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In chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in molecules with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the system. The compound may be cyclic, acyclic, linear or mixed. Conjugation is the overlap of one p-orbital with another across an intervening sigma bond (in transition metals d-orbitals can be involved).〔IUPAC Gold Book (- ''conjugated system (conjugation)'' )〕 A conjugated system has a region of overlapping p-orbitals, bridging the adjacent single bonds. They allow a delocalization of pi electrons across all the adjacent aligned p-orbitals.〔March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. ISBN 0-471-85472-7 〕 The pi electrons do not belong to a single bond or atom, but rather to a group of atoms. The largest conjugated systems are found in graphene, graphite, conductive polymers, and carbon nanotubes. ==Mechanism== Conjugation is possible by means of alternating single and double bonds. As long as each contiguous atom in a chain has an available p-orbital, the system can be considered conjugated. For example, furan (see picture) is a five-membered ring with two alternating double bonds and an oxygen in position 1. Oxygen has two lone pairs, one of which occupies a p-orbital on that position, thereby maintaining the conjugation of that five-membered ring. The presence of a nitrogen in the ring or groups α to the ring like a carbonyl group (C=O), an imine group (C=N), a vinyl group (C=C), or an anion will also suffice as a source of pi orbitals to maintain conjugation. There are also other types of conjugation. ''Homoconjugation''〔(IUPAC Gold Book - ''homoconjugation'' )〕 is an overlap of two π-systems separated by a non-conjugating group, such as CH2. For example, the molecule CH2=CH–CH2–CH=CH2 (1,4-pentadiene) is homoconjugated because the two C=C double bonds (which are π-systems because each double bond contains one π bond) are separated by one CH2 group.〔Some orbital overlap is possible even between bonds separated by one (or more) CH2 because the bonding electrons occupy orbitals which are quantum-mechanical functions and extend indefinitely in space. Macroscopic drawings and models with sharp boundaries are misleading because they do not show this aspect.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「conjugated system」の詳細全文を読む スポンサード リンク
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