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首页> 外文期刊>Zeitschrift fur Naturforschung. A, A journal of physical sciences >Chlorine Substituted Acetic Acids and Salts. Effect of Salification on Chlorine-35 NQR
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Chlorine Substituted Acetic Acids and Salts. Effect of Salification on Chlorine-35 NQR

机译：氯取代的乙酸和盐。盐化对氯35 NQR的影响

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The NQR of a quadrupolar probe nucleus is often used to investigate the effect of substituent in molecules. The inductive effect, based on a partial charge migration along the molecular skeleton is the only one present in saturated aliphatics, the conjugative effect appearing in conjugated molecules, especially aromatics. As the stepwise charge migration mechanism, formerly used to explain the inductive effect, is now believed obsolete, we have wanted to reexamined the case of chlorine substituted acetic acids and salts. The data in literature was extended by observing resonances and determining NQR frequencies in several acids and salts. The present analysis of the salification of mono-, di- and tri-chloroacetic acids, which is equivalent to a deprotonation or the substitution of the acid hydrogen by a negative unit charge, shows that a model based on the polarization of the chlorine atom(s) by the carboxyle group is consistent with experimental results: the polarization energy appears to be proportional to the NQR frequency shifts; experimental data show a correlation between the NQR frequency shifts accompanying salification and the variations of the intrinsic acidity measured in the gas phase; this, in turn shows that there is a proportionality between the polarization energy and the variations in the acid free enthalpy of dissociation. From the comparison between fluorine, chlorine, bromine and iodine, it also appears that an alternative mechanism, the polarization of the carboxyl group by the halogen, would be important only in the case of the fluoroacetic acid.
机译：四极探针核的NQR通常用于研究分子中取代基的作用。基于沿着分子骨架的部分电荷迁移的感应效应是饱和脂族中唯一存在的感应效应，共轭效应出现在共轭分子中，尤其是芳族化合物。由于以前认为是用于解释感应效应的逐步电荷迁移机制，现在已经过时了，我们希望重新研究氯取代的乙酸和盐的情况。通过观察共振并确定几种酸和盐中的NQR频率来扩展文献中的数据。目前对一氯，二氯和三氯乙酸盐化的分析，相当于去质子化或用负单位电荷取代酸氢，表明基于氯原子极化的模型（ s）羧基与实验结果相符：极化能量似乎与NQR频移成比例；实验数据表明，伴随盐化的NQR频移与气相中固有酸度变化之间存在相关性。这又表明极化能与解离的无酸焓的变化成比例。从氟，氯，溴和碘之间的比较来看，似乎另一种机理，即卤素对羧基的极化，仅在氟乙酸的情况下才是重要的。

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