The relationship between 19F and 13C substituent chemical shifts and electron densities. 2—p-phenylacetyl fluorides

✍ Scribed by Robert T. C. Brownlee; David J. Craik

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 893 KB
• Volume: 15
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270150308

✦ Synopsis

Abstract

The ^19^F substituent chemical shifts (SCS) of a series of para‐phenylacetyl fluorides (XPhCH~2~COF) are reported and compared with the related benzoyl fluoride series (XPhCOF). A dual substituent parameter analysis of the results for the new series shows that both inductive and resonance effects are reduced by one third when compared with the benzoyl fluorides. ^13^C shifts for the side chain carbonyl were also measured and found to follow a reversed trend in substituent effects, consistent with a pi polarization mechanism. SCS values for the fluorine and its adjacent carbon are not directly related. Ab initio (STO‐3G) calculations of the carbon and fluorine electron density for this series have been compared with the appropriate SCS values. From the electron densities and the observation that the fluorine SCS values follow a normal direction, whilst those for electron densities and the observation that the fluorine SCS values follow a normal direction, whilst those for the adjacent carbon are reversed, it is concluded that fluorine SCS values (and Δ__q__π values) result from polarization of the CF pi bond and do not merely monitor changes in electron density of the adjacent carbon.