A-level Chemistry/OCR (Salters)/Functional groups

Organic compounds are best thought of as relatively unreactive hydrocarbon skeletons decorated by functional groups — groups of atoms that undergo characteristic reactions. Compounds containing two or more different functional groups are described as polyfunctional. Functional groupFamilyFormulaStructureExamplechloroformyl groupacyl chlorideRCOCl100px100px 70px 100pxethanoyl chloride, CH3COClhydroxyl groupalcoholROH100px100px 70px 100pxethanol, C2H5OHformyl groupaldehydeRCHO100px100px 50px 100pxethanal, CH3CHOalkenyl groupalkeneR2C=CR2100px100px 50px 100pxethene, C2H4alkynyl groupalkyneRC≡CR100px100px 50px 100pxethyne, C2H2amide groupamideRCONH2100px100px 70px 100pxethanamide, CH3CONH2amino groupamine1°: RNH22°: R2NH3°: R3N100px100px 70px 100pxethylamine, C2H5NH2alpha amino acidH2CHRCOOH100pxstyle="text-align:center"100px 70px 100pxglycine (aminoethanoic acid), (CH3CO)2Oacid anhydride(RCO)2O100px100px 70px 100pxethanoic anhydride, (CH3CO)2Oazo groupazo compoundRN2R100px150px 150pxazobenzene, C6H5N2C6H5carboxyl groupcarboxylic acidRCOOH100px100px 70px 100pxethanoic acid, CH3COOHdiazonium groupdiazonium salt[RN2]+ X−100px150pxbenzenediazonium chloride, C6H5N2Clacyloxy groupesterRCOOR100px100px 70px 100pxethyl ethanoate, CH3COOCH3alkoxy groupetherROR100px100px 100px 100pxethoxyethane, CH3OCH3halo grouphaloalkaneRX100px100px 70px 100pxchloroethane, C2H5Clcarbonyl groupketoneRCOR100pxstyle="text-align:center"100px 70px 100pxpropanone, CH3COCH3cyano groupnitrileRCN100pxstyle="text-align:center"100px 70px 100pxethanenitrile, CH3CNnitro groupnitro compoundRNO2100px100px100px 70px 100pxnitroethane, C2H5NO2phenyl groupphenyl compoundC6H5R100px100pxhydroxyl groupphenolArOH100px100px 70px 100pxphenol, C6H5OHsulfo groupsulfonic acidRSO2OH / RSO3H100px100px 70px 100pxethanesulfonic acid, C2H5SO2OH Cyclic compounds and intramolecular reactions Exam questions often ask you to identify a functional group that forms part of a ring. Here are some examples: If a cyclic compound contains a ring with less than six members (i.e. three, four or five membered rings), the ring will be under strain and functional groups that make up part of the ring will often be much more reactive than they would in a straight-chain compound. For example, amides are normally very unreactive, but the amide group in a β-lactam ring is relatively easily hydrolysed because the four-membered ring is very strained and hydrolysis converts the ring to a straight chain, relieving the strain. Cyclic compounds are often formed by intramolecular reactions, meaning reactions in which different parts of the same molecule react with each other. For instance, if a molecule contains both an alcohol part (hydroxyl group) and a carboxylic acid part (carboxyl group), the two groups can react to form an ester. The reaction is identical in all respects to normal esterification (acid + alcohol → ester + water), except that the acid and alcohol are not two separate molecules but two different ends of the same molecule. Intramolecular reactions are usually much faster than intermolecular reactions, because the reacting groups are tethered together and are thus much more likely to collide.