The relation between the CN stretching frequency and Hammett's σ

An Appraisal of Valence-bond Structures and Hybridization in Compounds of the First-row elements.

“…This property might be a bond length (tables 16 and 22), a bond angle (table 15), a coupling constant (table 17), an inductive constant (table 18), an ionization potential (table 19; see, also, references 213 and 214); a heat of addition to a multiple bond (table 20), or a bond force constant-or its practical (though sometimes only approximate) equivalent: a characteristic group frequency. Group frequencies that have been treated in this manner include those for the cyanide group (90,91,155), the CH2 group (315), the OH group ( 12), and the nitro group (94). The data in table 24 illustrate one such correlation: that between the electronegativity of R TABLE 24 Effect of electronegative groups on the asymmetric valence vibration of the nitro group ( 94 in R-N02 and the asymmetric stretching frequency of the nitro group.…”