Whic f th tollowing satements most acurately describes the rign oft absorptin f

Question

Whic f th tollowing satements most acurately describes the rign oft absorptin f th folowing compounds in their UV-vis spectra? Select one: . All compounds will how absorptions due tonoand T-T' tansitions b.A Band Ei hwnraiollshow an abopnion u i ad Di ho an absorption due to a d-d transition C.A Cand E will ownar'transton whereas Band D wihowabsoptons due to d tanstions OdA BandEwilshwabsoptons ue no tstions whre cn ishoaso r transitions e.A, B and E vill how n-ar transtions whereas C willshow an absorption due to a dd tanstion and D villshow an absorption due to a T-T' transition

Explanation / Answer

The correct answer is (e) A, B and E will show n-sigma* transitions whereas C will show an absorption due to d-d transition and D will show an absorption due to pi-pi* transition

Explanation: In UV-visible spectra, transition takes place from HOMO to LUMO. Depending on the nature of HOMO and LUMO four distinct type of transitions are possible in organic molecules (1) sigma-sigma* (2) n-sigma* (3) pi-pi* (4) n-pi*.  

A, B and E are haloalkanes. Haloalkanes show absorption due to n-sigma* transitions. The lone-pair electrons on halogen (Cl and Br) are the electrons which interact with the radiation.

In metal complex (CrCl6)3- (C) the transition is due to excitation of d-orbital electron (specifically t2g electrons) of Cr to d-orbital (specifically eg orbital). So, this will show d-d transition

In unsaturated compounds like ethylene (D), the HOMO is pi-orbital, and during interaction with radiation electron from pi-orbital are excited to pi*-orbital (LUMO).

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