2-Pentanone and 3-methyl-2-butanone are a pair of __________ isomers.

Options

A. functional
B. chain
C. positional
D. stereo

Answer

To determine the type of isomers that 2-pentanone and 3-methyl-2-butanone represent, we will follow these steps:

### Step 1: Understand the Structures
First, we need to draw the structures of both compounds.

- **2-Pentanone**: This compound has a straight chain of 5 carbon atoms with a ketone group (C=O) on the second carbon. The structure can be represented as:
```
CH3-CO-CH2-CH2-CH3
```

- **3-Methyl-2-butanone**: This compound has a 4-carbon chain (butane) with a ketone group on the second carbon and a methyl group (CH3) on the third carbon. The structure can be represented as:
```
CH3
|
CH3-CO-CH2-CH3
```

### Step 2: Identify the Type of Isomers
Now we will analyze the two compounds to determine what type of isomers they are.

1. **Functional Isomers**: These have different functional groups. Both compounds have the same functional group (ketone), so they are not functional isomers.

2. **Chain Isomers**: These have the same molecular formula but differ in the arrangement of the carbon skeleton. Here, 2-pentanone has a straight chain of 5 carbons, while 3-methyl-2-butanone has a branched structure. Therefore, they are chain isomers.

3. **Positional Isomers**: These have the same carbon skeleton and functional group but differ in the position of the functional group. Since the carbon skeleton is different in these two compounds, they are not positional isomers.

4. **Stereoisomers**: These require the presence of chiral centers. Neither compound has a chiral carbon, so they cannot be stereoisomers.

### Conclusion
Based on the analysis, 2-pentanone and 3-methyl-2-butanone are a pair of **chain isomers**.

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