Organic Chemistry Conjugated Systems PDF

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Summary

Description and examples of Conjugated systems....

Description

Conjugated Systems A conjugated system occurs with alternating single and double carbon-carbon bonds. The conjugated system results in a general delocalization of the pi electrons. Conjugation in some cyclic structures results in aromaticity, a’la Benzene, and is the basis for it’s observed stability (NO ADDITION REACTIONS). Another interesting feature of these systems is that they absorb radiant energy, exciting the pi electrons, which in turn will emit energy back out into the environment. If the energy emitted is within the visible range, photoreceptors in the retina of your eye will be activated. Conjugated systems of fewer than eight conjugated double bonds absorb only in the ultraviolet region and are colorless to the human eye. However, if more double bonds are present, the system absorbs photons of lower energy (visible range), and the compound will produce pigment from yellow to red in color. Here are a couple of examples: Beta-Carotene (carrot orange, 11 pi bonds)

CH3

CH3

H3C

CH3

CH3

CH3 CH3

CH3

CH3

CH3

Lycopene (tomato red, 13 pi bonds)

H3C CH3

CH3

CH3

CH3 3C

CH3

11-Cis Retinal (colorless, uv absorption only, 6 pi bonds)

H3C

CH3

CH3

CH3

CH3

CH3 O

CH3

CH3...