Inductive effects can be measured through the Hammett equation.

The linear relationship fit well in the Hammett Equation.

In other words, for such reactions, application of the standard Hammett Equation does not produce a linear plot.

It was developed by Robert W. Taft in 1952 as a modification to the Hammett equation.

There are a number of linear free-energy relationships which have been used to quantify these effects, of which the Hammett equation is the best known.

The plot of the Hammett equation is typically seen as being linear, with either a positive or negative slope correlating to the value of rho.

A still very interesting application is the Hammett equation, Taft equation and pKa prediction methods.

Hammett equation (Equation 1) provides the relationship between the substituent on the benzene ring and the ionizing rate constant of the reaction.

He is known for the Hammett equation, which relates reaction rates to equilibrium constants for certain classes of organic reactions involving substituted aromatic compounds.

It is a modified version of the Hammett equation that accounts for enhanced resonance effects in electrophilic reactions of para- and meta-substituted organic compounds.

The Hammett equation predicts the equilibrium constant or reaction rate of a reaction from a substituent constant and a reaction type constant.

When the steric effects of substituents do not significantly influence the reaction rate the Taft equation simplifies to a form of the Hammett equation:

While the Hammett equation accounts for how field, inductive, and resonance effects influence reaction rates, the Taft equation also describes the steric effects of a substituent.

Other equations now exist that refine the original Hammett equation: the Swain-Lupton equation, the Taft equation, the Grunwald-Winstein equation, and the Yukawa-Tsuno equation.

The Yukawa-Tsuno Equation allows for treatment of both para- and meta- substituents, and it also better correlates data from reactions with high electron demand than the original Hammett Equation.

Since it has the same pattern with Hammett equation but dealing with the change of solvent system, we can also consider it as a supplement of Hammett Equation.

To correlate these deviations from linearity, Yasuhide Yukawa and Yuho Tsuno proposed a modification to the original Hammett Equation which accounts exclusively for enhanced resonance effects due to the high electron demand during such reactions.

The Hammett equation in organic chemistry describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents to each other with just two parameters: a substituent constant and a reaction constant.