Alkenes, Hydrocarbon Reactions, and Organic Isomerism

Comprehensive vocabulary flashcards covering the preparation, physical properties, bonding, mechanisms of electrophilic addition, industrial reactions, and structural and stereochemical isomerism of alkenes and related organic compounds.

Alkenes

Unsaturated hydrocarbons composed of hydrogen and carbon containing carbon-to-carbon double bonds, possessing two fewer hydrogen atoms than the corresponding saturated alkanes with the general formula $C_n H_{2n}$.

Elimination Reactions

Reactions in which small atoms (such as $H$, $OH$, or $X$) or small molecules (such as $H_2O$ or $HCl$) are removed from adjacent carbon atoms of saturated compounds to create a double bond.

Dehydration of Alcohols

The preparation of an alkene by heating an alcohol (such as ethanol) with an excess of concentrated sulphuric acid ($H_2SO_4$) at $180\,^\circ\text{C}$, which proceeds through an ethyl hydrogen sulphate intermediate to remove a water molecule.

Dehydrohalogenation of Alkyl Halides

The reaction in which an alkyl halide (such as ethyl bromide) is heated with alcoholic $KOH$, removing hydrogen and a halogen from adjacent carbon atoms to generate an alkene.

Pi ($\pi$) Bond

A covalent bond formed by the lateral (sideways) overlap of unhybridized parallel $p$-orbitals located perpendicular ($90^\circ$) to the plane of the $sp^2$ hybrid orbitals.

Electrophile

A species that can act as an electron pair acceptor, commonly symbolized as $E^+$.

Nucleophile

A species that can act as an electron pair donor, commonly symbolized as $Nu^-$.

Inductive Effect

The polarization of a $\sigma$ bond caused by the electron-withdrawing or electron-donating influence of adjacent atoms or groups within a molecule.

Carbocation

An alkyl group bearing a single positive charge on one of its carbon atoms, functioning as an electrophile.

Positive Inductive Effect ($+I$)

An electron-donating effect exerted by alkyl groups that push electrons toward a positively charged carbon atom, increasing carbocation stability in the order $3^\circ > 2^\circ > 1^\circ > \text{methyl}$.

Negative Inductive Effect ($-I$)

An electron-withdrawing effect exhibited by electronegative species (such as halogens) that pull bonded electrons away from a carbon-to-carbon bond, giving rise to a permanent dipole.

Electrophilic Addition Reaction

A reaction in which an electrophile adds to the high-electron-density double bond of an alkene to produce a carbocation intermediate, which then combines with a nucleophile.

Halogenation (of Alkenes)

The addition of halogens across a double bond; adding bromine water in an inert solvent like carbon tetrachloride ($CCl_4$) rapidly discharges its reddish-brown color, serving as a diagnostic test for unsaturation.

Hydrohalogenation

The addition of a dry gaseous hydrogen halide ($HX$) across the carbon-carbon double bond of an alkene at room temperature to form a halogenoalkane, with reaction rates increasing from $HF$ to $HI$.

Markovnikov's Rule

A rule stating that when an unsymmetrical polar reagent adds to an unsymmetrical alkene, the negative part of the reagent attaches to the double-bonded carbon holding the fewer number of hydrogen atoms.

Hydrogenation (of Alkenes)

The catalytic addition of molecular hydrogen ($H_2$) to an alkene using a nickel ($Ni$) or platinum ($Pt$) catalyst at $250\text{--}300\,^\circ\text{C}$ to form a saturated alkane, used industrially to produce margarine (Banaspati ghee) from vegetable oil.

Hydration (of Alkenes)

The reaction of gaseous alkenes with steam under high temperature and pressure in the presence of concentrated sulphuric acid ($H_2SO_4$) catalyst to form alcohols via a carbocation intermediate.

Halohydration

A reaction in which an alkene reacts with a halogen (such as bromine or chlorine) in the presence of water to synthesize a halohydrin (such as a bromohydrin or chlorohydrin).

Epoxidation

The oxidation of an alkene using oxidizing agents or molecular oxygen over a transition metal catalyst (such as silver, $Ag$) to generate an oxygen-containing three-membered cyclic ether called an epoxide.

Ozonolysis

The oxidative cleavage of alkenes using ozone ($O_3$) to form ozonides, which are subsequently reduced to carbonyl compounds (aldehydes or ketones); used to determine the position of the double bond.

Addition Polymerization

A process in which many monomer units containing at least one $C=C$ double bond join together through breaking their $\pi$-bonds to form long-chain polymers as the sole product.

Repeating Unit

The smallest constitutional group of atoms that, when linked sequentially, constitutes the complete polymer chain, shown inside square brackets in displayed and general formulas.

Conjugated Diene

A molecule containing two carbon-to-carbon double bonds separated by a single bond, allowing lateral $\pi$-orbital overlap across three or more adjacent atoms to delocalize electrons.

Isomerism

The phenomenon in which two or more chemical compounds have the identical molecular formula but distinct structural formulas and physical or chemical properties.

Structural Isomerism

A class of isomerism arising from differences in the order or connectivity of atoms within a molecule.

Chain Isomerism

A form of structural isomerism resulting from variations in the arrangement or branching of the carbon skeleton or carbon chain.

Position Isomerism

A form of structural isomerism caused by differences in the location of the same functional group along an identical carbon framework.

Functional Group Isomerism

A form of structural isomerism where compounds have the same molecular formula but different functional groups, such as methoxy methane and ethanol ($C_2H_6O$).

Metamerism

A type of structural isomerism arising from the unequal distribution of carbon atoms on either side of a bridging functional group within the same homologous series.

Tautomerism

A type of structural isomerism that arises through the intramolecular transfer of a proton from one atom to another within the same molecule.

Zwitterion

A dipolar internal ion formed when a proton shifts from the carboxylic acid group ($-COOH$) to the basic amine group ($-NH_2$) within an amino acid molecule.

Stereoisomerism

A class of isomerism where molecules possess the same structural formula and connectivity but differ in the spatial orientation of their atoms or groups in three-dimensional space.

Organic Redox Reactions

Reactions in organic chemistry characterized by the gain or loss of atoms, where organic oxidation involves the addition of oxygen or removal of hydrogen, and organic reduction involves the addition of hydrogen or removal of oxygen.