Chapter 1

Compare the hybridisation of the central carbon atoms in carbon dioxide \(\left(\mathrm{CO}_{2}\right)\) and allene \(\left(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}\right) .\) Which statement is correct? (a) The hybridisation types of these two carbons cannot be compared because of large electronegativity difference between carbon and oxygen in \(\mathrm{CO}_{2}\), that does not exist in allene. (b) The hybridisation of carbon in \(\mathrm{CO}_{2}\) cannot be determined, because the lone electron pairs on oxygen do not allow for angle measurements that are necessary to determine the hybridisation involved. (c) \(\operatorname{In} \mathrm{CO}_{2}\) the carbon is sp \(^{2}\) hybridised, but in allene the central carbon is sp hybridised. (d) In \(\mathrm{CO}_{2}\) the carbon is sp hybridised but in allene the central carbon is sp hybridised.

Choose the correct formula for epinephrine.

In allene \(\left(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}\right)\), the terminal carbons are sp \(^{2}\) hybridised. Each of the two terminal \(\mathrm{H}_{2} \mathrm{C}\) groups are situated in such a manner that the two "terminal" planes are \(90^{\circ}\) from each other. Other compounds with double bonds on successive carbons may also exist. They are called cumulenes. What is the relationship between the two terminal \(\mathrm{H}_{2} \mathrm{C}\) groups in a cumulene containing three consecutive double bonds \(\left(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}\right)\) ? (a) They are in perpendicular planes. (b) They are in two planes \(60^{\circ}\) from each other. (c) They are in the same plane. (d) They are in two planes \(120^{\circ}\) from each other.

Alkyne hydrogens are more acidic than alkene or alkane hydrogens because (a) The alkyne carbon has higher 's' character. (b) The anion formed is more stable. (c) The electrons in the sp orbital are closer to the nucleus. (d) All of the above.

The relative yield of the following alkenes produced by the reaction of trans-1-chloro-2methylcyclohexane with KOH/heat is (i) 1-methylcyclohexene (ii) methylenecyclohexane (iii) 3-methylcyclohexene (a) \(\mathrm{i}>\mathrm{ii}>\mathrm{iii}\) (b) \(\mathrm{ii}>\mathrm{iii}>\mathrm{i}\) (c) \(\mathrm{i}>\mathrm{iii}>\mathrm{ii}\) (d) \(\mathrm{iii}>\mathrm{i}>\mathrm{ii}\)

Imidazole has a \(\mathrm{pKa}=7\) with respect to its conjugate acid. Which \(\mathrm{N}\) is protonated in this conjugate acid and why? (a) N1 because imidazole is an aromatic heterocycle where \(n=1\) as per Huckel's rule. (b) N1 is protonated because it is \(\mathrm{sp}^{3}\) hybridised. (c) \(\mathrm{N} 3\) is protonated because it is \(\mathrm{sp}^{2}\) hybridised. (d) N1 is protonated because the lone pair is part of the aromatic pi system.

Cyclopentadiene has a \(\mathrm{pKa}=15\), whereas cyclopentane has a \(\mathrm{pKa}>50 .\) This is because (a) Cyclopentadiene is particularly unstable. (b) Cyclopentane contains no lone pairs. (c) Cyclopentadiene is a \(4 \pi\) anti-aromatic compound. (d) Cyclopentadiene is a \(4 \pi\) non-aromatic compound and after deprotonation it is aromatic.

The \(\alpha\) -hydrogens of esters typically have a \(\mathrm{pKa}=25\), whereas for ketones \(\mathrm{pKa}=20 .\) This is because: (a) There is no resonance stabilisation of the enolates of esters. (b) The inductive effect of the oxygen in the ester destabilises the ester enolate. (c) The electron donating alkoxy group in esters destabilises the enolate. (d) The electron donating alkoxy group in esters stabilises the enolate.

Rank, from the most stabilised to the least stabilised, the following free radicals according to their stabilisation energies. (i) \(\mathrm{CH}_{3} \mathrm{CH}_{2}\) (ii) \(\dot{\mathrm{C}} \mathrm{H}_{2} \mathrm{CH}_{3}\) (iii) \(\left(\mathrm{CH}_{3}\right)_{2} \dot{\mathrm{C}} \mathrm{H}\) (iv) \(\left(\mathrm{CH}_{2}=\mathrm{CH}-\dot{\mathrm{C}} \mathrm{H}_{2}\right)\) (a) \(\mathrm{iv}>\mathrm{iii}>\mathrm{ii}>\mathrm{i}\) (b) \(\mathrm{i}>\mathrm{iv}>\mathrm{iii}>\mathrm{ii}\) (c) \(\mathrm{iii}>\mathrm{iv}>\mathrm{i}>\mathrm{ii}\) (d) iii \(>\mathrm{iv}>\mathrm{ii}>\mathrm{i}\)

Arrange the following compounds in order of their acidity. (most to least) (i) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ii) \(\mathrm{CFH}_{2} \mathrm{CO}_{2} \mathrm{H}\) (iii) \(\mathrm{CF}_{2} \mathrm{HCO}_{2} \mathrm{H}\) (iv) \(\mathrm{CF}_{3}^{3} \mathrm{COOH}\) (v) \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) (a) \(\mathrm{iv}>\mathrm{iii}>\mathrm{ii}>\mathrm{v}>\mathrm{i}\) (b) \(\mathrm{iv}>\mathrm{iii}>\mathrm{ii}>\mathrm{i}>\mathrm{v}\) (c) \(v>\mathrm{ii}>\mathrm{iii}>\mathrm{iv}>\mathrm{i}\) (d) \(\mathrm{v}>\mathrm{iii}>\mathrm{iv}>\mathrm{ii}>\mathrm{i}\)

