The surge of interest in and scientific publications on the structure and properties of nanocomposites has made it rather difficult for the novice to comprehend the physical structure of these new materials and the relationship between their properties and those of the conventional range of composite materials. Some of the questions that arise are: How should the reinforcement volume fraction be calculated? How can the clay gallery contents be assessed? How can the ratio of intercalate to exfoliate be found? Does polymerization occur in the clay galleries? How is the crystallinity of semi-crystalline polymers affected by intercalation? What role do the mobilities of adsorbed molecules and clay platelets have? How much information can conventional X-ray diffraction offer? What is the thermodynamic driving force for intercalation and exfoliation? What is the elastic modulus of clay platelets? The growth of computer simulation techniques applied to clay materials has been rapid, with insight gained into the structure, dynamics and reactivity of polymer–clay systems. However these techniques operate on the basis of approximations, which may not be clear to the non-specialist. This critical review attempts to assess these issues from the viewpoint of traditional composites thereby embedding these new materials in a wider context to which conventional composite theory can be applied. (210 references)

The Heck–Mizoroki cross-coupling reaction is an important part of the synthetic chemist's toolbox, and it has been applied to a huge variety of different substrates. In contrast, the mechanism of the process is much less studied, and consequently less understood. There have been numerous studies reported over recent years, both experimental and theoretical, aimed at uncovering the inner working of this palladium-mediated coupling process. This perspective aims to review and compare these works and to provide an up-to-date view of this reaction.

Despite the amide formation reaction being one of the key cornerstone reactions in organic chemistry, the direct amide formation is both little used and little explored. Acceptance of the feasibility and general applicability of the reaction depends upon the ability of researchers to bring it into the mainstream by development of: (1) an understanding of the mechanism of the reaction; and (2) the design of catalysts which promote the reaction on a wide range of substrates and under ambient conditions. From the earliest report of the direct amide formation in the 19th century, there have been relatively few reports of mechanistic studies, though it is clear that there is not a simple relationship between ease of direct amide formation and the pK_a of the carboxylic acid and amine, or whether salt ammonium carboxylate formation is important. Consequently, direct amide formation has historically been run under higher temperature conditions. However, more recently, stoichiometric and catalytic boron compounds have been developed that considerably reduce the reaction temperatures under which direct amide formation will proceed. Limited attempts at mechanistic studies point to the formation of acyloxyborate or boronate species acting essentially as mixed anhydrides, though the exact order of these systems remains to be categorically determined.

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