Ch1b2010_Lecture2

Ch1b2010_Lecture2 - Delocalization and Conjugation in...

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Delocalization and Conjugation in Polyalkenes Polyalkenes that contain repeating units of double bond–single bond–double bond are “conjugated” polyalkenes 1,3,5-hexatriene β -carotene the alkene atoms must be coplanar for conjugation: the electrons can “delocalize” throughout the π orbitals, lowering the energy difference between the HOMO and LUMO.
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Benzene is Special Benzene (C 6 H 6 ) was discovered in 1825 • all of the C-C bond lengths are identical • all of the C-H bond lengths are identical • the heat of hydrogenation is substantially lower than that expected from a triene
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Hückel’s Rule Hückel’s Rule: planar, fully conjugated, monocyclic systems with (4n+2) π electrons have a closed shell of electrons all in bonding orbitals and are exceptionally stable. These systems are “ aromatic .” other examples of aromatic compounds: analogous systems with 4n π electrons are “ anti-aromatic cyclopentadienyl anion cycloheptatrienyl cation
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Substituted Benzene Isomers ortho ( o ) meta ( m ) para ( p ) common benzene derivatives: benzoic acid Name the substituents in alphabetical order. The lowest alphabetical substituent is assigned 1 . phenol anisole aniline
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Electronegativity electronegativity (EN): the measure of the ability of a bonded atom (or functional group) to attract electrons toward itself. • EN increases as you
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This note was uploaded on 10/27/2010 for the course CH 1b taught by Professor Natelewis during the Winter '09 term at Caltech.

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Ch1b2010_Lecture2 - Delocalization and Conjugation in...

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