Systems, Orbital Symmetry, and Ultraviolet Spectroscopy

15-1 Look for 1) the number of double bonds to be hydrogenated—the fewer C=C, the smaller the A// 2) conjugation—the more conjugated, the more stable, the lower the AH 3) degree of substitution of the alkenes—the more substituted, the more stable, the lower the AH. 

15-2 Reminder H—B is used to symbolize the general form for an acid, that is, a protonated base B is the conjugate base. 

The central carbon atom makes two 7C bonds with two p orbitals. These p orbitals must necessarily be perpendicular to each other, thereby forcing the groups on the ends of the allene system perpendicular. 

15-4 Carbocation stability depends on conjugation (benzylic, allylic), then on degree of carbon carrying the positive charge. 

The most basic species in the reaction mixture will remove this proton. The oxygen of ethanol is more basic than bromide ion. 

The key step is hydride shift from a 2° carbocation to a 2° allylic, resonance-stabilized carbocation, which can subsequently lose a proton to form a conjugated diene. 

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CONJUGATED SYSTEMS, ORBITAL SYMMETRY, AND ULTRAVIOLET SPECTROSCOPY 667... 

CHAPTER 15 Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy... 

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