The effect of solvent accessible surface on Hammett‐type dependencies of infinite dilution 29Si and 13C NMR shifts in ring substituted silylated phenols dissolved in chloroform and acetone |
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Authors: | Vratislav Blechta Stanislav Šabata Jan Sýkora Jiří Hetflejš Ludmila Soukupová Jan Schraml |
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Institution: | Institute of Chemical Process Fundamentals of the ASCR, v. v. i., , 16502 Prague, 6 Czech Republic |
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Abstract: | Infinite dilution 29Si and 13C NMR chemical shifts were determined from concentration dependencies of the shifts in dilute chloroform and acetone solutions of para substituted O‐silylated phenols, 4‐R‐C6H4‐O‐SiR′2R″ (R = Me, MeO, H, F, Cl, NMe2, NH2, and CF3), where the silyl part included groups of different sizes: dimethylsilyl (R′ = Me, R″ = H), trimethylsilyl (R′ = R″ = Me), tert‐butyldimethylsilyl (R′ = Me, R″ = CMe3), and tert‐butyldiphenylsilyl (R′ = C6H5, R″ = CMe3). Dependencies of silicon and C‐1 carbon chemical shifts on Hammett substituent constants are discussed. It is shown that the substituent sensitivity of these chemical shifts is reduced by association with chloroform, the reduction being proportional to the solvent accessible surface of the oxygen atom in the Si‐O‐C link. Copyright © 2012 John Wiley & Sons, Ltd. |
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Keywords: | 29Si NMR 13C NMR 1H NMR solvent accessible surface substituent effects chemical shifts Hammett‐type dependence |
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