room temperature. A mixture of -bromo and jS-nitroso ketones was formed from the photolysis of pentamethylcyclo-propyl nitrite (19) in bromotrichloromethane. " ... 

Several recent publications indicate that the role of intermediate complexes in ionic reactions is still controversial (21, 24, 25). Our interest in this and earlier observations of persistent complexes in alkyl halides already mentioned prompted us to study ionic reactions in ethyl chloride. The previously noted mass spectrometric investigations of alkyl halides did not include the chlorides, and radiolytic studies of these compounds have been limited to the propyl and butyl chlorides which apparently isomerize (39). The present investigation consists of two phases. In the initial phase, the ion-molecule reactions for ethyl chloride were probed by the sensitive mass spectrometric methods which we have applied in recent studies of a similar nature (3,12, 28, 43). In the latter part of this study, the gas-phase radiolysis and vacuum-ultraviolet photolysis of ethyl chloride have been studied to identify those products which arise from ionic precursors. More specifically, we wished to define the behavior under radiolytic conditions of those intermediate ionic species which the spectrometric studies suggested were important, and we hoped to arrive at a reasonable conciliation of the ionic reaction information derived from these different but complementary techniques. 

Propanol. 2-Propanol was chosen as a model for a simple alcohol. Irradiation under vacuum gave hydrogen and acetone as major products along with smaller amounts of methane, acetaldehyde, carbon monoxide, tert-butyl alcohol, and ethanol. These minor products must arise mainly from acetone. Acetaldehyde may be formed either by direct photolysis of 2-propanol, hydrogen atom abstraction by acetyl radical, or /3-scission of the 2-propyloxy radical. The formation of tert-butyl alcohol implies the presence of methyl and 2-hydroxy-2-propyl radicals. 

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