Valence Force Field of CX3YZ2and the Vibrational Spectra of CF3NO2, CCl3NO2, and CBr3NO2

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Abstract
Sets of valence‐type potential‐energy constants for CF3NO2, CCl3NO2, and CBr3NO2 were determined by using a minimum of 98% agreement between each calculated and observed vibrational frequency as a criterion, by imposing constraints inferred from data on other molecules and by maintaining a consistency expected from the related nature of these three molecules. C2v symmetry was used to factor the secular equations. The sensitivity of the potential energy constants to variations in the structure of the CNO2 framework is examined. The applicability of a previously proposed relationship between the electronegativity of the CX3 group, changes in the ONO angle and the strengths and s‐orbital character of the NO bonds is examined. An empirical relationship, Δω=74.0ε, is suggested by the behavior of the NO2 symmetric deformation frequency with changes in the electronegativity of the halogen atoms.