9.7 Alkyne Acidity: Formation of Acetylide Anions

Acetylide anions are negatively charged carbon-based species that are formed when the hydrogen atom of a terminal alkyne is removed, resulting in a highly reactive and nucleophilic species. These anions are central to understanding the acidity of alkynes and their subsequent reactivity in alkylation reactions.

Terminal Alkyne: A terminal alkyne is a type of alkyne where the triple bond is located at the end of the carbon chain, with a hydrogen atom attached to the carbon adjacent to the triple bond.

Nucleophilicity: Nucleophilicity is a measure of the ability of a species to donate electrons and participate in reactions where it attacks an electrophilic center.

Deprotonation: Deprotonation is the process of removing a proton (H+) from a molecule, resulting in the formation of a negatively charged species.

The s-character, or s-orbital character, refers to the degree of s-orbital contribution in the bonding of a particular atom or molecule. It is a crucial concept in understanding the acidity and reactivity of alkynes, as outlined in the topics of 9.7 Alkyne Acidity: Formation of Acetylide Anions.

Hybridization: The process of combining atomic orbitals to form new hybrid orbitals that have different shapes and energies compared to the original orbitals.

Acetylide Anion: The negatively charged species formed when a terminal alkyne donates its acidic hydrogen to a strong base, resulting in a highly reactive carbanion.

Electronegativity: The ability of an atom to attract shared electrons in a chemical bond, which influences the polarity and reactivity of the bond.

Terminal alkynes are a class of organic compounds that have a carbon-carbon triple bond at the end of the carbon chain. These unique functional groups are characterized by the presence of a terminal alkyne, which has significant implications in various organic chemistry reactions and transformations.

Alkynes: Alkynes are a homologous series of unsaturated hydrocarbons with a carbon-carbon triple bond.

Acetylide Anions: Acetylide anions are the negatively charged conjugate bases formed when terminal alkynes lose a proton, creating a highly reactive nucleophile.

Nucleophilic Addition: Nucleophilic addition is a type of reaction where a nucleophile adds to the carbon-carbon triple bond of an alkyne, resulting in the formation of new products.

The C-H bond is a covalent bond formed between a carbon atom and a hydrogen atom. This bond is fundamental to organic chemistry and is present in a wide range of organic compounds, from simple alkanes to complex biomolecules. The C-H bond is crucial in understanding the structure, reactivity, and stability of organic molecules.

Hybridization: The process of mixing atomic orbitals to form new, equivalent orbitals with specific geometries, which determines the shape and properties of molecules.

Bond Dissociation Energy: The amount of energy required to break a specific chemical bond, which is an important factor in understanding the reactivity and stability of molecules.

Acidity: The ability of a molecule or ion to donate a proton (H+) to another substance, which is influenced by the electronegativity and bond strengths within the molecule.

Sodium amide, also known as sodamide, is an inorganic compound with the chemical formula NaNH2. It is a white, crystalline solid that is commonly used as a strong base and nucleophile in organic chemistry reactions, particularly in the preparation of alkynes and the formation of acetylide anions.

Elimination Reaction: A type of organic reaction where two substituents are removed from a molecule, typically resulting in the formation of a new carbon-carbon double or triple bond.

Acetylide Anion: A negatively charged carbon-containing species derived from the deprotonation of an alkyne, which can then undergo further reactions.

Nucleophile: A species that donates electrons and attacks electrophilic centers in chemical reactions.

Alkali metal hydroxides are a class of strong ionic compounds formed by the combination of an alkali metal (such as lithium, sodium, potassium, rubidium, or cesium) and a hydroxide ion (OH-). These highly basic compounds are characterized by their ability to dissociate in water, producing a high concentration of hydroxide ions and resulting in a pH greater than 7.

Alkali Metals: The alkali metals are a group of highly reactive elements in the periodic table, including lithium, sodium, potassium, rubidium, and cesium. They are known for their low ionization energies and tendency to form positive ions.

Hydroxide Ion: The hydroxide ion (OH-) is a negatively charged species consisting of an oxygen atom bonded to a hydrogen atom. It is a strong base that can accept protons, leading to the formation of water.

pH: pH is a measure of the acidity or basicity of a solution, with a range from 0 to 14. Solutions with a pH greater than 7 are considered basic, and those with a pH less than 7 are considered acidic.

An acetylide salt is a type of salt formed when the hydrogen atom of an alkyne (a carbon-carbon triple bond) is replaced by a metal cation, creating an acetylide anion. These salts are important in organic chemistry as they can be used in various reactions, particularly in the formation of new carbon-carbon bonds.

Alkyne: An organic compound containing a carbon-carbon triple bond.

Nucleophile: A species that donates a pair of electrons to form a new covalent bond.

Electrophile: A species that accepts a pair of electrons to form a new covalent bond.

An sp-hybridized orbital is a type of hybrid atomic orbital that results from the mixing of one s-orbital and one p-orbital to form two equivalent hybrid orbitals. This type of hybridization is commonly observed in the bonding of alkyne functional groups, where the carbon atoms exhibit a linear geometry.

Hybridization: The process of mixing atomic orbitals to form new, equivalent hybrid orbitals with different shapes and energies than the original orbitals.

Alkyne: A functional group in organic chemistry characterized by a carbon-carbon triple bond.

Linear Geometry: A molecular geometry in which atoms are arranged in a straight line, with bond angles of 180 degrees.

pKa values are a measure of the strength of an acid or base, representing the negative logarithm of the acid dissociation constant (Ka). pKa values are used to predict the extent of acid-base reactions and the behavior of organic compounds in various chemical environments.

