MCQ on UV-Visible spectroscopy: Page-3

Here the base value of the benzoic acid is 230 nm. Amine group at meta position acts as auxochrome with an increment of 13 nm. Therefore the total calculated value for lambda max will be 230 + 13=243 nm. img

Acetophenone has bas value as 246 nm. Any alkyl or cycloalkyl group at ortho position adds an increment of 3 nm. Hence the total calculated value will be 246 +=249 nm

Cisoid are the cyclic compounds that has double bonds arranged in a fashion that both double bonds are same side to the sigma bond connecting them. On the other hand, transoids will have double bounds on opposite side to the sigma bond. Therefore homoannular dienes are cisoids while heteroannular dienes are transoids.

The structure at option Q is cisoid which shows more absorption with base value at 253 nm while transoid absorbs at 214 nm.

Cisoid has both of the double bonds within the same ring hence called as homoannular diene. Similarly, transoid has double bonds each in one ring hence called as heteroannular diene.