Spectroscopy I

70 lessons, pages 2971–3040.

What Is Spectroscopy? — Probing molecules with electromagnetic radiation
The Electromagnetic Spectrum for Chemists — Wavelength, frequency, wavenumber and photon energy
Quantised Energy Levels and Absorption — Electronic, vibrational, rotational and nuclear spin transitions
Absorption and Emission Spectra — How a spectrometer records a spectrum
Matching Techniques to Structural Questions — What IR, UV-visible, NMR and mass spectrometry each reveal
Reading a Spectrum: Axes, Peaks and Units — Intensity, position and shape of signals
Molecular Vibrations: Stretching and Bending — Symmetric, asymmetric and bending modes
The Bond as a Spring: Hooke's Law Model — Bond strength, reduced mass and vibrational frequency
IR Activity and Changing Dipole Moments — Why N₂ and O₂ are IR inactive but CO₂ absorbs
Anatomy of an IR Spectrum — Wavenumber axis, transmittance and the fingerprint region
IR Group Frequencies: The Key Table — Characteristic absorption ranges of common bonds
O–H Absorptions in Alcohols and Carboxylic Acids — Broad bands and the effect of hydrogen bonding
N–H Absorptions in Amines and Amides — One band or two: primary and secondary N–H
C–H Stretches and Hybridisation — sp³, sp² and sp C–H either side of 3000 cm⁻¹
The Carbonyl Stretch — The strong C=O band near 1700 cm⁻¹
Distinguishing Carbonyl Compounds by IR — Ketones, aldehydes, acids, esters, amides and acyl chlorides
Multiple Bonds and the Triple-Bond Region — C=C, C≡C and C≡N absorptions
The Fingerprint Region — Unique patterns below 1500 cm⁻¹ and C–O bands
Interpreting IR Spectra Systematically — A step-by-step strategy for identifying functional groups
IR Spectroscopy in Practice — Breathalysers, greenhouse gases and reaction monitoring
Electronic Transitions and UV-Visible Absorption — Promoting electrons between molecular orbitals
Chromophores and Types of Transition — π→π* and n→π* transitions
Conjugation and Absorption Wavelength — Why extended conjugation shifts λmax to longer wavelengths
Colour and Complementary Colours — Absorbed light, transmitted light and the colour wheel
Transmittance and Absorbance — The logarithmic relationship A = log(I₀/I)
The Beer–Lambert Law — A = εcl and what each term means
Molar Absorption Coefficient — Units, magnitude and dependence on wavelength
Beer–Lambert Calculations — Finding concentration, path length and ε
Calibration Curves in Colorimetry — Standard solutions and reading unknown concentrations
Limits of the Beer–Lambert Law — Deviations at high concentration and stray light
Choosing the Analytical Wavelength — Measuring at λmax for sensitivity and precision
UV-Visible Spectroscopy in Action — Kinetics, water analysis and sunscreens
Nuclear Spin and the Magnetic Field — Spin states of ¹H and ¹³C nuclei
Resonance: How an NMR Spectrometer Works — Radio-frequency absorption and spin flipping
Chemical Shift and the δ Scale — Parts per million relative to a reference
TMS as the Reference Standard — Why tetramethylsilane defines δ = 0
Shielding and Deshielding — Electron density around nuclei and signal position
Electronegativity and Chemical Shift — Effect of O, N and halogens on nearby protons
Ring Currents and Anisotropy — Why aromatic and aldehyde protons appear far downfield
The ¹H Chemical Shift Table — Typical δ ranges for proton environments
Equivalent Protons and Number of Signals — Using symmetry to count proton environments
Integration and Relative Numbers of Protons — Peak areas and integration traces
Spin–Spin Coupling and the n+1 Rule — Doublets, triplets, quartets and multiplets
Coupling Patterns of Common Groups — Recognising ethyl, isopropyl and tert-butyl groups
Coupling Constants — The J value in hertz and matched splittings
Exchangeable Protons and D₂O Shake — Identifying O–H and N–H signals
Deuterated Solvents in NMR — Why CDCl₃ is used and residual solvent peaks
Carbon-13 NMR Spectroscopy — Decoupled spectra and counting carbon environments
¹³C Chemical Shifts — Typical δ ranges from alkyl to carbonyl carbons
Interpreting ¹H NMR Spectra — Combining shift, integration and splitting to deduce structure
How a Mass Spectrometer Works — Ionisation, acceleration, deflection or flight time, and detection
Mass-to-Charge Ratio and the Mass Spectrum — The m/z axis and relative abundance
The Molecular Ion Peak — Finding relative molecular mass from M⁺
Isotope Patterns: M+1 and M+2 Peaks — Carbon-13, chlorine and bromine signatures
High-Resolution Mass Spectrometry — Exact masses and molecular formula determination
Fragmentation of the Molecular Ion — Radical cations breaking into ions and radicals
Carbocation Stability and Fragmentation — Why some fragments dominate the spectrum
The Base Peak — The most abundant ion and what it signals
Common Fragment Ions and Neutral Losses — m/z 15, 29, 43, 77 and losses of 15, 18 and 28
Fragmentation of Carbonyl Compounds — Alpha cleavage and acylium ions
Fragmentation of Alcohols, Amines and Halogenoalkanes — Loss of water and cleavage next to heteroatoms
Interpreting Mass Spectra — From molecular ion and fragments to a proposed structure
Degree of Unsaturation — Rings plus double bonds from a molecular formula
Combining IR and Mass Spectrometry — Functional group plus molecular mass
Combining NMR with Other Techniques — Building the carbon skeleton with supporting data
Structure Determination: Worked Problem I — Identifying an unknown carbonyl compound
Structure Determination: Worked Problem II — Distinguishing isomers with several spectra
Spectroscopy in Forensics, Medicine and Industry — Drug testing, MRI and quality control
Common Errors in Spectral Interpretation — Avoiding frequent exam and analysis mistakes
Spectroscopy I: Unit Review — IR, UV-visible, NMR and mass spectrometry brought together