the deprotonation of the α-carbon and the loss of the leaving group occur simultaneously in one concerted step. Molecules that undergo E2-elimination mechanisms have more acidic α-carbons than those that undergo E1 mechanisms, but their α-carbons are not as acidic as those of molecules that undergo E1cB mechanisms. The key difference between the E2 vs E1cb pathways is a distinct carbanion intermediate as opposed to one concerted mechanism. Studies have been shown that the pathways differ by using different halogen leaving groups. One example uses chlorine as a better stabilizing halogen for the anion than fluorine, which makes fluorine the leaving group even though chlorine is a much better leaving group. This provides evidence that the carbanion is formed because the products are not possible through the most stable concerted E2 mechanism. The following table summarizes the key differences between the three elimination reactions; however, the best way to identify which mechanism is playing a key role in a particular reaction involves the application of chemical kinetics. Chemical kinetics of E1cB-elimination mechanisms When trying to determine whether or not a reaction follows the E1cB mechanism, chemical kinetics are essential. The best way to identify the E1cB mechanism involves the use of rate laws and the kinetic isotope effect. These techniques can also help further differentiate between E1cB, E1, and E2-elimination reactions. Rate law When trying to experimentally determine whether or not a reaction follows the E1cB mechanism, chemical kinetics are essential. The best ways to identify the E1cB mechanism involves the use of rate laws and the kinetic isotope effect. The rate law that governs E1cB mechanisms is relatively simple to determine. Consider the following reaction scheme. Assuming that there is a steady-state carbanion concentration in the mechanism, the rate law for an E1cB mechanism. From this equation, it is clear the second order kinetics will be exhibited. E1cB mechanisms kinetics can vary slightly based on the rate of each step. As a result, the E1cB mechanism can be broken down into three categories: E1cBanion is when the carbanion is stable and/or a strong base is used in excess of the substrate, making deprotonation irreversible, followed by rate-determining loss of the leaving group (k1[base] ≫ k2). E1cBrev is when the first step is reversible but the formation of product is slower than reforming the starting material, this again results from a slow second step (k−1[conjugate acid] ≫ k2). E1cBirr is