Aromaticity- Chemical review

Aromaticity- Chemical review
byACS

Thematic Issues

Aromaticity-2001

In 1825, benzene was discovered by Michael Faraday. He determined its melting and boiling points, as well as the density, with remarkable accuracy. Each succeeding generation of chemists, while taking advantage of the structural integrity of benzene and its analogs for synthetic and practical purposes, has grappled with the elusive origin and essence of "aromaticity". Despite the very frequent use of aromatic and aromaticity in the current scientific literature, these designations, like many other useful and popular chemical terms, are nonreductive. They have no precise meaning and do not denote directly measurable quantities. Consequently, definitions, which continue to evolve since the 1865 Kekulé and the more general 1866 Erlenmeyer formulations, are now often based on experimental observables and, more recently, quantities obtained from theoretical computations. Aromatic compounds are more stable-often far more stable-and their geometries tend to be more regular than they "ought to be".

Historically, aromaticity has been a time-dependent phenomenon. Aromatic implies various features, properties, or behaviors to chemists with different backgrounds. While "benzene-like" still suffices for some, the "cyclic delocalization of mobile electrons" description now seems paramount. Its general implication for energies and structures, both geometrical and electronic, as well as magnetic and other properties, necessarily results in an ever increasing widening of the 19th century aromaticity concept. The reviews published here are designed to further the interest and the understanding of aromaticity in this newest century.

CONTENTS

Introduction: Aromaticity, Paul von Ragué Schleyer, University of Georgia and University of Erlangen-Nuremberg.
Three-Dimensional Aromaticity in Polyhedral Boranes and Related Molecules, R. Bruce King, University of Georgia.
Spherical Aromaticity of Fullerenes, Michael Bühl and Andreas Hirsch, Max-Planck-Institut für Kohlenforschung and Institut für Organische Chemie der Universit%26auml;t Erlangen-Nürnberg.
Homoaromaticity, Richard Vaughan Williams, University of Idaho.
Metallabenzenes, John R. Bleeke, Washington University.
Aromaticity of Phosphorus Heterocycles, László Nyulászi, Budapest University of Technology and Economics.
Cyclic Aromatic Systems with Hypervalent Centers, Vladimir I. Minkin and Ruslan M. Minyaev, Rostov State University.
Big Is Beautiful-"Aromaticity" Revisited from the Viewpoint of Macromolecular and Supramolecular Benzene Chemistry, Mark D. Watson, Andreas Fechtenk%26ouml;tter, and Klaus Müllen, Max-Planck-Institut für Polymerforschung.
Measuring Aromaticity by NMR, Reginald H. Mitchell, University of Victoria.
Antiaromaticity in Monocyclic Conjugated Carbon Rings, Kenneth B. Wiberg, Yale University.
Antiaromaticity in Open-Shell Cyclopropenyl to Cycloheptatrienyl Cations, Anions, Free Radicals, and Radical Ions, Annette D. Allen and Thomas T. Tidwell, University of Toronto.
Aromaticity and Ring Currents, J. A. N. F. Gomes and R. B. Mallion, Universidade do Porto and The King's School.
Structural Aspects of Aromaticity, Tadeusz Marek Krygowski and Michal Ksawery Cyranski, University of Warsaw.
Quantitative Measures of Aromaticity for Mono-, Bi-, and Tricyclic Penta- and Hexaatomic Heteroaromatic Ring Systems and Their Interrelationships, Alan R. Katritzky, Karl Jug, and Daniela C. Oniciu, University of Florida, Universit%26auml;t Hannover, and Alchem Laboratories Corporation.
Conceptual and Computational DFT in the Study of Aromaticity, Frank De Proft and Paul Geerlings, Vrije Universiteit Brussel.
Dewar Resonance Energy, L. J. Schaad and B. Andes Hess, Jr., Vanderbilt University.
- Energy Separation in Modern Electronic Theory for Ground States of Conjugated Systems, Karl Jug, Philippe C. Hiberty, and Sason Shaik, Universit%26auml;t Hannover, Université de Paris Sud, and Hebrew University.
A Different Story of -Delocalization-The Distortivity of -Electrons and Its Chemical Manifestations, Sason Shaik, Avital Shurki, David Danovich, and Philippe C. Hiberty, The Hebrew University and Université de Paris-Sud.
The Energetics of Aromatic Hydrocarbons: An Experimental Thermochemical Perspective, Suzanne W. Slayden and Joel F. Liebman, George Mason University and University of Maryland Baltimore