Comparison of 4-Fluorophenol Affinity and Basicity Scales

Arnett s data for 44 bases with the single hydrogen-bond donor 4-fluorophenol in CCI4 did not confirm the existence of a general AH—AS correlation [11]. However, in a plot of AH versus AG, some of the data could be resolved into separate lines corresponding to the families of pyridines, amides, sulfoxides and phosphoryl bases. Unfortunately, there were not enough data for other families of bases to enable this observation to be extended. 

The AH—AG relationship can now be re-examined from the 300 bases listed in Tables 4.3-4.26 and 4.30, for which both AH and AG have been measured. The AG values have been calculated from equilibrium constants obtained by a concentration variation method, while the AH values have been determined, in a separate experiment, by a temperature 

Lewis base 4-FC6 H4OH 3-FC6H4OH 3-CF3C6H4OH CH2CI2 

In summary, the correlation of hydrogen-bond affinity and basicity scales exhibits a scatter caused by family-dependent relationships and steric effects. For unhindered bases, the scatter can be analysed into a series of nearly parallel lines for (i) amines, (ii) pyridines, (iii) polar bases and (iv) jt bases. 

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