Question

What is an alkene addition reaction? Provide an example.

Short answer

An alkene addition reaction is where an alkene combines with a substance to produce a single product, with a common example being the hydrogenation of ethene to ethane, represented by the equation: \(C_2H_4 + H_2 \rightarrow C_2H_6\).

Step-by-step solution

Definition of Alkene Addition Reaction

An alkene addition reaction is a chemical reaction where an alkene reacts with a substance to form a single product. In this process, the pi bond in the alkene breaks, and new sigma bonds form, resulting in the addition of atoms or groups to the carbons of the double bond.

Characteristics of an Alkene Addition Reaction

This type of reaction is characterized by the transformation of the double bond into a single bond due to the addition of atoms. The most common addition reactions involve the addition of halogens, hydrogen halides, water (in the form of hydration), or hydrogen (in the form of hydrogenation).

Example of an Alkene Addition Reaction

A simple example of an alkene addition reaction is the hydrogenation of ethene (ethylene) to form ethane. The reaction is as follows: \[C_2H_4 + H_2 \rightarrow C_2H_6\]. This reaction involves the addition of hydrogen across the double bond of ethene, facilitated by a metal catalyst, typically platinum or palladium.

Key concepts

Chemical Reactions

Understanding chemical reactions is key to grasping many concepts in chemistry, especially when studying organic compounds such as alkenes. At its core, a chemical reaction is a process that leads to the transformation of one set of chemical substances to another.

Chemists classify reactions in many ways: by the type of product, by the types of reactants, or by the changes that occur. An alkene addition reaction is one such classification where two reactants combine to form a single product. During this reaction, the atoms of the reactants redistribute to form new chemical bonds. This type of reaction is fundamental in organic synthesis and industrial processes, often used in producing polymers, alcohols, and other organic compounds.

• An essential aspect of chemical reactions is understanding the energy changes and the role of catalysts.
• Catalysts can speed up reactions without being consumed by the reaction itself.
• They are especially important in alkene addition reactions, which sometimes require a catalyst to proceed at a reasonable rate.

Pi Bond

Alkenes are hydrocarbons with distinct features known as pi bonds that play a crucial role in addition reactions. The pi bond is formed by the side-to-side overlap of two p-orbitals on adjacent carbon atoms that share an electron pair. It is a weaker bond compared to the sigma bond, which is formed by a head-to-head overlap and constitutes a single bond.

A pi bond is characterized by its electron density above and below the plane of the atoms, leading to restricted rotation about the carbon-carbon bond axis. This restriction causes the particular geometry and reactivity patterns seen in alkenes. When a pi bond is present, reactions such as the addition reactions become possible.

• During an alkene addition reaction, the pi bond is broken as the electrons are used to form new sigma bonds with the added atoms or groups.
• The breaking of the pi bond is integral to the addition mechanism, as it allows for the conversion into a saturated compound.

Hydrogenation

A specific type of alkene addition reaction is hydrogenation, wherein hydrogen is added across the double bond of an alkene, converting it into an alkane. This process involves the breakage of the pi bond as hydrogen molecules form new sigma bonds with the carbon atoms of the alkene.

• Hydrogenation is not only significant in organic chemistry but also has vast applications in the food industry to produce saturated fats from unsaturated oils.
• This reaction typically requires the presence of a metal catalyst such as platinum or palladium to occur efficiently.
• The choice of catalyst and reaction conditions can affect the outcome, like the formation of trans fats during partial hydrogenation of vegetable oils.

In summary, hydrogenation is an exemplary illustration of how catalysts are used to facilitate vital industrial chemical reactions and highlights the practical implications of theoretical chemistry.