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Studying Molecules and Chemical Substances
Studying chemical processes at the single-molecule and nano- levels enables us to understand the nature of chemical reactions and to see the invisible in the molecular world. The whole array of physico-chemical methods is available for researchers to help make new fundamental discoveries that will shape the chemistry of the 21st century. These methods include NMR spectroscopy, mass spectrometry, IR spectroscopy/Raman spectroscopy, UV/Vis, single crystal X-ray analysis, and electron microscopy.
Phys. Chem. Chem. Phys., 2016,
DOI: 10.1039/C5CP05586E, CC-BY-NC
All of these methods and techniques fuel the development of modern chemistry and adjacent areas, such as organic synthesis, catalytic transformations, polymer chemistry, materials science, molecular electronics, and solar panels. It is difficult to place emphasis on any single method or technique because each of them is sensitive in its own way. Each one offers a unique set of data, shedding light on many fascinating questions, such as molecular structure, formulas, rules of forming and breaking bonds, etc.
"Modern electron microscopy in the study of chemical systems at the boundary of organic synthesis and catalysis",
Russ. Chem. Rev., 2016, 85, 1198–1214, DOI: 10.1070/RCR4681
Methods and Techniques
NMR spectroscopy – the technique used to obtain information about molecular structure. The sample is placed in a constant magnetic field and irradiated by radiofrequency waves. The technique registers resonant absorption of electromagnetic energy by the substance. Mass spectrometry – the technique utilized for determining molecular formulas of chemical compounds by ionizing samples and measuring and sorting ions based on their mass/charge ratio.
IR spectroscopy/Raman spectroscopy – the technique for studying absorption and dispersion of infrared radiation by molecules. The signal is present in the spectrum if the frequency of molecular bond vibration coincides with radiation frequency.
UV/Vis – the method of studying substances that absorb visible light and ultraviolet radiation. Characteristic lines of absorption help determine a large number of components in a sample.
Single crystal X ray analysis – the technique used to study reflection of X-rays from crystal surfaces in a sample in all possible projections. The technique determines precise structure of a molecule (excluding hydrogen atoms), as well as the manner these molecules are packed in the elementary lattice cell.
Correct identification of a research goal and accurate sample preparation will ensure getting reliable experimental data for analysis.
Table 1. Methods of study and minimum sample amounts.
|Method||Minimum sample amount, mg||Concentration range, mole/l|
|Regular analysis||Advanced studies|
|Single crystal X-ray analysis||50||1||Study of liquids impossible|
|NMR-spectroscopy||0.01 – 5||10–6 – 10–2||10–6 – 1|
|Mass-spectrometry||10–6 – 10–3||10–12 – 10–6||10–12 – 10–5|
"How Sensitive and Accurate are Routine NMR and MS Measurements?", Mendeleev Commun., 2015, 25, 454–456,
Materials and Surfaces
In recent years, electron microscopy has gained popularity among researchers due to the active development of nanotechnologies for studying substances and materials. It has become possible to study surface, morphology, and complex hierarchy of samples along with the structures of molecules. Please see Equipment and Interpreting Electron Microscopy Data for more detail on electron microscopy principles of operation.
The whole powerful complex of physico-chemical methods is indispensable for addressing the problems of modern chemistry.
Table 2. Informative value of studies for different physical forms.
|Physical form||NMR-spectroscopy||Mass-spectrometry||Electron microscopy|
|Gas||★ ★ ☆
|★ ★ ★
|Liquid||★ ★ ★
|★ ★ ☆
|★ ☆ ☆
|Solid||★ ★ ★
|★ ★ ☆
|★ ★ ★
"Target-oriented analysis of gaseous, liquid and solid chemical systems by mass spectrometry, nuclear magnetic resonance spectroscopy and electron microscopy", Rus. Chem. Rev., 2013, 82, 648–685,