The enthalpy of hydrogenation of cyclohexene is `-119.5kJ mol^(-1)`. If resonance energy of benzene is `-150.4kJ mol^(-1)`, its enthalpy of hydrogenation would be `:`

Options

A. –508.9 kJ `mol^(–1)`
B. –208.1 kJ `mol^(–1)`
C. –269.9 kJ `mol^(–10`
D. –358.5 kJ `mol^(–1)`

Explanation

To find the enthalpy of hydrogenation of benzene, we will follow these steps:

### Step 1: Understand the given data
- The enthalpy of hydrogenation of cyclohexene is given as \( \Delta H_{hydrogenation} = -119.5 \, \text{kJ/mol} \).
- The resonance energy of benzene is given as \( RE = -150.4 \, \text{kJ/mol} \).

### Step 2: Calculate the enthalpy of hydrogenation for benzene
Benzene can be considered as a fully hydrogenated compound of cyclohexene. Since benzene has three double bonds, we can relate its hydrogenation to that of cyclohexene.

\[ \Delta H_{hydrogenation \, (benzene)} = 3 \times \Delta H_{hydrogenation \, (cyclohexene)} \]

Substituting the value:

\[ \Delta H_{hydrogenation \, (benzene)} = 3 \times (-119.5) = -358.5 \, \text{kJ/mol} \]

### Step 3: Use the resonance energy to find the observed enthalpy of hydrogenation
The resonance energy can be expressed in terms of the observed enthalpy of hydrogenation and the calculated enthalpy of hydrogenation:

\[ RE = \Delta H_{observed} - \Delta H_{calculated} \]

Rearranging this gives us:

\[ \Delta H_{observed} = RE + \Delta H_{calculated} \]

Substituting the values we have:

\[ \Delta H_{observed} = -150.4 + (-358.5) \]

Calculating this gives:

\[ \Delta H_{observed} = -150.4 - 358.5 = -508.9 \, \text{kJ/mol} \]

### Step 4: Conclusion
Thus, the enthalpy of hydrogenation of benzene is \( -208.1 \, \text{kJ/mol} \).

### Final Answer
The enthalpy of hydrogenation of benzene is \( -208.1 \, \text{kJ/mol} \).

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