Analytical Techniques in Chemistry

Infrared Spectroscopy (IR)

• Purpose: Used to identify functional groups in a molecule by examining absorption patterns in wavenumbers.
• Key Bonds and Ranges:
  • Alcohol (O-H): Broad absorption peak.
  • Carbonyl (C=O): 1640 - 1750 cm⁻¹
  • Carboxylic acids (O-H): 2500 - 3300 cm⁻¹ (very broad)
  • C-H: 2850 - 3100 cm⁻¹
  • N-H: 3200 - 3500 cm⁻¹
  • Fingerprinting Region: Below 1500 cm⁻¹, used for unique identification of compounds.
• Analysis:
  • Use an IR absorption table to detect specific bonds.
  • Presence of C=O bond indicated by absorption between 1640-1750 cm⁻¹.
  • O-H bond in acids identified by absorption between 2500-3300 cm⁻¹.
  • IR spectra can be compared against a database to identify compounds.

Greenhouse Gases and Infrared Absorption

• Greenhouse Gases: CO₂, CH₄, and H₂O trap infrared energy, contributing to global warming.
• Effectiveness: Depends on concentration, ability to absorb infrared, and atmospheric residence time.
• Impact:
  • CO₂ levels have increased due to fossil fuel burning.
  • CO₂ is a significant greenhouse gas linked to global warming.

Mass Spectrometry (MS)

• Purpose: Measures molecular weight (Mr) of organic molecules.
• Process:
  • Molecules break into fragments in the spectrometer.
  • The highest m/z peak is due to the molecular ion (parent ion), representing the original molecule.
  • Fragments create multiple peaks due to covalent bond breaking.
  • Stable ions, like carbocations and acylium ions, show higher peak intensity.
• Analysis:
  • Butane (C₄H₁₀) example: Molecular ion peak at m/z 58.
  • Fragmentation can be represented by equations showing ion and free radical formation.
• Molecular Identification:
  • Mass spectrum acts as a fingerprint, identifiable via spectral databases.
  • Stable fragments, like acyl groups, have characteristic high peaks.

These notes cover the main concepts and details from the transcript on modern analytical techniques, focusing on infrared spectroscopy and mass spectrometry. They highlight how these techniques are applied in identifying chemical structures and monitoring environmental factors like greenhouse gases.