116 THE FORMATION OF CYCLIC KETONES Crafts reaction. 4 This chapter presents a discussion of these methods and the various problems involved in the formation of cyclic ketones by the ring closure of aryl-substituted aliphatic acids. 4 " The structural aspects which determine the inherent capability of these acids to undergo ring closure, and which consequently control the course of the cyclization, are: (a) the size of the ring formed; (6) the reactivity of the aromatic nucleus, including the effect of substituent groups; (c) steric considerations other than ring size. . In addition, the reagent and reaction conditions are sometimes critical and may have an extrinsic and secondary effect on the course of ring closure. THE SIZE OF THE RING In a study of the fundamental structural problems'involved in ring closure by intramolecular acylation, v. Braun and his collaborators found that the susceptibility of an acid to cyclization depends upon the size of the ring to be formed. The tendency toward formation
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