Alkenes and alcohols definitions

Alkenes: structure, electrophilic addition and Markovnikov's rule

Alkene

A hydrocarbon containing at least one carbon–carbon double bond; with one double bond and no ring, the general formula is CₙH₂ₙ.

Unsaturated

Containing at least one carbon–carbon multiple bond, as the C=C bond of an alkene, so that further atoms can be added to the molecule.

π bond

A bond formed by the sideways overlap of p orbitals, with its electron density above and below the line between the two nuclei.

Electrophile

An electron pair acceptor, attracted to a region of high electron density.

Electrophilic addition

A reaction in which the double bond of an alkene attacks an electrophile, and two groups add across the double bond to give one saturated product.

Carbocation

An ion in which a carbon atom has only three bonds and carries a positive charge.

Heterolytic fission

The breaking of a covalent bond in which both electrons of the bonding pair go to the same atom.

Induced dipole

A temporary separation of charge in a molecule caused by a nearby region of charge; the π electrons of an alkene repel the Br–Br bonding pair, making the nearer bromine δ+.

Inductive effect

The release of electron density along a σ bond by an alkyl group, which stabilises a positive charge on the carbon it is joined to.

Markovnikov's rule

When a hydrogen halide adds to an unsymmetrical alkene, the hydrogen bonds to the carbon of the double bond that already carries more hydrogen atoms.

Diol

A compound with two OH groups; cold dilute acidified manganate(VII) adds one to each carbon of a C=C bond.

Addition polymers

Monomer

A small molecule that joins with many others of the same kind to form a polymer.

Polymer

A long-chain molecule made by joining many monomer molecules together.

Addition polymerisation

The joining of many unsaturated monomer molecules, by opening their double bonds, to form a polymer and no other product.

Repeating unit

The smallest group of atoms in a polymer chain that, repeated, gives the whole chain; for an addition polymer, the two carbons of the monomer's double bond with their side groups.

Van der Waals forces

Weak attractions between all molecules, caused by temporary dipoles inducing dipoles in neighbouring molecules.

Plasticiser

A small molecule added to a polymer that gets between the chains, pushes them apart and weakens the forces between them, so the polymer becomes flexible.

Biodegradable

Able to be broken down by microorganisms in the environment into small molecules such as carbon dioxide and water.

Feedstock recycling

Heating waste polymer to crack it into small molecules that are used to make new polymers or fuels.

Photodegradable

Able to be broken down by light, usually ultraviolet absorbed by groups such as C=O built into the polymer chain.

Alcohols: hydration, fermentation and classification

Alcohol

A compound containing the hydroxyl group, OH, bonded to a saturated carbon atom.

Primary alcohol

An alcohol in which the carbon bonded to the OH group is bonded to one other carbon atom (or none, in methanol).

Secondary alcohol

An alcohol in which the carbon bonded to the OH group is bonded to two other carbon atoms.

Tertiary alcohol

An alcohol in which the carbon bonded to the OH group is bonded to three other carbon atoms.

Hydrogen bond

An attraction between a δ+ hydrogen atom bonded to nitrogen, oxygen or fluorine and a lone pair on a nitrogen, oxygen or fluorine atom of a neighbouring molecule.

Fermentation

The conversion of glucose into ethanol and carbon dioxide by enzymes in yeast, in the absence of air.

Hydration

The addition of water across a carbon–carbon double bond, as when ethene and steam form ethanol.

Biofuel

A fuel produced from renewable biological material, such as crops.

Carbon neutral

Describing an activity that has no net annual carbon emissions to the atmosphere.

Alkoxide ion

The anion RO⁻ formed when an alcohol loses the hydrogen of its OH group, as in sodium ethoxide, CH₃CH₂O⁻Na⁺.

Oxidation and elimination of alcohols

Oxidising agent

A species that accepts electrons, oxidising another species and being reduced itself.

Aldehyde

A compound containing the CHO group: a C=O at the end of a carbon chain, with a hydrogen on the carbonyl carbon.

Ketone

A compound containing a C=O group bonded to two other carbon atoms.

Carboxylic acid

A compound containing the carboxyl group, COOH, at the end of a carbon chain.

Distillation

Heating a liquid mixture so that the component with the lowest boiling point vaporises, then condensing it and collecting it separately.

Reflux

Continuous boiling and condensing of a reaction mixture, a vertical condenser returning the vapour to the flask, so it can be heated for a long time without losing volatile substances.

Elimination

A reaction in which a small molecule is removed from a larger one, leaving a double bond.

Dehydration

An elimination reaction in which a molecule of water is removed, as when an alcohol forms an alkene.