Using the values given for the relative atomic mass for each of the elements M_r = (18 x 12.01) + (26 x 1.01) + 35.45 + (3 x 14.01) + 16.00 = 335.92.

It is consistent to four significant figures (i.e. to 1 decimal place) but not to two decimal places. This is most probably because the values in the IB data booklet give no uncertainty as to the accuracy of the second decimal place figure. For example A_r for H is given elsewhere as 1.008. When this is multiplied by 18 it gives a value for M_r 0.036 lower than if the A_r of H is taken as 1.01.

Percentage of hydroxychloroquine in hydroxychloroquine sulfate = (336 ÷ 434) x 100 = 77.42%

Mass of hydroxychloroquine in 400 mg of hydroxychloroquine sulfate = (400 x 77.42) ÷ 100 = 310 mg.

The molecular formula is C₁₈H₂₆ClN₃O. Cl atoms behave as if they are H atoms, O atoms have no effect on the IHD and N atoms can be substituted for C atoms whilst at the same time adding one to the number of H atoms so the molecular formula is equivalent to C₂₁H₃₀. For it to be fully saturated with an IHD of zero (i.e. C_nH_(2n+2)) there would need to be 44 H atoms so the IHD is (44 − 30) ÷ 2 = 7.

Except for the two ring system all the bonds in the molecule are single bonds and have an IHD of zero. The two ring system contains the equivalent of five double bonds and each ring contributes one to the IHD giving a total of seven.

Alkyl, amine, hydroxyl and chloro

The only pi bonding in the molecule occurs in the two rings as all the other bonds in the hydroxychloroquine molecule are sigma bonds. All the nine carbon atoms and the nitrogen atom in the two fused rings are sp² hybridized. Each carbon atom also has one electron in a p orbital above and below the plane of the molecule. The nitrogen atom also has one electron in its p orbital (in addition to the two non-bonding electrons in one of its sp² orbitals). These ten electrons form a delocalized pi bond across all the ring atoms rather than alternate double bonds and single bonds.  Hence the bonds between the carbon atoms and between the nitrogen and carbon atoms consist of one sigma bond with bond angles of 120^o together with the delocalized pi bond.

Chiral carbon atom shown by *

In chloromethane the carbon atom is sp³ hybridized and the C−Cl bond is a normal sigma bond. In the quinoline ring in hydroxychloroquine the carbon atoms and the nitrogen atom are all sp² hybridized. A non-bonding pair of electrons in a p orbital on the chlorine atom can also combine with the electrons in the delocalized pi bond formed from the remaining p orbitals on the carbon (and nitrogen) atoms in the rings so increasing the bond strength and shortening the bond.

Because amines are basic they will react with the sulfuric acid so that the two positive charges will be located on the two nitrogen atoms in the R− chain. The secondary amine in the chain will form N⁺R₂H₂ and the tertiary amine will form N⁺R₃H. Although the non-bonding pair of electrons on the nitrogen atom in the quinoline group is in an sp² orbital and does not contribute to the delocalised pi bond, quinoline is a weaker base than secondary and tertiary amines so does not act as a Lewis base in this reaction. In fact the pK_b values for secondary and tertiary amines lie in the region of 3 to 4 whereas the pK_b value for quinoline is 9.1 so it is a considerably weaker base (data from D.R. Lide (Ed.), CRC Handbook of Physics and Chemistry, 88th Ed, 2007). This is often explained by stating that a non-bonding pair of electrons in an sp² hybridized orbital are closer to the N nucleus (so less attractive to a proton) than if they are in an sp³ hybridized orbital as the percentage of s orbital in the hybridization is greater.

5-chloro-2-pentanone (since the IB only requires you to be able to name compounds containing just one functional group other acceptable answers are 5-chloro-pentan-2-one, 1-chloro-4-pentanone and 1-chloropentan-4-one).

Nucleophilic substitution. This is covered in 10.2 on the IB syllabus although the only nucleophile referred to there is the hydroxide ion. Ammonia and amines also possess a non-bonding pair of electrons so are good nucleophiles. Because the chlorine atom is on the end carbon atom the mechanism is likely to be S_N2 as it is a primary halogenoalkane.

(a) The hydrogen is acting as a reducing agent (or hydrogenating agent) and (b) the solid nickel is acting as a heterogeneous catalyst.

This is another example of a nucleophilic substitution reaction.  The nucleophile is a primary amine whereas in Step 1 the nucleophile is a secondary amine.

4,5-dichloroquinoline. The numbering system starts from the N atom. From the given structure of 4,7-dichloroquinoline it can be seen that although there are a total of nine carbon atoms in the two rings, the two C atoms where the rings join are saturated with other carbon atoms and cannot bond to any other atoms without destroying the delocalization of the ring so do not count in the numbering system.