Discussion Fadi - Discussion: The second part of the 4th...

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Discussion: The second part of the 4th laboratory period involved the Bromination of (E)- Stilbene. Bromination is an electrophilic addition reaction in which a bromine molecule is added to the C=C carbons in an Alkene, so they produce Br-C-C-Br. An Alkene is a hydrocarbon containing at least 1 Carbon-Carbon double bond. Stilbene (an Alkene) has two carbons with a double bond, each carbon is bonded to a phenyl group and it can either be in the (E) =Trans or (Z) = cis form. Those have quiet different physical properties, and their MP’s are 5-6 °C and 125 °C for the Z and E Enantiomers, respectively. Alkenes’ pi electrons act as nucleophiles and attack electrophiles as they are the result of the side-by-side overlap of the two 2P orbitals on the two adjacent carbon atoms. Unlike Pi electrons, sigma-bonds are formed by the head-on overlap of the two sp2-hybridized orbitals and require much more energy to break. The mechanism of this experiment is as follows: the Pi electrons on the C=C double bond attack the Br atom that has a partially-positive instantaneous charge (due to Wander Waal’s interactions), breaking the Br-Br bond and adding this Br to the (E)- Stilbene molecule. The Br, now neutral and bonded to one carbon atom, would use one of its 3 lone pairs to bond with the adjacent, positively-charged carbon, resulting in a Cyclic Bromonium ion. The Cyclic Bromonium Ion is the major contributor of the Bromonium ion, considering the less stable Acyclic Bromonium Ion. The stability of the former is due to the
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This note was uploaded on 05/03/2010 for the course CHEM 210C taught by Professor Fjetland during the Spring '10 term at University of Texas at Austin.

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Discussion Fadi - Discussion: The second part of the 4th...

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