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Correlation between the Reactivity and Spectroscopic Properties of N-Substituted Secondary Thioamides. New Intramolecular N• •H+• •N Binding Approach and Proton Complexes Based on Thioamide Ligation
Abstract
From a comparison of chem. shifts and wavenumbers of several secondary thioamides and amides having monocationic substituents attached to thiocarbamoyl or carbamoyl groups by a polymethylene chain, new intramol. unconventional N···H+···N H bonding effects were discovered. It is argued that the CH2-N rotation is hindered and two +H···NHMe nonequiv. protons occur in a proton spectrum of hydrochloride RCH2C(S)NH(CH2)3NHMe-HCl (I; R = 1-thyminyl) (at 10.68 and 2.77 ppm, resp.) instead of two +NH2CH3 protons. Presumably, the above steric factors inhibit the acidic hydrolysis of I (stabilized by strong intramol. N···H+···N H bonds) to an amide and prevent intramol. cyclization of RCH2C(S)NH(CH2)3NHMe (R = 1-thyminyl) (stabilized by strong intramol. neutral-neutral N···HN H bonds) to a cyclic amidine. Postulation of addnl. dihydrogen bond formation is helpful in understanding the spectroscopic differences of RCH2C(O)NH(CH2)3NHMe-HCl (II; R = 1-thyminyl) and RCH2C(O)NH(CH2)2NHMe-HCl (R = 1-thyminyl). The above new bonding is also compared with intramol. N···H-N+ H bonds in primary amine salts RCH2C(O)NH(CH2)nCH2NH2-HCl (III; R = 1-thyminyl, n = 1-3) and MeCONH(CH2)3NH2-HCl (IV). In contrast to RCH2C(O)NH(CH2)3NHMe (R = 1-thyminyl), a cooperative H bonded system is obsd. in V and VI. The weak H bonds in III-VI facilitate the hydrolysis and cyclization reactions of secondary thioamides. The spectroscopic data for secondary (thio)amides are esp. useful for characterizing the electronic situation at the (thio)carbamoyl N atoms and they are perfectly correlated with the reactivity. Examples of chelation of protons by thioamides (VII and VIII), which contain strongly electron-donating pyrimidine groups, are presented to show the contribution of dihydrogen bonding in the protonation reaction similar to I and II.
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- Category:
- Magazine publication
- Type:
- Magazine publication
- Published in:
-
MAGNETIC RESONANCE IN CHEMISTRY
no. 41,
edition 3,
pages 169 - 176,
ISSN: 0749-1581 - Title of issue:
- Magnetic Resonance in Chemistry strony 169 - 176
- Publication year:
- 2003
- Bibliographic description:
- Jaroslaw Spychala, Correlation between the Reactivity and Spectroscopic Properties of N-Substituted Secondary Thioamides. New Intramolecular N• •H+• •N Binding Approach and Proton Complexes Based on Thioamide Ligation, Magnetic Resonance in Chemistry, vol. 41(3), pages 169-176, 2003.
- DOI:
- Digital Object Identifier (open in new tab) https://doi.org/10.1002/mrc.1157
- Verified by:
- No verification
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