自由基對前驅物（氮-苯磺醯取代的吡咯、咪唑及吲哚） 的合成與光化學反應

Abstract

一系列含氮-苯磺醯取代的吡咯化合物39、47、52及53在77 K，以MTHF為介質，利用230-325 nm的波長照射測得之EPR光譜，D'值分別為0.0228、0.0225、0.0190及0.0176 cm-1；而47在相同條件下變換低溫介質時，D'值介於0.0219∼0.0225 cm-1之間。在4 K的溫度下，化合物51及47其D'值為0.0239與.0237 cm-1；且分別在12-44 K、與8-52 K的溫度範圍，可得到線性之Curie plot，意即此兩化合物照光所得之自由基對為參重基態，或其單態與參態能階非常接近（ΔES-T ≦30 cal/mole）。由自由基捕捉實驗，亦可單離Ts基與捕捉試劑加成之產物；且具有氮-苯磺醯取代之化合物85、88亦可觀測到EPR之參態自由基訊號，說明氮硫間鍵結極易因照光斷裂，而產生自由基對。因此 Berson教授以化合物18在77 K相同光源及介質下，觀測到的參態自由基其D'值為0.0226 cm-1，此訊號極有可能源自於自由基對而非雙自由基。

A series of 39, 47, 52 and 53 in 2-methyltetrahydrofuran glass matrices at 77 K were irradiated with 230-325 nm (NiSO4-filtered, UV light), which gave triplet EPR spectra, and the zero-field splitting (zfs) parameters D' values are 0.0228, 0.0225, 0.0190 and 0.0176 cm-1, respectively. At 4 K, the D' values of 51 and 47 are 0.0239 and 0.0237 cm-1, respectively. The radical pairs derived from 51 (12-44 K) and 47 (8-52 K) both showed linear Curie plots, thereby indicating either the ground state are triplets or that singlet and triplet states are degenerate (≦30 cal/mole difference). An addition product of Ts and MNP was observed when 51 was photolyzed in the presence of spin trapping agent. N-benzenesulfonyl substituted hetercyclic molecules 85 and 88 also gave triplet EPR spectra, which are consistent with triplet radical pairs. Results indicate that nitro-sulfur bonds were easily cleaved by 230-325 nm photolysis, and the results are supported by ab initio calculations. Therefore, the reported D' value (0.0226 cm-1) of a biradical by Professor Berson in the photolysis of N-tosyl pyrrole diazene 18 (J. A. Berson, J. Am. Chem. Soc. 1997, 119, 1416.) may not be a triplet biradical and could be a triplet radical pair instead.