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Wittig Reaction Lab Report

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The purpose of this lab was to perform a Wittig reaction in order to test whether the counter ion in a base used in the reaction directly results in the formation of an E or Z product. Three bases -- LiOH, KOH, and NaOH -- will be reacted with acetonyl triphenylphosphonium chloride (a phosphonium salt). The product of that reaction will be reacted with p-annisaldehyde, and an NMR of each product will be taken and used to determine which isomer of each product is formed. In a Wittig reaction, an aldehyde or ketone is reacted with a ylide produced from an SN2 reaction with a phosphonium salt. A ylide is a molecule that is neutral overall, but contains neighboring atoms that have opposite charges. A Wittig reaction works when the negatively charged carbon attached to the phosphorous atom in the ylide donates its lone pair to the electrophilic carbon in the carbonyl in either the ketone or aldehyde, depending on which molecule is being used. The electrons from the double bond in the carbonyl are also donated …show more content…

Using this information to analyze the alkene peaks of the NMR spectra of the reactions using NaOH, KOH, or LiOH, one can conclude that the counter ion of the base used had no effect on the stereochemistry of the alkene formed from all three Wittig reactions ran in lab: all the NMR spectra show the same trans-alkene. Since there are two alkene protons in the product formed from all three Wittig reactions, there are two sets of peaks in the alkene region of the three NMR spectra. The two larger downfield peaks represent the two hydrogen atoms from the trans-alkene, while the two significantly smaller upfield peaks represent the two hydrogens from the cis-alkene, suggesting that the trans-alkene was formed in a much greater quantity than the cis product, confirming the predicted

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