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Basicity of Guanidines with Heteroalkyl Side Chains in Acetonitrile
Author(s) -
EckertMaksić Mirjana,
Glasovac Zoran,
Trošelj Pavle,
Kütt Agnes,
Rodima Toomas,
Koppel Ivar,
Koppel Ilmar A.
Publication year - 2008
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200800673
Subject(s) - chemistry , acetonitrile , intramolecular force , solvation , guanidine , hydrogen bond , affinities , molecule , titration , superbase , proton affinity , solvent , side chain , medicinal chemistry , computational chemistry , stereochemistry , organic chemistry , catalysis , protonation , ion , polymer
The p K a values of seven novel guanidine derivatives, six of them possessing heteroalkyl substituents capable of forming intramolecular hydrogen bonds, were determined in acetonitrile (MeCN) by using the UV/Vis spectrophotometric titration method. The obtained p K a values range from 24.7 to 27.2. The most basic among the studied guanidines was found to be by ca. 4 p K a units more basic than thewell‐known superbase N 1 , N 1 , N 3 , N 3 ‐tetramethylguanidine (TMG). The trends in the changes in the measured p K a values were compared with the experimental (determined by the extended kinetic method) and theoretical [B3LYP/6‐311+G(2df,p)//B3LYP/6‐31G(d)] gas‐phase proton affinities. It was shown that basicity ordering of the bases with dimethylaminopropyl substituents in acetonitrile follows the trend encountered in the gas phase. However, this is not the case for the methoxypropyl‐substituted guanidines indicating that in these molecules formation of the intramolecular hydrogen bonds is to large extent hindered due to solvation by acetonitrile.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)