Spectrometry

What is Spectroscopy?

Spectroscopy measures electromagnetic radiation absorbed or emitted by analytes.

Three principal types:

Emission Spectroscopy: Radiation emitted by analytes.

Absorption Spectroscopy: Radiation absorbed by analytes (e.g., UV-vis, IR).

Fluorescence Spectroscopy: Radiation absorbed and re-emitted at a lower energy.

Electromagnetic Radiation (EMR)

Displays wave-like properties:

Wavelength, frequency, amplitude.

Electric and magnetic fields oscillate perpendicularly.

Displays particle-like properties:

Energy in packets (photons), defined by E=hνE = h\nuE=hν (Planck's equation).

Related to frequency, wavelength, and wavenumber.

Applications of EM Radiation

Principle: Molecules absorb photons matching the energy gap between ground and excited quantum states.

Observing the absorption peak helps analyze chemical structures.

Radiation Effects Across Spectra

Radiowaves:

Used in NMR and EPR (Nuclear and Electron Magnetic Resonance).

Alters atomic nuclei or electron spins.

Microwaves: Induces molecular rotational changes.

Infrared (IR): Detects bond vibrations (stretching and bending).

Visible & UV: Excites outer electrons to higher orbitals.

X-rays and Gamma Rays:

Excites core electrons or changes particle configurations (e.g., Mössbauer spectroscopy).

Mass Spectrometry

Analyzes compounds by ionization.

Separates ions by their mass-to-charge ratio (m/zm/zm/z).

Provides:

Molecular mass.

Elemental composition (distinguishes isotopes).

Elemental Analysis

Combustion in oxygen analyzes gases produced.

Determines mass percentages (e.g., C, H, N).

Assess compound purity.

Identifying Organic Compounds

Key Questions:

Molecular mass

Elements present

Bond types Functional groups

Atom distribution

Spectroscopic Techniques for Functional Groups

UV-visible Spectroscopy:

Detects conjugated π\piπ-systems and certain functional groups.

Infrared (IR):

Identifies functional groups (e.g., carbonyl compounds via vibrations).

NMR Spectroscopy:

Details hydrogen/carbon environments.

Multiplet signals reveal structural details.

Quantitative Analysis

Peak intensities in UV-visible spectroscopy relate to concentrations.

Useful for quantifying known compounds against standards.

Choosing the Right Technique

Know the information required.

Select techniques accordingly to:

Determine molecular structure.

Identify functional groups.

Quantify known compounds.