How many isomeric alkynes on catalytic hydrogenation gives `3`-Ethyl-`4`-methylheptane ?

Explanation

To determine how many isomeric alkynes can yield 3-ethyl-4-methylheptane upon catalytic hydrogenation, we can follow these steps:

### Step 1: Understand the Target Compound
The target compound is 3-ethyl-4-methylheptane. Its structure can be drawn as follows:
- It has a total of 7 carbon atoms (heptane).
- The ethyl group (C2H5) is attached to the 3rd carbon.
- The methyl group (CH3) is attached to the 4th carbon.

### Step 2: Draw the Structure of 3-Ethyl-4-Methylheptane
The structure can be represented as:
```
CH3
|
CH3-CH2-C-CH-CH2-CH3
|
CH2-CH3
```
This shows that the main chain is heptane with substituents at the 3rd and 4th positions.

### Step 3: Identify Possible Alkynes
To find isomeric alkynes that can produce this compound upon hydrogenation, we need to consider where the triple bond can be placed in the carbon chain. The triple bond can be positioned in the following ways:
1. Between carbon 1 and carbon 2
2. Between carbon 2 and carbon 3
3. Between carbon 3 and carbon 4
4. Between carbon 4 and carbon 5
5. Between carbon 5 and carbon 6
6. Between carbon 6 and carbon 7

However, we must ensure that the placement of the triple bond does not interfere with the substituents.

### Step 4: Draw Isomeric Alkynes
1. **First Isomer**: Triple bond between C1 and C2
- Structure: CH3-C≡C-CH(CH3)-CH2-CH3 (with ethyl on C3 and methyl on C4)

2. **Second Isomer**: Triple bond between C2 and C3
- Structure: CH3-CH≡C-CH(CH3)-CH2-CH3 (with ethyl on C3 and methyl on C4)

3. **Third Isomer**: Triple bond between C5 and C6
- Structure: CH3-CH2-CH2-CH(CH3)-C≡C-CH3 (with ethyl on C3 and methyl on C4)

### Step 5: Count the Isomers
After analyzing the possible placements of the triple bond, we find that there are **three isomeric alkynes** that can yield 3-ethyl-4-methylheptane upon catalytic hydrogenation.

### Final Answer
**There are 3 isomeric alkynes that can produce 3-ethyl-4-methylheptane upon catalytic hydrogenation.**

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