Final answer:
Alkenes undergo electrophilic addition reactions with electrophiles, forming a carbocation intermediate and subsequently reacting with a nucleophile, leading to the addition of a reactant across the double bond.
Step-by-step explanation:
An alkene undergoes an electrophilic addition reaction when it reacts with an electrophile. In this type of reaction, the electron-rich π-bonds of the alkene interact with the electrophile, typically a positive ion or molecule with a partial positive charge. Subsequently, a carbocation intermediate is formed, which is then rapidly attacked by a nucleophile, resulting in the addition of a reactant across the double bond to form a single bond.
For example, the addition of halogen acids like H-Cl, H-Br, or H-I to alkenes follows this mechanism. Another common example is hydrogenation, where hydrogen is added to an alkene in the presence of a catalyst, such as platinum, to form an alkane. Electrophiles seek out regions on a molecule with high electron density, such as the π-bonds of alkenes, making them susceptible to such addition reactions.
Concepts such as regioselectivity, stereoselective and stereospecific reactions, and tautomerism help further characterize these reactions and explain the outcome of the electrophilic addition to alkenes and alkynes. These concepts are critical for understanding how different products can form based on the structure of the starting materials and the conditions of the reaction.