Conjugated Dienes and Ultraviolet Spectroscopy

Multiple bonds that alternate with single bonds are said to be conjugated. Thus, 1,3-butadiene is a conjugated diene, whereas 1,4-pentadiene is a non- conjugated diene. 

3-Butadiene (conjugated alternating double and single bonds) 

Problem 14.1 Which of the following molecule,s contains conjugation Circle the conjugated part in each. 

Conjugated dienes are generally prepared by the methods previously discussed for alkene synthesis. The base-induced elimination of HX from an allylic halide is one such reaction. 

3-Butadiene, a substance used industrially to make polymers, is prepared by thermal cracking of butane over a chromium oxide/aluminum oxide catalyst, but this procedure is of little use in the laboratory. 

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