Definitions A level Flashcards
Chiral Carbon
an asymmetric carbon atom/ a carbon atom bound to 4 different groups. This may also be called a chiral centre.
Displayed Formula
shows all the bonds between every atom in the compound.
Enantiomers
molecules which are non-superimposable mirror images of one another. Enantiomers have different effects on a plane of polarised light.
Optical isomerism
a type of stereoisomerism that occurs as a result of the presence of a chiral centre in a molecule. Optical isomers have different effects on a plane of polarised light.
Racemic Mixture (racemate)
a mixture containing equal amounts of enantiomers.
Stereoisomers
compounds that only differ in their arrangement of atoms in space.
Structural Formula
shows the arrangement of atoms in a molecule without the bonds drawn between them.
E.g.CH3 CH2 COCH3.
Aldehyde
a molecule containing the C=O functional group at the end of the molecule. Aldehydes can be distinguished from ketones using Fehling’s solution or Tollens’ reagent. Aldehydes produce a silver mirror with Tollens’ and a red precipitate with Fehling’s solution. Ketones do not react with either of these reagents.
Carbonyl group
a functional group with a C=O double bond.
Curly Arrow
used in mechanisms to show the movement of a pair of electrons
Hydroxynitrile
a molecule containing an alcohol group (OH) and a nitrile group (C≡N) bound to the same carbon. These can be formed in a nucleophilic addition reaction between a carbonyl and KCN followed by dilute acid (this reaction forms a mixture of enantiomers if an aldehyde or an unsymmetrical ketone is used).
Ketone
a molecule containing the C=O functional group in the middle of the molecule. Ketones can be distinguished from aldehydes using Fehling’s solution or Tollens’ reagent. Ketones do not react with either of these reagents while aldehydes produce a silver mirror with Tollens’ and a red precipitate with Fehling’s solution.
Nucleophile
an electron pair donor.
Nucleophilic Addition
a reaction in which an electrophilic π bond reacts with a nucleophile,
breaking the π bond and forming 2 new σ bonds.
Oxidation of Aldehydes
aldehydes can be oxidised using acidified potassium dichromate to form carboxylic acids.
Reduction of Aldehydes
aldehydes can be reduced to primary alcohols in a nucleophilic addition reaction with NaBH4 in aqueous solution.
Reduction of Ketones
ketones can be reduced to secondary alcohols in a nucleophilic addition reaction with NaBH4 in aqueous solution.
Alcohol
a molecule containing the OH functional group.
Biodiesel
a mixture of methyl esters of long-chain carboxylic acids. Biodiesel is produced by
reacting vegetable oils with methanol in the presence of a catalyst.
Carboxylic Acids
molecules containing the -COOH functional group. Carboxylic acids are weak acids that form CO2 when reacted with carbonates.
Esters
molecules containing the R-COO-R’ functional group which can be formed when carboxylic acids and alcohols react in the presence of an acid catalyst. Esters of glycerol (propane-1,2,3-triol) naturally occur in vegetable oils and animal fats and these esters can be hydrolysed in alkaline conditions to produce soaps and glycerol. Esters can be used to create solvents, plasticisers, perfumes and food flavourings.
Melting Point Apparatus
a piece of apparatus used to determine the melting point of a sample. The recorded melting point range is compared with known values to determine whether the sample is pure.
Hydrolysis of esters
under acidic conditions, esters will be hydrolysed to form alcohols and carboxylic acids. Under alkaline conditions, esters will be hydrolysed to form alcohols and carboxylate salts.
Nucleophile
an electron pair donor
Nucleophilic addition-elimination
a reaction in which a nucleophile is added to a molecule by breaking a π bond then a leaving group is removed to reform the π bond.
Primary Amide
a molecule containing the functional group shown below.
Recrystallisation
a technique used to purify a compound. A sample is dissolved in the minimum volume of hot solvent then filtered. The filtrate is then cooled before being filtered under reduced pressure. The residue on the filter paper is the purified compound.
Acyl Group
a group with the structure shown below, where R is an alkyl group.
Addition Reaction
a reaction in which molecules combine to form a single product.
Aromatic Compound
a compound containing at least one benzene ring.
Benzene
a 6 membered carbon ring (C6 H 6 ) containing a delocalised π system. Benzene has a planar structure and a bond length between a single and double bond. Delocalisation of the p electrons into the π system makes benzene more stable than expected.
Delocalisation of p electrons
in benzene, the empty p orbital on each carbon atom overlaps with the others to form a delocalised π system which contains 6 electrons.
Electrophile
an electron pair acceptor.
Electrophilic Substitution
a reaction in which an electrophile replaces an atom / group of atoms in a compound.
Enthalpy of Hydrogenation
the enthalpy change that takes place when one mole of an unsaturated compound reacts completely with hydrogen to form a saturated compound. Comparing the enthalpy of hydrogenation of benzene with that of the theoretical molecule cyclohexa-1,3,5-triene shows that benzene is more thermodynamically stable as more energy is needed to hydrogenate benzene.
Friedel-Crafts Acylation
an important synthetic reaction involving an electrophilic aromatic substitution reaction between benzene and acyl chlorides or anhydrides, used to form monoacylated benzene rings. AlCl3 is used as a catalyst.
Monosubstituted benzene ring
a benzene ring with one hydrogen replaced by another group,
e.g. C6 H5 NO2
Nitration
Nitration is important for synthesis, particularly for manufacturing explosives and for forming amines. Benzene can undergo nitration via an electrophilic substitution reaction, using concentrated nitric acid and a concentrated sulfuric acid catalyst at 50°C.
