7.7 Electrophilic Addition Reactions of Alkenes
2 min read•may 7, 2024
are key in understanding how react. These processes involve electrophiles and nucleophiles adding across carbon-carbon double bonds, forming new compounds. The mechanism typically follows a three-step process, with the formation of a being crucial.
Energy diagrams help visualize these reactions, showing the relative energies of reactants, products, and intermediates. Common electrophiles include hydrogen halides, water with acid catalysts, and halogens. The and resulting are important factors in predicting and understanding the products formed.
Electrophilic Addition Reactions of Alkenes
Mechanism of electrophilic addition
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- Involves addition of electrophile and across carbon-carbon double bond
- Electrophiles electron-poor species attracted to electron-rich alkenes (HX, H2O with acid catalyst, X2)
- Nucleophiles electron-rich species donate electrons to form new bond (halide ions, water)
- General mechanism follows three steps
- Electrophile approaches and forms bond with one alkene carbon resulting in carbocation intermediate
- More stable carbocation forms preferentially (tertiary > secondary > primary)
- Nucleophile attacks carbocation forming new bond and completing addition
- Proton transfer may occur to restore neutrality of molecule
- Electrophile approaches and forms bond with one alkene carbon resulting in carbocation intermediate
- determined by stability of carbocation intermediate
- more stable carbocation (usually more substituted) forms preferentially
Energy diagrams for addition reactions
- Show progress of reaction and relative energies of reactants, transition states, intermediates, and products
- Reactants and products represented as energy minima, transition states are energy maxima
- Carbocation intermediate represented as local energy minimum between two transition states
- Stability of carbocation intermediate affects overall energy profile of reaction
- Rate-determining step formation of carbocation intermediate (Step 1)
- Activation energy () difference in energy between reactants and first
- Overall energy change of reaction () difference in energy between reactants and products
Common electrophiles for alkenes
- Hydrogen halides (HX where X = F, Cl, Br, I)
- H-X bond polarized hydrogen acting as electrophile halide as nucleophile
- Reactivity HI > HBr > HCl > HF
- Water (H2O) in presence of acid catalyst
- Acid protonates alkene creating carbocation intermediate
- Water acts as nucleophile attacking carbocation forming alcohol
- Halogens (X2 where X = Cl, Br)
- Halogen molecule acts as electrophile forming cyclic intermediate
- Nucleophile (usually halide ion) attacks leading to vicinal dihalide product
- Other electrophiles
- (H2SO4)
- (Hg(OAc)2)
- (BH3)
Reaction Mechanism and Stereochemistry
- describes step-by-step process of bond breaking and formation
- represents highest energy point along reaction coordinate
- Intermediate species (e.g., carbocations) form during the course of the reaction
- Stereochemistry of products influenced by reaction mechanism
- Addition reactions often result in specific stereochemical outcomes
Key Terms to Review (44)
Addition Reaction: An addition reaction is a type of chemical reaction where two or more reactants combine to form a single product. In the context of organic chemistry, addition reactions typically involve the addition of atoms or molecules to an alkene or alkyne, resulting in the formation of a new compound with a different structure and properties.
Alcohols: Alcohols are organic compounds containing a hydroxyl (-OH) functional group attached to a saturated carbon atom. They are widely used in various chemical reactions and have diverse applications in industry, medicine, and everyday life.
Alkenes: Alkenes are a class of unsaturated organic compounds characterized by the presence of a carbon-carbon double bond. They are an important functional group in organic chemistry, with a wide range of applications and reactivity. Alkenes are closely related to the topics of chirality, isomerism, electrophilic addition reactions, halogenation, hydration, the E2 reaction, infrared spectroscopy, 13C NMR spectroscopy, alcohol preparation, and the Wittig reaction.
Alkyl Halides: Alkyl halides are organic compounds that consist of an alkyl group (a hydrocarbon chain) bonded to a halogen atom (fluorine, chlorine, bromine, or iodine). They are widely used in organic synthesis and have various applications in chemistry and biology.
Anti Addition: Anti addition refers to the stereochemical outcome of an electrophilic addition reaction, where the incoming electrophilic species adds to the opposite face of the alkene or alkyne relative to the existing substituents. This results in the formation of the anti-addition product, where the new substituents are arranged in an anti-configuration.
Anti stereochemistry: Anti stereochemistry describes the spatial arrangement in a chemical reaction where two substituents are positioned on opposite sides of a double bond or ring structure after the reaction. It is particularly relevant in the halogenation of alkenes, resulting in products where the added atoms are located across from each other.
Anti-Addition: Anti-addition is a type of organic reaction mechanism in which the incoming electrophile or nucleophile adds to the opposite side of the double bond, resulting in the formation of the opposite regioisomer compared to the typical addition reaction. This term is particularly relevant in the context of electrophilic addition reactions of alkenes, the hydration of alkenes via oxymercuration, and the reduction of alkynes.
