Activation energy dipole orientation

Theoretical calculations on the cycloaddition reactions of a range of 1,3-dipoles to ethene in the gas phase have been carried out (85) with optimization of the structures of these precursor complexes and the transition states for the reactions at the B3LYP/6-31G level. Calculated vibration frequencies for the orientation complexes revealed that they are true minima on the potential energy surface. The dipole-alkene bond lengths in the complexes were found to be about twice that in the final products and binding was relatively weak with energies <2 kcal mol . Calculations on the cycloaddition reactions of nitrilium and diazonium betaines to ethene indicate that the former have smaller activation energies and are more exothermic. 

The high dielectric constant of water, as well as that of ice, is not connected with this since it is as high as this for both H20 and DaO. In ice, as well as in heavy ice, it appears from the frequency- and temperature-dependence of the dielectric constant that the activation energy, associated with the orientation of the dipoles in an alternating electric field, is equal to 13.2 kcal/mole (Cole) which therefore points to the rupture of several hydrogen bonds. 

The ion-dipole interaction exerts a torque on the dipole, which reduces the activation energy of the rotation. For randomly oriented molecules, the average torque U exerted on a molecule with dipole moment by a singly charged ion at a distance r through a medium of dielectric constant is roughly... 

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