6.1 Kinds of Organic Reactions
3 min read•may 7, 2024
Organic reactions are the building blocks of chemical transformations. They come in four main types: addition, elimination, substitution, and rearrangement. Each type has unique characteristics and plays a crucial role in synthesizing new compounds.
Understanding these reactions helps predict products and design synthetic routes. By mastering the mechanisms and kinetics behind them, chemists can control reactions and create complex molecules. This knowledge is essential for developing new drugs, materials, and industrial processes.
Types of Organic Reactions
Differentiate between addition, elimination, substitution, and rearrangement reactions in organic chemistry.
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- Atoms or groups of atoms are added to a molecule
- Occur across a double or triple bond
- Form a single product with no leaving group
- Examples: , ,
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- Atoms or groups of atoms are removed from a molecule
- Molecule loses a small molecule (water, hydrogen halide) to form a double or triple bond
- Form a single product with a double or triple bond
- Examples: ,
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- An atom or group of atoms is replaced by another atom or group
- A leaving group is replaced by a nucleophile
- Form a single product with a new bond and a leaving group
- Examples: (, ),
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- Atoms or groups are redistributed within a molecule
- Molecule undergoes a structural change without gaining or losing atoms
- Form a single product with a different connectivity of atoms
- Examples: , , /contractions
Examples in processes and pathways
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- Hydrogenation of unsaturated fats produces saturated fats
- Hydration of alkenes forms alcohols (ethylene to ethanol)
- Addition of hydrogen cyanide to aldehydes or ketones forms
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- Dehydration of alcohols forms alkenes (ethanol to ethylene)
- Dehydrohalogenation of alkyl halides forms alkenes (2-bromobutane to 2-butene)
- Decarboxylation of β-keto acids forms ketones (acetoacetic acid to acetone)
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- Nucleophilic substitution synthesizes ethers ()
- synthesizes substituted benzenes (nitration, sulfonation, halogenation)
- reactions biosynthesize amino acids
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- synthesizes allyl phenyl ethers
- synthesizes amides from oximes
- converts 1,2-diols to aldehydes or ketones
Predicting organic reaction products
- Addition reactions
- Alkene + (with catalyst) → Alkane
- Alkene + (with acid catalyst) → Alcohol
- Alkene + (X = halogen) → Alkyl halide
- Elimination reactions
- Alcohol + heat (with acid catalyst) → Alkene +
- Alkyl halide + strong base → Alkene +
- β-Keto acid + heat → Ketone +
- Substitution reactions
- Alkyl halide + nucleophile (, , ) → Substituted product + leaving group
- Benzene + electrophile (, , ) → Substituted benzene + proton
- Amino acid + α-keto acid → New amino acid + New α-keto acid
- Rearrangement reactions
- Allyl phenyl ether + heat → o-Allylphenol
- Oxime + acid catalyst → Amide
- 1,2-Diol + acid catalyst → Aldehyde or ketone
Understanding Reaction Mechanisms and Kinetics
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- Step-by-step description of how bonds are broken and formed during a reaction
- Involve the formation and breakdown of
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- Study of reaction rates and factors affecting them
- Involves analysis of and energy barriers
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- Consideration of the three-dimensional arrangement of atoms in molecules and how it affects reactions
Key Terms to Review (40)
Adams’ catalyst: Adams' catalyst, also known as platinum dioxide, is a form of platinum used as a catalyst in certain organic reactions. It facilitates hydrogenation and dehydrogenation processes without the need for high pressure, making it valuable in both laboratory and industrial settings.
Addition reactions: Addition reactions occur when two or more reactants combine to form a single product, typically involving unsaturated molecules (like alkenes and alkynes) gaining atoms, eliminating their double or triple bonds. These reactions are fundamental in organic chemistry for creating more complex molecules from simpler ones.
Addition Reactions: Addition reactions are a type of organic chemical reaction where two or more reactants combine to form a single product. They are characterized by the addition of atoms or molecules to an unsaturated compound, such as an alkene or alkyne, resulting in the formation of a new saturated compound.
Alkyl Shifts: Alkyl shifts are a type of rearrangement reaction in organic chemistry where an alkyl group, such as a methyl or ethyl group, migrates from one position to another within a molecule. These shifts occur to stabilize a carbocation intermediate formed during the reaction.
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.
