Question

(vii) Which of the following compounds absorbs light with the longest wavelength ?
(a) 1, 3, 5, 7 octatetraene
(b) 1, 3, 5-octatriene
(c) 1, 3-butadiene
(d) 1, 3, 5-hexatriene
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Answer 1

Answer:

ans.. is 1.3 butadiene

Explanation:

b. cause it have high wavelength..as compared to... other... a..b...and..d

Answer 2

Answer:

1, 3, 5, 7 octatetraene absorbs light with the longest wavelength.

Explanation:

A conjugated molecule absorbs light with the longest wavelength. The longer the conjugation in a molecule, the greater will be its ability to absorb light with the longest wavelength.

• Conjugation in a molecule leads to the delocalisation of electrons. Greater the delocalisation, the spectrum will shift to a longer wavelength.  

This is because, in a conjugated system, the energy gap for π-π* transition is smaller than in the systems which do not possess conjugation. So, less amount of energy is required to cause the excitation of electrons from a lower to a higher energy level.

1, 3, 5, 7 octatetraene absorbs light with the longest wavelength. This is because it possesses four conjugated double bonds in comparison to the other given molecules, which contain fewer conjugated double bonds.

1, 3, 5-octatriene contains three conjugated double bonds.1, 3-butadiene contains two conjugated double bonds.1, 3, 5-hexatriene contains three conjugated double bonds.