Animated Solution for Chemistry - Chemistry in Everyday Life: The antifertility drug "Novestrol" can react with

When tackling questions involving complex pharmaceutical molecules like Novestrol (also known as ethinylestradiol), the first and most crucial step is to perform a thorough structural analysis. Novestrol is a widely used oral contraceptive, but for a chemistry student, it is a playground of functional groups.

To determine which reagents this molecule will react with, we must systematically scan its steroid skeleton and identify every reactive site. Let's break down the molecule ring by ring and see what chemical secrets it holds.

A Hub of Activity

Starting at the bottom left of the molecule, we encounter the A-ring. Notice that this is a fully aromatic benzene ring, and attached directly to it is a hydroxyl ($-OH$) group. This specific arrangement forms a phenol.

Phenols are highly reactive species. The oxygen atom donates electron density into the aromatic ring via resonance, strongly activating it towards electrophilic aromatic substitution. If we treat this molecule with bromine water (${\text{Br}}_2/{\text{H}}_2\text{O}$), the activated ring will rapidly undergo polybromination, yielding a characteristic white precipitate (similar to the formation of 2,4,6-tribromophenol).

Furthermore, phenols have a classic qualitative test: they form a distinct, intensely colored violet complex when mixed with neutral ferric chloride (${\text{FeCl}}_3$). Therefore, we can confidently say that Novestrol will give positive results for both ${\text{Br}}_2/\text{water}$ and ${\text{FeCl}}_3$.

The Lucas Test

Now, let's shift our focus to the top right of the molecule, specifically the five-membered D-ring. Here, we find another hydroxyl group. However, unlike the phenolic $-OH$, this one is attached to a saturated carbon atom.

If we look closely at that specific carbon, we see it is bonded to three other carbon atoms. This classifies the functional group as a tertiary ($3^{\circ }$) alcohol. How do we chemically distinguish a tertiary alcohol? We use the Lucas reagent, which is a mixture of anhydrous zinc chloride (${\text{ZnCl}}_2$) and concentrated hydrochloric acid ($\text{HCl}$).

Tertiary alcohols react almost instantaneously with the Lucas reagent via an $S_{N}1$ mechanism. The highly stable tertiary carbocation intermediate quickly captures a chloride ion to form an insoluble alkyl chloride, which manifests as immediate turbidity (cloudiness) in the test tube. Thus, Novestrol will also react positively with ${\text{ZnCl}}_2/\text{HCl}$.

A Bonus Functional Group

Before we conclude, it is vital to scan the entire molecule to ensure we haven't missed anything. Right next to the tertiary alcohol on the D-ring, there is a terminal alkyne group ($-C\equiv CH$).

Terminal alkynes possess a weakly acidic hydrogen atom. While it doesn't react with the reagents listed in our correct option, it is important to remember that it would react with Tollens' reagent or ammoniacal cuprous chloride (${\text{Cu}}_2{\text{Cl}}_2$) to form characteristic precipitates. Always keep an eye out for these hidden traps in JEE questions!

By dissecting the structure of Novestrol, we identified a phenolic $-OH$ and a $3^{\circ }$ alcohol. The phenol reacts with ${\text{Br}}_2/\text{water}$ and ${\text{FeCl}}_3$, while the $3^{\circ }$ alcohol reacts immediately with the Lucas reagent (${\text{ZnCl}}_2/\text{HCl}$).

Matching these findings with the given choices, we find that option (b) perfectly lists this exact combination of reagents.