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Carbonyls and carboxylic acids 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.

44 terms

Optical isomerism

Chiral centre: A carbon atom bonded to four different atoms or groups of atoms.
Enantiomers: Stereoisomers that are non-superimposable mirror images of each other.
Optical isomerism: Stereoisomerism that occurs when a molecule contains a chiral centre, giving two enantiomers.
Stereoisomers: Molecules with the same structural formula but a different arrangement of atoms in space.
Plane-polarised light: Light in which the vibrations occur in one plane only.
Optically active: Able to rotate the plane of plane-polarised light; the two enantiomers rotate it by equal amounts in opposite directions.
Racemic mixture: A mixture containing equal amounts of two enantiomers, which is optically inactive because their rotations cancel.
Chiral: Describes a molecule that cannot be superimposed on its mirror image, usually because it contains a chiral centre.
Inversion of configuration: The reversal of the arrangement of groups around a chiral centre when a nucleophile attacks from the side opposite the leaving group, as in an SN2 reaction.

Nucleophile: An electron pair donor: a species with a lone pair that it uses to form a new covalent bond.
Nucleophilic addition: A reaction in which a nucleophile attacks the δ+ carbon of a C=O bond and two molecules join to give one product.
Tollens' reagent: A solution of diamminesilver(I) ions, [Ag(NH₃)₂]⁺, which is reduced to a silver mirror when warmed with an aldehyde but not with a ketone.
Fehling's solution: An alkaline solution of copper(II) ions that gives a brick-red precipitate of Cu₂O when warmed with an aldehyde but not with a ketone.
Hydroxynitrile: A compound containing a hydroxyl group and a nitrile group, formed by nucleophilic addition of HCN to an aldehyde or ketone.
Hydride ion: H⁻, a hydrogen atom with an extra electron, which acts as a nucleophile through its lone pair; NaBH₄ is its source.
2,4-Dinitrophenylhydrazine: A reagent that gives a yellow or orange precipitate with any aldehyde or ketone; the melting point of the purified precipitate identifies the compound.
Derivative: A solid made from an unknown compound by a reaction of its functional group, whose melting point is compared with data to identify the compound.
Triiodomethane test: Warming with iodine and aqueous alkali; a pale yellow precipitate of CHI₃ shows a CH₃CO– group, or a CH₃CH(OH)– group that is oxidised to one.

Weak acid: An acid that is only slightly dissociated into ions in aqueous solution.
Carboxylate ion: The anion RCOO⁻ formed when a carboxylic acid loses the hydrogen ion from its COOH group.
Esterification: The reaction of a carboxylic acid with an alcohol, catalysed by a strong acid, to form an ester and water.
Condensation reaction: A reaction in which two molecules join together with the loss of a small molecule such as water.
Hydrolysis: The splitting of a molecule by reaction with water, here giving a carboxylic acid or its salt and an alcohol from an ester.
Triglyceride: An ester formed from propane-1,2,3-triol (glycerol) and three fatty acid molecules.
Biodiesel: A mixture of methyl esters of long-chain carboxylic acids, made by transesterification of vegetable oils with methanol.
Saponification: The alkaline hydrolysis of a fat or oil, giving glycerol and the salts of the fatty acids, which are soap.
Transesterification: The exchange of the alcohol part of an ester for another alcohol, as when methanol replaces glycerol in making biodiesel.

Acyl chloride: A compound containing the functional group –COCl, in which the OH of a carboxylic acid is replaced by a chlorine atom.
Acid anhydride: A compound with two acyl groups joined through one oxygen atom, (RCO)₂O.
Acylation: The substitution of an acyl group, RCO–, for a hydrogen atom on an O or N atom of a nucleophile.
Acyl group: The RCO– group: a carbonyl carbon bonded to an alkyl or aryl group, left when the OH is removed from a carboxylic acid.
Leaving group: An atom or group that departs with the bonding pair of electrons when its bond breaks, such as Cl⁻ from an acyl chloride.
Amide: A compound containing the group –CONH₂, formed when an acyl chloride or anhydride reacts with ammonia.
N-substituted amide: An amide in which one or both hydrogens on the nitrogen are replaced by alkyl groups, formed from a primary or secondary amine.
Nucleophilic addition–elimination: A mechanism in which a nucleophile adds to the carbonyl carbon of an acyl compound and a small molecule such as HCl is then eliminated, reforming the C=O bond.

Condensation polymerisation: The joining of monomers, each with two functional groups, into a polymer with the loss of a small molecule such as water or HCl at each link.
Polyester: A condensation polymer in which the monomer residues are joined by ester links, –COO–.
Polyamide: A condensation polymer in which the monomer residues are joined by amide links, –CONH–.
Addition polymerisation: The joining of many monomers containing C=C bonds into a polymer, with no other product.
Amide link: The –CONH– group joining monomer residues in a polyamide, formed from a carboxylic acid group and an amine group with loss of water.
Ester link: The –COO– group joining monomer residues in a polyester, formed from a carboxylic acid group and an alcohol group with loss of water.
Repeating unit: The smallest section of a polymer chain that, repeated, gives the whole chain, drawn with an open bond at each end.
Biodegradable: Able to be broken down into smaller molecules by microorganisms in the environment.
Photodegradable: Able to be broken down by absorbing light, usually ultraviolet, which breaks bonds in the polymer chain.