Intermolecular and intramolecular reactions

The measurement of accurate EM s, as defined above, clearly has very stringent requirements. First, the mechanisms of both intermolecular and intramolecular reactions must be known and have been shown to be the same. Then acceptable rate measurements must be carried out under the same conditions for both reactions. Generally it is not possible to measure the rates of both the intermolecular reaction and the intramolecular process (thus catalysed by the same group) under the same conditions measurements on the intermolecular reaction catalysed by a series of catalytic groups are necessary to define the EM accurately. 

Both intermolecular and intramolecular reactions can be measured for this reaction. EM is calculated as the ratio of the rate constants for the intramolecular (s ) and intermolecular reactions (dm3 mol-1 s 1). Data of Searles and Nukina, 1965... 

Intermolecular and Intramolecular Reactions of Substituted Norbomenyl Imides... 

Corresponding improvements in the semisynthesis of proteins have been developed (see Section 5.1.11). They, too, have involved intermolecular and intramolecular reactions to form normal peptide bonds between small synthetic peptides and large protein components derived from natural sources or produced by recombinant techniques. In this case, there is the potential to produce derivatives of much larger proteins than can currently be prepared by total chemical synthesis. The total synthesis and semisynthesis approaches are useful for somewhat different purposes, but can be considered complementary together, they greatly broaden the field of protein chemistry and biology. 

Like carbene insertions into carbon-hydrogen bonds, metal nitrene insertions occur in both intermolecular and intramolecular reactions.For intermole-cular reactions, a manganese(III) meio-tetrakis(pentafluorophenyl)porphyrm complex gives high product yields and turnovers up to 2600 amidations could be effected directly with amides using PhI(OAc)2 (Eq. 51). The most exciting development in intramolecular C—H reactions thus far has been the oxidative cychzation of sulfamate esters (e.g., Eq. 52), as well as carbamates (to oxazolidin-2-ones), ° and one can expect further developments that are of synthetic... 

A major source of acceleration in enzymic reactions is approximation, that is to say, the bringing together of two or more reactants in the active site. Once the reagents are in contact, the subsequent reaction is intra- rather than intermolecular. Comparisons of the rates of intermolecular and intramolecular reactions are, however, difficult because the rate constants for bimolecular reactions have the units of M "1 s-1, whereas rate constants for unimolecular reactions have the units of s l. The best one can do in comparing them is to state the molarity at which the reactants would have to be present in the bimolecular reaction to achieve the rate of the unimolecular process when the effective molarity is large-say 1000 M or more-one has some measure of the power of approximation to accelerate chemical reaction. 

The inclusion of a separate chapter on catalysed cyclopropanation in this latest volume of the series is indicative of the very high level of activity in the area of metal catalysed reactions of diazo compounds. Excellent, reproducible catalytic systems, based mainly on rhodium, copper or palladium, are now readily available for cyclopropanation of a wide variety of alkenes. Both intermolecular and intramolecular reactions have been explored extensively in the synthesis of novel cyclopropanes including natural products. Major advances have been made in both regiocontrol and stereocontrol, the latter leading to the growing use of chiral catalysts for producing enantiopure cyclopropane derivatives. 

Hydroxide ion coordinated to cobalt(IIl) has been observed to function as a nucleophile in both intermolecular and intramolecular reactions. The possibility that coordinated hydroxide is directly involved in the catalytic action of some metalloenzymes such as carbonic anhydrase has prompted a number of investigations of metal hydroxide reactivity towards organic substrates. Much of this chemistry has been reported and reviewed.21,23... 

Molecular beams are very important tools for characterizing intermolecular and intramolecular reactions. In fact, the 1988 Nobel Prize in Chemistry was awarded to Yuan Lee, Dudley Herschbach, and John Polanyi for studies which were mostly made possible by this technique. A particularly useful variant is the supersonic molecular beam, which in the simplest case pushes a high-pressure mixture of helium and trace amounts of some larger guest molecule through a nozzle. When the helium atoms enter the... 

In summary, the C-H insertion chemistry of rhodium carbenoids is a very powerful method for transformation of C-H bonds. Highly regioselective and stereoselective reactions are possible and several classes of chiral catalyst are capable of very high asymmetric induction. The chemoselectivity in this chemistry is exceptional, as illustrated by the numerous intermolecular and intramolecular reactions described in this overview. Most notably, this chemistry offers new and practical strategies for enantioselective synthesis of a variety of natural products and pharmaceutical agents. 

In enantioselective photocycloaddition reactions, 4-alkoxyquinolones perform in superior fashion to l,5-dihydropyrrol-2-ones and 5,6-dihydro-lff-pyridin-2-ones. Both, intermolecular and intramolecular reactions were performed with excellent enantioselectivity in the presence of the chiral template 115, or of its enantiomer ent-115 [147, 148], The well-established photocycloaddition reactions [149, 150] enabled access to a variety of chiral dihydroquinolones. 4-Methoxyquinolone (157) produced, upon direct irradiation in the presence of allyl acetate, the formal HT product 158 in 80% yield and with 92% ee (Scheme 6.56) [151]. 

