| This dissertation describes the results of dynamical investigations of a variety of organic reactions.;Chapter 1 explores the dynamics of 1,3-dipolar cycloaddition reactions by decomposing transition vector, quasi-classical trajectories, and single trajectories. Dipole bending makes the largest contribution to the TS distortion energy and constitutes the major part of transition state distortion energy in the favored concerted pathway.;In Chapter 2, energy partitioning of reactants among relative translation, vibration, and rotation in 1,3-dipolar cycloadditions of nine 1,3-dipoles with ethylene and acetylene has been investigated by quasi-classical trajectory and single trajectory calculations. The results are interpreted with an expanded version of Polanyi's rules for bimolecular reactions. Relative translation of reactants is the main contributor to surmounting the activation barrier, since all transition states are early with respect to sigma bond formation. Vibrational excitation in the dipole bending modes required for reactions is related to the lateness of the TS with respect to dipole bending. The timing of bond formation and relative reactivities of different 1,3-dipoles are discussed.;Finally, a detailed dynamical picture of carbene cycloadditions to alkenes on the UB3LYP/6-31G(d) surface is given in Chapter 3, especially issues of timing of bond formation and the duration of reactive event. A quantitative dynamical classification of reaction mechanism is established. All trajectories follow non-linear approach proposed by Roald Hoffmann. The reaction of CCl 2 with alkenes is dynamically a concerted process with average time gap of bond formation of around 50 fs and duration of reactive event of around 270 fs. The reactions of CF2 with alkenes are dynamically stepwise, and the diradical has an average lifetime of around 200-250 fs, while the duration of reactive event of 280-470 fs. |
