ASUC chem 02

ASUC chem 02 - CHEMISTRY 3B Professor Peter Vollhardt...

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CHEMISTRY 3B Professor Peter Vollhardt 9/2/08 Lecture 2 ASUC Lecture Notes Online is the only authorized note-taking service at UC Berkeley. Do not share, copy or illegally distribute (electronically or otherwise) these notes. Our student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. LECTURE REVIEW: ALLYLS Last time, we talked about the basic structure of ethene and asked the question, “What would happen if we add a third p-orbital?” In fact, the third p- orbital interacts and mixes in with the two existing p-orbitals to form a pi bond. As a quick review, propenyl has 2 p-orbitals that overlap to form a sigma bond and a third p-orbital that overlaps to make a new delocalized bond or pi bond. The resulting molecule is an allyl . We were able to generate a molecular orbital diagram for this molecule. There are three molecular orbitals—one above the zero line, one below, and one on the zero line. The net energy of the allyl is lower than that of 3 non-interacting p-orbitals; therefore, we found out that the allyl is very stable. Allyl hydrogens are weakly bound due to resonance. We can generate carbocations easily even for primary carbons from the allylic position. In addition, Sn2 reactions are accelerated because of the overlapping nature of the p-orbital in the transition state. And finally, allylic positions are relatively acidic, as the allylic hydrogens can more easily be deprotonated. CONJUGATED DOUBLE BONDS If we now add yet another p-orbital, we can end up with a conjugated double bond . E/Z NOMENCLATURE A molecule with two double bonds is a diene; 3 double bonds, a triene; and 4 double bonds, tetrene. Depending on where the substituents are added in relation to the double bond, the stereoisomer will either be of cis or trans conformation.
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CHEMISTRY 3B ASUC Lecture Notes Online: Approved by the UC Board of Regents 9/2/07 D O N O T C O P Y Sharing or copying these notes is illegal and could end note taking for this course. 2
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This note was uploaded on 10/07/2010 for the course CHEM 3b taught by Professor Pederson during the Fall '08 term at Berkeley.

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ASUC chem 02 - CHEMISTRY 3B Professor Peter Vollhardt...

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