Học. Phổ cơ bản cho sinh viên lười

o Introduction to Organic Spectroscopy Laurence M Harwood and Timothy D W Claridge I I I Se"~1 o X Fo AO $ e I ENe E PUB L I e A T ION s SfO"lor ZENECA Introduction to Organic Spectroscopy Laurence M Harwood Professor and Head of Organic Chemistry University of Reading Timothy O.w Claridge NMR Facility Manager, The Dyson Perrins Laboratory University of Oxford Series sponsor: ZENECA ZENECA is a major international company active in four main areas of business: Pharmaceuticals, Agrochemicals and Seeds, Specialty Chemicals, and Biological Products ZENECA's skill and innovative ideas in organic chemistry and bioscience create products and services which improve the world's health, nutrition, environment, and quality of life ZE!'IECA is committed to the support of education in chemistry and chemical engineering OXFORD UNIVERSITY PRESS Contents Introduetory theory Ultraviolet- visible speetroseopy 13 Infrared speetroseopy 22 Nuclear magnetie resonanee speetroseopy: the basies 33 Nuclear magnetie resonanee speetroseopy: further topies 55 Mass speetrometry 70 Exereise answers 84 Appendices 88 Index 92 Founding Editor's Foreword The deduction of chemicaI structure from spectroscopic data is an essentiaI skilI required of aH organic chemists, which is acquired mainly by the practice of interpreting original data Laurence Harwood and Tim Claridge provide in this primer the basic knowledge, in the four most important areas of spectroscopy, which will allow students to start interpreting their own data and hence gain this essential skill Oxford Chemistry Primers have been designed to provide concise introductions relevant to all students of chemistry and contain only the essential material that would normaI1y be covered in an 8-10 lecture course In this primer the authors introduce students to this enormous area of basic structural analysis in a logical and easy to follow fashion This primer wilI be of interest to apprentice and master chemist alike Stephen G Davies The Dyson Perrins Laboratory University of Oxford Preface The need to determine the structures of molecules efficiently lies at the heart of chemistry and the great strides made in the various techniques of spectroscopic analysis have been the root cause of the explosive burgeoning, particularly of organic chemistry, during the latter half of this century In response to the chemist's desire to analyse ever smaHer amounts of structures of increasing complexity, the advance of instrumentation and spectroscopic techniques shows no sign of slowing To the newcomer, the task of se1ecting a starting point within the bewildering array that falls under the heading of 'spectroscopy' must appear very daunting indeed The aim of this book is to provide a straightforward introduction to the basic principIes, operation, and analyses possible using four of the spectroscopic techniques most routine1y used by organic chemists-ultraviolet, infrared and nuclear magnetic resonance spectroscopy, and mass spectrometry Our thanks go to Dr Robin Aplin for helpfuI comments on the chapter on mass spectometry and Dr Katya Vines for proof-reading the manuscript We would like to dedicate this book to the memory of Andy Derome, our friend and coIleague, whose tragic and untimely death at the age of 33 in 1991 cut short the career of someone who had established himself as one of the leading exponents of NMR spectroscopy in the worId at the time We are aH the poorer for his passing away Óxford, Reading October 1996 L M H and T D W C Introductory theory 1.1 The electromagnetic spectrum The development of non-destructive spectroscopic methods of analysis which can be carried out on small amounts of material has provided the fundamental thrust behind the burgeoning of organic chemistry during the latter half of this century Identification of unknown molecules of high complexity can now be carried out more or less routinely on samples ranging from severa! nanograms to a milligram of material, and in many cases it may not even be necessary to obtain pure samples Four techniques are used routinely by organic chemists for structural analysis Ultraviolet spectroscopy was the first to come into general use during the 1930s This was followed by infrared spectroscopy in the 1940s, with the establishment of nuclear magnetic resonance spectroscopy and mass spectrometry during the following two decades Of these, the first three fall into the category of absorption spectroscopy,ASfhisteÍ'm sugges~-iliese aiialYfic-al-TeChniques·~-e··llbsorriÜon of S12ecific energies of electromaglletic radiationwhic~_c;orrespond exactly.in energy· to specific excihttions _.wIj:hir!~j:@.~lli9J~.Q~i~_bciđg exaIl11nec:t GenenilIy thererofe,-ii-[lows that knowledge of the tnlnsitiünswhich may be induced by absorption of a certain wavelength of electromagnetic radiation can be used to infer structural features In the classical treatment, electromagnetic radiation can be considered as a propagating wave of electrical energy with an orthogonal mágnetic component oscillating with exactly the same frequency (Fig 1.1) Following this approach, electro~_!I,g~Yº.H.cliMi2Il.J