标题：13C NMR chemical shift correlations in application of “tool of increasing electron demand” to stable long-lived carbocations: Comprehensive evaluation
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1981
卷号：78
期号：4
页码：1998-2002
DOI：10.1073/pnas.78.4.1998
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The reliability of 13C NMR chemical shift correlations in the application of the "tool of increasing electron demand" to stable long-lived carbocationic systems is demonstrated by a comprehensive analysis of 22 stable aryl-substituted carbocationic systems. The observation of slopes of less than unity in such chemical shift correlations for several cationic systems has been attributed to additional charge delocalizing mechanisms present in the system (such as homoallylic, cyclopropyl, and {pi} conjugations). The onset of nonclassical {sigma}-delocalization in 2-aryl-2-norbornyl cations with electron withdrawing-substituents previously observed was further verified by using {sigma}C+ substituent constants. Difficulties in relating the CNMR shifts in different carbocationic systems are also discussed.
关键词：stable carbocations ; chemical shift-substituent constant relationships ; onset of nonclassical σ delocalization
