Choose the correct set of reagents for the following conversion: Ethyl benzene 4-bromostyrene$$\text{Ethyl benzene} \longrightarrow \text{4-bromostyrene}$$ {{Q_IMG1}}

Related Formula

Nucleophilic Aromatic Substitution (SNAr$S_NAr$) occurs via a Meisenheimer complex intermediate, where strong electron-withdrawing groups (-NO₂$-\mathrm{NO}_2$) activate positions strictly ortho and para to themselves.

Core Logic

The reactant is 1,2-dibromo-4-nitrobenzene. Let us evaluate the two bromine positions relative to the nitro group:

• The bromine at C-1 is para to the strong activating -NO₂$-\mathrm{NO}_2$ group.
• The bromine at C-2 is meta to the -NO₂$-\mathrm{NO}_2$ group.

Since the para position facilitates effective negative charge delocalization onto the oxygen atoms of the nitro group during intermediate formation, the para-bromine undergoes substitution exclusively by the ethoxide ion (^-OC₂H₅$^-\mathrm{OC}_2\mathrm{H}_5$). This yields the final product shown below:

Pattern Recognition

In aromatic pathways activated by -NO₂$-\mathrm{NO}_2$, substitution happens exclusively at positions ortho or para relative to the nitro flag; meta positions remain unactivated.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Core Logic

KCN$KCN$ is predominantly ionic and provides cyanide ions (CN^-$CN^-$) in solution. Although both carbon and nitrogen are in a position to donate electron pairs, the attack takes place mainly through carbon because C-C bond is more stable than C-N bond, forming alkyl cyanides (nitriles) as major product.

However, AgCN$AgCN$ is mainly covalent in nature and nitrogen is free to donate an electron pair forming isocyanide as the main product.

Step 1: Final Conclusion

Assertion (A) is correct. Reason (R) states both are highly ionic, which is incorrect because AgCN$AgCN$ is largely covalent. Therefore, (A) is correct but (R) is not correct.

Pattern Recognition

Ambidentate nucleophile shortcut: Alkali metal cyanides (KCN$KCN$, NaCN$NaCN$) are ionic arrow$\rightarrow$ attack from Carbon arrow$\rightarrow$ Cyanide. Heavy metal cyanides (AgCN$AgCN$) are covalent arrow$\rightarrow$ attack from Nitrogen arrow$\rightarrow$ Isocyanide.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Core Logic

The structure of 2-chlorobutane is CH₃-CH(Cl)-CH₂-CH₃$CH_3-CH(Cl)-CH_2-CH_3$. There is exactly one chiral center in this molecule, which is the carbon atom at position 2 (bonded to H$H$, Cl$Cl$, CH₃$CH_3$, and CH₂CH₃$CH_2CH_3$).

For a molecule with n$n$ distinct chiral centers and no plane of symmetry, the number of optical isomers (stereoisomers) is 2ⁿ$2^n$.

Step 1: Calculate Isomers

Number of chiral centers n = 1$n = 1$. Total optical isomers = 2¹ = 2$2^1 = 2$ (one pair of enantiomers: the (R) and (S) configurations).

Pattern Recognition

1 chiral center always gives 2 optical isomers (a pair of enantiomers).

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes Class 11 Chemistry: Organic Chemistry Some Basic Principles and Techniques

Core Logic

In an SN1$\text{S}_\text{N}1$ pathway, a planar carbocation intermediate is produced. Attack by the nucleophile can take place with equal probability from either side, resulting in complete/partial racemisation. In an SN2$\text{S}_\text{N}2$ pathway, the nucleophile attacks exclusively from the backside opposite the leaving group, causing an absolute structural inversion (Walden inversion).

Pattern Recognition

SN1 arrow$S_N1 \rightarrow$ planar intermediate carbocation arrow$\rightarrow$ Racemisation. SN2 arrow$S_N2 \rightarrow$ direct backside launch arrow$\rightarrow$ Inversion.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes

Core Logic

Assertion (A): In phenols, the C-O$C-O$ bond possesses partial double bond character due to resonance (the lone pair of oxygen delocalizes into the benzene ring). Because of this strong C-O$C-O$ bond, nucleophilic substitution reactions where a halide ion would replace the hydroxyl group do not occur under normal conditions. Thus, aryl halides cannot be prepared directly from phenols by reaction with HX$HX$. The statement is True.

Reason (R): Phenols do NOT react violently with halogen acids. In fact, they practically do not react with halogen acids (HX$HX$) to form aryl halides because the C-O$C-O$ bond is difficult to break. The statement is False.

Step 1: Visualization

Given reason is false.

Step 2: Conclusion

Assertion (A) is correct but Reason (R) is false.

Chapter Mix

Class 12 Chemistry: Haloalkanes and Haloarenes Class 12 Chemistry: Alcohols Phenols and Ethers