Organic Chemistry: Some Basic Principles and Techniques

A methyl group adjacent to a carbocation donates electron density via hyperconjugation (overlap of σ–C–H orbitals with the vacant p orbital) and

+ Inductive effect. This stabilizes the positively charged center.

Statement-1 is correct: In partition chromatography, the stationary phase is a thin film of liquid on a solid support.

Statement-2 is incorrect: Paper chromatography is a type of partition chromatography where water trapped in cellulose fibers acts as the stationary phase.

Thus, the correct answer is Option A.

Correct Option: A – Resonance effect

The resonance effect arises when there is a π bond (double bond) and a lone pair of electrons on an adjacent atom. This allows delocalization of electrons through overlapping p-orbitals, creating multiple contributing structures (resonating structures) for a molecule.

In phenol, the lone pair on oxygen interacts with the π electrons of the benzene ring, resulting in resonance.

So, the interaction between a π bond and a lone pair on an adjacent atom is characteristic of the resonance effect.

Lassaigne's test is a method used to detect the presence of halogens, nitrogen, sulfur, and phosphorus in organic compounds. The organic compound is fused with sodium metal, converting the elements into their ionic forms (sodium salts) which can then be easily detected by subsequent tests.

The most stable carbocation forms from (Ph)₃C–Br (Option A). This is because the triphenylmethyl carbocation (Ph)₃C⁺ is highly stabilized by resonance. The three phenyl groups delocalize the positive charge, making it significantly more stable than the benzyl (C₆H₅CH₂⁺) or alkyl-substituted benzyl carbocations.

• Benzoic acid (C₆H₅COOH) is acidic → it reacts with NaOH to form sodium benzoate (C₆H₅COO⁻ Na⁺), an ionic, water-soluble salt → it moves to the aqueous layer.

• Aniline (C₆H₅NH₂) is basic; in basic NaOH it is not protonated (no salt formation), so it remains neutral and organic-soluble → stays in the ethyl acetate (organic) layer.

• Chlorobenzene is neutral and nonpolar → stays in the organic layer.

Statement-1 is correct: In partition chromatography, the stationary phase is a thin film of liquid on a solid support.

Statement-2 is incorrect: Paper chromatography is a type of partition chromatography where water trapped in cellulose fibers acts as the stationary phase.

Thus, the correct answer is Option A.

The resonance effect (also called mesomeric effect) arises due to the interaction between a π bond and a lone pair of electrons (or another π bond) on an adjacent atom. This interaction allows electrons to be delocalized, creating multiple contributing structures (resonance structures) that help stabilize the molecule.

• In phenol, the lone pair on the oxygen interacts with the π electrons of the benzene ring.

• In carboxylate ion (COO⁻), the lone pair on one oxygen is delocalized through resonance with the C=O π bond.

The stability of carbocation depends upon the +I effect ,+M effect , hyperconjugation, and resonance effect . The cyclotropylium carbocation is the most stable among all due to the presence of aromaticity.

$$\begin{gathered} {\mathrm{PH}}_3{\mathrm{C}}^{+} \mathrm{is} \mathrm{more} \mathrm{stable} \mathrm{than} {\mathrm{Ph}}_2{\mathrm{CH}}^{+}\mathrm{due} \mathrm{to} \mathrm{more} \mathrm{number} \mathrm{of} \mathrm{resonating} \mathrm{structure} \\ {\mathrm{CH}}_3{\mathrm{CH}}_2{{\mathrm{CH}}_2}^{+}{\mathrm{CH}}_3 \mathrm{is} \mathrm{least} \mathrm{stable} \mathrm{becuse} \mathrm{it} \mathrm{is} \mathrm{stablised} \mathrm{by} +\mathrm{I} \mathrm{effect} \mathrm{and} \mathrm{hyperconjugation} , \mathrm{which} \mathrm{is} \mathrm{less} \mathrm{dominating} \mathrm{than} +\mathrm{M} \mathrm{effect} \end{gathered}$$

In paper chromatography, a special quality paper known as chromatography paper is used. Chromatography paper contains water trapped in it, which acts as the stationary phase

The correct IUPAC name of the given compound is 4-methoxycarboxy-2-methylpentanoic acid.

Lassaigne extract is made with sodium metal, and not with magnesium metal.

In Kjeldahl’s method, CuSO₄ is added as a catalyst. It speeds up the digestion of the organic compound so that nitrogen is completely converted into ammonium sulphate.

Species having atom containing lone pair available for donation can act as nucleophile.