Borane: Borane is a chemical compound with the formula BH3, consisting of a boron atom bonded to three hydrogen atoms. It is a highly reactive and flammable gas that serves as a key intermediate in organic chemistry, particularly in reactions involving alkenes, alkynes, and carboxylic acids.
Bromine: Bromine is a dense, reddish-brown liquid halogen element that is highly reactive and widely used in organic chemistry. It is particularly relevant in the context of electrophilic addition reactions of alkenes, the naming and structures of alkyl halides, and electrophilic aromatic substitution reactions involving bromination.
Bromonium ion: A bromonium ion is a reactive intermediate formed during the halogenation of alkenes when a bromine molecule reacts with an alkene to form a cyclic structure where the bromine atom is covalently bonded to two carbon atoms. This ion is positively charged and highly electrophilic, making it susceptible to nucleophilic attack.
Bromonium Ion: The bromonium ion is a cyclic, three-membered ring intermediate formed during the addition of hydrobromic acid (HBr) or bromine (Br2) to alkenes. It serves as a key intermediate in various organic reactions involving the electrophilic addition of bromine to alkenes.
Carbocation: A carbocation is a positively charged carbon atom that is part of an organic molecule. These reactive intermediates play a crucial role in various organic reactions, including electrophilic additions, nucleophilic substitutions, and elimination reactions.
Electrophilic Addition: Electrophilic addition is a type of organic reaction where an electrophile, a species that is attracted to electrons, adds to the carbon-carbon double bond of an alkene. This results in the formation of a new carbon-carbon single bond and the incorporation of the electrophile into the molecule.
Electrophilic addition reaction: An electrophilic addition reaction is a chemical process in which an electrophile reacts with a nucleophile, typically an alkene or alkyne, forming a new sigma bond by adding across the double or triple bond. This reaction is key in organic synthesis, resulting in the addition of atoms or groups to the carbon atoms involved in the multiple bond.
Electrophilic addition reactions: Electrophilic addition reactions are a type of chemical reaction where an electrophile reacts with an alkene to form a new compound by adding across the double bond. These reactions typically proceed through the formation of a carbocation intermediate.
Halogenation: Halogenation is the process of introducing a halogen atom (fluorine, chlorine, bromine, or iodine) into an organic compound, typically through a substitution or addition reaction. This term is closely tied to various topics in organic chemistry, including functional groups, alkane properties, reaction mechanisms, and the reactivity of different classes of organic compounds.
Halohydrins: Halohydrins are organic compounds that contain both a halogen atom (such as chlorine, bromine, or iodine) and a hydroxyl group (-OH) attached to adjacent carbon atoms within a molecule. They are formed through the electrophilic addition of a halogen and water to an alkene.
Halonium ion: A halonium ion is an intermediate species formed during the addition of a halogen (X2) to an alkene, characterized by a three-membered ring structure consisting of two carbon atoms and one halogen atom. This positively charged ion is highly reactive and plays a crucial role in facilitating the addition of halogens across the double bond of alkenes.
Halonium Ion: A halonium ion is a reactive intermediate formed during the electrophilic addition of halogens (X2, where X = F, Cl, Br, I) to alkenes. It is a cyclic, three-membered ring structure that contains a positive charge on one of the carbon atoms and a halogen atom attached to the other two carbon atoms.
Hydration: Hydration is the process of adding water to a chemical compound, typically involving the addition of water across a double bond or the incorporation of water into the structure of a molecule. This term is particularly relevant in the context of organic chemistry, where it plays a crucial role in various reactions and transformations.
Hydrogen Bromide: Hydrogen bromide is a colorless, corrosive gas with a pungent odor. It is a key compound in the context of electrophilic addition reactions of alkenes, as it can serve as a source of the electrophilic bromonium ion species that initiates these addition reactions.
Hydrogen Chloride: Hydrogen chloride is a colorless, pungent gas that is formed by the direct combination of hydrogen and chlorine. It is a key compound in the context of electrophilic addition reactions of alkenes, as it serves as a source of the electrophilic species that adds to the alkene.
Hydrogen Fluoride: Hydrogen fluoride is a colorless, corrosive gas that is formed when hydrogen gas reacts with fluorine gas. It is a key compound in the context of electrophilic addition reactions of alkenes, as it can act as both an electrophile and a nucleophile during these organic chemistry processes.
Hydrogen Iodide: Hydrogen iodide, also known as hydriodic acid, is a colorless, fuming gas with a pungent odor. It is a key compound in the context of electrophilic addition reactions of alkenes, as it can be used to add an electrophilic hydrogen and an iodide ion to an alkene, forming a haloalkane product.
Hydrohalogenation: Hydrohalogenation is a type of organic reaction where an alkene or alkyne reacts with a hydrogen halide (HX, where X is a halogen such as F, Cl, Br, or I) to form an alkyl halide. This process adds the hydrogen and halogen atoms across the carbon-carbon double or triple bond.
