A Wittig reaction with an aldehyde gives

Options

A. Ketone compound
B. A long chain fatty acid
C. Olefin compound
D. Epoxide

Explanation

To answer the question regarding the product of a Wittig reaction with an aldehyde, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Wittig Reaction**: The Wittig reaction is a chemical reaction that involves the reaction of a phosphonium ylide with a carbonyl compound (like an aldehyde or ketone) to form an alkene.

2. **Identify the Reactants**: In this case, we have an aldehyde (RCHO) and a phosphonium ylide (commonly represented as Ph3P=CR2).

3. **Reaction Mechanism**: When the ylide reacts with the aldehyde, the nucleophilic carbon of the ylide attacks the electrophilic carbon of the carbonyl group in the aldehyde. This leads to the formation of a four-membered intermediate known as an oxaphosphetane.

4. **Formation of Alkene**: The oxaphosphetane then undergoes a rearrangement to eliminate the phosphine oxide (Ph3PO), resulting in the formation of an alkene (olefin) as the final product.

5. **Conclusion**: Therefore, the product of a Wittig reaction with an aldehyde is an alkene.

### Final Answer:
The product of a Wittig reaction with an aldehyde is an **alkene**.

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