Question

The typical reaction of olefinic bond is (1) Clectrophilic substitution reactions (2) Clectrophilic addition reactions (3) Nucleophilic substitution reactions (4) Nucleophilic addition reactions

Short answer

Electrophilic addition reactions.

Step-by-step solution

Understand the Olefinic Bond

An olefinic bond refers to a carbon-carbon double bond typically found in alkenes. This double bond is characterized by a region of high electron density, making it reactive towards particular types of reagents.

Identify Types of Reactions

Determine the definitions of the listed reactions: 1. Electrophilic substitution reactions involve the replacement of an atom or a group in a molecule with an electrophile.2. Electrophilic addition reactions involve an electrophile adding to the electron-rich double bond of an alkene.3. Nucleophilic substitution reactions involve the substitution of an atom or group with a nucleophile.4. Nucleophilic addition reactions involve a nucleophile adding to a carbon-heteroatom multiple bond.

Match Reaction Type to Olefinic Bond

Since an olefinic bond in alkenes is electron-rich, it attracts electrophiles. The simplest reaction for this bond type involves breaking the double bond and incorporating the electrophile into the molecule. This aligns with the electrophilic addition reaction.

Conclusion

The typical reaction mechanism for an olefinic bond in alkenes corresponds to electrophilic addition reactions as it involves the addition of an electrophile across the double bond.

Key concepts

electrophilic addition

Electrophilic addition is a fundamental reaction in organic chemistry, particularly involving alkenes. Here, an electrophile reacts with an electron-rich double bond, found typically in alkenes, to form a more stable product. This reaction proceeds in two main steps:

Firstly, the electrophile attacks the double bond, leading to the formation of a carbocation intermediate. Since double bonds have high electron density, they are prime targets for electrophiles, which are electron-poor species.

Secondly, a nucleophile interacts with the carbocation, resulting in the addition product. This step stabilizes the intermediate. For example, in the reaction of ethene (an alkene) with bromine (an electrophile), the double bond breaks, and a bromonium ion intermediate forms. Subsequently, another bromide ion (nucleophile) attacks this intermediate, leading to the final addition product, 1,2-dibromoethane.

alkenes

Alkenes are hydrocarbons containing at least one carbon-carbon double bond. This double bond characterizes their reactivity and properties. Alkenes, also known as olefins, are unsaturated hydrocarbons meaning they have fewer hydrogen atoms than alkanes with the same number of carbon atoms.

The presence of the double bond imparts important properties to alkenes:

• Increased reactivity compared to alkanes
• Ability to participate in addition reactions
• Geometric isomerism possibilities, resulting in different physical properties.

Common alkenes like ethene (C2H4) and propene (C3H6) are fundamental in industrial applications and serve as building blocks for polymers. Understanding their reactivity, particularly their tendency for electrophilic addition, is crucial for manipulating these molecules in synthetic chemistry.

double bond reactivity

The reactivity of a double bond, particularly in alkenes, is central to numerous chemical reactions. The carbon-carbon double bond consists of one sigma (σ) bond and one pi (π) bond. Unlike the sigma bond, the pi bond is formed by the sideways overlap of p-orbitals, making it less stable and more reactive.

This reactivity is due to:

• High electron density in the pi bond
• The pi bond is more accessible to electrophiles

As a result, double bonds participate readily in reactions like electrophilic addition, where an electrophile targets the electron-rich pi bond.

For example, in the presence of hydrogen bromide (HBr), the double bond of an alkene breaks as the electrophilic hydrogen attaches to one carbon, and the bromide ion attaches to the other, forming bromoalkane.

electrophilic substitution

Electrophilic substitution is another significant reaction type but differs from what typically occurs with alkenes. In electrophilic substitution, an electrophile replaces an atom or group in a compound, usually seen in aromatic systems rather than alkenes.

For instance, in benzene, an aromatic hydrocarbon, electrophilic substitution involves replacing a hydrogen atom with an electrophile. The reaction follows these steps:

• Formation of a complex between the electrophile and the pi electrons of the benzene ring
• Formation of a carbocation intermediate as the electrophile attaches
• Loss of a proton, restoring the aromaticity of benzene

Understanding electrophilic substitution is crucial for exploring mechanisms that sustain the aromatic stability, yet it's not the typical pathway for alkene reactions, where electrophilic addition is more common.