Prof. McBride, J. Michael, CHEM 125b, Freshman Organic Chemistry II, Spring 2011, YALE Open Courses: Yale University, Chemistry (Accessed 16/09/2014), http://oyc.yale.edu/chemistry/chem-125b/lecture-17 License: Creative Commons BY-NC-SA The special stability of conjugated systems requires considering delocalized orbitals or "resonance." Equilibrium constants, rates, and regiochemistry in systems involving allylic cations, anions, transition states, and free radicals demonstrate that allylic conjugation is worth about 13 kcal/mole. Regioselection in addition of DCl to 1,3-pentadiene reveals rapid collapse of an allylic ion pair. Allylic substitution of bromine can be favored over Br2 addition by using NBS to control Br2 concentration. Diene conjugation is worth much less than allylic conjugation.