NMR-SPECTRA OF PORPHYRINS .13. RING CURRENT MODEL FOR PORPHYRIN AND CHLORIN (7,8-DIHYDROPORPHYRIN) RINGS
NMR-SPECTRA OF PORPHYRINS .13. RING CURRENT MODEL FOR PORPHYRIN AND CHLORIN (7,8-DIHYDROPORPHYRIN) RINGS
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DOI：
10.1002/mrc.1270090617
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发表时间：
1977-01-01
期刊：
影响因子：
--
通讯作者：
SMITH, KM
中科院分区：
文献类型：
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作者：
ABRAHAM, RJ;FELL, SCM;SMITH, KM
苯中环电流位移的等效偶极模型被证明与众所周知的两个电流回路计算的等效偶极模型是等效的。本文用双偶极近似描述了卟啉体系中环电流效应的网络模型，计算了卟啉体系中的环电流位移，这与观察到的质子在环平面内和环平面上的位移是一致的。对模型作一个简单的修改，就可以处理二氢卟酚环中的环电流位移。这些模型可以用来提供，非常简单，很好的估计环电流位移的卟啉和二氢卟酚环的点以上和外部的电流回路;协议是足够好，允许外围取代基的分配，并提供有关其方向的信息。该模型与游离碱卟啉及其金属络合物中的外围环电流回路一致。这些结果的关系，在多环芳烃和卟啉的质子化位移的计算进行了讨论。
The equivalent dipole model of the ring current shift in benzene is shown to be equivalent to that of the well‐known two current loop calculation. A network model of the ring current effect in the porphyrin system is described, using the double–dipole approximation, to give a calculation of the ring current shifts in the porphyrin system; this agrees with the observed shifts of protons both in the ring‐plane and above it. A simple modification of the model enables treatment of ring current shifts in the chlorin ring. These models may be used to provide, very simply, good estimates of the ring current shifts of the porphyrin and chlorin rings at points above and outside the current loops; the agreement is sufficiently good to allow assignments of peripheral substituents to be made, and to provide information on their orientation. The model is consistent with a peripheral ring current loop in both the free‐base porphyrins and their metal complexes. The relationship of these results to calculations in polycyclic aromatics and to protonation shifts in porphyrins is discussed.