酚类化合物苯环碳原子的化学位移与其净电荷的关系(Ⅱ)--单卤代酚化合物

用从头算RHF/6-31G*方法对卤代酚苯环碳原子的电荷分布进行量子化学计算,从标准图谱上查阅了这些化合物苯环碳原子的化学位移.氟能使其邻、对位负电荷明显增加,化学位移减小.氯、澳的效应不明显,碘呈现出相反的作用.苯环各碳原子Ci的化学位移δi与其净电荷Qi值基本呈线性关系.较大的卤素取代基本身起大的电荷屏蔽作用,使邻近碳原子化学位移受到影响.化学位移有助于判断卤代酚类化合物的反应活性.可推测氟代酚具有较高的亲核-亲电反应活性.

CHEMICAL SHIFT AND CHARGE DISTRIBUTION OF CARBON ATOMS ON THE BENZENE RING OF HALOGENATED PHENOLS

The net charges on the carbon atoms of benzene rings are calculated by ab initio method at HF/6 31G * level for mono halogenated phenols and the corresponding C 13 NMR chemical shifts of these carbon atoms from standard data are presented. Fluorine can apparently enhance the negative charges on the carbon atoms of its ortho and para positions and reduce the corresponding values of chemical shift. The effects of chlorine and bromine are not apparent and inverse effects are observed for iodide. Linear relationship between the values of the chemical shift and net charges of the carbon atoms is investigated among these compounds. Larger halogen substituents take more shielding effects on adjacent carbon atoms and influence the values of chemical shift. The values of chemical shifts are helpful in estimating the reactivity of the halogenated phenols. Fluorophenols can be predicted with high nucleophilic electrophilic reactivity.