extendedconjugation

Extended conjugation refers to a system of alternating single and multiple bonds that extends over more than two adjacent atoms within a molecule. This pattern, often involving pi (π) electron systems, leads to delocalization of electrons across the entire conjugated network. Unlike simple conjugation, which typically involves two adjacent pi bonds, extended conjugation encompasses a longer chain of alternating double and single bonds, or a double bond conjugated with an aromatic ring, or two conjugated aromatic rings.

This extensive electron delocalization significantly influences the molecule's properties. A key characteristic is the absorption of light at longer wavelengths, meaning molecules with extended conjugation are often colored. The greater the extent of conjugation, the lower the energy required for electronic transitions, leading to absorption in the visible or even near-infrared regions of the spectrum. This phenomenon is fundamental to the color of many organic dyes and pigments.

Furthermore, extended conjugation can affect chemical reactivity, making certain positions within the molecule more susceptible to electrophilic or nucleophilic attack. It also contributes to increased stability due to the delocalization of electron density. Examples of molecules exhibiting extended conjugation include carotenoids, which are responsible for the vibrant colors of many fruits and vegetables, and polyenes with many alternating double and single bonds. The concept is also crucial in understanding the electronic properties of organic semiconductors and conducting polymers.