Norrish studies

Norrish, Ronald George Wreyford (1897-1978) British physical chemist. Norrish made important contributions to the study of fast chemical reactions, particularly those initiated by light. Between 1949 and 1965 he developed the techniques of flash photolysis and kinetic spectroscopy with George PORTER to study fast chemical reactions. Norrish and Porter shared the 1967 Nobel Prize for chemistry with Manfred EIGEN for this work. In his later years Norrish studied chain reactions and the kinetics of polymerization. 

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. 

Majeti11 has studied the photochemistry of simple /I-ketosulfoxides, PhCOCH2SOCH3, and found cleavage of the sulfur-carbon bond, especially in polar solvents, and the Norrish Type II process to be the predominant pathways, leading to both 1,2-dibenzoylethane and methyl methanethiolsulfonate by radical dimerization, as well as acetophenone (equation 3). Nozaki and coworkers12 independently revealed similar results and reported in addition a pH-dependent distribution of products. Miyamoto and Nozaki13 have shown the incorporation of protic solvents into methyl styryl sulfoxide, by a polar addition mechanism. 

Time-resolved spectroscopic techniques are important and effective tools for mechanistic photochemical studies. The most widely used of these tools, time-resolved UV-VIS absorption spectroscopy, has been applied to a variety of problems since its introduction by Norrish and Porter almost 60 years ago. Although a great deal of information about the reactivity of organic photochemical intermediates (e.g., excited states, radicals, carbenes, and nitrenes) in solution at ambient temperatures has been amassed with this technique, only limited structural information can be extracted from... 

The technique of flash photolysis was originally developed by Norrish and Porter as a method for studying reactive species such as triplets and radicals with relatively short lifetimes (r > 1 x 10 6 sec).<6) The beauty of this technique is that it involves the direct observation of the species of interest. The principal problem, however, is to determine the identity of the species causing the new electronic absorption. For their efforts in the development of this technique Norrish and Porter, along with Eigen, received the Nobel Prize in chemistry in 1961. 

First the interaction of selected tetramethylpiperidine (TMP) derivatives with radicals arising from Norrish-type I cleavage of diisopropyl ketone under oxygen was studied. These species are most probably the isopropyl peroxy and isobutyryl peroxy radicals immediately formed after a-splitting of diisopropyl ketone and subsequent addition of O2 to the initially generated radicals. Product analysis and kinetic studies showed that the investigated TMP derivatives exercise a marked controlling influence over the nature of the products formed in the photooxidative process. The results obtained point to an interaction between TMP derivatives and especially the isobutyryl peroxy radical. 

The flash photolysis study of Norrish et al,415 has confirmed the suggestions of earlier workers that CIO is an important reaction intermediate. It reaches its maximum concentration during the photolytic flash and is clearly generated in... 

It is clear, however, that a simultaneous increase in polymerization rate and molecular weight could either follow from a reduction in the rate of termination or from an increase in the rate of propagation. This last possibility has seldom been considered, except in some of the very early studies such as in the work of BENGOUGH and NORRISH (2J on the bulk polymerization of vinyl chloride where a "catalytic" action was attributed to the precipitated polymer. 

The technique of flash photolysis (Figure 10.6) employed by Norrish and Porter in 1949 revolutionised the study of short-lived transient species as it proved capable of generating and analysing chemical species with lifetimes shorter than a few milliseconds. 

Supramolecular concepts involved in the size- and shape-selective aspects of the channels and cavities of zeolites are used to control the selectivity of reactions of species produced by photoexcitation of molecules encapsulated within zeolites. The photochemistry of ketones in zeolites has been extensively studied. Photoexcitation of ketones adsorbed on zeolites at room temperature produces radical species by the Norrish type 1 reaction. A geminate (born together) radical pair is initially produced by photolysis of the ketone, and the control of the reaction products of such radicals is determined by the initial supramolecular structure... 

The end result of these studies showed very clearly that two major processes were important, i.e. photolysis and photo-oxidation. Photolysis reactions were posited to be the result of the well-known Norrish Type 1 and Norrish Type 2 cleavage reactions. As we shall see, the Type 1 cleavage followed by several subsequent reactions can account for many of the observed degradation products. 

The behaviour of triplet acyl-diphenylmethyl biradicals 0=C -(CH2) 2-C Ph2, generated from the Norrish type-I reaction of 2,2-diphenylcycloalkanones (CK) with various ring sizes, n = 6, 7, 9, 11, 12, 13, was the subject of a study. Eor 2,2-diphenylcycloalkanones where n = 6 and 7 an intramolecular disproportionation takes place giving rise to a diphenylalkenal (94). The primary products in the photolysis... 

Al-for-Fe substitution in natural goethites was originally discovered, with the aid of X-ray diffraction, in marine, oolithic, iron ores from the Jurassic era by Correns von Engelhardt as early as in 1941 and twenty years later found in soils by Norrish and Taylor (1961). Since then, a large number of studies has revealed that Al substitution in goethites from the weathered zone, e.g. in soils (see chap. 16), appears to be the rule rather than the exception. It should be noted that Al located in the struc-... 

Fordham, A.W. Norrish, K. (1979) Electron microprobe and electron microscope studies of soil day partides. Aust. J. Soil Res. 17 283-306... 

This technique for the study of a fast reaction is gas phase or liquid phase was developed by Norrish and Poster. This is an example of Pulse method which initiates a reaction by creating new reactive species—excited electronic states, radicals, ions in the system under study. The method uses a light flash of high intensity for a very short duration (10- s) to produce atoms or free radicals or excited species in a system. These are at a fairly high concentration and undergo further reactions which are followed spectroscopically. A spectroscopic flash of light is followed by the initial flash by some fraction of a millisecond. The absorption spectra of all the species that are formed within the system can be recorded. One cannot only get indications of what species are formed but also how these species give rise to others. Thus a very direct picture of the kinetic behaviour of a fast reaction can be obtained. 

Norrish type-I reaction, has been studied over the years in extreme detail, with every imaginable physical and theoretical method at hand. Data gathered through studying such reactions on the femtosecond time scale, together with new theoretical work prompted by the dynamics observed, have provided a detailed picture of the processes involved and a fresh perspective on nonconcerted ot-cleavage events. 

Since the photochemistry of many compounds that have been used as triplet sensitizers has been well studied, we will not attempt to cover these reactions in detail. Unless the investigator is unaware of them, common photochemical processes such as the Norrish Type II cleavage are not ordinarily a complication and as will be mentioned later, they can actually serve as mechanistic probes. A discussion of the mechanisms of triplet energy transfer1,3,9 is beyond the scope of this review as are other specific reactions which have been recently covered elsewhere. 

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