STRUCTURE-BASICITY RELATIONSHIPS IN CARBONYL-COMPOUNDS

Substituent effects on the basicity of 39 carbonyl compounds XiXjCO were studied by measuring ∆H° and ∆GC° for the formation of iodine complexes in heptane, the solvent sensitivity α. the infrared shift ∆ υ(OH) of phenol complexes, and the carbonyl stretching vibration wavenumber. The iodine enthalpic basicity scale is well correlated with the SbCl5 and protonation scales and, provided that comparison is made with the n band maximum, with ∆ υ(OH). α parallels roughly ∆GC° indicating localized association of solvent on the oxygen lone pair. The carbonyl vibrator is not isolated, so no general correlation between basicity and carbonyl frequency exists. The formation of iodine complexes follows the isoequilibrium relationship and, in terms of linear free energy relationships, carbonyl compounds from ureas to acid halides are considered to form a homogeneous series. The cumulative effect of the two substituents Xi, and Xj follows the additive relationship for ∆H° and ∆Gc° and the simplest nonadditive relationship for a. The dual substituent parameter equation is obeyed using (υR+, which shows that inductive effects are the dominant factor controlling the basicity of the carbonyl group toward iodine. © 1979, American Chemical Society. All rights reserved.