Transition state

[3] The concept of a transition state has been important in many theories of the rates at which chemical reactions occur.

This started with the transition state theory (also referred to as the activated complex theory), developed independently in 1935 by Eyring, Evans and Polanyi, and introduced basic concepts in chemical kinetics that are still used today.

Femtochemical IR spectroscopy was developed for that reason, and it is possible to probe molecular structure extremely close to the transition point.

Often, along the reaction coordinate, reactive intermediates are present not much lower in energy from a transition state making it difficult to distinguish between the two.

Transition state structures can be determined by searching for first-order saddle points on the potential energy surface (PES) of the chemical species of interest.

[6] The structure–correlation principle states that structural changes that occur along the reaction coordinate can reveal themselves in the ground state as deviations of bond distances and angles from normal values along the reaction coordinate.

The DFT -determined geometry for the transition state of the above reaction. [ 2 ] Distances are listed in angstroms . Note the elongated C-Br and C-O bonds, and the trigonal bipyramidal structure .