OCR A-Level Chemistry A 4.1.1-4.1.3 Definitions

-Organic Chemistry -Nomenclature of organic compounds -Representing formulae of organic compounds -Isomerism -Reaction mechanisms -Properties of alkanes -Reactions of alkanes -Properties of alkenes -Stereoisomerism -Reactions of alkenes -Electrophilic addition -Polymerisation of alkenes

Saturated hydrocarbon

A hydrocarbon containing single carbon-carbon bonds only

Unsaturated hydrocarbon

A hydrocarbon containing at least one multiple carbon-carbon bond, or aromatic rings

Homologous series

A series of organic compoundsd having the same functional group but with each successive member differing by CH2

Functional group

The group of atoms responsible for the characteristic reactions of a compound

Empirical formula

The simplest whole number ratio of atoms of each element present in a compound

Molecular formula

The actual number and type of atoms of each element in a molecule of a compound

Structural formula

The minimal detail that shows the arrangement of atoms in a molecule

Displayed formula

The relative positioning of atoms and the bonds between them

Skeletal formula

A simplified organic formula shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups.

Isomerism

When two or more organic molecules have the same molecular formula but different arrangements of atoms

Structural isomers

Compounds with the same molecular formula but different structural formulae

Stereoisomers

Compounds with the same structural formula but a different spatial arrangement of the atoms

E/Z isomers

An example of stereoisomerism due to restricted rotation around a C=C bond where there are two different groups attached to each carbon atom of the C=C group

Cis-trans isomerism

A special case of E/Z isomerism in which two of the substituent groups attached to each carbon atom in the C=C bond are the same

Homolytic fission

A covalent bond is broken with each bonding atom receiving one electron from the bonded pair, forming two radicals

Heterolytic fission

A covalent bond is broken with one of the bonded atoms receiving both electrons from the bonded pair, forming two oppositely charged ions

Radical

A very reactive species with an unpaired electron

Addition reaction

Two reactant molecules join together to form a single product

Substitution reaction

An atom or group of atoms exchanges with a different atom or group of atoms

Elimination reaction

A molecule loses a small molecule

Sigma bond

A bond caused by orbital overlap directly between the bonding atoms

Pi bond

A bond caused by sideways overlap of adjacent p-orbitals above and below the atoms

Reaction mechanism

A series of steps that show how a reaction takes place

Electrophile

A species that can accept a pair of electrons to form a new covalent bond

Carbocation

A positively charged species with the positive charge on a carbon atom