CHEM 3580 Lecture Notes - Lecture 3: Stereochemistry, Polar Effect, Pericyclic Reaction
12 Feb 2017
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Lectures: 1/25/17 1/27/17: chapter 15 dienes, resonance and aromaticity. Review guide #1: dienes three kinds, ordinary dienes (sapling uses isolated dienes) have two double bonds separated by more than one single bond. B. conjugated dienes are compounds with two double bonds separated by one single bond. They have additional stability (~5 kcal/mol), relative to unconjugated isomers, due to the continuous overlap of their p orbitals and to strong sp2-sp2 single bonds. C. cumulated dienes (cumulene, allene) are compounds in which one or more carbon atoms are each part of two double bonds. They have no extra stability as in a conjugated system. A cumulene with two cumulated double bonds is an allene adjacent bonds in a cumulene are perpendicular to each other. The central carbon of an allene is sp hybridized. The overlap of the electrons in the 2p orbitals and the strong sp2-sp2 bond strength give enhanced stability to conjugated dienes.
