Analytical Techniques in Organic Chemistry

Infrared (IR) Spectroscopy measures the vibrations of chemical bonds. Different bonds absorb different frequencies of IR light, acting like a 'fingerprint' for functional groups. The most critical regions to memorize are: - **Carbonyl ($C=O$):** A strong, sharp peak around $1700\text{ cm}^{-1}$. - **Hydroxyl ($-OH$):** A broad, 'tongue-shaped' peak between $3200-3500\text{ cm}^{-1}$. - **Carbon-Hydrogen ($C-H$):** Peaks just below $3000\text{ cm}^{-1}$ for alkanes. If you see a broad peak at $3300$ and a sharp peak at $1700$, you likely have a carboxylic acid!

**Proton NMR ($^1H$ NMR)** is the most powerful tool for structure determination. It tells us about the environment of hydrogen atoms. Three things matter: 1. **Chemical Shift ($\delta$):** Where the peak is. Downfield (higher ppm) means the H is near electronegative atoms like O or N. 2. Integration: The area under the peak, representing the ratio of hydrogens. 3. Splitting (n+1 Rule): A peak will split into $n+1$ peaks, where $n$ is the number of neighboring hydrogens on adjacent carbons. A 'quartet' means the H has 3 neighbors.