IB Chemistry home > Syllabus 2016 > Data Processing > Spectroscopic identification of organic compounds

Syllabus ref: 11.3 Syllabus ref: 21.1

Organic chemistry is a vast science which has brought many benefits to mankind in the form of novel compounds with a huge number of applications.

The development of new compounds involves identification, synthesis and purification procedures for which modern electronic instrumentation has helped enormously.

The data obtained appears as data which is presented in various graphical and numerical forms. This data then must be read and interpreted. The process of interpretation is a skill that must be learned

Nature of science:

Improvements in instrumentation-mass spectrometry, proton nuclear magnetic resonance and infrared spectroscopy have made identification and structural determination of compounds routine.

Models are developed to explain certain phenomena that may not be observable - for example, spectra are based on the bond vibration model.

Improvements in modern instrumentation-advances in spectroscopic techniques (IR, 1H NMR and MS) have resulted in detailed knowledge of the structure of compounds.


Essential idea: Analytical techniques can be used to determine the structure of a compound, analyse the composition of a substance or determine the purity of a compound. Spectroscopic techniques are used in the structural identification of organic and inorganic compounds.

The degree of unsaturation or index of hydrogen deficiency (IHD) can be used to determine from a molecular formula the number of rings or multiple bonds in a molecule

Mass spectrometry (MS), proton nuclear magnetic resonance spectroscopy (1H NMR) and infrared spectroscopy (IR) are techniques that can be used to help identify compounds and to determine their structure.

Understandings - HL

Essential idea: Although spectroscopic characterization techniques form the backbone of structural identification of compounds, typically no one technique results in a full structural identification of a molecule.

Structural identification of compounds involves several different analytical techniques including IR, 1H NMR and MS.

In a high resolution 1H NMR spectrum, single peaks present in low resolution can split into further clusters of peaks.

The structural technique of single crystal X-ray crystallography can be used to identify the bond lengths and bond angles of crystalline compounds.

Applications and skills

Determination of the IHD from a molecular formula.

Deduction of information about the structural features of a compound from percentage composition data, MS, 1H NMR or IR.

Applications and skills - HL

Explanation of the use of tetramethylsilane (TMS) as the reference standard.

Deduction of the structure of a compound given information from a range of analytical characterization techniques (X-ray crystallography, IR, 1H NMR and MS).

Chapter contents