NJC Organic Chem Structured revision set Answer

Organic Chemistry Revision Booklet (Structured Qn) 2024 National Junior College 1 Worked Solutions to Organic Chemistry Revision Booklet (Structured Questions) 1) Organic Synthesis 1. (a) Cl C O H D Cl C O OH E (b) Step 2: NaOH(aq); heat Step 3: KMnO4,H2SO4 (aq), heat or K2Cr2O7, H2SO4 (aq), heat (c)(i) (ii) NH2 OH CH3 CH3 and HO C O O− K + *remember to check for acid-base reaction after hydrolysis 2. (a) *Hydrolyse the amide, S, to deduce the structures of R and Q. *Displayed formula shows all the bonds in the correct shape (i.e. trigonal planar, bent)

Organic Chemistry Revision Booklet (Structured Qn) 2024 National Junior College 2 (b) Step 1: Oxidation (1o alcohol to aldehyde) [controlled oxidation] Step 2: Nucleophilic addition (of HCN) Step 3: Reduction (of nitrile) (c) C O O C H CH2NH2 C H H Cl Cl Acyl chloride, R, can undergo condensation reaction with alcohol in Q to form an ester. 3. (a) cis-trans isomerism OH H H H H OH cis, cis- H H H H OH OH cis, trans- ,H2SO4(aq), cold cold

Organic Chemistry Revision Booklet (Structured Qn) 2024 National Junior College 3 OHH H H H OH trans,cis- HH H H OH OH trans,trans- (b) Q (C11H12O2) Ester – undergoes acidic hydrolysis with aq HCl CH3CH2CO2H R (C3H6O2) S (undergoes reduction of alkene to give T) T (Phenol undergoes electrophilic substitution with Br2(aq) – multiple substitutions) U (C8H7OBr3) 4 (i) 1. Primary amine 2. Tertiary alcohol 3. amide 4. ester

Organic Chemistry Revision Booklet (Structured Qn) 2024 National Junior College 4 (ii) cold HCl(aq) only acid-base reaction takes place (ester & amide hydrolysisrequire heat) C CH2NH3 + CH2 OH N C CH2CH3 H O OC O CH3 Hot NaOH(aq) alkaline hydrolysis followed by acid-base reaction of the products. CH3CO2Na CH3CH2CO2Na OH CH2NH2 CH2NH2 +Na-O 5 (i) AlBr3 or FeBr3 or AlCl3 or FeCl3 , anhydrous (ii) Benzene, although electron rich, is stabilised by resonance. Hence, benzene requires a strong electrophile for the electrophilic attack to take place. The presence of a lewis acid catalyst (eg. AlBr3) is necessary for the formation of the strong electrophile, (CH3)2CHCH2+. (iii) CH3 C CH3H C HH S O CCl T O O C U (iv) V is an aliphatic aldehyde as it gives a reddish brown ppt with Fehling’s solution. CH3 C CH3 H CH2Br CH3 C CH3 H C O H NaOH(aq) heat CH3 C CH3 H CH2OH K2Cr2O7, dil H2SO4 heat with immediate distillation V Cl –

Organic Chemistry Revision Booklet (Structured Qn) 2024 National Junior College 5 6 (a) Condensation (Nucleophilic acyl substitution) (b) CH3CO2CH3 + CH3CH2OH → CH3CO2CH2CH3 + CH3OH (c) Methyl ethanoate should be the limiting reagent. Ethanol should be in excess so that all the methyl ethanoate can be converted. (d) More energy is required to overcome the stronger h ydrogen bond s between methanol molecules during boiling than the permane