In pursuit of the objective of the series which is to present considered reviews of areas concerned with the quantitative study of organic compounds and their behaviour - physical organic chemistry in its broadest sense - in a manner accessible to general readership, this 28th volume contains five contributions on a diversity of topics. Two of these reflect the increasing importance of physical organic studies in providing fundamental knowledge relevant to the development of new materials with novel physical properties. The others represent more traditional areas of physical organic chemistry, where recent research has thrown more light.