Structure 3.2.12
Structural Analysis
The final step: Combining data from different techniques to solve the molecular puzzle.
Structural Elucidation: The Triangulation Method
Never rely on one technique. Combine MS, IR, and NMR to solve the puzzle.
1. Mass Spec
Goal: Determine Molar Mass & Fragments.
- M-15: Loss of Methyl
- M-29: Loss of Ethyl/CHO
2. Infrared (IR)
Goal: Identify Functional Groups.
- 1700-1750: C=O (Sharp)
- 3200-3600: O-H (Broad)
3. Proton NMR
Goal: Map Carbon Skeleton.
- Integration: How many H?
- Splitting: Neighbors (n+1 rule).
Click a technique to see its role in the method.
The Triangulation Strategy
Step 1: Mass Spec
Check the Molecular Ion peak for molar mass. Look at fragmentation to chop off pieces (e.g., loss of 15 means methyl).
Step 2: Infrared
Identify the functional groups. Is there a C=O? An O-H? This tells you the "family" (e.g., ketone vs alcohol).
Step 3: NMR
Build the skeleton. Count the signals (environments) and use splitting to see who is connected to who.