During the forty years which have passed since Masuzo Shikata published his paper on the reduction of nitrobenzene at a dropping mercury electrode, the number of polarographic studies of organic compounds in the literature has risen to several thousands. The ever­ increasing amount of experimental data was in need of some unified method of classification which would yield unambiguous and possibly complete information on the polarographic behavior of organic substances. Dr. Zuman's book presents an original attempt to meet this need by providing a system based on correlations between the polaro­ graphic half-wave potentials of organic depolarizers and their Hammett constants. I consider this a very happy conception, for, more than any other book yet written, it brings polarography nearer to the organic chemist; and it will undoubtedly convince him that, in its application to his subject, the method is more than a mere analytical tool. The author hardly needs any introduction. During many years of research in the field of organic polarography, he has published numerous papers on a variety of problems; his latest interest is the application of the Hammett-Taft equation to polarographic measure­ ments, in which he has done pioneering work. It remains for me to hope that this book, which opens up new prospects for the fruitful application of polarography, may inspire vii viii Foreword some reader with useful ideas in his search for new paths in his research problems.

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I Introduction.- 1. Development of the Study of Structural Relations.- 2. Classification of Structural Effects.- 3. Techniques in the Polarographic Study of Structural Effects.- II General Equation for the Relation Between the Polarographic Half-Wave Potentials and Substituent Effects.- 1. General.- 2. Influence of Polar Effects.- 3. Influence of Polar and Resonance Effects in Combination.- 4. Influence of Polar and Steric Effects in Combination.- 5. The General Case.- 6. The Role and Importance of the General Equation.- 7. The Conditions for the Application of the General Equation.- III Benzene Derivatives.- 1. General.- 2. Selection of Values of the Substituent Constants.- 3. Selection and Treatment of Half-Wave Potential Values.- 4. Reaction Series for which Equations (27), (31), and (37) Hold.- 5. Range of Validity of Equation (27); Significance of Deviations for the Discussion of Electrode Process Mechanism.- 6. Additivity of Substituent Effects.- 7. Application of the Constants ?X? and the Determination of New Values of the Substituent Constants ?X.- 8. Ortho Derivatives-Application of Equation (37).- 9. Hindrance of Coplanarity due to Ortho Substituents.- 10. The Question of Hydrogen Bonds in Ortho-Substituted Compounds.- 11. Factors Affecting the Reaction Constant ??,R.- 12. Other Empirical Relationships.- 13. Applications of (27) and Related Equations.- IV Monocyclic Heterocyclic Compounds.- 1. General.- 2. Classification of Reaction Series.- 3. Reducible Heterocyclic Rings.- 4. Reduction in the Side Chain.- V Reaction Series in which the Electroactive Group is Directly Attached to an Alkyl or Aryl Substituent.- 1. General.- 2. Reactions for which Equations (25), (29), and (36) Hold.- 3. Effect of Changes in the Mechanism of the Electrode ProcessReflected in Deviations from Linear Free Energy Relations and Changes in the Sign of the Reaction Constant.- 4. Effect of Exchange of Methyl for Phenyl.- 5. Effect of Transfer Coefficient..- 6. Additivity of Substituent Effects.- 7. Factors Affecting the Value of the Reaction Constant ??,R*.- 8. Application of Equations (25) and (29) for the Determination of New Values of the Substituent Constants ?XI and ?X*.- 9. Other Empirical Quantitative Relations.- 10. Two Functional Groupings in a Molecule.- VI Effects of Substituents in Condensed Polycyclic Hydrocarbons.- 1. General.- 2. Classification of Reaction Series.- 3. Electroactive Aromatic System with One Substituent.- 4. Polysubstituted Electroactive Aromatic Systems.- 5. Effects of a Substituent in a Condensed Aromatic Hydrocarbon on the Reduction of a Functional Grouping in Another Position in the Ring System.- 6. Effect of the Nature of the Aromatic Ring on Reduction in the Side-Chain.- 7. Substituent in a Reducible Side-Chain.- VII Effects of Substituents in Polycyclic Heterocyclic Compounds.- 1. General.- 2. Classification of Reaction Series.- 3. Effect of a Substituent in an Electroactive Heterocyclic Ring.- 4. Effect of Substituents in the Benzene Ring and in Both Rings on the Reduction of the Heterocyclic Ring.- 5. Effect of Substitution in a Phenyl Group Attached to Electroactive Heterocyclic Ring.- 6. Correlation of the Reactivities of Various Heterocyclic Compounds by the Use of Dimroth Equation.- 7. Effect of Substitution in the Heterocyclic Ring on Reduction in a Side-Chain on the Same Ring.- 8. Effect of Substitution in the Benzene Ring on Reduction in a Side-Chain on the Heterocyclic Ring.- 9. Effect of the Position and Nature of the Heterocyclic Ring on Reduction in the Side-Chain.- VIII Effects ofSubstituents in Quinonoid Compounds.- 1. General.- 2. Classification of Reaction Series.- 3. Monocyclic Quinonoid Systems.- 4. Bicyclic Quinonoid Systems.- 5. Polycyclic Quinonoid Systems.- IX Alicyclic Systems.- 1. Effects of Substituents in the Ring on an Electroactive Group Attached to the Ring.- 2. Effect of Ring Size and Type on an Electroactive Group Attached to the Ring.- 3. Effect of Ring Size and Type on Electroactive Groups that Form Part of the Cyclic System.- 4. Conclusions.- Author Index.