Study GuideOrganic Chemistry I–Conjugated Dienes1.Preparation of Conjugated DienesConjugated dienesare a type of molecule that contains two double bonds in a row, with a singlebond in between. They are made in reactions that are similar to those used to create regular alkenes.The two most common ways to create conjugated dienes are:1.Dehydration of diols(alcohol molecules with two hydroxyl groups)—this removes waterfrom the molecule.2.Dehydrohalogenation of dihalides(molecules with two halogen atoms)—this removes ahalogen atom.Whether the product is aconjugated dieneor anisolated dienedepends on how the originalmolecules were arranged.Conjugated vs. Isolated Dienes•Conjugated dienes: These have alternating single and double bonds, like inbutadiene.They often form when molecules likevicinal diols(diols with hydroxyl groups on adjacentcarbon atoms) orvicinal dihalides(dihalides with halogen atoms on adjacent carbon atoms)are involved in elimination reactions.•Isolated dienes: These have two double bonds, but they're separated by more than onesingle bond. Certain reactant structures can lead to either conjugated or isolated dienes.Reaction Examples1.Dehydration of diols:oExample: Whenbutane-1,4-diolundergoes dehydration, it forms1,3-butadiene.oAnother example:pentane-1,5-diolcan form1,4-pentadiene.Preview Mode
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