10.
Which of the following compounds does not undergo ozonolysis reaction?
a. 3-methyl-1-butene
b. 2,3-dimethyl-butane
c. 2-methyl-2-butene
d. 2-methyl-1-butene
Answer: b. 2,3-dimethyl-butane
Ozonolysis cleaves carbon-carbon double bonds in alkenes to form carbonyl compounds like aldehydes and ketones. Only compounds with C=C bonds undergo this reaction; alkanes with only single bonds do not react.
Option Analysis
a. 3-methyl-1-butene (CH₂=CH-CH(CH₃)CH₃)
This terminal alkene has a double bond between C1 and C2. Ozonolysis yields formaldehyde (HCHO) and 3-methylpropanal ((CH₃)₂CHCHO).
b. 2,3-dimethyl-butane (CH₃CH(CH₃)CH(CH₃)CH₃)
This branched alkane contains only C-C single bonds, lacking a double bond. It does not undergo ozonolysis.
c. 2-methyl-2-butene (CH₃C(CH₃)=CHCH₃)
This internal alkene has a trisubstituted double bond between C2 and C3. Ozonolysis produces acetone (CH₃COCH₃) and acetaldehyde (CH₃CHO).
d. 2-methyl-1-butene (CH₂=C(CH₃)CH₂CH₃)
This alkene features a double bond between C1 and C2. Ozonolysis gives formaldehyde (HCHO) and methyl isopropyl ketone (CH₃COCH(CH₃)CH₃).
Which compound does not undergo ozonolysis reaction among 3-methyl-1-butene, 2,3-dimethyl-butane, 2-methyl-2-butene, and 2-methyl-1-butene? This common CSIR NET organic chemistry MCQ tests understanding of ozonolysis specificity. Ozonolysis reaction cleaves C=C double bonds in alkenes to carbonyls, but alkanes remain unreactive.
Ozonolysis Reaction Mechanism
Ozone (O₃) adds to the alkene double bond, forming a molozonide that rearranges to ozonide. Reductive workup (Zn/H₂O or DMS) yields aldehydes/ketones; oxidative workup gives carboxylic acids. Alkanes lack the pi bond, so no reaction occurs.
Detailed Option Breakdown
| Compound | Structure Type | Undergoes Ozonolysis? | Products |
|---|---|---|---|
| 3-methyl-1-butene | Terminal alkene | Yes | HCHO + (CH₃)₂CHCHO |
| 2,3-dimethyl-butane | Branched alkane | No | None |
| 2-methyl-2-butene | Internal alkene | Yes | CH₃COCH₃ + CH₃CHO |
| 2-methyl-1-butene | Disubstituted alkene | Yes | HCHO + CH₃COCH(CH₃)CH₃ |
Correct Answer: b. 2,3-dimethyl-butane – The only alkane without a double bond.
