| Popis: |
The basicities of certain cyclotriphosphazatrienes containing amino-, chloro-, and phenyl-groups in various combinations have been measured in nitrobenzene. The data are used in conjunction with those of earlier Parts of the Series to calculate substituent constants αR and γR for the groups R = NH2, NHMe, NHEt, NHPrn, NHPri, NHBun, NHBut, NHC6H11, NHCH2Ph, NHPh, NH·C6H4Me-p, NH·NHPh, NMe2, NEt2, and piperidino. Among aliphatic amino-groups, the primary are, on average, more base-strengthening, both in alpha and in gamma positions, than the secondary; reasons for this are discussed. The substituent constants are used to calculate ‘corrected’ pK′a,1 values for the fully aminolysed derivatives N3P3R6, where R is aliphatic. If R is secondary the ‘corrected’ values are close to those observed; but, if R is primary, the ‘corrected’ exceed the observed values by ca. 2 pK′ units, confirming that a ‘saturation effect’ limits the observed pK′a,1 values in the latter case, as predicted earlier in the Series. The pK′a,2 values of the amino- and aminophenyl-derivatives are shown to be structurally significant. The value of substituent constants in the determination of structure from basicity measurements is demonstrated. |
