Abstract
The following hypothesis is proposed: When additivity is valid, the molecular frequency distribution (MFD) is a weighted sum of group frequency distributions (GFDs). On the basis of the transformation rules for distribution functions from statistical theory and the rigid-rotator harmonic oscillator approximation, it is shown analytically that the hypothesis leads to group additivity of vibrationally dependent thermochemical parameters. Graph theory has been used to find the structure of the matrices used to determine group additivity values, and the results show that, within the rigid-rotator harmonic oscillator approximation, additivity of the vibrational contributions leads to the experimentally observed group additivity of the total group contributions. Support for the hypothesis is obtained from ab initio and DFT frequency calculations of a total 182 different compounds from seven polymeric series. In agreement with the hypothesis, remarkable similarities of the MFDs are observed throughout each series. Molecular frequencies can be satisfactorily calculated from model calculations based on the hypothesis, and temperature dependent heat capacities for the monomeric units can be derived that are in agreement with experimental values.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.