Question

Which of these species cannot be isolated in a reaction: activated complex, product, intermediate?

Short answer

The species that cannot be isolated in a reaction is the activated complex.

Step-by-step solution

Understanding Activated Complex

An activated complex, also known as the transition state, represents the highest potential energy along the reaction path. It is the state corresponding to the highest energy along the reaction coordinate and is not stable. It cannot be isolated because it is so highly reactive and exists for a very brief moment during a reaction. So, the activated complex cannot be isolated.

Understanding Product of a Reaction

Product(s) are the substance(s) which are formed after the completion of a chemical reaction. They exist at the end of a reaction and as they are stable, they can be isolated.

Understanding Intermediate

An intermediate is a molecular entity that forms as a reaction progresses, and its concentration will go to a maximum and then decrease. While they are more stable than an activated complex, they are usually still highly reactive and exist only for a brief period during a reaction. However, under very specific conditions, some intermediates may be isolated.

Key concepts

Activated Complex

An activated complex, often called the transition state, is a short-lived structure in a chemical reaction that represents the highest energy point on the reaction pathway. It acts as a kind of "peak" that the reactants must reach in order to be transformed into products.
The activated complex is a fleeting, unstable assembly of atoms that forms momentarily as reactants are converted into products. It possesses high potential energy because bonds are in the process of breaking and forming.
Due to its instability, an activated complex cannot be isolated. It is like a rapid, momentary pause between reactants turning into products. This temporary state has only a brief existence, just enough time to decide whether it will proceed forward to products or revert to reactants.

• Represents the peak energy point on a reaction path
• Exists for an extremely short time
• Is highly energetic and unstable

Understanding the role of the activated complex helps explain why some reactions occur quickly while others are slow. By studying these transition states, chemists can manipulate reaction conditions to achieve desired outcomes.

Intermediate Species

Intermediate species in chemical reactions are more stable than the activated complex but still transient in nature. They form during the reaction process and have finite lifespans, which are longer than that of the activated complex, but they typically remain reactive.
These species are crucial as they often provide insight into the stepwise nature of a reaction. They appear during a transformation, reaching a peak concentration before decomposing into the final products or further intermediates.
Although less stable, intermediates can sometimes be isolated or detected under specific conditions. This provides valuable evidence for understanding how reactions proceed on a molecular level.

• Form temporarily and then disappear
• Can sometimes be detected or isolated
• Provide insights into reaction pathways

By investigating intermediates, scientists can better understand reaction mechanisms and develop methods to control chemical reactions, leading to innovations in synthesis and chemical design.

Chemical Reactions

Chemical reactions are the processes by which chemical substances transform into different substances. During a reaction, bonds between atoms break and reform, leading to a change in the chemical composition of molecules.
These reactions are often characterized by different stages, including the formation of an activated complex and any potential intermediates. Reactions generally have defined starting materials, or "reactants", which undergo transformations to yield "products" at the end of the process.
Understanding how chemical reactions work involves studying the energy changes and molecular structures throughout the reaction. This knowledge is crucial for fields such as chemistry and materials science.

• Involve breaking and forming of bonds
• Have identifiable stages, including intermediates and transition states
• Transform reactants into new products

Thorough understanding of these processes enables chemists to manipulate conditions such as temperature, concentration, and catalysts to control product formation and reaction speed, which is critical in both industrial applications and research settings.