Intermediate: An intermediate is a chemical species that is formed during the course of a chemical reaction, existing temporarily between the reactants and the final products. Intermediates play a crucial role in understanding the mechanisms and energetics of chemical transformations, particularly in the context of organic chemistry topics such as reaction energy diagrams, electrophilic addition reactions, and halohydrin formation.
Markovnikov's Rule: Markovnikov's rule is a principle in organic chemistry that describes the orientation of addition reactions involving unsaturated compounds, such as alkenes. It states that in the addition of a hydrogen halide (HX) to an alkene, the hydrogen atom of the HX bond attaches to the carbon atom of the alkene that can best stabilize the resulting carbocation intermediate.
Mercury(II) Salts: Mercury(II) salts are a class of inorganic compounds containing a mercury(II) cation (Hg2+) and one or more anions. These salts are known for their diverse applications and unique properties, particularly in the context of organic chemistry reactions and the preparation of ethers.
Nucleophile: A nucleophile is a species that donates a pair of electrons to form a covalent bond with another atom or molecule. Nucleophiles are central to understanding many organic reactions, including polar reactions, electrophilic addition reactions, and nucleophilic substitution reactions.
Peroxide: A peroxide is a chemical compound that contains an oxygen-oxygen single bond (O-O). Peroxides are commonly encountered in the context of electrophilic addition reactions of alkenes and radical additions to alkenes, which are important topics in organic chemistry.
Phosphoric Acid: Phosphoric acid is a colorless, odorless, and highly corrosive inorganic compound with the chemical formula H3PO4. It is a key player in various chemical reactions, particularly in the context of electrophilic addition reactions of alkenes and the preparation of alkenes through elimination reactions.
Phosphoric acid anhydride: Phosphoric acid anhydride refers to a compound that results from the dehydration of phosphoric acid, leading to a more reactive form often involved in biochemical energy transfer. It plays a critical role in synthesizing ATP, the energy currency of cells, by forming high-energy phosphate bonds.
Pi Bond: A pi (π) bond is a type of covalent chemical bond formed by the side-to-side overlap of atomic orbitals, resulting in electron density concentrated above and below the internuclear axis between two atoms. Pi bonds are crucial in the structure and reactivity of many organic compounds.
Reaction intermediate: A reaction intermediate is a transient species that is formed during the conversion of reactants into products in a chemical reaction and does not appear in the final reaction equation. It plays a crucial role in determining the pathway and mechanism by which the reaction proceeds.
Reaction mechanism: A reaction mechanism is a step-by-step sequence of elementary reactions by which overall chemical change occurs. It outlines the specific way in which reactants convert to products, including the formation and breaking of bonds.
Reaction Mechanism: A reaction mechanism is the step-by-step sequence of elementary reactions by which overall chemical change occurs. It describes the detailed pathway that a reaction follows, including the formation and rearrangement of chemical bonds, the generation of intermediates, and the movement of electrons. Understanding reaction mechanisms is crucial for predicting the products of a reaction, explaining reactivity trends, and designing new synthetic pathways.
Regioselectivity: Regioselectivity refers to the preference of a chemical reaction to occur at a specific site or region of a molecule, leading to the formation of one regioisomeric product over another. This concept is particularly important in the context of electrophilic addition reactions of alkenes, electrophilic aromatic substitution, and other organic transformations.
Sigma Bond: A sigma bond is a type of covalent chemical bond formed by the overlap of atomic orbitals along the internuclear axis between two atoms. Sigma bonds are the strongest type of covalent bonds and are responsible for the structural stability and geometry of molecules.
Stereochemistry: Stereochemistry is the study of the three-dimensional arrangement of atoms in molecules and how this arrangement affects the chemical and physical properties of the substance. It examines the spatial orientation of atoms and their relationship to one another, which is crucial in understanding many organic chemistry concepts.
Stereoselectivity: Stereoselectivity refers to the preference of a chemical reaction to form one stereoisomeric product over another. It is a crucial concept in organic chemistry that describes the ability of a reaction to control the spatial arrangement of atoms in the final product.
Sulfuric Acid: Sulfuric acid (H2SO4) is a highly corrosive, dense, and oily liquid that is one of the most important and widely used industrial chemicals. It is a strong mineral acid that plays a crucial role in various chemical reactions and processes.
Syn Addition: Syn addition is a type of organic reaction where two substituents are added to the same side of a carbon-carbon double bond, resulting in the formation of a new stereocenter with a specific stereochemical configuration. This term is particularly relevant in the context of various organic chemistry topics, including electrophilic addition reactions of alkenes, hydration of alkenes, reduction of alkenes, and oxidation of alkenes.
Transition state: In organic chemistry, the transition state is a high-energy, temporary condition where reactants are transformed into products during a chemical reaction. It represents the point of maximum energy on the energy diagram before the formation of products.
Transition State: The transition state is a key concept in organic chemistry that describes the highest-energy intermediate along the reaction pathway. It represents the point where the reactants are being converted into products, with the system at its most unstable and energetically unfavorable configuration.