Beckmann Rearrangement: The Beckmann rearrangement is a chemical reaction that involves the conversion of an oxime (the product of the reaction between a ketone or aldehyde and hydroxylamine) into an amide. This reaction is an important tool in organic chemistry, particularly in the context of understanding the chemistry of amides.
Claisen rearrangement: The Claisen rearrangement is a chemical reaction where an allyl vinyl ether is transformed into a γ,δ-unsaturated carbonyl compound through a [3,3]-sigmatropic shift. This reaction involves the movement of sigma bonds and the reorganization of electrons without the formation of free intermediates.
Claisen Rearrangement: The Claisen rearrangement is a sigmatropic rearrangement reaction in organic chemistry where an allyl vinyl ether is converted into a substituted cyclohexenone. It is a powerful tool for forming carbon-carbon bonds and creating complex cyclic structures.
Cyanohydrins: Cyanohydrins are organic compounds formed by the addition of hydrogen cyanide (HCN) to the carbonyl group of an aldehyde or ketone. They are important intermediates in organic synthesis, particularly in the preparation of various nitrogen-containing compounds.
Dehydration: Dehydration is a chemical process in which water is removed from a compound, typically resulting in the formation of a new compound with fewer hydrogen and oxygen atoms. This term is particularly relevant in the context of various organic reactions and transformations, where dehydration plays a crucial role in the preparation and interconversion of different functional groups.
Dehydrohalogenation: Dehydrohalogenation is an elimination reaction in organic chemistry where a hydrogen atom and a halogen atom (such as chlorine, bromine, or iodine) are removed from an organic compound, resulting in the formation of an alkene or alkyne. This process is a key step in the preparation of unsaturated hydrocarbons from alkyl halides.
Electrophilic aromatic substitution: Electrophilic aromatic substitution is a chemical reaction in which an atom, typically hydrogen, attached to an aromatic system, such as benzene, is replaced by an electrophile. This process preserves the aromaticity of the compound while introducing a functional group.
Electrophilic Aromatic Substitution: Electrophilic aromatic substitution is a fundamental organic reaction in which an electrophile (a species that is attracted to electrons) replaces a hydrogen atom on an aromatic ring, resulting in the formation of a new carbon-electrophile bond. This reaction is crucial in understanding the behavior and reactivity of aromatic compounds, which are prevalent in many organic molecules and have widespread applications.
Elimination reactions: Elimination reactions are a type of organic reaction where two atoms or groups are removed from a molecule, resulting in the formation of a double bond. These reactions often involve the loss of small molecules like water or hydrogen halides from larger organic molecules.
Elimination Reactions: Elimination reactions are a class of organic reactions where two atoms or groups are removed from a molecule, typically resulting in the formation of a new carbon-carbon double bond. These reactions are an important aspect of organic chemistry, as they allow for the conversion of various functional groups and the synthesis of alkenes and other unsaturated compounds.
Heat of hydrogenation: The heat of hydrogenation is the amount of energy released when a double bond in an alkene reacts with hydrogen gas to form a single bond, turning it into an alkane. This process is exothermic, indicating that energy is given off during the conversion.
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.
Hydride Shifts: A hydride shift is a type of rearrangement reaction in organic chemistry where a hydride (H-) group migrates from one carbon atom to an adjacent carbon atom. This intramolecular rearrangement is an important process in many organic reactions, particularly in the context of carbocation intermediates and the stability of carbocations.
Hydrogenated: In the context of organic chemistry, hydrogenation refers to the chemical reaction that involves the addition of hydrogen (H2) to an organic compound, typically in the presence of a catalyst. This process usually converts unsaturated bonds to saturated ones, making oils more solid at room temperature.
Hydrogenation: Hydrogenation is a chemical reaction in which hydrogen gas (H2) is added to an organic compound, typically an alkene or alkyne, to produce a more saturated compound. This process is commonly used in the food industry to convert unsaturated fats into more stable, saturated fats.
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.
Nucleophilic Substitution: Nucleophilic substitution is a fundamental organic reaction where a nucleophile (a species that donates electrons) replaces a leaving group attached to a carbon atom, resulting in the formation of a new carbon-nucleophile bond. This process is central to many organic transformations and is particularly relevant in the context of alkyl halides, alcohols, carboxylic acids, and amines.
