| Abstract |
Twenty-four pairs of meta and para Hammett sigma constants recommended by IUPAC for normal substituents, i.e. dipolar groups without a lone pair of electrons (and with a full octet) in the atom next to the aromatic ring, were analysed with respect to their meta-para interrelationship. In terms of a previous hyperbolic model, the para/meta ratio of the universal electric effect is found to be 0.964 with a standard error of 0.028 estimated by Monte Carlo simulation. This value for benzoic acid derivatives supports the view that the universal electric effect, which is proposed to be termed the Electra effect, is transmitted through space. For normal substituents, it is demonstrated that the hyperbolic model predicts lower bounding values of sigma(m) and sigma(p) constants. It is proposed that organometallic substituents in which a metallic atom is bounded to the alpha carbon should not be considered as normal substituents. It is asserted that no normal substituent should exist for which either sigma(m) is less than -0.1 or sigma(p) is less than -0.3 in the Hammett sigma scale. |
