19.5 Nucleophilic Addition of H2O: Hydration
3 min read•may 7, 2024
Water's dance with carbonyls is a chemical tango. Aldehydes and ketones invite H2O to join, forming diols in a delicate balance. Factors like and electronic effects play matchmaker, influencing whether the or form takes the lead.
This waltz can be led by bases or acids, each with their own choreography. Electronegative partners like and join in too, adding their own flair to the carbonyl's transformation. It's all about Lewis acid-base chemistry in motion.
Nucleophilic Addition of H2O: Hydration
Process of carbonyl hydration
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- of water to the carbonyl group of aldehydes and ketones (, )
- Water acts as the attacks the carbonyl carbon
- Results in the formation of geminal diols (hydrates)
- Two groups bonded to the same carbon atom
- Carbonyl carbon becomes an carbon with two hydroxyl groups attached
- Factors affecting the equilibrium of hydration:
- Steric hindrance: Bulky substituents near the carbonyl group hinder the approach of water shift the equilibrium towards the carbonyl compound (t-butyl ketones)
- Electronic effects: groups () stabilize the carbonyl form, while groups (alkyl) favor the form
- Solvent effects: (water, ethanol) can stabilize the geminal diol form through
- : Carbonyl compounds with extended conjugation may have reduced reactivity due to resonance stabilization
Base vs acid-catalyzed nucleophilic addition
- Base-catalyzed mechanism:
- Base () deprotonates water to form a more reactive (HO-)
- Hydroxide ion acts as the nucleophile attacks the electrophilic carbonyl carbon
- Resulting is deprotonated by water to form the geminal diol
- Acid-catalyzed mechanism:
- Acid () protonates the carbonyl oxygen, making the carbonyl carbon more electrophilic
- Water acts as the nucleophile attacks the protonated carbonyl carbon
- Resulting tetrahedral intermediate is deprotonated to form the geminal diol
- Acid catalyst is regenerated by protonation of the geminal diol
- Both mechanisms follow a involving nucleophilic addition and proton transfer steps
Reactions with electronegative nucleophiles
- Electronegative nucleophiles (cyanide, bisulfite, Grignard reagents) can add to the carbonyl group of aldehydes and ketones
- Nucleophile attacks the electrophilic carbonyl carbon, forming a tetrahedral intermediate
- Tetrahedral intermediate is stabilized by the electronegative atom bonded to the former carbonyl carbon
- Reversibility of these reactions depends on the stability of the tetrahedral intermediate and the leaving group ability of the nucleophile
- Cyanide addition is usually irreversible due to the formation of a stable and the poor leaving group ability of cyanide
- Bisulfite addition is reversible because the bisulfite ion is a good leaving group
- Grignard addition is irreversible due to the formation of a stable and the poor leaving group ability of the organometallic species ()
Lewis acid-base interactions in hydration
- Carbonyl compounds act as Lewis bases, donating electron pairs to Lewis acids
- Water molecules can act as both Lewis acids and bases in the hydration process
- The for hydration reactions is influenced by the Lewis acidity of the carbonyl carbon and the Lewis basicity of water
- changes during the reaction affect the strength of these Lewis acid-base interactions
Key Terms to Review (42)
Acetone: Acetone is a simple organic compound with the chemical formula CH3COCH3. It is a colorless, volatile, flammable liquid that is widely used as a solvent and in various chemical processes. Acetone is a key term that is relevant in the context of several important organic chemistry topics.
Aldehyde: An aldehyde is a class of organic compounds containing a carbonyl group (C=O) where the carbon atom is bonded to one hydrogen atom and one alkyl or aryl group. Aldehydes are important functional groups in organic chemistry and are involved in various reactions and synthesis pathways.
Alkoxide Ion: An alkoxide ion is a negatively charged species formed when an alkyl group (R-) is bonded to an oxygen atom. It is a key intermediate in various organic chemistry reactions, including the preparation of ethers, nucleophilic addition reactions of aldehydes and ketones, and the hydration of carboxylic acids.
Alkoxide ion, RO–: An alkoxide ion is the conjugate base of an alcohol, formed by the deprotonation of the hydroxyl group (OH) in an alcohol molecule, resulting in a negatively charged oxygen atom bonded to an alkyl group (R). It plays a crucial role in various organic reactions, especially as a strong nucleophile.
Bisulfite: Bisulfite, also known as hydrogen sulfite, is a chemical compound with the formula HOSO3- or HSO3-. It is an important intermediate in various chemical processes, including the nucleophilic addition of water (hydration) to carbonyl compounds.
Carbonyl: The carbonyl group is a functional group consisting of a carbon atom double-bonded to an oxygen atom. It is a key structural feature in many organic compounds, including aldehydes, ketones, carboxylic acids, and esters, and plays a crucial role in their chemical reactivity and properties.