To date, NMR has been used to study (a) the structures of indoles, substituted in both heterocyclic as well as the benzenoid ring (recently, there have been a number of publications wherein NMR is used to elucidate the complicated structures of biologically important antibiotics95,110-112 and alkaloids113-117 containing the indole skeleton) (b) tautomeric structures and equilibria 96, 118-120 (c) the stereochemistry of side-chain substituents and (d) the protonation of indoles. It is hoped that in the future many significant applications of NMR in the indole field, such as a study of intermolecular and intramolecular reactions and the rates of fast reactions, will be found. 

Free radical reactions proceed under essentially neutral conditions that are compatible with various functional and protective groups used for saccharides. C-Glycosylation by means of radical reaction has been extensively developed [63]. This section will discuss intermolecular and intramolecular reactions for control of the stereochemistry of the C-glycoside linkage. 

The purpose of this chapter is to review those methods for constructing C—C bonds from unactivated C—H bonds that appear to have some synthetic generality. Both intermolecular and intramolecular reactions will be considered. 

Having introduced the stereochemical course followed by reactions involving glycosidic free radicals, the remainder of this chapter will present examples of the utility of these species in both intermolecular and intramolecular reactions. 

This chapter has endeavored to present approaches to the preparation of C-glycosides utilizing the chemistry of free radicals. Through the use of intermolecular and intramolecular reactions, a variety of novel structures are available. Further insight into the variations available within this technology, reviewed by Descotes,29 include discussions of the kinetics of radical systems and topics complimenting the specific realm of C-glycosides. 

A number of recent reviews exist about intermolecular and intramolecular reactions of the iV-acyl-iminium intermediate. Moreover, detailed accounts of the application in alkaloid synthesis have recently appeared. This chapter deals with reactions of species (1) with nucleophilic alkenes (and alkynes). Other synthetically useful nucleophiles like aromatic rings, active methylene compounds and organome-tallics will not be discussed here. In (1) R, and R are hydrogen or carbon substituents, and R may also be a hetero substituent, such as alkylamino or alkoxy. This chapter differs from previous reviews, as the material is ordered here on the basis of the structural features of the A -acyliminium intermediate. Major emphasis is placed on recent developments and stereochemical details. 

As is the case with hydrolysis of epoxidised vegetable oils, by alcoholysis the hydroxyl numbers obtained are always lower than theoretically expected. The explanation is the same the intermolecular and intramolecular reactions between the formed hydroxyl groups and the unreacted epoxidic rings. These reactions conserve the number of hydroxyl groups and do not generate new hydroxyl groups. By intramolecular reactions dimers and trimers of lower hydroxyl number and higher functionality are formed. 

Both intermolecular and intramolecular reactions can be either reversible or irreversible (termination). In reversible reactions true chain transfer takes place when the rate constant of the backward reaction (k ) becomes comparable with the rate constant of propagation. This is valid in the case of cyclic acetal polymerization in which the product of chain transfer is equally active in propagation. 

Four different types of (2 + 2)-cycloaddition and -cycloreversion reactions of heterocyclic compounds are known intermolecular and intramolecular reactions, both thermal and photochemical. Three of these have already been discussed in the previous sections on (2 + 2)-cycloadditions, and as far as the mechanism is concerned both the forward and the reverse reaction suffer from the same ambiguity Do they proceed via a concerted or a nonconcerted mechanism do they involve an ionic or a diradical intermediate are they symmetry-allowed or forbidden So far only one reaction type is known to be limited to the reverse reaction, viz., the thermal intramolecular reaction [Eq. (10)], in which one o-bond is broken and a conjugated -electron system is... 

If the two halogens are on the same or adjacent carbons, two consecutive E2 dehydrohalogenations can result in the formation of a triple bond. The Williamson ether synthesis involves the reaction of an alkyl halide with an alkoxide ion. If the two functional groups of a bifunctional molecule can react with each other, both intermolecular and intramolecular reactions can occur. The reaction that is more likely to occur depends on the concentration of the bifunctional molecule and the size of the ring that will be formed in the intramolecular reaction. 

When [S]o = EM 12, the termolecular complex S T-S undergoes intermolecular and intramolecular reaction at equal rates. The factor of 2 results from the fact that we have a reaction between two identical substrate molecules. 

A particularly important consideration is the potential for competitive intermolecular and intramolecular reactions ... 

The rate-theory description of random polymerisations considers subsets of states of the monomer units involved in a polymerisation and the reaction routes by which they interconvert through intermolecular and intramolecular reaction. Unlike cascade theory( ) it allows analytical expressions for ring fractions, gel point, sol fraction, gel fraction and numbers of loops to be derived(3,24). It has also been found to provide a... 

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