Negative hyperconjugation and red-, blue- or zero-shift in X-Z center dot center dot center dot Y complexes

Joy, Jyothish and Jemmis, Eluvathingal D and Vidya, Kaipanchery (2015) Negative hyperconjugation and red-, blue- or zero-shift in X-Z center dot center dot center dot Y complexes. In: FARADAY DISCUSSIONS, 177 . pp. 33-50.

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Abstract

A generalized explanation is provided for the existence of the red-and blue-shifting nature of X-Z bonds (Z = H, halogens, chalcogens, pnicogens, etc.) in X-Z center dot center dot center dot Y complexes based on computational studies on a selected set of weakly bonded complexes and analysis of existing literature data. The additional electrons and orbitals available on Z in comparison to H make for dramatic differences between the H-bond and the rest of the Z-bonds. The nature of the X-group and its influence on the X-Z bond length in the parent X-Z molecule largely controls the change in the X-Z bond length on X-Z center dot center dot center dot Y bond formation; the Y-group usually influences only the magnitude of the effects controlled by X. The major factors which control the X-Z bond length change are: (a) negative hyperconjugative donation of electron density from X-group to X-Z sigma* antibonding molecular orbital (ABMO) in the parent X-Z, (b) induced negative hyperconjugation from the lone pair of electrons on Z to the antibonding orbitals of the X-group, and (c) charge transfer (CT) from the Y-group to the X-Z sigma* orbital. The exchange repulsion from the Y-group that shifts partial electron density at the X-Z sigma* ABMO back to X leads to blue-shifting and the CT from the Y-group to the sigma* ABMO of X-Z leads to red-shifting. The balance between these two opposing forces decides red-, zero- or blue-shifting. A continuum of behaviour of X-Z bond length variation is inevitable in X-Z center dot center dot center dot Y complexes.

Item Type:	Journal Article
Publication:	FARADAY DISCUSSIONS
Publisher:	ROYAL SOC CHEMISTRY
Additional Information:	Copy right for this article belongs to the ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND
Keywords:	O HYDROGEN-BOND; HALOGEN BOND; SIGMA-HOLE; CHARGE-DENSITY; CARBON BOND; AB-INITIO; CL; CHALCOGEN; IMPROPER; BR
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	22 May 2015 07:47
Last Modified:	22 May 2015 07:47
URI:	http://eprints.iisc.ac.in/id/eprint/51576

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