# Step-by-Step Solution Let's break down the problem: - **Given molecular formula:** \( C_5H_{12}O \) (implied, as it's an alcohol with \( C_5H_{12} \); the "O" comes from it being an alcohol) - **Given data from \( ^1H \) NMR:** - 3H, singlet, around 3.6–3.8 ppm - 9H, singlet, around 1. ppm - The spectrum suggests only **two signals** (integrations 3:9). Let's deduce the structure step by step. --- ## 1. **Molecular Formula Analysis** - **C5H12O** - Degree of unsaturation: \[ \text{DU} = \frac{2C + 2 - H}{2} = \frac{2 \times 5 + 2 - 12}{2} = \frac{10 + 2 - 12}{2} = \] - **No double/triple bonds or rings.** - Must be a **saturated alcohol**. --- ## 2. **Interpret the NMR Spectrum** ### a. **Signal at 3.6–3.8 ppm, 3H, singlet** - This chemical shift is **typical for protons on a methyl group adjacent to an oxygen atom** (i.e., O–CH₃). - Integration: **3H** → **methyl group**. ### b. **Signal at 1. ppm, 9H, singlet** - Integration: **9H** → **three equivalent methyl groups.** - Chemical shift (1. ppm) → **alkyl methyls** (not adjacent to electronegative atoms). - All in **identical environments** (singlet). --- ## 3. **Propose Possible Structures** We need an alcohol with: - **One methyl group attached to O** (-OCH₃, methyl ether), but since it's an alcohol, the O is more likely part of an -OH group. - **Three other methyl groups (9H) in identical environments.** But notice: The **3H singlet at 3.6–3.8 ppm** is usually for **O-CH₃** (a methyl ether), not an alcohol -OH proton. But the question says "alcohol" and "C₅H₁₂." ### Let's try **tert-amyl alcohol (2-methyl-2-butanol):** - Structure: ``` CH3 | CH3-C-CH2-CH3 | OH ``` - But this has **three types of protons**, not two. - Let's try **tert-pentyl alcohol (tert-amyl alcohol):** - IUPAC: 2-methyl-2-butanol - Structure: ``` CH3 | CH3-C-OH | CH2CH3 ``` - But again, this would not give two singlets. ### What about **tert-butyl alcohol with a methyl group**? - **tert-Butyl alcohol** is \( (CH_3)_3COH \), which is **C_4H_{10}O**. - We need **C_5H_{12}O**. - Let's try **tert-pentyl alcohol (2-methyl-2-butanol):** - Structure: ``` CH3 | CH3-C-OH | CH2CH3 ``` - Protons: - 6H on two methyls (equivalent, attached to same C) - 2H on CH₂ - 3H on terminal CH₃ - 1H on OH - **Not matching 3:9 integration.** ### Let's Try **Methoxy Substituted Compound (Ether)** - If we consider **methoxybutane**: - E.g., tert-butyl methyl ether (\( (CH_3)_3COCH_3 \)), also called MTBE. - Structure: ``` CH3 | CH3-C-O-CH3 | CH3 ``` - Molecular formula: \( C_5H_{12}O \) - NMR: - The three methyls attached to the central carbon (tert-butyl group) are equivalent: **9H, singlet, ~1. ppm** - The OCH₃ group: **3H, singlet, ~3.6 ppm** - **Two signals, integration 9:3, matching the spectrum.** **Although the question says "alcohol," the NMR and formula match an ether (MTBE), not an alcohol!** --- ## 4. **Final Structure and Answer** ### **Structure: tert-butyl methyl ether (MTBE, \( (CH_3)_3COCH_3 \))** - **Molecular formula:** \( C_5H_{12}O \) - **NMR signals:** - 9H, singlet, 1. ppm (tert-butyl methyls) - 3H, singlet, 3.6–3.8 ppm (OCH₃) - **Structure:**  *tert-butyl methyl ether (MTBE) structure; a central carbon with three methyl groups and one OCH₃ group* --- ## 5. **Conclusion** **The unknown compound is tert-butyl methyl ether (MTBE), not an alcohol.** ### **Summary Table** | Signal (ppm) | Integration | Assignment | |--------------|-------------|------------------| | 3.6–3.8 | 3H, singlet | OCH₃ | | 1. | 9H, singlet | (CH₃)₃C– | --- ### **Drawn Structure (Skeletal):** ``` CH3 | CH3–C–O–CH3 | CH3 ``` --- ## **Final Answer** > **The structure is tert-butyl methyl ether, \(\mathbf{(CH_3)_3COCH_3}\) (MTBE). The NMR spectrum matches 9H singlet (tert-butyl) and 3H singlet (OCH₃).**