Which compound in each pair would have a higher wavelength a

Which compound in each pair would have a higher wavelength and why. H2N-CH=CH-CO-CH3 or (NH3+)-CH=CH-CO-CH3. CH3O-CH=CH-CO-CH3 or CH3-CH=CH-CO-CH3

Solution

Answer:

H2N-CH=CH-CO-CH3 will have higher wavelength because in this compound, nitrogen has one lone pair which involves in conjugation more.Whereas in (NH3+)-CH=CH-CO-CH3, there is no lone pair, so there is less conjugation when compared to H2N-CH=CH-CO-CH3.Higher the conjugation higher the wavelength.

Likewise in CH3O-CH=CH-CO-CH3, oxygen atom in methoxy group has lone pair which involves in conjugation more compared to CH3-CH=CH-CO-CH3.So it has higher wavelength.Whereas in CH3-CH=CH-CO-CH3, there is no lone pair, so its conjugation is less.

Therefore CH3O-CH=CH-CO-CH3 has higher wavelength.