Kinetic studies of the reaction of Z-aryl cyclobutanecarboxylates with X-pyridines in acetonitrile at $55.0^{circ}C$ have been carried out. The reaction proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterion ic tetrahedral intermediate, T $pm$ . These mechanistic conclusions are drawn based on (i) the large magnitude of ${ ho}X$ and $ hoZ$, (ⅱ) the positive sign of ${ ho}XZ$ and the larger magnitude of $ hoXZ$ than normal SN2 processes, (ⅲ) a small positive enthalpy of activation, ${Delta}H{ eq}$, and a large negative, ${Delta}S{ eq}$, and lastly (iv) adherence to the reactivity-selectivity principle (RSP) in all cases.