Chapter15 Conjugated Systems
Chapter15 Conjugated Systems Chem 2325
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Popular in Chemistry
This 7 page Class Notes was uploaded by Faiqa Rahman on Thursday February 11, 2016. The Class Notes belongs to Chem 2325 at University of Texas at Dallas taught by Dr. Christina Thompson in Spring 2016. Since its upload, it has received 25 views. For similar materials see Organic Chemistry in Chemistry at University of Texas at Dallas.
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Date Created: 02/11/16
Chapter 15 -‐ Conjugated Systems Systems in conjugation are higher in energy and more stable than systems not in conjugation • Not in • In conjugation conjugation • More stable • Less stable Molecular Orbital: Node: where amplitude + equals zero − + − p-‐orbital + − σ bonding: If the two s-‐orbitals are in the same phase then they are bonding If the two s-‐orbitals are not in the same phase then they are antibonding The phase must overlap for bonding to occur Anytime bonding occurs, the number of atomic orbitals must equal to the number of molecular orbitals. Higher energy= out of phase and are antibonding Lower Energy= in phase and are bonding All electrons are on the bottom because they are bonding. π-‐π bonding: + + Constructive which means they are bonding and the energy required is low − − + − Deconstructive which means that they are not bonding and the energy required is high. − + You are always looking for the lowest energy possible!! Because there are p orbital clouds on the double bonds, the two double bonds (C and 2 C ) 3 l make a partial double bond here because they are in conjugation and are overlapping Because of this, electron from C can move to C . 1 4 It is also flat! If you were to twist it like this: It won’t work because you lose the pi cloud that formed. Example: π 4 π 3 Four electrons in pi bond in 1,3 butadiene π 2 Electrons are π now 1 constrained. Basic energy situation: Two alkenes not in conjugation + + + + π 1 Lowest energy No nodes − − − − + + − − Only one node π 2 − − + + Now there are + − − + two nodes π 3 − + + − + − + − Highest energy π 4 3 nodes − + − + The lowest energy is the resonance stabilization of the conjugated diene. Trans is more stable than cis because the Hydrogens are not bumping into each other. Allylic: sp 2 p orbitals can interact with sp 3 unhybridized p orbitals making sp 2 it more stable . + -‐ Cation Radical Anion Allylic anion goes on C or C , but not C because it is sitting 1 in 3 2 the middle. Same goes for radical and cation as well.
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