Principles Related to Practical Chemistry: Chemistry | JEE Main
Number of compounds giving (i) red colouration with ceric ammonium nitrate and also (ii) positive iodoform test from the following is
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Hint 1 of 3
What functional group feature is necessary to produce a red colouration with ceric ammonium nitrate (CAN)?
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Correct answer
Three compounds contain the required secondary alcohol structure containing a methyl group, CH3CH(OH)−, giving both a red coloration with ceric ammonium nitrate and a positive iodoform test.
Option analysis
Why each option works or fails
Reviewed route
Solution
StepWorking
01given
A set of organic compounds containing alcohol/carbonyl groups tested with: (i) Ceric ammonium nitrate (CAN) giving a red colouration, and (ii) Iodoform test (I2/NaOH) giving a positive yellow precipitate.
02strategise
1. CAN test: Alcohols (primary, secondary, or tertiary aliphatic/alicyclic alcohols) react with CAN to give a red complex Ce(IV) alkoxy complex. (Phenols generally give brown/black colours or precipitate, not the characteristic red coloration of alcohols).
2. Iodoform test: Requires a methyl carbonyl group (CH3C=O) or a methyl carbinol group (CH3CH(OH)−R, where R=H, alkyl, or aryl).
3. Thus, a compound meeting BOTH criteria must have an alcoholic group (for CAN test) AND specifically the CH3CH(OH)− group (for iodoform test). Carbonyl compounds with CH3C=O lack the alcoholic -OH group and fail the CAN test unless an alcohol is also present.
03execute
Screen each given structure:
1. Ethanol (CH3CH2OH): Alcoholic -OH (passes CAN) + contains CH3CH(OH)H (passes iodoform) → YES (1).
2. 2-Propanol / Isopropanol (CH3CH(OH)CH3): Secondary alcohol (passes CAN) + contains CH3CH(OH)− (passes iodoform) → YES (2).
3. 1-Phenylethanol (Ph-CH(OH)CH3): Secondary alcohol (passes CAN) + contains CH3CH(OH)Ph (passes iodoform) → YES (3).
4. Other species such as methanol, acetone, acetophenone, or tertiary alcohols either fail the iodoform test (e.g., methanol, t-butanol) or fail the CAN test (e.g., ketones like acetone/acetophenone lack the alcoholic -OH). Total count = 3.
✓verify
Total count is 3 compounds containing the secondary or primary methyl carbinol moiety CH3CH(OH)−. All three have an alcoholic -OH (CAN positive) and the oxidisable methyl carbinol group (iodoform positive).
Hints that build this answer step by step
What functional group feature is necessary to produce a red colouration with ceric ammonium nitrate (CAN)?
An alcoholic hydroxy group (−OH)
To give BOTH a positive CAN test (red colour) and a positive iodoform test, what specific structural unit must the compound possess?
CH3−CH(OH)−
Counting only the structures containing the CH3−CH(OH)− unit among the given set, what is the total number of valid compounds?
No, ceric ammonium nitrate (CAN) is a characteristic qualitative reagent for alcohols, which form a red-coloured cerate alkoxy complex. Simple carbonyl compounds like ketones do not give this red colour.
