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Negative hyperconjugation and red-, blue- or zero-shift in X-Z∙∙∙Y complexes.

Jyothish Joy¹, Eluvathingal D Jemmis, Kaipanchery Vidya

¹School of Chemistry, Indian Institute of Science Education and Research-Thiruvananthapuram, Thiruvananthapuram, Kerala 695016, India.

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|February 6, 2015

Summary

This study explains why X-Z bonds shift red or blue in X-Z∙∙∙Y complexes. Differences arise from electron availability on Z, with X-group and Y-group interactions dictating bond length changes.

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Area of Science:

Computational Chemistry
Chemical Physics
Molecular Interactions

Background:

X-Z bonds exhibit red- and blue-shifting in X-Z∙∙∙Y complexes.
Hydrogen bonds differ significantly from other Z-bonds due to electron availability on Z.

Purpose of the Study:

To provide a generalized explanation for red- and blue-shifting of X-Z bonds in weakly bonded complexes.
To elucidate the factors controlling X-Z bond length variations in X-Z∙∙∙Y systems.

Main Methods:

Computational studies on selected weakly bonded complexes.
Analysis of existing literature data on X-Z∙∙∙Y interactions.

Main Results:

X-group influences X-Z bond length changes; Y-group modulates the magnitude.
Key factors include negative hyperconjugation, induced negative hyperconjugation, and charge transfer (CT).
Exchange repulsion causes blue-shifting, while CT from Y to X-Z σ* orbital causes red-shifting.

Conclusions:

The balance between exchange repulsion and charge transfer determines the observed red-, zero-, or blue-shifting.
A continuum of X-Z bond length variation is inherent in X-Z∙∙∙Y complexes.