Reactions and Reaction Mechanisms

Organic Reactions

There are many types of organic reactions: acid-base reactions, nucleophilic addition and substitution reactions, electrophilic addition and substitution reactions, and radical reactions. There are many parts to a reaction, including starting materials, products, reaction arrows, reagents, solvents, and conditions.

Carbon can form covalent bonds with up to four other atoms. Carbon can form single, double, and triple bonds. The diverse bonding behavior of carbon means that organic (carbon-containing) compounds may be involved in an infinite number of organic reactions. Organic chemistry is the discipline of chemistry that studies carbon and its compounds. General chemistry is often associated with inorganic chemistry, which is the discipline of chemistry that studies nonorganic (without carbon) compounds.

Organic species include ions, compounds, and molecules. Reactions occur when a species undergoes a chemical change. Those changes, or reactions, are further divided into types that can have similar mechanisms, similar physical and chemical properties, or similar products. Classifying reactions by type helps predict whether the reaction will take place and under what conditions. For example, substitution reactions depend on certain conditions, such as the temperature, solvent, and strength of reagents. Therefore, if a different reaction is also a substitution reaction, the identity of the product(s) and the distribution of product(s) (such as a major product or minor product) can be determined based on how substitution reactions behave. There are many types of reactions, including but not limited to acid-base reactions, nucleophilic addition reactions, substitution reactions, electrophilic addition reactions, electrophilic substitution reactions, and radical reactions. Often, chemical reactions may be classified under more than one type of reaction.

Reactions may be broken down into the parts (or components) of the reaction: starting materials, reaction arrows, reagents, solvents, and products.

  • The reactants (or starting materials) are the elements, molecules, and compounds necessary for a type of reaction to occur. The amount of reactant is an important consideration. There must be enough of each reactant for the reaction to occur. When discussing a chemical reaction, reactant is the preferred term, but starting material is synonymous. Starting material is used more often in the lab.
  • Reaction arrows are used in the chemical equation to indicate the direction of the reaction, from starting material to product. Some reactions will have the starting material react to form the product and then have the reaction reverse, with the product re-forming the starting material. A smaller arrow facing backward is drawn to indicate a small reversal. If the reaction reverses as much as it goes forward, two equal-length arrows (one going forward and one going backward) are drawn.
  • Reagents are substances added to a reaction to prompt the reaction to occur. Unlike reactants, reagents are not necessarily consumed in the reaction.
  • Solvents are the substance in a reaction with the largest volume and are often in liquid form but may exist as a gas or solid. Solvents dissolve the reactants and reagents into a solution for the reaction to proceed. For example, the addition of water to table salt (NaCl) will dissolve the salt.
  • Products are the end result in a chemical reaction. There may be one or more products formed. The amount of product is determined by the reactants and other factors or conditions, such as solvents, temperature, pressure, and catalysts.