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Arrange the following in the order of th...

Arrange the following in the order of their incresing reactivity towards HCN:
`CH_(3)CHO, CH_(3)COCH_(3), HCHO, C_(2)H_(5)COCH_(3)`

A

`CH_(3)CHOgtCH_(3)COCH_(3)gtC_(2)H_(5)COCH_(3)`

B

`C_(2)H_(5)COCH_(3)gtCH_(3)COCH_(3)gtCH_(3)CHO`

C

`CH_(3)COCH_(3)gtCH_(3)CHOgtC_(2)H_(5)COCH_(3)`

D

`CH_(3)COCH_(3)gtC_(2)H_(5)COCH_(3)gtCH_(3)CHO`

Text Solution

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The correct Answer is:
To arrange the following compounds in order of their increasing reactivity towards HCN (Hydrogen Cyanide), we need to consider the electrophilic nature of the carbonyl carbon in each compound. The reactivity towards HCN is influenced by the electron-donating or electron-withdrawing effects of the substituents attached to the carbonyl group. The compounds given are: 1. CH₃CHO (Acetaldehyde) 2. CH₃COCH₃ (Acetone) 3. HCHO (Formaldehyde) 4. C₂H₅COCH₃ (Butan-2-one) ### Step-by-Step Solution: 1. **Identify the Electrophilic Carbon**: In all these compounds, the carbonyl carbon (C=O) is the site of nucleophilic attack by HCN. The more electrophilic this carbon is, the more reactive the compound will be towards HCN. 2. **Analyze Electron-Donating and Electron-Withdrawing Effects**: - **CH₃CHO (Acetaldehyde)**: The carbonyl carbon is bonded to a methyl group (CH₃), which is an electron-donating group. This reduces the electrophilicity of the carbonyl carbon but not significantly. - **CH₃COCH₃ (Acetone)**: The carbonyl carbon is bonded to two methyl groups. The electron-donating effect is stronger here than in acetaldehyde, making it less electrophilic and thus less reactive towards HCN. - **HCHO (Formaldehyde)**: The carbonyl carbon is bonded to two hydrogens. There are no electron-donating groups, making it more electrophilic and more reactive towards HCN compared to acetaldehyde and acetone. - **C₂H₅COCH₃ (Butan-2-one)**: The carbonyl carbon is bonded to an ethyl group and a methyl group. The ethyl group is larger and has a stronger electron-donating effect than the methyl group, making it less reactive than formaldehyde and acetaldehyde. 3. **Order of Reactivity**: Based on the analysis: - HCHO (most reactive) - CH₃CHO (less reactive than HCHO) - C₂H₅COCH₃ (less reactive than CH₃CHO) - CH₃COCH₃ (least reactive) ### Final Arrangement: The increasing order of reactivity towards HCN is: **CH₃COCH₃ < C₂H₅COCH₃ < CH₃CHO < HCHO**
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