9.2 Preparation of Alkynes: Elimination Reactions of Dihalides

A triple bond is a chemical bond where three pairs of electrons are shared between two atoms. It is the strongest and shortest type of covalent bond found in molecules.

Covalent Bond: A type of chemical bond where two atoms share one or more pairs of valence electrons.

sp Hybridization: The process of mixing one s orbital and one p orbital from an atom to form two equivalent hybrid orbitals, often associated with triple bonded structures such as acetylene.

Molecular Orbital Theory: A theory that describes the distribution of electrons in molecules in terms of molecular orbitals that can spread over several atoms or the entire molecule

A triple bond is a covalent bond in which three pairs of electrons are shared between two atoms, resulting in a very strong and stable chemical connection. This type of bond is particularly important in the context of organic chemistry, as it is a key structural feature in certain classes of compounds known as alkynes.

sp Hybridization: A type of atomic orbital hybridization in which an atom's s orbital and two of its p orbitals combine to form three equivalent sp hybrid orbitals, often seen in the structure of alkynes.

Acetylene: The simplest alkyne, with the chemical formula C₂H₂, characterized by the presence of a triple bond between the two carbon atoms.

Degree of Unsaturation: A measure of the number of carbon-carbon double or triple bonds, as well as the number of rings, present in a organic compound.

An alkyne is a hydrocarbon compound containing a carbon-carbon triple bond. Alkynes are a class of unsaturated organic compounds that play a crucial role in various topics within organic chemistry, including sp hybridization, functional groups, degree of unsaturation, nomenclature, and synthetic transformations.

sp Hybridization: The process by which an atom's atomic orbitals mix to form new hybrid orbitals, allowing for the formation of a carbon-carbon triple bond in alkynes.

Unsaturated Compounds: Organic compounds that contain one or more carbon-carbon multiple bonds, such as the triple bond found in alkynes, resulting in a higher degree of unsaturation.

Organic Synthesis: The design and construction of complex organic molecules, often involving the use of alkynes as key intermediates or building blocks.

Vicinal refers to the spatial relationship between two substituents or functional groups that are positioned next to each other, typically on adjacent carbon atoms, in a molecule.

Geminal: Geminal describes substituents or functional groups that are attached to the same carbon atom.

Cis-trans Isomerism: Cis-trans isomerism is a type of stereoisomerism that arises when two identical substituents are positioned on the same side (cis) or opposite sides (trans) of a carbon-carbon double bond.

Elimination Reaction: An elimination reaction is a type of organic reaction where two substituents are removed from a molecule, typically resulting in the formation of a carbon-carbon double bond.

Double dehydrohalogenation is a type of elimination reaction that involves the removal of two halogen atoms (typically bromine or chlorine) and two hydrogen atoms from an organic compound, resulting in the formation of an alkyne. This process is a key method for the preparation of alkynes from dihalide precursors.

Elimination Reaction: A type of organic reaction where atoms or groups are removed from a molecule, often resulting in the formation of a new double or triple bond.

Dihalide: An organic compound containing two halogen atoms (such as bromine or chlorine) attached to a carbon chain or ring.

Alkyne: An unsaturated hydrocarbon containing a carbon-carbon triple bond.

A strong base is a type of chemical compound that completely dissociates into its constituent ions in an aqueous solution, resulting in a high concentration of hydroxide ions (OH-) and a high pH. Strong bases are important in various organic chemistry reactions, such as the preparation of alkynes via elimination reactions and the Wittig reaction involving phosphorus ylides.

Weak Base: A weak base is a chemical compound that only partially dissociates into its constituent ions in an aqueous solution, resulting in a lower concentration of hydroxide ions (OH-) and a relatively lower pH compared to strong bases.

pH: pH is a measure of the acidity or basicity of a solution, with a range from 0 to 14. A pH value above 7 indicates a basic or alkaline solution, with a higher pH corresponding to a stronger base.

Hydroxide Ion (OH-): The hydroxide ion (OH-) is the conjugate base of water and is the primary contributor to the basic or alkaline nature of a solution. Strong bases have a high concentration of hydroxide ions.

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.

Potassium tert-butoxide is a strong base used in organic chemistry, particularly in elimination reactions to prepare alkenes and alkynes. It is a white, crystalline solid that is highly reactive and must be handled with care.

Elimination Reaction: A type of organic reaction where two substituents are removed from a molecule, often resulting in the formation of a pi bond.

