Select one from the following pair of isomer that has higher heat of combustion, justifying your choice.

Options

A.
B.
C.
D.

Answer

To determine which isomer has a higher heat of combustion, we need to analyze the stability of the isomers in question. The heat of combustion is the amount of energy released when one mole of a substance is burned in excess oxygen. Generally, the less stable an isomer is, the higher its heat of combustion will be, because less stable compounds have higher potential energy.

### Step-by-Step Solution:

1. **Identify the Isomers**: Start by identifying the two isomers being compared. For example, let’s say we have two isomers of butene: 1-butene (CH2=CH-CH2-CH3) and 2-butene (CH3-CH=CH-CH3).

2. **Determine Stability**: Assess the stability of each isomer. Stability can often be determined by the number of alkyl substituents on the double bond. More substituted alkenes are generally more stable due to hyperconjugation and the inductive effect. In our example, 2-butene is more stable than 1-butene because it is more substituted (it has two alkyl groups attached to the double bond).

3. **Relate Stability to Heat of Combustion**: Remember the principle that higher stability corresponds to lower heat of combustion. Therefore, the less stable isomer (1-butene) will have a higher heat of combustion compared to the more stable isomer (2-butene).

4. **Calculate or Estimate Heat of Combustion**: If exact values are needed, you can calculate the heat of combustion using standard enthalpies of formation or refer to tabulated values. However, for qualitative comparisons, knowing the relative stabilities is sufficient.

5. **Justify Your Choice**: Conclude by stating that since 1-butene is less stable than 2-butene, it will release more energy upon combustion, thus having a higher heat of combustion.

### Conclusion:
In the case of 1-butene and 2-butene, 1-butene has a higher heat of combustion due to its lower stability compared to 2-butene.