CHEM 373 Wittig Reaction Overview: Much like the Grignard reaction, the Wittig r

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CHEM 373 Wittig Reaction Overview: Much like the Grignard reaction, the Wittig reaction is one of the dlassic methods in organic chemistry for the formation of C-C bonds. In the Wittig reaction a carbon atom from an alkyl halide forms a carbon-carbon double bond with the carbonyl compound of a ketone or aldehyde. The reaction occurs in several steps. The first involves the Sn2 reaction of a phosphine, typically PPha, with an alky halide to form a phosphonium salt which can be deprotonated by a strong base to form an ylide. Ph P RH2C-X yide salt The ylide can then react with an aldehyde or a carbonyl in a two-step process. In the first step, a four-member ring structure called an oxaphosphetane is formed. The oxaphosphetane then undergoes an elimination reaction to form triphenylphosphine oxide and an organic compound with a new carbon- carbon double bond. R' H R PhyP- CHR As a carbon-carbon double bond is formed in the reaction, one of two isomers, the Zor the E can be formed. In today's experiment, we will synthesize an ylide from benzyl bromide and triphenylphosphine using sodium hydroxide as the base. We will then react the ylide with trans- cinnamaldehyde to form one of two possible isomers of 1,4-diphenyl-1,3-butadiene. We will use the melting point of the product along with NMR spectroscopy to determine the stereochemistry of the final product Br NaOH PPhs PPhy NaBr H2O PPhy H (E,E or (E Z-1,4-diphenyl-1,3-butadiene

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CHEM 373 Wittig Reaction Overview: Much like the Grignard reaction, the Wittig r

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