WAEC 2017 Chemistry · Question 13
The name of the compound is
Options
- A.propyl pentanoate
- B.pentyl propanoate
- C.butyl propanoate
- D.propyl butanoate
Answer: A. propyl pentanoate
Explanation written with AI and checked against the answer key
Analyze the question: We need the IUPAC name of an ester written as C₄H₉COOC₃H₇.
Concept: An ester has the general formula R–COO–R′.
- The alkyl group R′ attached to the oxygen (the alcohol part) is named first, as the "alkyl" word.
- The R–COO part (the acid part) is named second, with the ending "-oate". Its carbon count includes the carboxyl carbon.
Solution:
- Acid part: C₄H₉–COO– • C₄H₉ has 4 carbons, and the COO carbon adds 1 more, so 5 carbons in total. • A 5-carbon acid is pentanoic acid, so this part becomes pentanoate.
- Alcohol part: –C₃H₇ • 3 carbons, so it is a propyl group.
- Combine them, alkyl group first: propyl pentanoate.
Check the other options:
- B (pentyl propanoate) would be C₂H₅COOC₅H₁₁, so the groups are swapped.
- C (butyl propanoate) would be C₂H₅COOC₄H₉.
- D (propyl butanoate) would be C₃H₇COOC₃H₇, which has only 4 carbons in the acid part.
Answer: A. propyl pentanoate
Tip: Count the carbon of the –COO– group as part of the acid chain. Name the group after the oxygen first, then the acid part. For example, CH₃COOC₂H₅ is ethyl ethanoate.
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