Naslov
Basicity of guanidines with heteroalkyl side chains in acetonitrile

Autori
Eckert-Maksić, Mirjana ; Glasovac, Zoran ; Trošelj, Pavle ; Kütt, Agnes ; Rodima, Toomas ; Koppel, Ivar ; Koppel, Ilmar A.

Izvornik
European Journal of Organic Chemistry (1434-193X) 2008 (2008), 30; 5176-5184

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
guanidines; hydrogen bonds; UV/vis spectroscopy; basicity; density functional calculations

Sažetak
The pKa 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 pKa values range from 24.7 to 27.2. The most basic among the studied guanidines was found to be by ca. 4 pKa units more basic than thewell-known superbase N1, N1, N3, N3-tetramethylguanidine (TMG). The trends in the changes in the measured pKa 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.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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