Q.(a)

(a) Lucas test distinguishes 1°/2°/3° alcohols by how fast they turn turbid, and anisole is nitrated mainly at the ortho and para positions. (b) Formic acid shows aldehyde-like reducing behaviour, and aniline undergoes the carbylamine reaction with chloroform and alcoholic KOH.

(a)(i) Lucas test: Lucas reagent is a mixture of concentrated HCl and anhydrous $ZnCl_2$ (which acts as a Lewis-acid catalyst). The alcohol reacts to form the corresponding alkyl chloride (insoluble in the aqueous reagent, so the solution turns cloudy/turbid) via an $S_N1$ mechanism through a carbocation intermediate:

$ROH + HCl \xrightarrow{ZnCl_2} RCl + H_2O$

The rate of this reaction - and hence how quickly turbidity appears - depends on how stable the intermediate carbocation is, which follows $3^{\circ}>2^{\circ}>1^{\circ}$:

• Tertiary (3°) alcohol: turbidity appears immediately (within about a minute), at room temperature, since a $3^{\circ}$ carbocation forms readily.
• Secondary (2°) alcohol: turbidity appears after about 5-10 minutes at room temperature (sometimes needs gentle warming).
• Primary (1°) alcohol: shows no turbidity at room temperature; turbidity appears only on heating, since a $1^{\circ}$ carbocation is highly unstable and the reaction proceeds very slowly.

(a)(ii) Nitration of anisole: The methoxy group ($-OCH_3$) of anisole donates its oxygen lone pair into the aromatic ring by resonance, strongly activating the ring and directing incoming electrophiles to the ortho and para positions. Nitrating anisole with conc. $HNO_3$/conc. $H_2SO_4$ (which generates the electrophile $NO_2^+$) therefore gives mainly a mixture of ortho-nitroanisole and para-nitroanisole (the para isomer usually predominates), with only a negligible amount of the meta isomer:

$C_6H_5OCH_3 + HNO_3 \xrightarrow{Conc.\,H_2SO_4} o\text{-}O_2NC_6H_4OCH_3 + p\text{-}O_2NC_6H_4OCH_3$

(b)(i) Reducing property of formic acid: Formic acid, $HCOOH$, is structurally unusual among carboxylic acids because the carboxyl carbon is directly bonded to a hydrogen atom (i.e. it can be written as $H-COOH$, resembling both a carboxylic acid and an aldehyde). This aldehyde-like $-CHO$ character gives formic acid genuine reducing properties, unlike other carboxylic acids:

• It reduces Tollens' reagent (ammoniacal $AgNO_3$) to metallic silver (silver mirror test): $HCOOH + 2[Ag(NH_3)_2]^+ + 2OH^- \rightarrow 2Ag\downarrow + CO_2 + 2H_2O + 4NH_3$
• It reduces Fehling's solution ($Cu^{2+}$ complex) to a brick-red precipitate of cuprous oxide, $Cu_2O$. …