OriginsFew scientists acquainted with the chemistry of biological systems at the molecular level can avoid being inspired. Evolution has produced chemical compounds exquisitely organized to accomplish the most complicated and delicate of tasks. Many organic chemists viewing crystal structures of enzyme systems or nucleic acids and knowing the marvels of specificity of the immune systems must dream of designing and synthesizing simpler organic compounds that imitate working features of these naturally occurring compounds. We had that ambition in the late 1950's. At that time, we were investigating n-complexes of the larger [m.n]paracyclophanes with (NC),C=C(CN),, and envisioned structures in which the a-acid was sandwiched by two benzene rings. Although no intercalated structures were observed, [','] we recognized that investigations of highly structured complexes would be central to simulation of enzymes by relatively simple organic compounds.In 1967, Pedersen's first papers a~p e a r e d '~.~] which reported that alkali metal ions bind crown ethers to form highly structured complexes. We immediately recognized this work as a n entree into a general field. The 1969 papers on the design, synthesis, and binding properties of the cryptands by J.-M. Lehn, J.-P. Sauvage, and B. D i e t r i~h l~.~' further demonstrated the attractions and opportunities of complexation chemistry. Although we tried to interest graduate students in synthesizing chiral crown ethers from

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The taming of cyclobutadiene was accomplished in the interior of the hemicarcerand 1. Cyclobutadiene is a stable compound with a singlet ground state when it is synthesized in the interior of 1. In order to synthesize the incarcerated cyclobutadiene and to characterize its structure, one bimolecular, three photochemical, and two thermal reactions were carried out in the interior of 1. The authors consider it both realistic and useful to regard the internal phase of carcerands and hemicarcerands as a new state of matter.

Dedicated to Professor Uadimir Prelog on the occasion of his 80th birthdayThis article assesses the importance of molecular preorganization to the rapidly developing field of complexation involving designed synthetic organic compounds. Since its birth as a science, organic chemistry has drawn heavily on biological chemistry as a vast storehouse of evolutionary structures, reactions, and control mechanisms that serve as inspiration for designed organic-compound mimics. Biological systems, through highly structured complexation, accomplish complicated tasks. The receptor sites of enzymes, the genes, the antibodies, and ionophores possess high degrees of preorganization. In other words, their functional groups act cooperatively as binding or catalytic sites which are largely collected and oriented prior to complexation.-The strength of the organic chemist derives from his ability to design organic compounds, organic reactions, synthetic sequences, and test systems to evaluate hypotheses. The design of highly structured complexes and the discovery of the rules that govern their behavior are described here. Research in this field is particularly rewarding because scientific and aesthetic content merge and become visible in the structures of many of the complexes.