Study 6.33 Photoremovable protecting groups chemistry of carbohydrates

Case Study 6.33 Photoremovable protecting groups - chemistry of carbohydrates 

Explain the following concepts and keywords photofragmentation photoextrusion. 

Entry Starting material3 Product(s) Mechanism Section 

Photohalogenation a photoinitiated reaction between a halogen donor, such as a halogen molecule and a substrate proceeds typically via a radical chain mechanism therefore, the reaction quantum yield, closely related to the average chain length, is greater than unity.155 

The absorption spectra of chlorine and bromine molecules have 2max at 330 nm (s = 651 mol 1 cm and 420 nm =1651 lmol 1 cm ), respectively.155 Since their dissociation energies are 243 and 192 kJ mol which correspond to photons of 492 and 623 nm wavelength, respectively, they readily undergo homolytic fission upon excitation, even when using visible (incandescent) low-power radiant sources. 

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