Advanced physical chemistry The figure bellow illustrates the appearance of CT (

Question

Advanced physical chemistry

The figure bellow illustrates the appearance of CT (charge transfer) spectra of tetracyanoethylene (TCE) and a variety of enol ether donors. The ionization potentials (IP) of the donors are give in the figure. The maxima of the CT bands shift to longer wavelengths as the IP of he donor drops. Give a interpretation of this generalization. For example, draw energy level diagrams for the general CT absorption process and discuss the trend in maxima wavelength with IP of the donor.

OR NC CN OR acceptor donor charge transfer complex lonization potential (e.V)8.58.3 8.0 7.6 7.4 7.4 OMe Et EtO OEt OMe OEt 420 440 460 480 500 520 540

Explanation / Answer

If we see the donor structure and its ionization energy from left to right is keep on decreasing. In general, if the donor structure possess high ionization energy means the structure is more stable and pi-bond donating ability will be less, in turn the formation of charge transfer complex will be less prominent compared to that of the one donor structure which is having more pi-bond donating ability. If more effective the charge transfer complex between the acceptor and donor, means energy band gap will be less thus the absorption take place at higher wavelength.

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