Acid Dissociation Constant (Ka): The equilibrium constant that describes the extent to which an acid dissociates in water, providing a quantitative measure of the acid's strength.

pH: The measure of the acidity or basicity of a solution, calculated as the negative logarithm of the hydrogen ion concentration.

Conjugate Acid-Base Pairs: The relationship between an acid and its conjugate base, or a base and its conjugate acid, where the conjugate species differs by a single proton.

An sp2-hybridized carbon atom is a carbon atom that has formed three equivalent sigma (σ) bonds with other atoms, resulting in a planar trigonal arrangement around the carbon. This hybridization is particularly important in the context of alkyne reactivity and the formation of acetylide anions.

Hybridization: The process of mixing atomic orbitals to form new hybrid orbitals, which can be used to describe the geometry and bonding of molecules.

Trigonal Planar Geometry: The arrangement of three atoms bonded to a central atom in a flat, triangular shape.

Sigma (σ) Bond: A type of covalent bond formed by the overlap of atomic orbitals along the internuclear axis, resulting in high electron density between the nuclei.

A carbanion is a negatively charged carbon atom with three bonds and a lone pair of electrons. These reactive intermediates play a crucial role in various organic chemistry reactions and concepts, including formal charges, reaction intermediates, alkyne acidity, and Grignard reagents.

Formal Charge: The charge assigned to an atom in a molecule, based on the difference between the number of valence electrons and the number of bonds formed by that atom.

Reaction Intermediate: A short-lived species that is formed and consumed during the course of a chemical reaction, typically more reactive than the reactants or products.

Acetylide Anion: A carbanion formed by the deprotonation of an alkyne, which can then undergo further reactions.

Electron-withdrawing groups are functional groups or substituents in a molecule that have a strong affinity for electrons, making them attractive to electrons. This property can significantly influence the reactivity, stability, and spectroscopic properties of the molecule.

Inductive Effect: The ability of a substituent to either attract or repel electrons through the sigma bonds of a molecule, affecting the electron density at other positions.

Resonance Effect: The ability of a substituent to stabilize or destabilize a molecule by participating in resonance, altering the electron distribution.

Electronegativity: The ability of an atom to attract shared electrons in a chemical bond, which determines the strength of electron-withdrawing or electron-donating effects.

Hydrocarbon anion stability refers to the relative stability of negatively charged carbon-based species, which is an important concept in the context of alkyne acidity and the formation of acetylide anions.

Carbanion: A negatively charged carbon-centered species that is stabilized through various electronic and structural factors.

Resonance Stabilization: The stabilization of a molecule or ion through the delocalization of electrons across multiple atoms, reducing the overall charge concentration.

Hybridization: The mixing of atomic orbitals to form new hybrid orbitals, which can impact the stability and reactivity of a molecule or ion.

Alkenyl anions are negatively charged carbon-based species containing a carbon-carbon double bond. They are formed through the deprotonation of alkynes, resulting in highly reactive nucleophilic species that can participate in various organic reactions.

Acetylide Anion: A specific type of alkenyl anion formed by the deprotonation of an alkyne, typically acetylene. Acetylide anions are highly reactive and can be used as nucleophiles in organic synthesis.

Alkyne Acidity: The ability of alkynes to undergo deprotonation and form alkenyl anions due to the relatively high acidity of the alkyne hydrogen atoms.

Nucleophilicity: The ability of a species to donate electrons and attack electrophilic centers, a key characteristic of alkenyl anions that allows them to participate in various reactions.

Alkyl anions are negatively charged organic ions derived from the removal of a proton (H+) from an alkane or alkyl group. They are highly reactive and serve as important intermediates in many organic reactions, particularly in the formation of acetylide anions during the acidity of alkynes.

Nucleophile: A nucleophile is a species that donates an electron pair to form a covalent bond, typically attacking an electrophilic center.

Carbanion: A carbanion is a negatively charged carbon atom with three bonds, often stabilized by adjacent electronegative atoms or groups.

Acetylide Anion: An acetylide anion is a specific type of alkyl anion formed by the removal of a proton from the terminal carbon of an alkyne, resulting in a highly reactive, negatively charged species.

Resonance structures are a set of contributing structures that describe the delocalization of electrons in a molecule. They represent the different ways in which the atoms in a molecule can be bonded to satisfy the octet rule and create the most stable arrangement of electrons.

Resonance Hybrid: The actual structure of a molecule that is best described by a weighted average of its resonance structures, rather than any single contributing structure.

Conjugation: The overlap of p-orbitals in adjacent multiple bonds or lone pairs, which allows for the delocalization of electrons and the formation of resonance structures.

Formal Charge: The charge assigned to an atom in a molecule, calculated by subtracting the number of nonbonding electrons and half the number of bonding electrons from the atom's atomic number.

Nucleophilicity refers to the ability of a species to donate electrons and form a covalent bond with an electrophilic center. It is a key concept in organic chemistry that governs the reactivity and selectivity of many important reactions, including substitution, addition, and elimination reactions.

Electrophilicity: Electrophilicity describes the ability of a species to attract and accept electrons, forming a covalent bond with a nucleophilic center.

Reactivity: Reactivity refers to the propensity of a chemical species to undergo a chemical reaction, which is influenced by factors such as nucleophilicity and electrophilicity.

Selectivity: Selectivity is the preference of a reaction to occur at a particular site or with a particular functional group, which is often determined by the relative nucleophilicities and electrophilicities of the reactants.