Question

Give reason for the following:
  1. b-carotene is a red coloured compound.
  1. Carbonyl compounds absorb radiation in the infrared region.
  1. CDCl3 is used as a solvent for recording the NMR spectrum of a compound.
25 Jan 2018
Answer :
Word Count : 606

i. The conjugated chain in carotenoids means that they absorb in the visible region and hence are coloured. The absorption spectrum below shows that beta-carotene absorbs most strongly between 400-500 nm. This is the green/blue part of the spectrum. So beta-carotene appears orange, because the red/yellow colours are reflected back to us.
Image ignouacademy-com--p-ignou-75743

Natural colours

Carotenoids are one of the most important groups of natural pigments. They are responsible for many of the yellow and orange colours of fruit and vegetables. Beta-carotene is most abundant in carrots, of course, but is also found in pumpkins, apricots and nectarines. Dark green vegetables such as spinach and broccoli are another good source. In these the orange colour is masked by the green colour of chlorophyll. This can be seen in leaves; in autumn, when the leaves die, the chlorophyll breaks down, and the yellow/red colours of the more stable carotenoids can be seen.

ii. An important observation made by early researchers is that many functional group absorb infrared radiation at about the

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