Competition experiments are a useful tool for preliminary study of the linear free energy relationship of organic reactions. This article describes a physical organic experiment for upper-level undergraduates to identify the rate-determining step of the Claisen–Schmidt condensation of benzaldehyde and acetophenone by studying the linear free energy relationship. Substituent electronic effects were studied by competition experiments and the product ratios were determined by gas chromatography. Hammett plots were constructed from the relative rates, and the reaction constants (ρ) obtained in varying the substituents at the para position of benzaldehyde and acetophenone were 3.09 and 1.59, respectively. The reaction rates were found to be more sensitive to the substituents on benzaldehyde. The positive reaction constants suggested that nucleophilic addition (the first step) is the rate-determining step as the reaction rates were enhanced by increasing the electrophilicity of benzaldehyde as well as the acidity of the α-H of acetophenone.
The benzylisoquinoline derivative, 4',6-00-dimethyl-laudanosoline [ (*)-reticuline] has been synthesised in improved yield, and oxidised under mild aqueous conditions with ferricyanide a t pH 6 to (*)-isoboldine in 5-6s yield. The relevance of this to biogenetic theory is discussed.THE possibility that alkaloids of the aporphine and morphine types might arise in nature by the oxidative coupling of the two aromatic nuclei of suitable benzylisoquinoline alkaloids was first put forward in 1925 by Robins0n.l Independent attempts by Robinson and Schopf 3 to verify it experimentally for the aporphine
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