Substituent survey

C-Linked substituents behave in pyrazoles and indazoles as in other azoles (Section 4.02.3.3). The classical aromatic chemistry of these compounds has given rise to a great number of publications (66AHC(6)347, 67HC(22)1, B-76MI40402), but not to a specific pyrazole chemistry. For this reason, only a brief survey will be given here. 

FULLY CONJUGATED RINGS REACTIVITY OF SUBSTITUENTS 4.17.7.1 General Survey of Reactivity... 

For reasons discussed in Section VI, a survey of the purine series (29) is being made in this Department, but so far no example (including 2-hydroxy- and 8-trifluoromethyl-2-hydroxy-purine) of covalent hydration has come to light. An examination of ionization constants disclosed no apparent anomalies, although the interpretation is made more difficult by the ease of anion formation in the 9-position, which often competes with that from other anionic substituents. The only abnormal spectrum seems to be that of the anion of 2-mercaptopurine which is being further examined. 

Yukawa and coworkers (1972)84 determined a0 values from the rate constants for alkaline hydrolysis of m- and p-substituted-benzyl benzoates in 70% (v/v) aqueous acetone at 25 °C. ap° values for SOMe and S02Me were found to be 0.573 and 0.749 respectively. These were compared with 0.564 and 0.721, respectively, for values determined from the rate constants of alkaline hydrolysis of substituted ethyl benzoates in 85% aqueous ethanol. From these values there is no evidence for any — R cross-conjugative effect of SOMe as a substituent in the benzoate moiety, which is eliminated when it is in the benzyl. However, both the values for SOMe are substantially higher than most of the ap values for SOMe which we have surveyed previously. For S02Me the order ap° > if significant,... 

There have been no reports of 1,2,3-oxadiazoles synthesized by transformation of another ring since the last survey <1996CHEC-II(4)165> other than those involving cyclization of substituents attached to benzene (Section 5.03.9). 

Numerous transformations of substituents have been carried out by applying established routine reactions. In this section, a concise survey on these transformations is provided. 

Taft and coworkers106a, have recently reviewed the substituent and structural effects in a comprehensive analysis of substituents constants1063, followed by a survey of structural effects in organic chemistry1066. 

Effects of various substituents on 13C chemical shifts can be found in textbooks (2-5,11) or reviews concerned with applications of l3C NMR spectroscopy to specific classes of chemical compounds (16-24,142). Therefore, this section is limited to recent information about effects of less common substituents and to reference data for various carbo- and heterocyclic molecules. It is not the author s intention to present a comprehensive survey rather, a number of typical examples have been selected. The reader may use this section as an entry into the original papers and the references cited therein. 

The fourth chapter in this volume, contributed by Helmut Duddeck, is an exceptionally thorough survey of substituent effects on carbon-13 nuclear magnetic resonance (NMR) chemical shifts. Organic chemists and others who are routinely dependent on 13C NMR for structure elucidation and for information about stereochemistry will welcome the summary presented here. Although... 

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