Why does a UV absorbing compound appear as a dark spot on the TLC plate when illuminated with UV light?

These lamps may be found as part of a standard organic chemistry research or teaching lab. While exposing these TLC plates to UV light, you will notice that the silica gel will fluoresce, while any organic molecule which absorbs UV light will appear as a dark blue spot.Click to see full answer. In this manner, why do you use UV light to detect the organic compounds on a TLC plate?Using UV light to identify spots( compounds) on a TLC plate is very common as it is an easy and non-destructive method. Aromatic systems and highly conjugated systems strongly absorb UV light. Most TLC plates have Zinc sulfide, which makes the TLC plates appear green under short wavelength UV.Likewise, what compounds show up under UV light? Visualization Summary UV Light: For aromatics + conjugated systems Iodine: Visualizes ~half the time. Strongly reacts with aromatics Permanganate: For alkenes, alkynes, or oxidizable groups (aldehydes, alcohols) Phosphomolybdic Acid (PMA): For alcohols, phenols, alkenes, and many carbonyl compounds Subsequently, question is, why is UV light used in chromatography? That means that if you shine UV light on it, it will glow. That glow is masked at the position where the spots are on the final chromatogram – even if those spots are invisible to the eye. That means that if you shine UV light on the plate, it will all glow apart from where the spots are.What makes a compound UV active and appear on a fluorescent TLC plate?The silica gel manufacturer coats the silica gel on the TLC plate with a material that fluoresces (illuminates) green under ultraviolet (UV) light (more specifically 254 nm light). To be UV-active compounds must possess a certain degree of conjugation, most commonly aromatic compounds.

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