Infrared spectroscopy and symmetry

Thread starter Chemist20
Start date May 29, 2012
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Infrared Spectroscopy Symmetry

In summary, infrared spectroscopy is a technique used in analytical chemistry to identify and analyze molecules based on their vibrational energy levels. It is commonly used in research fields such as chemistry, biochemistry, and materials science. The symmetry of a molecule plays a crucial role in its infrared spectrum, with symmetrical molecules producing simpler spectra and asymmetrical molecules producing more complex spectra. Infrared spectroscopy differs from other spectroscopic techniques in that it specifically measures the absorption of infrared light. However, it does have limitations, including its inability to analyze symmetrical molecules and provide absolute structural information, as well as difficulties with analyzing very small or large molecules.

May 29, 2012

Chemist20

is it true to say that any molecule having a centre of symmetry will have the symmetric stretching IR inactive?

thanks!

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May 30, 2012

Dr Transport

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http://www.chemvista.org/ramanIR4.html

no change in dipole moment == no ir active mode for symmetric stretch

What is infrared spectroscopy?

Infrared spectroscopy is a technique used in analytical chemistry to identify and analyze molecules based on their vibrational energy levels. It measures the absorption of infrared light by a molecule, which is dependent on the molecule's structure and symmetry.

How is infrared spectroscopy used in research?

Infrared spectroscopy is used in a variety of research fields, including chemistry, biochemistry, and materials science. It can be used to identify unknown substances, determine the composition of a sample, and study the structure and dynamics of molecules.

What is the relationship between infrared spectroscopy and symmetry?

The symmetry of a molecule plays a crucial role in its infrared spectrum. Symmetrical molecules have fewer vibrational modes and therefore produce simpler spectra, while asymmetrical molecules have more vibrational modes and produce more complex spectra. The symmetry of a molecule can also determine which types of bonds and functional groups are present and their relative strengths.

What is the difference between infrared spectroscopy and other spectroscopic techniques?

Infrared spectroscopy specifically measures the absorption of infrared light, which corresponds to the vibrational energy levels of a molecule. Other spectroscopic techniques, such as UV-Vis and NMR spectroscopy, measure different types of energy levels, such as electronic and nuclear spin states, respectively.

What are the limitations of infrared spectroscopy?

Infrared spectroscopy is limited to molecules that have a permanent dipole moment, which excludes symmetrical molecules such as noble gases. It is also unable to provide information about the absolute structure of a molecule, only the relative positions of atoms. Additionally, infrared spectroscopy is not suitable for analyzing very small or large molecules, as their absorption bands may overlap and be difficult to interpret.