Modern Analytical Techniques: Spectroscopy in Chemistry

Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Modern analytical chemistry relies heavily on various spectroscopic techniques for identification and quantification.

UV-Visible Spectroscopy

UV-Vis spectroscopy measures the absorption of ultraviolet and visible light (200-800 nm).

**Principle:** Electronic transitions from ground state to excited state.

**Beer-Lambert Law:** A = εbc

Where A is absorbance, ε is molar absorptivity (L·mol⁻¹·cm⁻¹), b is path length (cm), and c is concentration (mol/L).

**Applications:** - Quantitative analysis of colored solutions - Determining concentration of transition metal complexes - Monitoring reaction kinetics

Infrared (IR) Spectroscopy

IR spectroscopy measures the absorption of infrared radiation, causing molecular vibrations.

**Key Regions:** - 4000-2500 cm⁻¹: X-H stretching (O-H, N-H, C-H) - 2500-2000 cm⁻¹: Triple bonds (C≡C, C≡N) - 2000-1500 cm⁻¹: Double bonds (C=O, C=C, C=N) - 1500-400 cm⁻¹: Fingerprint region

Nuclear Magnetic Resonance (NMR)

NMR spectroscopy exploits the magnetic properties of certain nuclei (¹H, ¹³C).

**Key Information:** - Chemical shift (δ): Electronic environment - Integration: Number of equivalent protons - Splitting pattern: Number of neighboring protons (n+1 rule) - Coupling constant (J): Distance between split peaks

Mass Spectrometry

Mass spectrometry measures the mass-to-charge ratio (m/z) of ionized molecules.

**Key Information:** - Molecular ion (M+): Molecular weight - Fragmentation pattern: Structural information - Isotope patterns: Elemental composition