Which of the following compound has the highest boiling point? (a) \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (d) \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\)

What is the Lewis structure of \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CHO} ?\)

Which is the electronic configuration that describes \(\mathrm{Na}^{+}\) ? (a) \(1 S^{2}, 2 S^{2}, 2 P^{6}\) (b) \(1 S^{2}, 2 S^{2}, 2 P^{6}, 3 S^{2}, 3 P^{6}\) (c) \(1 S^{2}, 2 S^{2}\) (d) \(1 S^{2}, 2 S^{2}, 2 P^{6}, 3 S^{2}\)

Which molecules are non-polar? (i) \(\mathrm{NH}_{3}\) (ii) \(\mathrm{CO}_{2}\) (iii) \(\mathrm{H}_{2} \mathrm{O}\) (iv) \(\mathrm{CF}_{4}\) (v) \(\mathrm{Br}_{2}\) (vi) \(\mathrm{BF}_{3}\) (vii) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (viii) \(\mathrm{H}_{2} \mathrm{O}_{2}\) (a) \(\mathrm{ii}, \mathrm{iv}, \mathrm{v}, \mathrm{vi}\) (b) \(\mathrm{i}, \mathrm{iv}, \mathrm{vi}\), viii (c) iii, \(\mathrm{iv}, \mathrm{v}, \mathrm{vi}\) (d) i, iii, vii, viii

Hyperconjugation is best described as: (a) delocalisation of \(\mathrm{p}\) electrons into a nearby empty orbital (b) delocalisation of \(\sigma\) electrons into a nearby empty orbital (c) the effect of alkyl groups donating a small amount of electron density inductively into a carbocation (d) the migration of a carbon or hydrogen from one carbocation to another

Which of the following statements best explains why 1-propyne can be deprotonated by the ethyl anion \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}^{-}\right) ?\) (a) The acetylide anion is a stronger base than the ethyl anion. (b) Ethane has a lower \(\mathrm{pK}\), than acetylene. (c) The lone-pair orbitals in acetylide anions have more s character than those in alkyl anions. (d) The acetylide anion is a weaker base than an alkyl anion.

Which of the following statements is NOT true for ethylene \(\left(\mathrm{CH}_{2}=\mathrm{CH}_{2}\right)\) molecule? (a) Both carbons are sp \(^{2}\) hybridised. (b) \(\mathrm{C}=\mathrm{C}\) bond length is shorter than the \(\mathrm{C}-\mathrm{C}\) bond length in ethane. (c) The two \(C=C\) bonds are equally strong. (one is pi and the other is sigma.) (d) The entire molecule has a planar geometry.

The nitrogen in trimethylamine is (a) \(\mathrm{sp}^{2}\) hybridised (b) \(\mathrm{sp}^{3}\) hybridised (c) sp hybridised (d) \(\mathrm{sp}^{3} \mathrm{~d}^{2}\) hybridised

Which of the following statements about resonance structures is false? (a) Individual resonance structures are imaginary, not real. (b) Resonance forms differ only in the placement of their \(\pi\) - or non- bonding electrons or unpaired electron. (c) Different resonance structures of a substance do not have to be equivalent. (d) In valid resonance structures, all atoms from the second row of the periodic table must have an octet of electrons.

\(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{NH}_{2} \frac{\mathrm{NaNO}_{2}}{\mathrm{HCl}} \rightarrow[\mathrm{P}] ;\) Products of the reaction are: (a) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{OH}\) (b) Et-Cl (c) \(\mathrm{Et}-\mathrm{C}-\mathrm{H}\) (d) \(\mathrm{Et}-\mathrm{ONO}\)

Which of the following alkane can not be synthesised by Wurtz reaction in good yield? (a) \(\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}-\left(\mathrm{CH}_{3}\right)_{2}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}-\left(\mathrm{CH}_{3}\right)_{2}\) (c) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Test for identification of But-2-ene and benzene is (a) Tollen's Reagent test (b) \(1 \%\) Alkaline \(\mathrm{KMnO}_{2}\) (c) Iodoform test (d) \(\mathrm{Br}_{2}+\mathrm{H}_{2} \mathrm{O}\) test

Which of the following is most acidic in character? (a) o-nitrobenzoic acid (b) \(\mathrm{p}\) -nitrobenzoic acid (c) m-nitrobenzoic acid (d) Benzoic acid

Arrange acidity of the given compounds increasing order (i) p-nitrophenol (ii) \(\mathrm{p}\) -fluorophenol (iii) \(\mathrm{p}\) -chlorophenol (a) (i), (ii), (iii) (b) (ii), (i), (iii) (c) (ii), (iii), (i) (d) (iii), (ii), (i)

Which of the following statements are correct for \(\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CCl}_{3} ?\) (a) \(\mathrm{CCl}_{3}\) group is electron withdrawing due to the -I effect and reverse hyperconjugation. (b) \(\mathrm{CCl}_{3}\) group is meta directing due to the \(-\mathrm{M}\) effect. (c) \(\mathrm{CCl}_{3}\) group is o, p-directing because it is \(+\mathrm{R}\) group. (d) \(\mathrm{CCl}_{3}\) group can exert \(+\mathrm{M}\) effect.