



To determine the correct enol form of ethyl-3-oxobutanoate, we analyze the compound's tendency to undergo keto-enol tautomerism.
Step-by-step Analysis:
1. Structure of Ethyl-3-oxobutanoate: This is a β-keto ester with a ketone at the 3-position and an ester at the 1-position. Such compounds readily exhibit keto-enol tautomerism.
2. Enol Formation: The hydrogen at the alpha carbon (between the ester and ketone groups) is acidic and can be removed to form a double bond with the carbon adjacent to the ketone. The carbonyl oxygen of the ketone becomes an OH group.
3. Stability of Enol: The most stable enol is typically the one where the OH group is hydrogen bonded to the ester oxygen, forming a six-membered ring. Additionally, conjugation between the C=C bond and the ester group enhances stability.
4. Evaluating the Options: Among the given images, the correct enol form is the one where:
- A C=C bond is formed between the alpha and carbonyl carbon
- The ketone oxygen is converted into an OH group
- Intramolecular hydrogen bonding and conjugation are possible
Conclusion: The correct enol form is shown in the third image.
The reaction sequence given below is carried out with 16 moles of X. The yield of the major product in each step is given below the product in parentheses. The amount (in grams) of S produced is ____. 
Use: Atomic mass (in amu): H = 1, C = 12, O = 16, Br = 80