A transition state is a first-order saddle point on a potential energy surface (PES). The vibrational spectrum of a transition state is characterized by one imaginary frequency (implying a negative force constant), which means that in one direction in nuclear configuration space, the energy is maximum, whereas in all other (orthogonal) directions, the energy is minimum. In contrast, this characteristic is missing in reactants and products, which are minimum along all coordinates.

The objective of this experiment is to perform a frequency calculation of all the stationary points in the SN2 reaction.