Here are the essential concepts you must grasp in order to answer the question correctly.
Acidity of Hydroxyl Groups
In organic chemistry, the acidity of hydroxyl groups (-OH) attached to aromatic rings, such as in alizarin, is enhanced due to resonance stabilization. This means that the negative charge formed after deprotonation can be delocalized over the aromatic system, making these hydroxyl groups more acidic than typical alcohols. This property is crucial for understanding the behavior of alizarin in the presence of strong bases like KOEt.
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Base-Induced Deprotonation
When a strong base like KOEt is added to a solution containing alizarin, it can deprotonate the acidic hydroxyl groups. This deprotonation leads to the formation of an alkoxide ion, which alters the electronic structure of the dye. The resulting species can have different light-absorbing properties, which explains the color change from orange to blue.
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Nitrogenous Bases Example 3
Color Change in Dyes
The color of organic dyes, such as alizarin, is determined by their electronic structure and the wavelengths of light they absorb. When the structure is altered through deprotonation, the energy levels of the molecular orbitals change, leading to a shift in the absorption spectrum. This shift can result in a visible color change, which in this case is from orange to blue upon the addition of KOEt.
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