Reactivity of hydrogen atoms attached to different carbon atoms in alkane has the order:

Options

A. (a) `Tertiary gt Primary gt Secondary`
B. (b) `Tertiary gt Secondary gt Primary`
C. (c) `Secondary gt Tertiary gt Primary`
D. (d) Both (a) and (c).

Explanation

To determine the reactivity of hydrogen atoms attached to different carbon atoms in alkanes, we can analyze the stability of the radicals formed during reactions. The order of reactivity is influenced by the type of carbon atom (primary, secondary, tertiary) to which the hydrogen is attached. Here’s a step-by-step solution:

### Step 1: Understand the Types of Carbons
- **Primary Carbon (1°)**: A carbon atom bonded to one other carbon atom.
- **Secondary Carbon (2°)**: A carbon atom bonded to two other carbon atoms.
- **Tertiary Carbon (3°)**: A carbon atom bonded to three other carbon atoms.

### Step 2: Identify the Stability of Radicals
- The stability of the radicals formed during reactions is crucial. Tertiary radicals are more stable than secondary radicals, which in turn are more stable than primary radicals.
- This stability is due to hyperconjugation and the inductive effect of alkyl groups.

### Step 3: Analyze Bond Dissociation Energies
- The bond dissociation energy (BDE) is the energy required to break a bond. In alkanes, the C-H bond dissociation energies decrease in the order:
- Primary > Secondary > Tertiary
- This means that the hydrogen atoms attached to tertiary carbons are more reactive because they are easier to remove.

### Step 4: Establish the Reactivity Order
- Based on the stability of the radicals and the bond dissociation energies, we can establish the order of reactivity for hydrogen atoms in alkanes:
- **Tertiary > Secondary > Primary**

### Step 5: Conclusion
- Therefore, the reactivity of hydrogen atoms attached to different carbon atoms in alkanes follows the order: **Tertiary > Secondary > Primary**.

### Final Answer
The order of reactivity of hydrogen atoms attached to different carbon atoms in alkanes is: **Tertiary > Secondary > Primary**.

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