৪৯তম বিসিএস ⎯ প্রাণ রসায়ন [৬০১]

Aldehyde produce silver mirror reacting with Tolen Reagent thus it can be differentiate between any aldehyde and ketone.

Alkanes undergo combustion, halogenation (free radical substitution), hydrogenation (at high T, Pt/Ni catalyst). Aromatization is characteristic of cycloalkanes/alkenes, not open-chain alkanes.

Reagent to distinguish between alkane and alkene: Bromine water & KMnO₄ (D)
​Alkanes do not react with bromine water in dark, while alkenes decolorize it. Alkenes also get oxidized by alkaline KMnO₄ (Baeyer’s test).

Major product of 2-butene + HBr (with peroxides): 1-Bromobutane (B)
Peroxide effect (Kharasch effect) → anti-Markovnikov addition of HBr to alkenes. So Br attaches to terminal carbon → 1-bromobutane.

Number of isomers of C₅H₁₂: 3 (B)
They are: n-pentane, isopentane (2-methylbutane), neopentane (2, 2-dimethylpropane).

Which alkyne reacts with ammoniacal AgNO₃? Propyne (A)
Only terminal alkynes give a precipitate with AgNO₃ (formation of silver acetylide). Propyne is terminal; 2-butyne & internal alkynes do not.

Lucas reagent = HCl + ZnCl₂. Tertiary alcohols react instantly, secondary moderately, primary slowly → turbidity test.

Dehydration of ethanol with conc. H₂SO₄: Ethene (B)
​Conc. H₂SO₄ acts as dehydrating agent at 170°C → ethanol → ethene.

Test positive for aldehydes, not ketones: Fehling’s test (B)
Aldehydes reduce Fehling’s solution to red Cu₂O, ketones generally do not.

Acetone + I₂/NaOH gives yellow ppt: Iodoform test (C)
Methyl ketones (–COCH₃ group) undergo iodoform reaction → yellow CHI₃ ppt.

Catalytic hydrogenation, LiAlH₄, NaBH₄ all reduce aldehydes to primary alcohols.

Solubility decreases with larger hydrophobic groups; aromatic ring reduces solubility compared to small-chain acids.

Esterification of acetic acid + ethanol + conc. H₂SO₄: Ethyl acetate (A)
Acid + alcohol (in presence of H₂SO₄) → ester + water. Here: CH3COOH + C₂H₅OH → CH₃COOC₂H₅ (ethyl acetate).

Compound with both acidic & basic character: Amide (B)
​ –CONH₂ has lone pair on N (basic) and carbonyl group (weakly acidic).

Here AlCl₃ is a neutral electrophile which has attraction for electron. 

Here option (iii) has one ring but only 2 pi electron that does not fit it into Hackle's theory of aromaticity. Other two option comply so the answer will be (A)

All three of the functions you listed are correct and interconnected. Concentrated sulfuric acid serves a dual role in the nitration of aromatic compound
**It acts as a catalyst to produce the nitro group's precursor.** Concentrated sulfuric acid is a very strong acid. It protonates nitric acid HNO₃, allowing it to lose a water molecule and generate the highly reactive electrophile, the nitronium ion. This ion is what actually attacks the benzene ring.

**It absorbs water produced in the reaction.** Nitration is a dehydration reaction. The formation of the nitronium ion and its subsequent reaction with the aromatic ring both produce water. Sulfuric acid's strong affinity for water makes it an excellent dehydrating agent, effectively removing the water from the reaction mixture.
​
**It helps to direct the forward reaction.** By absorbing the water and consuming the reactants to generate the nitronium ion, the sulfuric acid drives the equilibrium of the reaction forward, ensuring a high yield of the desired product.

Methyl Phenyl Ether (Anisole): The substituent is a methoxy group (−OCH3). The oxygen atom has lone pairs that can be donated to the ring via the resonance effect (+R). Although oxygen is electronegative and withdraws electrons via the inductive effect (-I), the resonance effect is much stronger.

Effect: +R > -I

Conclusion: The −OCH
3
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group is an activating group. Methyl phenyl ether is more reactive than benzene.

P-acetamide phenol is known as paracetamol. So option C is the correct structure

Nitroglycerin is used to prevent angina (chest pain) caused by coronary artery disease. This medicine is also used to relieve an angina attack that is already occurring.

The primary reason the amino group is a strong activator and an ortho, para-director is the resonance effect. The lone pair of electrons on the nitrogen atom can be delocalized into the benzene ring, creating a negative charge at the ortho and para positions. This increases the electron density of the ring, making it more reactive towards electrophiles and specifically directing the attack to the ortho and para positions.

This reaction is called diazotization. A primary aromatic amine (aniline) reacts with nitrous acid, which is generated in situ from sodium nitrite and hydrochloric acid, to form a highly unstable but synthetically useful diazonium salt, benzene diazonium chloride. The low temperature is crucial to prevent the decomposition of the diazonium salt.

The acidity of an alcohol or phenol is determined by the stability of its conjugate base. When phenol loses a proton, it forms the phenoxide ion. The negative charge on the oxygen atom can be delocalized into the benzene ring via resonance, stabilizing the ion and making the conjugate acid (phenol) more acidic. In contrast, the conjugate base of cyclohexanol (the cyclohexoxide ion) has no resonance stabilization.

The cumene process is the dominant industrial method for producing phenol. Cumene (isopropylbenzene) is oxidized to form cumene hydroperoxide, which is then cleaved with acid to yield phenol and acetone.

The hydroxyl group (-OH) on phenol is an extremely strong ortho, para-director. When treated with excess bromine water, it activates the ring so strongly that bromination occurs at all available ortho and para positions simultaneously, resulting in the formation of 2,4,6-tribromophenol. The product is a white precipitate.

An aromatic amine is a compound where the amino group (-NH₂) is directly attached to an aromatic ring. Aniline fits this description as it is a benzene ring bonded to an amino group. Methylamine is an aliphatic amine, cyclohexylamine is a cyclic aliphatic amine, and toluene is an aromatic hydrocarbon.

When benzene diazonium chloride is heated with water, the diazonium group is replaced by a hydroxyl group, a process known as hydrolysis. This is a common method for synthesizing phenols.

Due to resonance and the delocalization of the pi-electrons, the six carbon-carbon bonds in benzene are identical in length, lying between the length of a typical single bond and a double bond. The molecule is planar, and all bond angles are 120°, not109°

The methyl group (-CH₃) is a mild activating group and an ortho, para-director. Therefore, when toluene undergoes electrophilic aromatic substitution (sulfonation in this case), the major products will be a mixture of the ortho and para isomers. The para isomer is typically the major product due to less steric hindrance, but both are formed.

4-Chloro-3,5- dimethyl phenol is the major component of Dettol and used as antiseptic.