What is the difference between IR and UV/vis spectroscopies?

Answer 1

IR spectroscopy is largely qualitative, whereas UV-vis spectroscopy can be (highly) quantitative.

IR spectroscopy gives a good indication of the functional groups present in a molecule. Absorptions from carbonyl groups #C=O# stick out like things on a dog, and if there is a carbonyl group present, the #IR# spectrum will identify it straightforwardly. #C-H# groups are of course present in the IR spectrum, but because all organic species have #C-H# bonds (at least usually), this is not very definitive. Where the compound has an active hydrogen (i.e. an alcohol, or a carboxylic acid) sometimes the #H# can be replaced by a deuterium label, which can be observed at at a predictable lower frequency (this sounds much easier than in fact it is; I have seen some fabulous stretches of imagination to identify a #O-D# stretch).

A much more quantitative method is UV-vis spectroscopy, which permits the use of aqueous solutions at very low concentrations (water absorbs in the IR spectrum far too strongly to be used as a solvent!). The Beer-Lambert law (sometimes!) allows quantitative determination of some analyte.

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Answer 2

Infrared (IR) spectroscopy measures the absorption of infrared radiation by molecules, providing information about molecular vibrations and functional groups. UV/visible (UV/vis) spectroscopy measures the absorption of ultraviolet and visible light by molecules, providing information about electronic transitions and chromophores. While both techniques involve the absorption of electromagnetic radiation, they differ in the energy range of radiation used and the type of molecular information obtained.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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