Explain the following observations: (1) The ortho-para ratio of the products obtained by sulfonation of toluene is lower than that of nitration; (2) The ortho-para ratio of the products obtained by nitration of isopropylbenzene is lower than that of nitration of toluene.

First, let's discuss the two reactions: sulfonation and nitration. Sulfonation of an aromatic compound involves the reaction of the compound with sulfuric acid (\(H_2SO_4\)), leading to the substitution of a hydrogen atom with a sulfonate group (-SO3H). Nitration involves the reaction of an aromatic compound with a mixture of concentrated nitric acid (\(HNO_3\)) and sulfuric acid (\(H_2SO_4\)) to substitute a hydrogen atom with a nitro group (-NO2). Both sulfonation and nitration reactions follow the mechanism of electrophilic aromatic substitution (EAS). However, the reaction rates of these two processes are different, with sulfonation being slower than nitration. This is because the sulfonating electrophile (\(HSO_3^{+}\)) is less powerful and more sterically demanding compared to the nitrating electrophile (\(NO_2^{+}\)). Now, let's consider the effect of the methyl group in toluene. The methyl group is an activating group in EAS reactions, making the ortho- and para- positions more reactive relative to the meta- position. Activating groups can stabilize the intermediate arenium ion via hyperconjugation. In the case of sulfonation, the large, bulky sulfonate group has a higher steric hindrance than the nitro group, which results in a lower o/p ratio compared to nitration. In essence, the greater steric hindrance prevents the sulfonate group from preferentially attaching to ortho- and para- positions.

Now, let's compare the nitration of isopropylbenzene with that of toluene. Both toluene and isopropylbenzene have activating alkyl groups (methyl and isopropyl, respectively) that increase the reactivity of the ortho- and para- positions. However, the isopropyl group in isopropylbenzene is bulkier than the methyl group in toluene. The larger size of the isopropyl group can lead to greater steric hindrance in the ortho- and para- positions of isopropylbenzene, making it more difficult for the electrophile (\(NO_2^{+}\)) to react with these positions compared to the ortho- and para- positions in toluene. This results in a lower o/p ratio for the nitration of isopropylbenzene compared to that of toluene. In conclusion, the observed differences in the ortho-para ratios of the products obtained from the sulfonation and nitration of toluene and isopropylbenzene can be attributed to the steric hindrance and relative reactivity of the electrophiles involved in these reactions.