SN MECHANISM IN AROMATIC COMPOUNDS .38. COMPARATIVE REACTIVITY OF 1-HALOGENO-2,6-DINITROBENZENES AND SOME OTHER HALOGENONITROBENZENES

The reactivity of 1-halogeno-2,6-dinitrobenzenes with methanolic methoxide has been studied quantitatively and compared with the results of similar studies of o- and p-halogenonitrobenzenes and 1-halogeno-2,4-dinitrobenzenes. Adverse steric interactions of the ortho-nitro group are very small in the o-halogenonitro- and 1-halogeno-2,4-dinitrobenzenes. The interactions are substantially larger in the reactions of 1-halogeno-2,6-dinitrobenzenes in displacement of Cl, Br, and I, but not of F, but they are small compared to steric interactions found in many other classes of reactions. Steric effects are observed as a reduction in rates affecting values of the Substituent Rate Factors of the o-nitro group, and affecting also the mobility as a leaving group of Cl, Br, and I, but not of F. However, since Cl is the usual reference standard for leaving group mobility, that of F appears as having an unusually high value. Nevertheless a depression of the mobility of iodine from its typical range is also evident. © 1969, CSIRO. All rights reserved.