The Wittig reaction, first discovered by George Wittig in 1954, is very important to organic synthesis, primarily for the formation of alkenes. One of the advantages of the Wittig reaction is that the location of the double bond is fixed, unlike other methods such as dehydration reactions. The first step involves making a phosphorus ylide; an ylide is a compound that has opposite charges on adjacent atoms. An ylide is typically formed from reacting triphenylphosphine and an alkyl halide followed by base. The ylide is stabilized through resonance and has the form Ph3P+ -CHR, where the carbanion acts as a nucleophile towards the carbon in carbonyl (C=O) bonds. The mechanism proceeds through the formation of a cyclic intermediate, shown…show more content… First, the ylide was prepared by mixing benzyltriphenylphosphonium chloride with NaOH (Figure 1). Next, the ylide attacked cinnamaldehyde, the starting C=O compound, to produce either (E,E)-1,4-diphenyl-1,3-butadiene or (E,Z)-1,4-diphenyl-1,3-butadiene. Throughout the experiment, thin layer chromatography (TLC) analysis was done to make sure there was product forming from the Wittig reaction. TLC is a chromatography technique which uses a thin stationary phase (plate) to separate the components of a mixture. Multiple ‘spots’ of different organic compounds are made at the bottom of the plate, and the solvent is allowed to travel up the plate. The components of the starting materials separate and travel according to their solubility with respect to the solvent, leaving separated spots throughout the length of the plate. Individual components can be identified using the retention factor (Rf) value. The Rf value is defined as (Distance traveled by sample)/(Distance traveled by solvent). Due to the fact that the sample can never travel past the solvent, the retention factor values must always be between 0 and 1 in magnitude. In this lab, silica gel plates were used as the stationary phase while petroleum ether was used as the mobile solvent. In addition to the TLC, proton NMR spectroscopy was also analyzed to determine the ratio between products and confirm their
