The Electronic Properties of Fluoroalkyl Groups. Fluorine p-π Interaction1
The Electronic Properties of Fluoroalkyl Groups. Fluorine p-π Interaction1
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氟烷基的电子性质 p-π 相互作用1。
DOI：
10.1021/ja01089a020
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发表时间：
1965
影响因子：
15
通讯作者：
W. A. Sheppard
中科院分区：
文献类型：
--
作者：
W. A. Sheppard
由pKA测定确定的五氟乙基、非氟正丁基和七氟异丙基对苯甲酸和苯胺的诱导和共振效应与三氟甲基相似。从氟离子的超共轭和-诱导效应的角度对这些结果进行了讨论，并对氟烷基的+R特性提出了新的解释。氟的p电子与芳环的-体系的相互作用使电子密度显著地返回到环上，部分抵消了正常的强诱导引退。这一效果在元位置比段落位置更重要，因此段落位置看起来更强烈地停用。对其他氟化基团，如C(OH)(CF3)2，N(CFJ)2和SFS的参数的讨论有力地支持了这一假说，并提出了一种新的方法来解释F19化学位移与取代基参数的相关性。三氟甲基的强烈失活作用得到了很好的认识。定量测量表明，这一效应主要归因于诱导退缩，但在芳香族体系中，也发现了共轭贡献(+R特征)的显著增强。2硝基或氰基类型的相互作用是不可能的，已经提出了另外两种机制来解释+R
The inductive and resonance effects of the pentafluoroethyl, nonafluoro-n-butyl, and heptafluoroisopropyl groups determined from pKa measurements on benzoic acids and anilines are similar to those of a trifluoromethyl group. These results are discussed in terms of fluoride ion hyperconjugation and-inductive effect, and a new explanation is proposed for the+ R character of the fluoroalkyl groups. The interaction of p-electrons of the fluorines with the-system of the aromatic ring causes significant return of electron density to the ring, partly counteracting the normal strong inductive withdrawal. This effect is more important at the meta than the para position so that the para position appears more strongly deactivated. This hypothesis is strongly supported by a discussion of-parameters for other fluorinated groups, such as C (OH)(CF3) 2, N (CFj) 2, and SFs, and a new approach to interpretation of F19 chemical shift correlations with substituent parameters for benzotrifluorides and arylsulfur pentafluorides.The strongly deactivating effect of the trifluoromethyl group is well recognized. Quantitative measurements have shown that this effect can be mainly attributed to an inductive withdrawal, but in aromatic systems a sig-nificant enhancementby a conjugative contribution (+ R character) is also found. 2 Mutual interactions of the nitro or cyano type are not possible, and two other mechanisms have been proposed to explain the+ R