Cyanide: Cyanide is a chemical compound containing a carbon-nitrogen triple bond. It is a highly toxic substance that can interfere with cellular respiration and is found in various forms, including potassium cyanide and hydrogen cyanide. Cyanide is relevant in the context of SN2 reactions, hydration reactions, and the chemistry of nitriles.
Cyanohydrin: A cyanohydrin is a compound formed by the addition of hydrogen cyanide (HCN) to the carbonyl group of an aldehyde or ketone, resulting in the formation of a new carbon-carbon bond and a hydroxyl group. This reaction is a type of nucleophilic addition and is an important tool in organic synthesis.
Electron-donating: Electron-donating refers to the ability of a chemical species to provide or contribute electrons to another species in a chemical reaction. This property is particularly relevant in the context of nucleophilic addition reactions, such as the hydration of carbonyl compounds, where the electron-donating ability of the nucleophile plays a crucial role.
Electron-withdrawing: Electron-withdrawing refers to the ability of certain atoms or functional groups to attract or withdraw electrons away from other atoms or groups within a molecule. This property is crucial in understanding the reactivity and stability of organic compounds, particularly in the context of nucleophilic addition reactions and hydration processes.
Electrophilic: Electrophilic refers to a species or reagent that is attracted to or seeks out electron-rich regions, typically in organic chemistry reactions. These species are often positively charged or have a partial positive charge, and they interact with and form bonds with nucleophiles, which are electron-rich species.
Equilibrium Constant: The equilibrium constant is a quantitative measure of the extent to which a reversible chemical reaction proceeds to completion. It represents the ratio of the concentrations of the products to the reactants at equilibrium, and provides insight into the position and direction of a reaction at equilibrium.
Formaldehyde: Formaldehyde is a simple aldehyde compound with the chemical formula CH2O. It is a colorless, flammable gas with a pungent odor that is widely used in various industrial and commercial applications. Formaldehyde is a key term that is important in the context of several organic chemistry topics, including functional groups, oxidation of alkenes, naming aldehydes and ketones, nucleophilic addition of water, and spectroscopy of aldehydes and ketones.
Geminal: In organic chemistry, geminal refers to the position of two substituents attached to the same carbon atom. This term is often used when discussing functional groups or atoms in molecules, especially in the context of hydration reactions where water adds to aldehydes and ketones.
Geminal Diol: A geminal diol is a chemical compound containing two hydroxyl (-OH) groups attached to the same carbon atom. This structural feature is commonly observed in the context of nucleophilic addition reactions, specifically the hydration of carbonyl compounds.
Grignard Reagent: A Grignard reagent is an organometallic compound consisting of an alkyl or aryl group bonded to a magnesium atom. These versatile reagents are widely used in organic synthesis to form new carbon-carbon bonds and introduce various functional groups, making them an essential tool in the preparation of alcohols from carbonyl compounds.
Hybridization: Hybridization is a fundamental concept in chemistry that describes the process of mixing atomic orbitals to form new hybrid orbitals, which are used to explain the geometry and bonding patterns of molecules. This term is closely related to the development of chemical bonding theory, valence bond theory, and molecular orbital theory, as well as the structure and properties of various organic compounds.
Hydrate: A hydrate is a chemical compound that has water molecules incorporated into its molecular structure. These water molecules can be essential for the compound's stability and properties, and are often found in crystalline solids or solutions.
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.
Hydrochloric Acid: Hydrochloric acid (HCl) is a strong, corrosive inorganic acid that is produced naturally in the human stomach and plays a crucial role in the process of digestion. It is a key component in the context of the topics 19.5 Nucleophilic Addition of H2O: Hydration.
Hydrogen Bonding: Hydrogen bonding is a special type of dipole-dipole interaction that occurs when a hydrogen atom covalently bonded to a highly electronegative element, such as nitrogen, oxygen, or fluorine, experiences an attractive force with another nearby highly electronegative element. This intermolecular force is stronger than a typical dipole-dipole interaction and has a significant impact on the physical and chemical properties of many organic compounds.
Hydroxide Ion: The hydroxide ion (OH-) is a negatively charged species consisting of one oxygen atom and one hydrogen atom. It is an important chemical species that plays a crucial role in various organic chemistry reactions, particularly in the context of nucleophilic addition of water (hydration) and the chemistry of esters.
Hydroxyl: The hydroxyl group (–OH) is a functional group consisting of a hydrogen atom bonded to an oxygen atom. It is a key structural feature in many organic compounds and plays a crucial role in various chemical reactions and biological processes.
