Substituent constant physical significance

Sterigmatocystin, 48 Stevens rearrangements, 293 Stobbe reaction, 228 Substituent constant, a, 362 constancy of, 368, 372 determination of, 363 physical significance of, 364 and, 362... 

The next significant advances were made by attempts to use substituent constants rather than physical measurements on the whole molecule. In 19 f0 Hammett (16) developed the (o ) substituent constants, which measure the degree of electron release/withdrawcil of aromatic substituents. Based on the Hammett equation, Hcinsen (17) correlated bacterial growth inhibition of a series of compounds with their Hammett [Pg.178]

Despite the availability of a significant number of sigma constants, some model systems for evaluating substituent effects failed when steric effects were intensive or complex. One of the first measures of steric effects in physical organic... 

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