Number of molecules from below which cannot give iodoform reaction is :
Ethanol, Isopropyl alcohol, Bromoacetone, 2-Butanol, 2-Butanone, Butanal, 2-Pentanone, 3-Pentanone, Pentanal and 3-Pentanol
Ethanol (CH₃CH₂OH$\mathrm{CH_3CH_2OH}$) arrow$\rightarrow$ Gives test (Gives CHI₃$\mathrm{CHI_3}$)
Isopropyl alcohol (CH₃CH(OH)CH₃$\mathrm{CH_3CH(OH)CH_3}$) arrow$\rightarrow$ Gives test
Bromoacetone (BrCH₂COCH₃$\mathrm{BrCH_2COCH_3}$) arrow$\rightarrow$ Gives test
2-Butanol (CH₃CH(OH)CH₂CH₃$\mathrm{CH_3CH(OH)CH_2CH_3}$) arrow$\rightarrow$ Gives test
2-Butanone (CH₃COCH₂CH₃$\mathrm{CH_3COCH_2CH_3}$) arrow$\rightarrow$ Gives test
Butanal (CH₃CH₂CH₂CHO$\mathrm{CH_3CH_2CH_2CHO}$) arrow$\rightarrow$Does NOT give test
2-Pentanone (CH₃COCH₂CH₂CH₃$\mathrm{CH_3COCH_2CH_2CH_3}$) arrow$\rightarrow$ Gives test
3-Pentanone (CH₃CH₂COCH₂CH₃$\mathrm{CH_3CH_2COCH_2CH_3}$) arrow$\rightarrow$Does NOT give test
Pentanal (CH₃CH₂CH₂CH₂CHO$\mathrm{CH_3CH_2CH_2CH_2CHO}$) arrow$\rightarrow$Does NOT give test
3-Pentanol (CH₃CH₂CH(OH)CH₂CH₃$\mathrm{CH_3CH_2CH(OH)CH_2CH_3}$) arrow$\rightarrow$Does NOT give test
Step 1: Final Count
The 4 compounds that cannot give the iodoform reaction are: Butanal, 3-Pentanone, Pentanal, and 3-Pentanol.
Pattern Recognition
Requires CH₃-CO-$\mathrm{CH_3-CO-}$ or CH₃-CH(OH)-$\mathrm{CH_3-CH(OH)-}$ group.
Aldehydes other than acetaldehyde do not give iodoform test.
Symmetrical 3-ketones and 3-alcohols fail the test.
Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
The reaction depicts the partial reduction of an acid chloride (benzoyl chloride) to an aldehyde (benzaldehyde) using hydrogen gas in the presence of a poisoned palladium catalyst (Pd supported on BaSO₄$BaSO_4$).
The image shows the catalytic hydrogenation of benzoyl chloride to benzaldehyde in the presence of Pd-BaSO4.
This specific reaction is known as the Rosenmund reduction.
Pattern Recognition
Acid Chloride + H₂, Pd/BaSO₄$H_2, Pd/BaSO_4$arrow$\rightarrow$ Aldehyde is strictly the Rosenmund reduction. The BaSO₄$BaSO_4$ poisons the catalyst to prevent over-reduction to an alcohol.
Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Pathway 1 (Upper): Toluene is treated with Reagent 'A' and acetic anhydride (CH₃CO)₂O$(CH_3CO)_2O$ to form an intermediate (benzylidene diacetate), which on hydrolysis gives benzaldehyde. The reagent used here is Chromic oxide (CrO₃$CrO_3$). Thus, A is CrO₃$CrO_3$.
Pathway 2 (Lower): Toluene is treated with Reagent 'B' in CS₂$CS_2$ to form a chromium complex intermediate, which on hydrolysis yields benzaldehyde. This is the Etard reaction, and the reagent used is Chromyl chloride (CrO₂Cl₂$CrO_2Cl_2$). Thus, B is CrO₂Cl₂$CrO_2Cl_2$.
The image shows the oxidation of toluene to benzaldehyde via two different pathways requiring reagents A and B.
Step 1: Selection
Therefore, A = CrO₃$CrO_3$ and B = CrO₂Cl₂$CrO_2Cl_2$.
Pattern Recognition
Etard reaction always uses Chromyl chloride (CrO₂Cl₂$CrO_2Cl_2$). Oxidation of toluene with acetic anhydride uses Chromic acid (CrO₃$CrO_3$). Both stop the oxidation at the aldehyde stage via intermediate formation.
Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Ethanal (CH₃CHO$CH_3CHO$) reacts with semicarbazide (H₂N-NH-CO-NH₂$H_2N-NH-CO-NH_2$) via nucleophilic addition followed by elimination of water to form a semicarbazone.
Step 1: Product Analysis
The product is Ethanal semicarbazone: CH₃-CH=N-NH-CO-NH₂$CH_3-CH=N-NH-CO-NH_2$.
Counting the nitrogen atoms in this structure:
The imine nitrogen (=N-$=N-$)
The amine nitrogen (-NH-$-NH-$)
The amide nitrogen (-NH₂$-NH_2$)
Total = 3 Nitrogen atoms.
Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
Qjee_main_2024_31_jan_eveningPreparation of Aldehydes and Ketones
Identify the name reaction.
The image shows the conversion of benzene to benzaldehyde using CO, HCl, and Anhydrous AlCl3/CuCl.
The reaction of benzene with carbon monoxide (CO$CO$) and hydrogen chloride (HCl$HCl$) in the presence of anhydrous aluminium chloride (AlCl₃$AlCl_3$) and cuprous chloride (CuCl$CuCl$) to give benzaldehyde is known as the Gatterman-Koch reaction.
The image shows the conversion of benzene to benzaldehyde using CO, HCl, and Anhydrous AlCl3/CuCl.
Pattern Recognition
CO + HCl arrow$CO + HCl \rightarrow$ Formyl chloride intermediate (in situ) with Lewis acid arrow$\rightarrow$ formylation of benzene. This is definitively the Gatterman-Koch formylation.
Chapter Mix
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
More Aldehydes, Ketones and Carboxylic Acids Questions — jee_main_2025_03_april_morning
Practice past-year questions one chapter at a time. Pick an exam → subject → chapter and get every PYQ for that topic — pulled together from all past papers — with the chapter's key formulas alongside.
