{"title":"3,3,4,4,5,5-Hexamethyl-1,2-bis(methylene)cyclopentane","authors":"H. Mayr, J. Baran, U. W. Heigl","doi":"10.5282/UBM/EPUB.3939","DOIUrl":"https://doi.org/10.5282/UBM/EPUB.3939","url":null,"abstract":"","PeriodicalId":12702,"journal":{"name":"Gazzetta Chimica Italiana","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"1991-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75271029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The carbon shifts of 2,6-di-t-butyl-4-arylpyrylium and thiopyrylium cations (aryl = XC6H4- with X = p-N02 , m-Cl, p-Cl, H, p-Me, p-MeO, p-NMe2 ) have been determined in CD3CN. While the C-4 chemical shifts of the two heteroaromatic rings are largely affected by rr-polarization, as shown by the shielding induced by electron-withdrawing substituents, the C-2 (C-6) chemical shifts are free from such effect. The C-2 (C-6) and C-4 chemical shifts have been compared with the corresponding second-order rate constants for the methoxide attachment to C-2 (C-6) and C-4 positions (k2 and k4 , respectively), obtained in MeOH at 25 °C. For both the cation series the C-2 (C-6) chemical shifts are linearly correlated with the corresponding log k2 values, thus suggesting a charge control for the methoxide attachment to these cations. At variance, the C-4 chemical shifts do not show any correlation with log k4 values. Thus, whenever the chemical shifts are affected by 1t -polarization, they are no longer reliable indicators of reactivity changes, despite the dominant role of charge-charge interactions in the transition state.
{"title":"13C NMR Study of 2,6-Di-t-butyl-4-arylpyrylium and Thiopyrylium Cations. Carbon Shifts versus Reactivities","authors":"G. Cerichelli, G. Doddi, G. Ercolani","doi":"10.1002/CHIN.198837059","DOIUrl":"https://doi.org/10.1002/CHIN.198837059","url":null,"abstract":"The carbon shifts of 2,6-di-t-butyl-4-arylpyrylium and thiopyrylium cations (aryl = XC6H4- with X = p-N02 , m-Cl, p-Cl, H, p-Me, p-MeO, p-NMe2 ) have been determined in CD3CN. While the C-4 chemical shifts of the two heteroaromatic rings are largely affected by rr-polarization, as shown by \u0000the shielding induced by electron-withdrawing substituents, the C-2 (C-6) chemical shifts are free from such effect. The C-2 (C-6) and C-4 chemical shifts have been compared with the corresponding second-order rate constants for the methoxide attachment to C-2 (C-6) and C-4 positions (k2 and k4 , respectively), obtained in MeOH at 25 °C. For both the cation series the C-2 (C-6) chemical shifts are linearly correlated with the corresponding log k2 values, thus suggesting a charge control for the methoxide attachment to these cations. At variance, the C-4 chemical shifts do not show any correlation with log k4 values. Thus, whenever the chemical shifts are affected by 1t -polarization, they are no longer reliable indicators of reactivity changes, despite the dominant role of charge-charge interactions in the transition state.","PeriodicalId":12702,"journal":{"name":"Gazzetta Chimica Italiana","volume":"35 1","pages":"291-294"},"PeriodicalIF":0.0,"publicationDate":"1988-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86271193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Berti, G. Catelani, F. Colonna, M. Ferretti, L. Monti
{"title":"RING CONTRACTIONS IN THE CONVERSION OF UNHINDERED RACEMIC PYRANOSIDE 4-O-MESYLATES INTO FURANOSIDE 5-O-BENZOATES","authors":"G. Berti, G. Catelani, F. Colonna, M. Ferretti, L. Monti","doi":"10.1002/CHIN.198525358","DOIUrl":"https://doi.org/10.1002/CHIN.198525358","url":null,"abstract":"","PeriodicalId":12702,"journal":{"name":"Gazzetta Chimica Italiana","volume":"181 1","pages":"85-90"},"PeriodicalIF":0.0,"publicationDate":"1985-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76260907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Phase-Transfer Catalysts: Synthesis and Catalytic Activity of Alkyl Substituted Aza-Macrobicyclic Polyether","authors":"M. Cinquini, F. Montanari, P. Tundo","doi":"10.1002/CHIN.197736282","DOIUrl":"https://doi.org/10.1002/CHIN.197736282","url":null,"abstract":"","PeriodicalId":12702,"journal":{"name":"Gazzetta Chimica Italiana","volume":"11 1","pages":"11-14"},"PeriodicalIF":0.0,"publicationDate":"1977-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88010711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Synthesis and Properties of Cobalt(I) and Iron(II) Complexes with Carbonyls, Phosphines, and Isocyanides","authors":"G. Albertin, E. Bordignon, U. Croatto, A. Orio","doi":"10.1002/CHIN.197506380","DOIUrl":"https://doi.org/10.1002/CHIN.197506380","url":null,"abstract":"","PeriodicalId":12702,"journal":{"name":"Gazzetta Chimica Italiana","volume":"191 1","pages":"1041-1057"},"PeriodicalIF":0.0,"publicationDate":"1974-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83064434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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