A compound has the molecular formula C5H10O and the 1H-NMR spectrum contains four peaks. The compound could be

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Question recap: A compound has the molecular formula C5H10O and the 1H-NMR spectrum contains four peaks. The compound could be

- The options are not provided in full, but the given correct choice is b. pentan-2-one.

Analysis of the information and each aspect:

- First, interpret the formula C5H10O. This formula corresponds to a carbonyl-containing compound (an aldehyde, ketone, or ester) or a cyclic ether/ester with appropriate degrees of unsaturation. A straight-chain ketone with five carbons is a common and plausible possibility, such as pentan-2-one, which has the formula CH3-CO-CH2-CH2-CH3.

- Next, consider the NMR data: four distinct proton environments (four peaks). For pentan-2-one, the structure CH3-CO-CH2-CH2-CH3 has four distinct types of protons:
  1) The methyl group attached to the carbonyl (–CH3 adjacent to CO) typically resonates around 2.1–2.3 ppm.
  2) The methylene directly adjacent to the carbonyl (–CO-CH2–) also appears in the downfield region, commonly around 2.3–2.6 ppm, giving a separate signal from the methyl group.
  3) The central methylene (the second CH2 in the chain, not directly next to the carbonyl) typically resonates in the 1.2–1.8 ppm region, providing another distinct signal.
  4) The terminal methyl at the end of the chain (–CH3–) usually appears around 0.9–1.0 ppm, giving the fourth signal.
  This arrangement yields four distinct proton environments, consistent with four NMR peaks.

- Why this fits well compared to other C5H10O isomers: many other possibilities (e.g., cyclopentanol, cyclopentanone, or other carbonyl-containing isomers) can often produce more or fewer distinct proton environments depending on symmetry and substitution pattern. For example, a highly symmetric compound might give fewer peaks, while other structural motifs might yield more than four. The specific four-peak pattern aligns cleanly with a simple straight-chain ketone like pentan-2-one where each set of protons is chemically non-equivalent and lacks extra symmetry that would merge signals.

- Addressing the nature of the given answer: The selection b. pentan-2-one is consistent with the molecular formula C5H10O and the observation of four distinct proton environments in the 1H-NMR spectrum. It represents a straightforward, conventional ketone in this formula class.

- If we were to consider the other hypothetical choices (had they been provided): we would evaluate whether they also reconcile with C5H10O and four distinct NMR signals. Some alternatives might predict fewer or more signals due to symmetry or different functional groups (e.g., an aldehyde or an ether with different substitution patterns). Since those options are not shown here, the four-peak, five-carbon ketone remains a consistent and plausible match.

In summary, pentan-2-one (CH3-CO-CH2-CH2-CH3) satisfies both the molecular formula C5H10O and the four distinct proton environments observed in the 1H-NMR spectrum, making it a plausible candidate given the provided data.

MUF0042 Chemistry Unit 2 - Semester 1, 2025 8.20 Quiz: NMR Spectroscopy

A compound has the molecular formula C5H10O and the 1H-NMR spectrum contains four peaks. The compound could be

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