NJC 2026 Organic Chemistry Revision Booklet (MCQ)_Worked Solutions v2

Organic Chemistry Revision Booklet (MCQ) 2026 National Junior College 1 Worked Solutions for Organic Chemistry Revision (MCQ) Answer Key: 1 D 28 A 55 A 82 B 109 B 136 A 163 D 2 D 29 C 56 C 83 A 110 A 137 D 164 B 3 A 30 B 57 C 84 A 111 D 138 C 165 D 4 C 31 B 58 C 85 B 112 C 139 D 166 A 5 C 32 D 59 B 86 A 113 B 140 A 167 A 6 B 33 C 60 B 87 A 114 B 141 D 168 B 7 C 34 B 61 C 88 D 115 D 142 C 169 B 8 C 35 B 62 D 89 D 116 B 143 C 170 D 9 C 36 B 63 C 90 A 117 B 144 D 10 C 37 C 64 D 91 C 118 C 145 A 11 B 38 A 65 D 92 C 119 B 146 C 12 D 39 B 66 C 93 C 120 B 147 D 13 A 40 C 67 C 94 B 121 D 148 D 14 C 41 C 68 C 95 D 122 A 149 D 15 C 42 D 69 B 96 B 123 B 150 A 16 B 43 C 70 D 97 D 124 D 151 D 17 D 44 D 71 C 98 D 125 D 152 A 18 C 45 C 72 A 99 C 126 A 153 A 19 D 46 A 73 D 100 A 127 D 154 A 20 A 47 B 74 B 101 B 128 B 155 B 21 C 48 A 75 B 102 A 129 A 156 C 22 C 49 A 76 A 103 D 130 D 157 B 23 C 50 B 77 D 104 D 131 D 158 A 24 C 51 D 78 C 105 A 132 C 159 D 25 D 52 D 79 C 106 B 133 B 160 B 26 B 53 A 80 D 107 A 134 C 161 B 27 C 54 D 81 C 108 B 135 C 162 B

Organic Chemistry Revision Booklet (MCQ) 2026 National Junior College 2 General properties of organic compounds 1. D Structure Implication on Reactivity Benzene consists of delocalised π electrons above and below the plane. Susceptible to attack by electrophiles The ring of delocalised π electrons gives benzene additional aromatic stability. Reaction that destroys the aromatic ring requires an additional input of energy and is thus unfavourable. ● As such, even though benzene is highly unsaturated, it does not undergo addition reactions. ● Instead, benzene mostly undergoes substitution reactions. 2. D Option A: A catalyst is used to generate strong electrophile E+. (e.g. AlCl3 + Cl2 → AlCl4− + Cl+ conc HNO3 + conc H2SO4 → NO2+ + HSO4− + H2O) Option B: The carbon atom that forms a bond with the incoming E+ becomes sp3 hybridised. Option C: There is a loss of H hence the relative molecular mass of the organic product is 34.5 greater than that of benzene. Option D: During the rate -determining step (SLOW STEP), two of the six π electrons are used to form a dative bond with E +. This leaves four π electrons delocalized over the remaining five carbon atoms in the positively-charged arenium carbocation intermediate. 3. A Both butanal and pentane are simple covalent molecules. Both have instantaneous dipole - induced dipole interactions between molecules and Butanal, being polar, has additional permanent dipole- dipole interactions due to the net dipole moment in (C=O). More energy is thus required to overcome the stronger intermolecular forces in butanal resulting in higher boiling point. *Only intermolecular forces of at