Nucleophilic substitution reactions: Nucleophilic substitution reactions are a class of chemical reactions in organic chemistry where an electron-rich nucleophile selectively bonds with or attacks the positive or partially positive charge of an atom or a group of atoms to replace a leaving group. The reaction is characterized by the substitution of a nucleophile for a leaving group, which can occur via different mechanisms (SN1 or SN2).
Pinacol Rearrangement: The Pinacol rearrangement is a type of organic reaction that involves the rearrangement of a pinacol compound, which is a 1,2-diol, to form a ketone or aldehyde. This rearrangement is an important tool in organic synthesis for the formation of carbon-carbon bonds and the creation of more complex molecules.
Reaction Kinetics: Reaction kinetics is the study of the rates and mechanisms of chemical reactions. It examines the factors that influence the speed and efficiency of a reaction, such as temperature, pressure, and the presence of catalysts. This concept is crucial in understanding organic reactions, as the rate and pathway of a reaction can have a significant impact on the products formed and the overall efficiency of the process.
Reaction Mechanisms: Reaction mechanisms describe the step-by-step process by which a chemical reaction occurs, including the rearrangement of atoms, the formation and breaking of chemical bonds, and the movement of electrons. Understanding reaction mechanisms is crucial for predicting the products of a reaction, explaining experimental observations, and designing new synthetic routes in organic chemistry.
Reactive Intermediates: Reactive intermediates are short-lived, high-energy species that are formed as transient steps in organic reactions. These intermediates play a crucial role in determining the pathway and outcome of chemical transformations, as they are highly reactive and can undergo further reactions to form the final products.
Rearrangement reactions: Rearrangement reactions are a type of organic reaction where the structure of a molecule is rearranged to form a new product. This involves the shifting of atoms and bonds within a molecule without adding or removing any atoms.
Rearrangement Reactions: Rearrangement reactions are a class of organic reactions in which the carbon skeleton of a molecule is reorganized, leading to the formation of a new structural isomer. These reactions involve the migration of atoms or functional groups within the molecule, resulting in a different arrangement of the atoms.
Ring Contractions: Ring contractions refer to a type of organic reaction in which a cyclic compound undergoes a reduction in the number of atoms in the ring. This process involves the cleavage of a carbon-carbon bond within the ring, resulting in the formation of a smaller cyclic structure.
Ring Expansions: Ring expansions are a type of organic reaction in which the size of a cyclic compound's ring is increased, typically by the addition of one or more carbon atoms. This process is an important tool in organic synthesis, allowing for the construction of larger ring systems from smaller ones.
SN1: SN1, or Nucleophilic Substitution Reaction, is a type of organic reaction mechanism in which a nucleophile attacks a neutral, trigonal planar carbocation intermediate to displace a leaving group, resulting in the substitution of one functional group for another. This mechanism is characterized by a stepwise process involving the formation of a carbocation intermediate.
SN2: SN2 is a type of nucleophilic substitution reaction in organic chemistry where a nucleophile attacks the backside of a carbon atom bearing a good leaving group, resulting in the displacement of that leaving group and the inversion of stereochemistry at the carbon center.
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.
Substitution reactions: In organic chemistry, substitution reactions are a type of chemical reaction where an atom or a group of atoms in a molecule is replaced by another atom or group of atoms. These reactions are fundamental to synthesizing new compounds and modifying the structures of existing ones.
Substitution Reactions: Substitution reactions are a class of organic reactions where one atom or group in a molecule is replaced by another atom or group. These reactions are fundamental in organic chemistry and are essential for understanding various chemical transformations.
Transamination: Transamination is a fundamental biochemical reaction in which an amino group is transferred from one organic molecule to another, typically from an amino acid to a keto acid. This process is crucial for the synthesis and catabolism of amino acids, as well as the regulation of nitrogen balance in the body.
Transition States: Transition states are short-lived, high-energy molecular configurations that represent the point of maximum energy along the reaction coordinate during a chemical transformation. They are critical in understanding the kinetics and mechanisms of organic reactions.
Williamson ether synthesis: Williamson ether synthesis is a method used in organic chemistry to form ethers by reacting an alkoxide ion with a primary alkyl halide under basic conditions. This reaction involves nucleophilic substitution of the halide leading to the formation of an ether.
Williamson Ether Synthesis: The Williamson ether synthesis is a chemical reaction used to prepare symmetrical and unsymmetrical ethers from alkoxides and alkyl halides. It is a widely used method for the synthesis of ethers, a class of organic compounds with the general formula R-O-R'.