The absorbance spectrum of 1,3-butadiene displays an absorption in the UV region (λmax = 217 nm), while the absorption spectrum of 1,2-butadiene does not display a similar absorption because the bonds in 1,2-butadiene are .

Cumulative

Explanation:

Cumulative double bonds usually consists of three contiguous carbon atoms joined by double bonds such as in an allene. They are also called twinned double bonds. Allenes are not as stable as conjugated systems such as 1,3-butadiene.

Conjugated systems show an absorption maxima in the UV-visible portion spectrum at longer wavelengths due to conjugation of the double bonds which shifts the absorption maxima to longer wavelengths. This is known as Bathchromic shift.

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