Alkene: An unsaturated hydrocarbon containing a carbon-carbon double bond.

Alkyne: An unsaturated hydrocarbon containing a carbon-carbon triple bond.

The E2 mechanism, or bimolecular elimination reaction, is a type of organic reaction where a base removes a hydrogen atom and a leaving group from adjacent carbon atoms, resulting in the formation of a carbon-carbon double bond. This mechanism is particularly important in the preparation of alkynes through the elimination of dihalides, as well as in the dehydration of aldol products to form enones.

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

Bimolecular: Referring to a reaction involving two reactant molecules.

Leaving Group: An atom or group that is removed from a molecule during a reaction, typically a halide or a weak base.

A vinylic halide is an organic compound containing a carbon-carbon double bond (a vinyl group) directly bonded to a halogen atom, such as chlorine, bromine, or iodine. These compounds are important intermediates in the preparation of alkynes through elimination reactions of dihalides, as described in the topic 9.2 Preparation of Alkynes.

Vinyl Group: A vinyl group is a functional group consisting of a carbon-carbon double bond with one hydrogen atom attached to each carbon.

Dihalide: A dihalide is an organic compound containing two halogen atoms (e.g., chlorine, bromine, iodine) bonded to a carbon-carbon single bond.

Elimination Reaction: An elimination reaction is a type of organic reaction where two substituents are removed from a molecule, often resulting in the formation of a carbon-carbon double bond.

A vicinal dihalide is a compound that contains two halogen atoms (such as chlorine, bromine, or iodine) attached to adjacent carbon atoms in an organic molecule. These compounds are important intermediates in various organic reactions, particularly in the preparation and reactions of alkynes.

Halogenation: The process of adding one or more halogen atoms (such as chlorine, bromine, or iodine) to an organic compound.

Elimination Reaction: A reaction in which two atoms or groups are removed from a molecule, often resulting in the formation of a new carbon-carbon double or triple bond.

Addition Reaction: A reaction in which two or more reactants combine to form a single product, often involving the addition of a molecule across a carbon-carbon double or triple bond.

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.

Halogen: A group of five highly reactive nonmetallic elements (fluorine, chlorine, bromine, iodine, and astatine) that readily form compounds with other elements.

Substitution Reaction: A reaction in which an atom or group in a molecule is replaced by another atom or group.

Addition Reaction: A reaction in which two or more reactants combine to form a single product, with no atoms being removed.

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.

Elimination Reaction: A type of organic reaction where two atoms or groups are removed from a molecule, often resulting in the formation of a π bond.

Alkyl Halide: An organic compound containing a halogen atom (such as chlorine, bromine, or iodine) bonded to an alkyl group.

Unsaturated Hydrocarbon: An organic compound containing one or more carbon-carbon double or triple bonds, such as alkenes and alkynes.

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.

Electrophile: An electrophile is a species that is attracted to electrons and seeks to form new bonds by donating a pair of electrons.

Carbocation: A carbocation is a positively charged carbon species that is an intermediate in many electrophilic addition reactions.

Markovnikov's Rule: Markovnikov's rule states that in the addition of an unsymmetrical reagent (such as HX) to an alkene, the hydrogen atom attaches to the carbon atom that can best stabilize the resulting carbocation.

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.

Syn Addition: Syn addition is the stereochemical outcome of an electrophilic addition reaction where the incoming electrophilic species adds to the same face of the alkene or alkyne as the existing substituents, resulting in the formation of the syn-addition product.

Stereochemistry: Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this arrangement affects the chemical and physical properties of the molecule.

Electrophilic Addition: Electrophilic addition is a type of organic reaction where an electrophilic species adds to an alkene or alkyne, forming a new carbon-carbon bond and often resulting in the formation of a new stereocenter.

Anti elimination is a type of elimination reaction where the leaving groups depart in an anti-periplanar fashion, resulting in the formation of an alkyne. This process is particularly important in the context of preparing alkynes from dihalides through elimination reactions.

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

Syn Elimination: A type of elimination reaction where the leaving groups depart in a syn-periplanar fashion, leading to the formation of an alkene.

Dihalides: Organic compounds containing two halogen atoms attached to the same carbon atom.

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.

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

Nucleophilic Substitution: A reaction in which a nucleophile replaces a leaving group, leading to the formation of a new covalent bond.

Condensation Reaction: A reaction in which two molecules combine, with the elimination of a small molecule, typically water, to form a larger molecule.