## Step : Analyzing the Mass Spectrum The spectrum shows two notable peaks at **m/z = 63** and **m/z = 65**. The molecular formula given is **C₂H₃ClO** (acid chloride). - **Chlorine isotopes**: Cl has two common isotopes, ³⁵Cl and ³⁷Cl, with a natural abundance ratio of about 3:1. - The two peaks (63 and 65) are separated by 2 mass units, matching the presence of these isotopes. **Explanation:** The presence of two major peaks separated by 2 and a ~3:1 intensity ratio is a signature for a molecule containing one chlorine atom. --- ## Step 2: Proposing the Structure Given: **C₂H₃ClO** and the functional group is acid chloride. - Acid chloride functional group: **-COCl** - The remaining atoms: 1 more carbon, 3 hydrogens Combine the pieces: - Attach the -COCl group to a methyl group (CH₃). - Structure: **CH₃COCl** (acetyl chloride) **Explanation:** This structure uses all atoms in the formula and fits the acid chloride functional group requirement. The mass spectrum's isotopic pattern supports the presence of a single Cl atom. --- ## **Final Answer** ### **Structure: Acetyl chloride (CH₃COCl)** - **Molecular formula:** C₂H₃ClO - **Structure:** ``` H O | || H—C—C—Cl | H ``` - **Mass spectrum:** Matches the expected isotopic pattern for one Cl atom in the molecule.