A hydrocarbon of molecular weight `72gmol^(-1)` has a 2-methyl group. What is the IUPAC name? Also drawn its bond-line structure?

Answer

To solve the problem of determining the IUPAC name and drawing the bond-line structure of a hydrocarbon with a molecular weight of 72 g/mol and a 2-methyl group, we can follow these steps:

### Step 1: Determine the Molecular Formula
Given the molecular weight of the hydrocarbon is 72 g/mol, we can assume the hydrocarbon has the general formula \( C_xH_y \). The molar mass of carbon (C) is approximately 12 g/mol and that of hydrogen (H) is approximately 1 g/mol.

### Step 2: Calculate Possible Values for x and y
We can set up the equation based on the molecular weight:
\[ 12x + y = 72 \]
We need to find integer values for \( x \) and \( y \) that satisfy this equation.

### Step 3: Test Possible Values for x
1. If \( x = 6 \):
\[ 12 \times 6 + y = 72 \implies 72 + y = 72 \implies y = 0 \quad \text{(not possible for a hydrocarbon)} \]
2. If \( x = 5 \):
\[ 12 \times 5 + y = 72 \implies 60 + y = 72 \implies y = 12 \]
This gives us the molecular formula \( C_5H_{12} \).

### Step 4: Identify the Structure Based on the 2-Methyl Group
Since we have a 2-methyl group, we need to identify the main chain and the position of the methyl group. The longest carbon chain here is butane (4 carbons), and we have one methyl group attached to the second carbon.

### Step 5: Write the IUPAC Name
The IUPAC name for the compound is derived from the longest chain and the substituents:
- The longest chain is butane (4 carbons).
- The methyl group is on the second carbon.
Thus, the IUPAC name is **2-methylbutane**.

### Step 6: Draw the Bond-Line Structure
The bond-line structure can be represented as follows:

```
CH3
|
CH3-CH-CH2-CH3
```

In bond-line notation, it would look like this:

```
CH3
|
CH3-CH-CH2-CH3
```

### Final Answer
The IUPAC name of the hydrocarbon is **2-methylbutane**, and the bond-line structure is as shown above.

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