Ketone: A ketone is a functional group in organic chemistry that consists of a carbonyl group (a carbon-oxygen double bond) bonded to two alkyl or aryl groups. Ketones are widely encountered in various organic chemistry topics, including the hydration of alkynes, oxidative cleavage of alkynes, organic synthesis, oxidation and reduction reactions, and the chemistry of aldehydes and ketones.
Lewis Acid-Base Theory: The Lewis acid-base theory is a conceptual framework that defines acids and bases based on their ability to accept or donate electron pairs, respectively. It provides a broader perspective on acid-base interactions beyond the Brønsted-Lowry definition, which focuses on the transfer of protons.
Methylmagnesium bromide: Methylmagnesium bromide, also known as Grignard reagent, is an organometallic compound that is widely used in organic chemistry for the formation of carbon-carbon bonds through nucleophilic addition reactions. It is a key reagent in various transformations, including the hydration of aldehydes and ketones, the conjugate addition to α,β-unsaturated carbonyl compounds, and the synthesis of esters.
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.
Nucleophilic Addition: Nucleophilic addition is a fundamental organic reaction in which a nucleophile, a species that donates electrons, adds to an electrophilic carbon center, typically a carbonyl carbon, to form a new product. This reaction is central to understanding many important topics in organic chemistry, including functional groups, polar reactions, carbocation stability, reaction stereochemistry, and the chemistry of aldehydes, ketones, alcohols, and other carbonyl-containing compounds.
Nucleophilic addition reaction: A nucleophilic addition reaction is a chemical process where a nucleophile forms a bond with an electrophilic carbon atom of a compound, typically found in aldehydes and ketones. This reaction results in the conversion of the carbonyl group into a more complex, often larger, molecule.
Protic Solvent: A protic solvent is a type of solvent that contains hydrogen atoms bonded to highly electronegative atoms, such as oxygen or nitrogen, and can donate protons (H+) to solutes. This ability to donate protons makes protic solvents excellent for facilitating reactions involving the transfer of protons, such as acid-base reactions and some nucleophilic additions.
Protic solvents: Protic solvents are substances that have a hydrogen atom attached to an oxygen (as in alcohol or water) or nitrogen atom, making them capable of forming hydrogen bonds. They play a crucial role in facilitating SN2 reactions by stabilizing the transition state and reactants through hydrogen bonding.
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.
Resonance: Resonance is a fundamental concept in organic chemistry that describes the ability of certain molecules to exist in multiple equivalent structures or resonance forms. This phenomenon arises from the delocalization of electrons within the molecule, leading to the stabilization of the overall structure and the distribution of electron density across multiple atoms.
Sodium Hydroxide: Sodium hydroxide, also known as caustic soda or lye, is a highly alkaline and corrosive chemical compound that plays a crucial role in various organic chemistry processes, including the oxidation of alkenes, the nucleophilic addition of water, and the production of soap.
Sp3-Hybridized: sp3-hybridized refers to the type of hybridization that occurs in carbon atoms with four single bonds, resulting in a tetrahedral molecular geometry. This hybridization is a key concept in understanding the structure and reactivity of organic compounds, particularly in the context of prochirality and nucleophilic addition reactions involving water.
Steric Hindrance: Steric hindrance, also known as steric strain or steric effect, refers to the repulsive forces that arise between atoms or groups of atoms in a molecule due to their physical size and spatial arrangement. This phenomenon can significantly impact the stability, reactivity, and conformations of organic compounds.
T-Butyl Ketone: t-Butyl ketone, also known as 2,2-dimethylpropanone, is a simple ketone with a tertiary butyl group attached to the carbonyl carbon. It is an important organic compound that is relevant in the context of nucleophilic addition reactions, specifically the hydration of ketones.
Tetrahedral: Tetrahedral refers to a three-dimensional molecular geometry in which a central atom is bonded to four other atoms, forming a shape resembling a pyramid with a triangular base. This arrangement is a fundamental concept in chemistry, particularly in the context of chemical bonding theory, organic chemistry, and stereochemistry.
Tetrahedral Intermediate: A tetrahedral intermediate is a key reaction step that occurs in many organic chemistry reactions, where a trigonal planar carbonyl carbon temporarily becomes a tetrahedral carbon with four bonded atoms. This transient intermediate is crucial for understanding the mechanisms of various nucleophilic addition and substitution reactions.
Trifluoromethyl: The trifluoromethyl group, represented as -CF3, is a highly electronegative and hydrophobic functional group commonly found in organic compounds. It is an important structural feature that can significantly impact the physical, chemical, and biological properties of molecules.
β Diketone: A β-diketone is an organic compound containing two ketone groups separated by a carbon atom, which is the beta (β) position relative to each ketone group. These molecules are characterized by the presence of hydrogen atoms on the carbon between the two carbonyl (C=O) groups, making them acidic and prone to enolate ion formation.