Kinetically-controlled

Describes a process or reaction whose outcome is determined primarily by the rate at which the reaction proceeds, rather than by the thermodynamic stability of the products. This contrasts with thermodynamically-controlled reactions, where the equilibrium state and the relative stability of the products dictate the final distribution. Kinetic control often occurs at lower temperatures or shorter reaction times, favoring the formation of the product that forms fastest, even if it's less thermodynamically stable. Factors like activation energy and reaction pathways are crucial in influencing the results. These reactions can be highly sensitive to changes in conditions such as temperature, catalysts, or solvents.

Kinetically-controlled meaning with examples

• In the formation of a certain polymer, low-temperature conditions favored a kinetically-controlled process. The faster-forming isomer, despite being less stable, was primarily produced due to its lower activation energy pathway. This example demonstrates how reaction conditions can be tuned to favor a desired outcome based on reaction speed over thermodynamic stability.
• The synthesis of a drug molecule in a laboratory may utilize kinetically-controlled reactions. Short reaction times and specific catalysts might selectively produce the desired isomer, even if other, more stable isomers exist thermodynamically. Careful manipulation is necessary to guide the reaction toward the intended product.
• In an organic synthesis, using a strong base at a lower temperature favors a kinetically-controlled deprotonation reaction. The resulting product, while not the most thermodynamically stable, forms quickly because of its lower energy barrier, highlighting how speed determines the outcome of the reaction.
• During the initial stages of protein folding, intermediate conformations are often kinetically trapped. This means that the protein adopts a state determined by the speed of folding rather than the ultimate lowest energy state. The final conformation depends on the folding pathway.
• A chemical reaction might be kinetically-controlled when a specific catalyst is added. The catalyst lowers the activation energy for one product, thereby speeding up its formation, even if another product is thermodynamically more stable under those conditions. This shows catalytic control.