The absorption spectra of 1,3-butadiene showing absorption in the UV region ( λ max = 217nm) and the absorption spectra of 1,2-butadiene is not showing any absorption in the UV region should be explained. Concept introduction: The compounds having two C = C π bonds or C = C bond with C = O bonds are called dienes . Based on the proximity of C = C bonds in dienes, they are classified into three. Cumulated dienes : the C = C bonds are located adjacent carbons. Conjugated dienes : the C = C bonds or C = C and C = O are separated by one σ-bond. Isolated dienes : the C = C bonds are separated by two or more σ-bonds. The π-systems of conjugated dienes absorb UV or visible light (200nm – 800nm). The π-systems of cumulative diene absorbs below 200nm. To explain: the absorption spectra of 1,3-butadiene showing absorption in the UV region ( λ max = 217nm) and the absorption spectra of 1,2-butadiene is not showing any absorption in the UV region.

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Chapter 16, Problem 41PP

Interpretation Introduction

Interpretation:

The absorption spectra of 1,3-butadiene showing absorption in the UV region ( $λmax$ = 217nm) and the absorption spectra of 1,2-butadiene is not showing any absorption in the UV region should be explained.

Concept introduction:

The compounds having two $C = C$ π bonds or $C = C$ bond with $C = O$ bonds are called dienes.

Based on the proximity of $C = C$ bonds in dienes, they are classified into three.

Cumulated dienes: the $C = C$ bonds are located adjacent carbons.

Conjugated dienes: the $C = C$ bonds or $C = C$ and $C = O$ are separated by one σ-bond.

Isolated dienes: the $C = C$ bonds are separated by two or more σ-bonds.

The π-systems of conjugated dienes absorb UV or visible light (200nm – 800nm).

The π-systems of cumulative diene absorbs below 200nm.

To explain: the absorption spectra of 1,3-butadiene showing absorption in the UV region ( $λmax$ = 217nm) and the absorption spectra of 1,2-butadiene is not showing any absorption in the UV region.

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