1a. How many 1H NMR peaks (ignore splitting) do you expect for 3-carbethoxycouma

Question

1a. How many 1H NMR peaks (ignore splitting) do you expect for 3-carbethoxycoumarin?

1b. Do you think 3-carbethoxycoumarin will absorb at longer orshorter wavelengths than benzene? Why?

1c. Compounds with an OH group usually have smaller Rf. However, salicylaldehyde is expected to have a larger Rf value than 3-carbethoxycoumarin. Why?

1d. What would happen if you reflux 3-carbethoxycoumarin with NaOH in aqueous solution? (Hint: What are the byproducts of the synthesis of 3-carbethoxycoumarin?)

Explanation / Answer

Answer 1a: seven 1H-NMR peak will appear in 3-carbethoxycoumarin because of seven different proton present in it.

Answer 1b. 3-Carbethoxycoumarin will absorb at longer wavelengths than benzene because 3-Carbethoxycoumarin contain extra chromophore (Functional froups like carbonyl group and olefin) that reduece the energy gap between two orbitals. Hence, it can absorb at higher wavelength than benzene.

Answer 1c. Because of presence of two ester group (one cyclic and one acyclic) group in 3-carbethoxycoumarin, polariy will increase compared to salicyldehyde. Therefore, Rf value of 3-carbethoxycoumarin will be less than salicyldehyde

Answer 1d. if you reflux 3-carbethoxycoumarin with NaOH in aqueous solution, the -COOEt will hydrolize to the acid group i.e. -COOH and will form EtO- as by product.

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