## Step-by-Step Solution: McLafferty Rearrangement ### 1. **Identify the Molecule** You did not specify the molecular structure. The McLafferty rearrangement is most commonly discussed for a generic **ketone** or **aldehyde** with a suitable alkyl chain. Let's use **2-hexanone** as a representative example: ``` CH3-CO-CH2-CH2-CH2-CH3 ``` (2-hexanone: carbonyl at C2) --- ### 2. **Locate the Carbonyl Group** - The carbonyl group is at C2 (the "CO" group). - The **McLafferty rearrangement** requires a hydrogen atom on the **gamma (γ) carbon** relative to the carbonyl. --- ### 3. **Identify the γ-Hydrogen** - **α-carbon**: adjacent to carbonyl (C3) - **β-carbon**: next carbon (C4) - **γ-carbon**: next carbon (C5) So, the γ-hydrogen is on C5. --- ### 4. **McLafferty Rearrangement Mechanism** - A six-membered cyclic transition state forms. - A γ-hydrogen is transferred to the carbonyl oxygen. - The bond between the α and β carbons breaks. - The molecule cleaves, forming: - An **enol (or its tautomer, a ketone/aldehyde) radical cation** - An **alkene fragment (neutral molecule, not observed in MS)** --- ### 5. **Draw the Rearrangement** **Before:** ``` CH3-CO-CH2-CH2-CH2-CH3 | | | | | C1 C2 C3 C4 C5 C6 ``` - Carbonyl at C2 - γ-hydrogen at C5 **After McLafferty Rearrangement:** - The C2–C3 bond breaks - The hydrogen from C5 attaches to the carbonyl oxygen #### **Daughter Ion Structure (Observed in MS):** ``` CH3-COH=CH2^+ ``` or ``` CH2=CH-CO-CH3^+ ``` The cation is at the enol/ketone fragment. For 2-hexanone, the fragment is **CH2=CH-CO-CH3^+** (enol form), or its keto tautomer **CH3-CO-CH3^+** (acetone cation). --- ### 6. **Final Answer: Draw the Daughter Ion** **The observed daughter ion from McLafferty rearrangement of 2-hexanone is:** ``` O || CH3–C–CH3^+ ``` *(acetone molecular ion, m/z = 58)* OR as a structure: ``` O || H3C–C–CH3^+ ``` **[Acetone cation]** --- ## **Summary Table** | Step | Description | Structure | |-----------|------------------------------------------|-------------------------------| | Precursor | 2-hexanone | CH3–CO–CH2–CH2–CH2–CH3 | | Daughter | Acetone cation (after McLafferty) | CH3–CO–CH3^+ | --- ## **General McLafferty Rearrangement** - **Always forms:** - A neutral alkene (lost) - A charged enol/ketone/aldehyde species (detected in MS) --- ## **Diagram**  *McLafferty rearrangement of 2-hexanone: acetone cation and propene formed.* --- ## **Final Answer** **The daughter ion observed is the acetone cation:** ``` O || CH3–C–CH3^+ ``` with **m/z = 58**.