We have used a Brownian dynamics numerical algorithm to simulate reversible intramolecular reactions taking place in flexible polymer chains in dilute solutions. The simulations are based on the Gaussian chain model, with the possibility of including long range interactions to mimic excluded volume conditions. Hydrodynamic interactions are considered at different levels of detail. We have extended our previous study of end-to-end cyclizations to longer chains and added the analysis of cyclization processes involving inner units. The numerical results of the cyclization rate constants are systematically compared with the results of the classical cyclization theory of Wilemski and Fixman, to better understand the effect of the theoretical approximations. The conclusions previously described for shorter chains are confirmed in general, though in some cases they become slightly corrected by the more accurate results of this work. In addition, we have extended our analysis to end-to-interior and interior-to-interior intramolecular processes.