SC CHEM 333 - Reactions of Carbocations Pre-Lab (6 pages)

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Reactions of Carbocations Pre-Lab



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Organic Chemistry 333L section 03M Laboratory Pre Lab Reactions of Carbocations By Cameron Kahn 22 October 2013 TA James Collie Objectives In this lab one will synthesize triphenylmethyl bromide from triphenylmethanol through a tritylcarbocation intermediate This experiment will also teach one how to find the mass melting point and percent yield of triphenylmethyl bromide Theory In 1912 Victor Grignard received the Nobel Prize in chemistry for his work on the reaction that bears his name a carbon carbon bond forming reaction by which almost any alcohol may be formed from appropriate alkyl halides and carbonyl compounds University of Missouri In this experiment it is very similar to what Victor Grignard tested Carbocations are reactive intermediates in many organic reactions Triphenylmethanol is a tertiary alcohol and is the reason why it undergoes an SN1 reaction It is important to note that tertiary alcohols undergo Sn1 reactions and in order for the alcohol to react it must first form a carbocation and then the covalent bond can form Handy It is because of this that a 3o alcohol is needed in the reaction The following table shows the criteria for an Sn1 and Sn2 reactions 1 Page Criteria Sn1 Sn2 Solvent Choice Polar protic solvents Paolar aprotic solvents Methanol ethanol water DMSO Acetone acetic acid etc dichloromethane diethyl ether Leaving Group 3o 2o Methyl 1o 2o Nucleophile Moderate to weak Moderate to strong CN N3 Nucleophiles H2O CH3OH CH3S HO Br INH3 CH3CO RSH Rearrangement of Final product is a racemic Final product is an inversion Stereocenter mixture of stereochemistry Forms Carbocation Yes Rate Limiting Step No concentrated reaction the table is courtesy of the Chemistry 333 Lab Manual with copyrights to George Handy and Salman Ali Another thing to mention is that in general carbocations have a center carbon atom that is sp2 hybridized and has an order of stability that goes like this Allylic 3o 2o 1o methyl The more alkyl groups attached to the



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