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Norrish

The first application of the time-resolved CIDNP method by Closs and co-workers involved tire Norrish 1 cleavage of benzyl phenyl ketone [24, 25]. Geminate RPs may recombine to regenerate the starting material while escaped RPs may fonn the starting ketone (12), bibenzyl (3), or benzil (4), as shown below. [Pg.1604]

Norrish R G W and Porter G 1949 Chemioal reaotions produoed by very high light intensities Nature 164 658... [Pg.2968]

Transient species, existing for periods of time of the order of a microsecond (lO s) or a nanosecond (10 s), may be produced by photolysis using far-ultraviolet radiation. Electronic spectroscopy is one of the most sensitive methods for detecting such species, whether they are produced in the solid, liquid or gas phase, but a special technique, that of flash photolysis devised by Norrish and Porter in 1949, is necessary. [Pg.67]

When the polymers are exposed to ultraviolet radiation, the activated ketone functionahties can fragment by two different mechanisms, known as Norrish types I and II. The degradation of polymers with the carbonyl functionahty in the backbone of the polymer results in chain cleavage by both mechanisms, but when the carbonyl is in the polymer side chain, only Norrish type II degradation produces main-chain scission (37,49). A Norrish type I reaction for backbone carbonyl functionahty is shown by equation 5, and a Norrish type II reaction for backbone carbonyl functionahty is equation 6. [Pg.476]

A Norrish type I reaction for side-chain carbonyl functionahty is equation 7, and a Norrish type II reaction for side-chain carbonyl functionahty is equation 8. [Pg.476]

Norrish type I chemistry is claimed to be responsible for about 15% of the chain scission of ethylene—carbon monoxide polymers at room temperature, whereas at 120°C it promotes 59% of the degradation. Norrish I reactions are independent of temperature and oxygen concentration at temperatures above the T of the polymer (50). [Pg.476]

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. [Pg.476]

Attaching the ketone groups to the polymer backbone is more efficient on a chain scission/ketone basis because some of the light energy that the pendent ketone absorbs leads direcdy to chain scission via the Norrish type II mechanism, as well as photooxidation via the Norrish type I mechanism (see... [Pg.512]

Studies of the copolymerization of VDC with methyl acrylate (MA) over a composition range of 0—16 wt % showed that near the intermediate composition (8 wt %), the polymerization rates nearly followed normal solution polymerization kinetics (49). However, at the two extremes (0 and 16 wt % MA), copolymerization showed significant auto acceleration. The observations are important because they show the significant complexities in these copolymerizations. The auto acceleration for the homopolymerization, ie, 0 wt % MA, is probably the result of a surface polymerization phenomenon. On the other hand, the auto acceleration for the 16 wt % MA copolymerization could be the result of Trommsdorff and Norrish-Smith effects. [Pg.430]

A consequence of the orientation of the 11-carbonyl function towards the C-19 methyl group which is retained in the excited state is the exclusive functionalization at C-19. Ring cleavage products of the Norrish II type are not observed but the reaction is rather sensitive to conformational changes in the substrate. In a series of experiments conducted under comparable conditions (24 hr irradiation) the yield of cyclobutanols drops... [Pg.261]

Carbonyl compounds can undergo various photochemical reactions among the most important are two types of reactions that are named after Norrish. The term Norrish type I fragmentation refers to a photochemical reaction of a carbonyl compound 1 where a bond between carbonyl group and an a-carbon is cleaved homolytically. The resulting radical species 2 and 3 can further react by decarbonylation, disproportionation or recombination, to yield a variety of products. [Pg.212]

Since the quantum yield of the Norrish type I reaction is generally low, it has been assumed that the initial homolytic cleavage is a reversible process. Evidence came from an investigation by Barltrop et al. which has shown that erythro-2,3-dimethylcyclohexanone 12 isomerizes to t/zreo-2,3-dimethylcyclohexanone 13 upon irradiation ... [Pg.214]

As a side reaction, the Norrish type I reaction is often observed. The stability of the radical species formed by a-cleavage determines the Norrish type 1/Norrish type II ratio. For example aliphatic methyl ketones 10 react by a Norrish type II-mechanism, while aliphatic tcrt-butyl ketones 11 react preferentially by a Norrish type I-mechanism. [Pg.216]


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A-cleavage, Norrish type I reaction

By William M. Horspool 1 Norrish Type I Reactions

Carbonyl compounds Norrish type

Carbonyl compounds Norrish type I reaction

Carbonyl compounds Norrish type II elimination

Cyclization Norrish-Yang

Dauben-Turro-Salem analysis Norrish type

Disproportionation ketones, Norrish type

Elimination, Norrish

Excited-state reactions ketones, Norrish type

Horspool 1 Norrish Type I Reactions

Ketones Norrish Type 1 reactions

Ketones Norrish type

Multiplicity, Norrish type

Norrish I and II reactions

Norrish I intermediate

Norrish I reaction

Norrish II process

Norrish II reactions

Norrish Type 1 reactions

Norrish Type I Cleavage Reaction of Carbonyl Compounds

Norrish Type I and

Norrish Type I and II reactions

Norrish Type I cleavage

Norrish Type I fragmentation

Norrish Type I process

Norrish Type II

Norrish Type II Reaction of Carbonyl Compounds

Norrish Type II hydrogen abstraction

Norrish Type II process

Norrish Type processes

Norrish acceleration

Norrish cleavage

Norrish cleavage of alkylphenacyl sulfides

Norrish cleavage/cyclization ratio

Norrish effect

Norrish hydrogen abstraction

Norrish mechanism

Norrish photo-cleavage

Norrish photoprocess

Norrish reaction

Norrish solvents

Norrish studies

Norrish typ

Norrish type

Norrish type 1 cleavage

Norrish type 1 photo-cleavage

Norrish type 1 ring expansions

Norrish type I and II processes

Norrish type I mechanism

Norrish type I photoreaction

Norrish type I reaction

Norrish type I split

Norrish type II cleavage

Norrish type II cyclization

Norrish type II fragmentation

Norrish type II mechanism

Norrish type II photochemistry

Norrish type II photocyclization

Norrish type II photoelimination of ketones

Norrish type II photoelimination,

Norrish type II photofragmentation

Norrish type II photoreaction

Norrish type II reaction

Norrish type fragmentation

Norrish type ketone photoelimination

Norrish type mechanisms

Norrish type n reaction

Norrish type-1 mechanism Cleavage

Norrish, Ronald

Norrish, Ronald George Wreyford

Norrish-I cleavage

Norrish-Tromsdorff effect

Norrish-Yang Photocyclization

Norrish-Yang Type

Norrish-Yang reaction

Norrish-Yang reaction zeolites

Norrish/Yang type II reaction

Photochemical reactions Norrish

Photocyclizations Norrish type

Photofragmentation Norrish type

Photolytic cleavage Norrish Type

Proline derivatives, Norrish-Yang

Quantum yield Norrish type II reaction

Smith-Norrish effect

State correlation diagrams Norrish type

The Norrish Type II Reaction

Triplet-state radical pairs from Norrish type I processes

Trommsdorf-Norrish effect

Trommsdorff Norrish

Trommsdorff-Norrish effect

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