What is the Hammett equation as a linear free energy relationship?

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.

What is Taft steric factor?

is the ratio of the rate of the substituted reaction compared to the reference reaction, ρ* is the sensitivity factor for the reaction to polar effects, σ* is the polar substituent constant that describes the field and inductive effects of the substituent, δ is the sensitivity factor for the reaction to steric effects.

What is the application of Hammett equation?

The Hammett equation is one of the most widely applied relations between the structure and reactivity of organic compounds. This equation relates the relative reactivities of the series of di- and poly-substituted benzene derivatives.

What are the limitations of Hammett equation?

Limitations of the Hammett Equation The problem is that ortho substituents are close enough to the reaction site to exert significant “proximity” effects, which may be polar as well as steric in origin.

What is Taft equation in organic chemistry?

The Taft equation is a linear free energy relationship (LFER) used in physical organic chemistry in the study of reaction mechanisms and in the development of quantitative structure–activity relationships for organic compounds. It was developed by Robert W. Taft in 1952 as a modification to the Hammett equation.

What is Hammett substituent constant?

1 Hammett Substituent Constants for Benzoic Acids (σm and σp) The electronic property of an aromatic substituent is expressed by the Hammett substituent constant σ. This constant for a given substituent is arrived at by measuring its effect on the dissociation of benzoic acid.

What is the Hansch equation?

An equation relating the differences in the partitions of variously substituted compounds between an organic and an aqueous phase to the hydrophobicity constant, π of the substituent.

What is a Craig plot used for?

This plot allows the selection of substituents with diverse properties—substituents should be selected in this case from different quadrants, but it also helps to select groups that are close together on the assumption that they will have similar effects on bioactivity.

What does a negative value of Sigma signify for the substituent?

A negative value of σ signifies an electron donating substituent whereas a positive value signifies an electron withdrawing substituent. A value close to zero would indicate a neutral electronic effect.

Which technique is used for measuring rate of fast reaction?

The speed of relaxation is measured by a physical method such as spectroscopy, and analysis of the results leads to the reaction rate. The most common way of changing the external conditions is to change the temperature, and the method is called the temperature-jump, or T-jump, method.

What does the Hammett substituent constant sigma measure?

The substituent constant is a measure of the total polar effect exerted by substituent X (relative to no substituent) on the reaction centre. Electron-withdrawing m-NO2 ( = +0.71) increases stability of tetrahedral intermediate compared to electron- donating m-CH3 ( = -0.07).

What is substituent hydrophobicity constant?

The substituent hydrophobicity constant is a measure of how hydrophobic a substituent is, relative to hydrogen. A positive value of π indicates that the substituent is more hydrophobic then hydrogen. A negative value indicates that the substituent is less hydrophobic.