NJC 9 Polymer Part 2

National Junior College SH1 H1 Chemistry 1 Polymers (Part 2) – Reactions of Functional Groups Learning Outcomes Students should be able to: describe the chemistry of the following classes of compounds: (i) alkanes (exemplified by ethane) as being generally unreactive except in terms of combustion and substitution by chlorine (ii) alkenes (exemplified by ethene) in terms of combustion and addition reactions with bromine (in CCl4) and hydrogen (iii) halogenoalkanes (exemplified by bromoethane) in terms of substitution reaction to alcohols and elimination reactions to alkenes (iv) aldehydes (exemplified by ethanal) and ketones (exemplified by propanone) in terms of their reduction to primary and secondary alcohols respectively; and oxidation of aldehydes to carboxylic acids (v) alcohols (exemplified by ethanol) in terms of combustion, oxidation to carboxylic acids and elimination to alkenes (vi) carboxylic acids (exemplified by ethanoic acid) in terms of conden sation with alcohols to form esters (in the presence of concentrated sulfuric acid), and amines (exemplified by ethylamine) to form amides (in the presence of dicyclohexylcarbodiimide, DCC) (vii) esters (exemplified by ethyl ethanoate) and amides (exemplified by ethanamide) in terms of hydrolysis with acids and bases

National Junior College SH1 H1 Chemistry 2 Success Criteria: • I can understand alkanes are generally unreactive except it undergoes o combustion reaction to form CO2 and H2O o substitution reaction by chlorine to form halogenoalkane C CH H H H H H ethane 1 Alkanes Alkanes are saturated hydrocarbons. (i.e. contains only C−H and C−C single bonds) All the C atoms in alkanes forms 4  bonds, therefore every C atom has a tetrahedral shape. methane butane CH4 They are generally unreactive, except in terms of combustion and substitution by chlorine or bromine. Reasons: o They are non -polar molecules (Since C and H have very similar electronegativity). o Since C−C and C−H bonds are very strong, large amount of energy is required to break the C−C and C−H bonds in order for reaction to occur. 1.1 Physical Properties Since the electronegativity of C and H are similar (i.e. negligible electronegativity difference), C–H bond is non –polar, alkanes molecules are non –polar and are held together by weak instantaneous dipole–induced dipole attraction. (a) Boiling and melting point Boiling and melting points increases as number of carbon atoms in the alkane increases. This is because incresing amount of energy is required to overcome the increasing strength of instantaneous dipole-induced dipole interaction between molecules as the size of electron cloud increases. Straight–chain alkanes: C1 to C4 are gases, C5 to C17 are liquids, C18 and above are solids at r.t.p. Boiling points of branched alkanes are lower than the boiling poi