Chemistry › Definitions › Alkanes and halogenoalkanes

Alkanes and halogenoalkanes definitions

Every term the lessons in this unit define, lesson by lesson, worded as the lessons use them. Each lesson title links to its notes.

37 terms

Alkanes: fractional distillation, cracking and combustion

Hydrocarbon: A compound that contains hydrogen and carbon atoms only.
Saturated: Containing only single bonds between carbon atoms, so that no more atoms can be added to the molecule.
Homologous series: A family of compounds with the same functional group and general formula, in which each member differs from the next by CH₂.
Fraction: A mixture of hydrocarbons with similar chain lengths, and so with boiling points in a narrow range.
Fractional distillation: Separation of a mixture into fractions by boiling point, in a column with a temperature gradient that is hottest at the bottom.
Cracking: The breaking of C–C bonds in long-chain alkanes to form shorter alkanes and alkenes.
Complete combustion: Burning in a plentiful supply of oxygen, in which the carbon in a fuel is oxidised to carbon dioxide and the hydrogen to water.
Incomplete combustion: Burning in a limited supply of oxygen, giving carbon monoxide or carbon as well as, or instead of, carbon dioxide.
Greenhouse gas: A gas whose molecules absorb infrared radiation emitted by the Earth's surface and re-emit it, warming the lower atmosphere.
Reforming: The conversion of straight-chain alkanes into branched alkanes and cyclic hydrocarbons, over a platinum catalyst, to give fuels that burn more efficiently.
Photochemical smog: A haze formed when nitrogen oxides and unburnt hydrocarbons react in sunlight, containing ground-level ozone and PAN.

Radical: A species with an unpaired electron.
Homolytic fission: The breaking of a covalent bond in which each atom takes one electron from the bonding pair, forming two radicals.
Free-radical substitution: A reaction in which an atom in a molecule is replaced by another, by way of a chain of steps involving radicals.
Fishhook arrow: A curly arrow with half a head, showing the movement of a single electron.
Chain reaction: A reaction in which each propagation step regenerates a radical, so that one initiation step leads to many cycles of reaction before termination.
Initiation: The step in which radicals are first formed, here by homolytic fission of Cl₂ in ultraviolet light.
Propagation: A step in which a radical reacts with a molecule to give a product and another radical, so the number of radicals is unchanged.
Termination: A step in which two radicals combine to form a molecule, removing both radicals from the chain.

Halogenoalkane: A compound in which one or more hydrogen atoms of an alkane have been replaced by halogen atoms.
Heterolytic fission: The breaking of a covalent bond in which one atom takes both electrons of the bonding pair, forming two ions.
Nucleophile: An electron pair donor: a species with a lone pair of electrons that attacks an electron-deficient atom to form a new covalent bond.
Nucleophilic substitution: A reaction in which a nucleophile attacks an electron-deficient carbon and replaces an atom or group attached to it.
Primary halogenoalkane: A halogenoalkane in which the carbon bonded to the halogen is bonded to only one other carbon atom.
Hydrolysis: The splitting of a bond in a molecule by reaction with water or hydroxide ions.
Nitrile: A compound containing the C≡N group, named from the whole carbon chain including the carbon of the C≡N.
Amine: A compound in which one or more hydrogen atoms of ammonia have been replaced by alkyl groups.
SN2: Nucleophilic substitution in one step, with two species, the halogenoalkane and the nucleophile, in the rate-determining step.
SN1: Nucleophilic substitution in two steps, in which the C–X bond breaks to form a carbocation in the rate-determining step, with one species in that step.

Elimination: A reaction in which a small molecule is removed from a larger one, leaving a double bond.
Base: A proton acceptor: a species that accepts an H⁺ ion using a lone pair.
Position isomers: Structural isomers with the same carbon skeleton and the same functional group at a different position on the chain.
E/Z isomers: Stereoisomers that exist because rotation about a C=C bond is restricted and each carbon of the double bond carries two different groups.
Ozone layer: The region of the stratosphere where ozone is concentrated, which absorbs most of the ultraviolet radiation from the Sun.
CFC: A chlorofluorocarbon: a halogenoalkane containing only carbon, chlorine and fluorine.
HFC: A hydrofluorocarbon: a compound of hydrogen, fluorine and carbon with no chlorine, used to replace CFCs.
Catalyst: A substance that increases the rate of a reaction without being used up, by providing an alternative route with a lower activation energy.