Spectroscopic Analysis of Flavonoids

Study Notes

Flavonoids and Their Spectroscopic Analysis

Flavonoids are a diverse group of polyphenolic compounds widely distributed in plants, possessing various biological activities and antioxidant properties.
Spectroscopic techniques play a crucial role in identifying and characterizing flavonoids, particularly hesperidin and quercetin.

Infrared (IR) Spectroscopy

Provides information about functional groups present in the flavonoid molecule.
Characteristic peaks include aromatic C=C stretches, C-O stretches (from hydroxyl groups and glycosides), and carbonyl (C=O) stretches (if present).
Hesperidin's IR spectrum shows prominent peaks for aromatic C=C stretches, multiple C-O stretches, and a weak carbonyl (C=O) peak.
Quercetin's IR spectrum exhibits characteristic peaks for aromatic rings, hydroxyl groups, and the absence of a carbonyl group.

Ultraviolet (UV) Spectroscopy

Flavonoids exhibit characteristic UV absorption due to their conjugated π-electron systems.
The position and intensity of absorption bands provide information about the substitution pattern on the aromatic rings and the presence of specific functional groups.
Hesperidin shows UV absorption maxima around 260 nm and 340 nm, characteristic of flavonoid aglycones with a glycosidic linkage.
Quercetin exhibits UV absorption maxima around 256 nm and 368 nm, reflecting the substitution pattern on its aromatic rings.

Nuclear Magnetic Resonance (NMR) Spectroscopy

Provides detailed information about the chemical environment of individual protons and carbons within the flavonoid molecule.
Analysis of ¹H NMR and ¹³C NMR spectra helps identify the number and type of protons and carbons present, their connectivity, and the substitution pattern on the aromatic rings.
Hesperidin's ¹H NMR reveals distinct peaks for aromatic protons, sugar protons, and methyl groups.
Quercetin's ¹H and ¹³C NMR spectra provide detailed information about the specific proton and carbon environments, allowing for the identification of the substitution pattern on its aromatic rings.

Mass Spectrometry (MS)

Provides the molecular weight of the intact flavonoid molecule and fragmentation patterns, aiding in structural analysis.
Techniques like Electrospray Ionization (ESI-MS) are often used due to the polarity of flavonoids.
MS can help differentiate between closely related flavonoids with similar structures.
Hesperidin exhibits a characteristic molecular ion peak in its ESI mass spectrum, which helps confirm its identity along with the presence of the sugar moiety.
Quercetin also shows a distinct molecular ion peak in its mass spectrum, allowing for its differentiation from hesperidin or other flavonoids.

Description

This quiz covers the spectroscopic techniques used to identify and characterize flavonoids, including hesperidin and quercetin. Learn about the role of IR, UV, NMR, and MS analysis in flavonoid analysis.