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Use UV-vis; the product would show an absorbance at a longer lambda_max from tha

ID: 502104 • Letter: U

Question

Use UV-vis; the product would show an absorbance at a longer lambda_max from that of the starting material Use UV-vis; the product would show an absorbance at a shorter lambda_max from that of the starting material UV-vis will not be useful as no change in lambda_max would occur. Use IR; the starting material has a strong broad peak at 3200- 3400 cm^-1, but the product does not. Use IR; the product has a strong broad peak at 3200- 3400 cm^-1, but the starting material does not. Use IR; the starting material has a sharp narrow peak at 3100 cm^-1, but the product does not Use IR; the product has a sharp narrow peak at 3100 cm^-1, but the starting material does not IR will not be useful as no detectable change in the spectrum will occur.

Explanation / Answer

The substrate and the product can be distinguished using various spectroscopic techniques,

UV-Vis : As conjugation increases, delocalisation increases which increases the lambda-max

IR : The -OH stretch shows up as broad peak in IR at 3200-3400 cm-1 ; Product being aromatic shows a strong peak for sp2 =C-H stretch at 3100 cm-1

Thus,

Use Uv-Vis : Product would show an absorbance at longer wavelength lambda-max than that of the starting material

Use IR : the starting material has a strong broad peak at 3200-3400 cm-1, but the starting material does not.

Use IR : the product has a sharp narrow peak at 3100 cm-1, which the product does not.