GCE A-level Chemistry Archives

Nitrogen Compounds Primary AmineSecondary AmineTertiary Amine‎‎‎ Formation of Alkyl Amines Substitution R–X + NH3 → R–NH2 + HX(g) Type of reaction: nucleophilic substitution Reagent: hot conc. NH3 in ethanol Condition: heat under reflux ReductionR–C ‎≡‎ N + 4[H] ‎→‎ R–CH2NH2R–CO–NH2 + 4[H] → R–CH2NH2 + H2OType of reaction: reduction of a nitrileType of reaction: reduction of an amideReagent: hydrogen gasReagent: hydrogen gasReducing Agents (catalyst): LiAlH4 in dry ether NickelReducing Agent (catalyst): LiAlH4 in dry etherConditions: high temp. and pressureConditions: r.t.p. Formation of Aryl Amines Reduction ‎ Type of reaction: reduction of nitrobenzene Reagent: conc. HCl with Tin Condition: Heat Basicity of Amines Bases are proton acceptors (electron donors) N-atoms in amines have a lone pair of e-s N donates lone pair and accepts H+ forming dative bond ‎ Relative Basicity ‎ Phenyl amine weaker than ammoniaAmmoniaEthylamine stronger than ammonia ‎Lone pair of e-s on N gets partially delocalized by interaction with benzene e- cloudEthyl e- donating group, increases e- density on NLone pair less available for coordination to protonEnhanced ability to donate lone pair of e-s to proton Alkyl ammonium cation formed more stable than NH4+ cation from ammonia Reactions of phenyl amine Bromination Type of reaction: electrophilic substitution Reagent: aq. Bromine Conditions: r.t.p. (no catalyst) Forms a white ppt. Diazotization (–N2+ is called diazonium ion) Type of reaction: diazotization reaction Reagent: nitrous acid (NaNO2 with excess HCl(aq)) (HNO2 weak, unstable acid so produced by reaction NaNO2 with excess HCl) Condition: low temp. (5 0C) Note: Diazonium salts of aryl amine stabilized by delocalization of –N2+ ion's e-s over benzene ring However, diazonium ion highly unstable and can decompose above 10oC to Coupling Reactions of Diazonium Salts Type of reaction: electrophilic substitution Reagent: aromatic amines or phenols Azo compounds are complex compounds involving a minimum of two aromatic rings joined by N=N coupling Benzene diazonium ion carries a +ve charge and readily reacts with cold alkaline solutions of aromatic amines and phenols to give brightly coloured azo-compounds Bright orange dye formed By using alterative aryl compounds to phenol, a range of brightly coloured dye can be formed. Formation of Amides Formation Primary Amides: Secondary Amides: Type of reaction: nucleophilic substitution Reagent: conc. NH3(aq) Condition: r.t.p. Example: ‎ ethanoyl chloride + methyl amine → N-methyl methanamide Neutrality of Amides The presence of the electron withdrawing oxygen atom means that the lone pair on the amide's nitrogen atom is not available to be donated to e.g. H+ ions Hence, amides are neutral Hydrolysis of Amides ‎ Amino Acids Optical activity: all amino acids (except glycine) have a chiral carbon therefore they are optically active Acid/Base Properties of Amino Acids Basic amino group and acidic carboxyl group interact: Carboxyl group donates a proton to amino group Amino group accepts proton and zwitterion formed Zwitterion: ion that contains regions of +ve & –ve charge Amino acids solids at r.t.p. due to ionic bonds that exist between zwitterions Presence of zwitterions means that amino acids are soluble in water Amino Acids in Acidic/Basic Conditions If acid added, the –COO- part of the zwitterion accepts an H+ ion, reforming –COOH group, leaving +ve charge If alkali added, the –NH3+ part of the zwitterion donates an H+ ion to the OH-, reforming –NH2 group and H2O, leaving a -ve charge ‎ Peptide Bonds Amide link formed by nucleophilic attack of –NH2 group of one amino acid on –COOH group of another Reaction is a condensation reaction as H2O eliminated Reaction can continue to occur as product still has –NH2 and –COOH group present Dipeptide → Tripeptide → Polypeptide (protein) Proteins are polymers of amino acids; many polypeptide chains held together by intermolecular forces Hydrolysis: involves breaking of peptide links by reaction with water catalysed by an acid or alkali catalyst, giving back the amino acids, temp. nearly 90oC Electrophoresis It is used to separate, identify and purify amino acids obtained when protein hydrolysed Technique based on separating ions placed in an electric field. When sample placed between two electrodes: +ve charge ions move towards –ve charged electrode –ve charge ions move towards +ve charged electrode Sample placed on absorbent filter paper (or gel) Buffer solution carries ions along (back or forth) Factors that Determine theDirection of TravelSpeed of MovementpH of buffer solution Charge on amino acidVoltage applied Temperature Size (Mr) of amino acid Magnitude of chargeLarger ions with longer side chain move slower More highly charge ions move faster

Category: GCE A-level Chemistry

Nitrogen Compounds

Phenols

Chemistry Data Booklet

Air pollution and control

Waste management

What is Nano Technology

Application of Nano Technology

Platinum group metals

Phase equilibria