$\mathrm{Ph}-\mathrm{SH}, {\mathrm{OH}}^{-}, {\mathrm{CH}}_2={\mathrm{CH}}_2, {\left({\mathrm{CH}}_3\right)}_2\mathrm{C}=\mathrm{N}-{\mathrm{CH}}_3 , {\mathrm{CH}}_3{\mathrm{COCH}}_3, {\mathrm{CH}}_3-\mathrm{S}-{\mathrm{CH}}_3$

The correct order of acidity of given compounds

2,4 -Dinitrophenol (iii) > 4-Nitrophenol (ii)> Phenol (iv) > n-Butanol (i)

The sodium fusion extract of organic compound having N & S gives blood red colour with ${\mathrm{FeSO}}_4 \mathrm{and} {\mathrm{Na}}_4\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]$.

The Lassaigne's Test is a general method for detecting halogens, nitrogen, and sulphur in organic compounds. The organic substances are covalently bound to these elements. These must be transformed into their ionic forms to be detected.

The technique used for the purification of solid substances based on the principle of changing directly from solid to vapor state without passing through the liquid state is called Sublimation.

Species having atom containing lone pair available for donation can act as nucleophile.

$\mathrm{Ph}-\mathrm{SH}, {\mathrm{OH}}^{-}, {\mathrm{CH}}_2={\mathrm{CH}}_2, {\left({\mathrm{CH}}_3\right)}_2\mathrm{C}=\mathrm{N}-{\mathrm{CH}}_3 , {\mathrm{CH}}_3{\mathrm{COCH}}_3, {\mathrm{CH}}_3-\mathrm{S}-{\mathrm{CH}}_3$

The stability of carbocation depends upon the +I effect ,+M effect , hyperconjugation, and resonance effect . The cyclotropylium carbocation is the most stable among all due to the presence of aromaticity.

$$\begin{gathered} {\mathrm{PH}}_3{\mathrm{C}}^{+} \mathrm{is} \mathrm{more} \mathrm{stable} \mathrm{than} {\mathrm{Ph}}_2{\mathrm{CH}}^{+}\mathrm{due} \mathrm{to} \mathrm{more} \mathrm{number} \mathrm{of} \mathrm{resonating} \mathrm{structure} \\ {\mathrm{CH}}_3{\mathrm{CH}}_2{{\mathrm{CH}}_2}^{+}{\mathrm{CH}}_3 \mathrm{is} \mathrm{least} \mathrm{stable} \mathrm{becuse} \mathrm{it} \mathrm{is} \mathrm{stablised} \mathrm{by} +\mathrm{I} \mathrm{effect} \mathrm{and} \mathrm{hyperconjugation} , \mathrm{which} \mathrm{is} \mathrm{less} \mathrm{dominating} \mathrm{than} +\mathrm{M} \mathrm{effect} \end{gathered}$$

The correct IUPAC name of the given compound is 4-methoxycarboxy-2-methylpentanoic acid.

Lassaigne extract is made with sodium metal, and not with magnesium metal.

D. Resonance effect

The resonance effect (also called mesomeric effect) arises due to the interaction between a π bond and a lone pair of electrons (or another π bond) on an adjacent atom. This interaction allows electrons to be delocalized, creating multiple contributing structures (resonance structures) that help stabilize the molecule.

• In phenol, the lone pair on the oxygen interacts with the π electrons of the benzene ring.

• In carboxylate ion (COO⁻), the lone pair on one oxygen is delocalized through resonance with the C=O π bond.

Dumas method is a classical method used for the quantitative estimation of nitrogen in organic compounds. In the Dumas method, nitrogen gas $\left(N_2\right)$ is directly liberated and measured, while in the Kjeldahl method, nitrogen is converted into ammonium sulphate.

Sublimation is the transition of a substance from a solid directly to a gas without passing through the liquid phase. Upon cooling, the vapour condenses back into a solid. This is seen in the transformation from solid (X) to vapour and then back to solid (X) on cooling.

$q_p=n{C}_p\Delta T$

$500=0.5\times \frac{5}{2}\times 8.3\times \left(T_f-298\right)$

Solve for $T_f$ :

$T_f=348.2K \simeq 348 K$

Since $\frac{\Delta H}{\Delta U}=\frac{5}{3}$, the internal energy change is:

$\Delta U=\frac{3}{5}\times 500=300J$

The correct order of acidity of given compounds

2,4 -Dinitrophenol (iii) > 4-Nitrophenol (ii)> Phenol (iv) > n-Butanol (i)