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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

4.2.4 Analytical techniques

Combined techniquesInfrared spectroscopyMass spectrometry

Combined Techniques

Specification reference 4.2.4 (a)–(g)

Quick Notes

  • IR spectroscopy → tells you about functional groups from characteristic absorptions; the region <1500 cm−1 is the fingerprint region for confirming a specific molecule.
  • Mass spectrometry → gives M+ (molecular ion) for Mr, plus fragmentation peaks (parts of the structure) and a small M+1 peak from 13C.
  • In exams you must be able to use both at the same time: IR to say what groups are present, MS to confirm the overall mass and support the structure with fragments.

Infrared Spectroscopy (IR) is covered in detail here and Mass Spectrometry is covered in detail here.

IR vs MS — what each gives you

Technique What you read What it tells you What it cannot do alone
IR spectroscopy Absorptions at characteristic wavenumbers (cm−1); fingerprint region <1500 cm−1 Identifies functional groups (e.g. broad O–H, sharp C=O) Does not give the exact molecular mass; different molecules can share similar IR patterns
Mass spectrometry M+ (molecular ion) for Mr; fragment peaks; small M+1 peak Confirms molecular mass; fragments suggest pieces of the structure; M+1 hints at carbon count Does not directly tell you which functional groups are present

How to use both together (simple 3-step approach)

  1. Start with IR: list the key absorptions → propose functional groups (e.g. broad O–H, sharp C=O).
  2. Check MS M+: confirm the Mr matches your proposed structure; note M+1 if relevant.
  3. Use fragments: match any strong fragment peaks to sensible pieces of your proposed molecule. If given, use the IR fingerprint region for final confirmation.

Checklist for answers