What is the number of all (structurally isomeric) alkynes with molecular formula `C_(6)H_(10)`.

Options

A. 6
B. 7
C. 8
D. 9

Answer

To determine the number of structurally isomeric alkynes with the molecular formula \( C_6H_{10} \), we can follow these steps:

### Step 1: Understand the Molecular Formula
The molecular formula \( C_6H_{10} \) indicates that we are dealing with an alkyne. Alkynes are characterized by having at least one carbon-carbon triple bond. The general formula for alkynes is \( C_nH_{2n-2} \), which fits our formula since \( n = 6 \).

### Step 2: Identify the Carbon Skeletons
We need to consider different carbon skeletons that can accommodate a triple bond. The main chain can vary in length and can have different arrangements of carbon atoms.

1. **Straight-chain (linear) alkyne**: The simplest structure is a straight chain of 6 carbon atoms.
2. **Branched-chain alkynes**: We can create branched structures by varying the position of the triple bond and adding methyl (CH₃) groups as substituents.

### Step 3: Draw Possible Structures
We will now draw possible structures for \( C_6H_{10} \):

1. **Linear alkyne**:
- 1-hexyne: \( CH_3CH_2CH_2C \equiv CCH_3 \)

2. **Branched alkynes**:
- 2-hexyne: \( CH_3CH_2C \equiv CCH_2CH_3 \)
- 3-hexyne: \( CH_3C \equiv CCH_2CH_2CH_3 \)

3. **Alkynes with branching**:
- 1-pentyne with a methyl group:
- 2-methyl-1-butyne: \( CH_3C \equiv CCH_3CH_3 \)
- 2-pentyne with a methyl group:
- 3-methyl-1-butyne: \( CH_3C \equiv C(CH_3)CH_2CH_3 \)
- 2,2-dimethyl-1-butyne: \( (CH_3)_2C \equiv CCH_3 \)

### Step 4: Count the Isomers
After drawing all possible structures, we can count the distinct structural isomers:

1. 1-Hexyne
2. 2-Hexyne
3. 3-Hexyne
4. 2-Methyl-1-pentyne
5. 3-Methyl-1-butyne
6. 2,2-Dimethyl-1-butyne
7. 2-Methyl-2-pentyne
8. 3-Methyl-2-butyne

### Conclusion
The total number of structurally isomeric alkynes with the molecular formula \( C_6H_{10} \) is **8**.

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