Learn what catalysts are and how they affect the activation energy and reaction rate of a chemical reaction.
A catalyst is a chemical substance that affects the rate of a chemical reaction by altering the activation energy required for the reaction to proceed. This is called catalysis. A catalyst is not consumed by the reaction and it may participate in multiple reactions at a time. The only difference between a catalyzed reaction and an uncatalyzed reaction is that the activation energy is different. There is no effect on the energy of the reactants or the products. The ΔH for the reactions is the same.
Usually when someone refers to a catalyst, they mean a positive catalyst, which is a catalyst which speeds up the rate of a chemical reaction by lowering its activation energy. There are also negative catalysts or inhibitors, which slow the rate of a chemical reaction or make it less likely to occur.
A promoter is a substance that increases the activity of catalyst. A catalytic poison is a substance that inactivates a catalyst.
Catalysts permit an alternate mechanism for the reactants to become products, with a lower activation energy and different transition state. A catalyst may allow a reaction to proceed at a lower temperature or increase the reaction rate or selectivity. Catalysts often react with reactants to form intermediates that eventually yield the same reaction products and regenerate the catalyst. Note that the catalyst may be consumed during one of the intermediate steps, but it will be created again before the reaction is completed.
————————
This is an example of the reaction of a ketone with a Grignard reagent, which gives a tertiary alcohol. The paper presents a study of several different idol-3-ones reacting with Grignard reagents. Idol-3-ones are potentially useful intermediates in the synthesis of alkaloids and pharmaceutical agents.
Going one step further: due to the lack of stability in the tertiary alcohol, a rearrangement is observed on the alcohol molecule, creating a gain in resonance stabilization in the final molecule. The study examined a variety of conditions under which the rearrangement occurred, in order to recognize the most efficient one. It was determined that the rearrangement took place with great facility under acidic or basic conditions or was thermally induced.
There are four types of reactions:
The reactions in which an atom or group of atoms in a molecule is replaced or substituted by different atoms or group of atoms are called substitution reaction. For example,
These reactions can be of two types:
Nucleophilic Substitution
In this type of substitution, atom or group of atoms in the molecule is replaced by a nucleophile. These can be either SN1 (substitution, nucleophilic, unimolecular) or SN2 (substitution, nucleophilic, bimolecular) type.
Read More
