Question

substituted chalcones will be synthesized. In this reaction, 3-hydroxy-4-methoxy benzaldehyde will be reacted with a substituted acetophenone in the presence of NaOH. In light of this, why is it necessary to protect the alcohol group of 3-hydroxy-4-methoxy benzaldehyde?

Briefly explain how IR analysis will help you determine if the desired protected alcohol product were synthesized; in other words, what peaks would you expect to disappear and what peaks would you expect to appear? BE SPECIFIC – include absorption values (cm-1)!

Answer 1

The substituted chalcone derivatives can be prepared by stirring a mixture of substituted acetophenone (0.01 mol) and substituted aromatic benzaldehyde (0.01 mol) in adequate amount of ethanol for 3-4 hrs in presence of 40% NaOH.

3-hydroxy-4-methoxy benzaldehyde + substituted acetophenone -- ^NaOH --> substituted chalcones

The presence of hydroxy group has been suggested by various scientists, a holdup efficiency for facile synthesis of molecules. Thus, protection of this hydroxy group was needed to proceed with the synthesis. Consequently, methylation could carried out to obtained medicinal compounds (antimalarial, antihelmintic, antiviral, antibacterial, anti-inflammatory, antifungal, anticancer, antioxidant, analgesic and antiulcer).

In the IR spectra of chalcones asymmetric and symmetric stretching vibrations of the aromatic (C=O) are seen at 1650 and 1691 cm^‐1, (C=C) group at 1571-1591 cm^‐1 and (‐OH) group at 2982-3261 cm^‐1. The presence of only trans-(s- cis)-chalcone in the solid state caused disappearance of the splitting of the carbonyl in the IR spectra. 2’-OH chalcones have intramolecular bond between the H of the OH group at position 2’ and the carbonyl oxygen atom. The intramolecular bond has changed the spectroscopic properties of 2’-OH chalcones. The benzoyl and cinnamoyl groups of 2’-OH chalcones interact with the carbonyl group by σ and π bonds, favoring the delocalization of the π electrons.

Due to these interactions, the carbonyl group loses part of its individual character and partially integrates into the adjacent olefinic group. This phenomenon causes transference of electron deficiency from the CO carbon atom to the C atom at position β so, intramolecular hydrogen bond formation occurs.