An organic compound having molecular formula $C_{3}H_{6}O$ gives triplet at 1.05 ppm, quartet at 2.3 ppm and singlet at 9.77 ppm in NMR spectroscopy. It's structure is:

Question

Accepted Answer

The given organic compound has the molecular formula $C_{3}H_{6}O$ and exhibits specific NMR signals: a triplet at 1.05 ppm, a quartet at 2.3 ppm, and a singlet at 9.77 ppm. Let's analyze why Option 4, $CH_{3}CH_{2}CHO$, is the correct structure based on these NMR signals.

### Explanation for Option 4: $CH_{3}CH_{2}CHO$

1. **Triplet at 1.05 ppm**: This signal corresponds to the methyl group ($CH_3$) adjacent to a methylene group ($CH_2$). In $CH_{3}CH_{2}CHO$, the $CH_3$ group is next to the $CH_2$ group, which causes the $CH_3$ protons to split into a triplet due to the $n+1$ rule (where $n$ is the number of neighboring protons, here $n=2$).

2. **Quartet at 2.3 ppm**: This signal is characteristic of the methylene group ($CH_2$) adjacent to a methyl group ($CH_3$). In $CH_{3}CH_{2}CHO$, the $CH_2$ group is next to the $CH_3$ group, resulting in a quartet due to the splitting by the three protons of the $CH_3$ group ($n=3$).

3. **Singlet at 9.77 ppm**: This signal is indicative of an aldehyde proton. The chemical shift is typical for a proton attached to a carbonyl group in an aldehyde. In $CH_{3}CH_{2}CHO$, the $CHO$ group is present, and its proton appears as a singlet because there are no neighboring protons to cause splitting.

### Explanation for Why Other Options Are Incorrect

1. **Option 1: $CH_3COCH_3$ (Acetone)**
   - Acetone would show a singlet for the $CH_3$ groups because they are equivalent and there are no neighboring protons to cause splitting. This does not match the triplet and quartet observed in the NMR data.

2. **Option 2: $CH_3CH(OH)CH_3$ (Isopropanol)**
   - Isopropanol would show a doublet for the $CH_3$ groups due to the splitting by the $CH$ group, and a multiplet for the $CH$ group due to the splitting by the $CH_3$ groups. This does not match the observed triplet, quartet, and singlet pattern.

3. **Option 3: $CH_{2}=CH-CH_{2}OH$ (Allyl alcohol)**
   - Allyl alcohol would show complex splitting patterns due to the presence of vinyl protons and the $CH_2$OH group. The chemical shifts and splitting patterns would not match the simple triplet, quartet, and singlet observed.

In conclusion, the NMR data provided is consistent with the structure of $CH_{3}CH_{2}CHO$, making Option 4 the correct answer. The triplet, quartet, and singlet observed in the NMR spectrum align perfectly with the expected splitting patterns and chemical shifts for this compound.