Competition between inter‐ and intramolecular hydrogen bonding in molecules with donor and acceptor groups. Solvatochromic and thermochromic evidence in n‐(nitrophenyl)alkylenediamines

Abstract

Solvent effects on the absorption spectra of N-@-nitrophenyl)dimethylenediamine (la), N-(p-nitropheny1)trimethylenediamine (Ib), N-@-nitrophenyl)tetramethylenediamine(Ic), N-methyl-N-@-nitropheny1)tetramethylenediamine (111, N-butyl-p-nitroaniline (111) and N-(o-nitropheny1)trimethylenediamine (IV) were studied at different temperatures. Whereas 11, Ill and 1V do not show any variation in their spectra characteristics with changes in temperature, I shows a hypsochromic shift with a hypochromic effect when the temperature is increased. The Kamlet and Taft solvatochromic comparison method was applied. A strong effect of the fl parameter on I and 111 was interpreted as being due to the hydrogen bond donor ability of the H atom in the aromatic amino groups. In I, the fl inEuence increases with increase in temperature. These facts are explained by proposing the formation of intramolecular hydrogen bonds between amine groups in all compounds I, besides the intermolecular interactions between compounds I and the solvent. On the other hand, the values of vor s and b for Ib are smaller than the corresponding values for Ia and Ic. Since in Ib a six-membered ring may be formed, a more stable bond is expected.Comparative 'H N M R of the aniline hydrogen for I and IV (in non-hydrogen bond acceptor solvents) shows a particular downfield chemical shift for I which suggests hydrogen bond formation. Since this effect is independent of concentration, the hydrogen bond is assumed to be intramolecular, in agreement with solvatochromic and thermochromic studies. These conclusions were corroborated by IR spectroscopy in the solid state and in chloroform solutions.

Intramolecular versus Intermolecular Hydrogen Bonding in the Adsorption of Aromatic Alcohols onto an Acrylic Ester Sorbent

“…Second, the geometry of the bonded conformer affects the strength of the intramolecular hydrogen bond. For compounds with little conformational flexibility, such as ortho-substituted phenols, intramolecular hydrogen bonding is generally favorable when planar, five- or six-membered rings are formed, with six-membered ring structures being the more stable. , Likewise, for a series of flexible N- ( p- nitrophenyl)alkylenediamines, it has been reported that intramolecular hydrogen bonds do form, and that the strongest bond occurs for the molecule that is able to form a six-membered ring . The molecules in the present study all form either a five- or six-membered ring when in an intramolecularly hydrogen-bonded conformer.…”

“…15,16 Likewise, for a series of flexible N-(p-nitrophenyl)alkylenediamines, it has been reported that intramolecular hydrogen bonds do form, and that the strongest bond occurs for the molecule that is able to form a six-membered ring. 17 The molecules in the present study all form either a five-or six-membered ring when in an intramolecularly hydrogen-bonded conformer.…”

Determination of lipophilic descriptors of antihelmintic 6,7‐diaryl‐pteridine derivatives useful for bioactivity predictions

“…1 the spectra of compound 14 corresponding to the tautomer A (Goya et al, 1988; see Scheme 2) at three different temperatures are shown as an example. This result suggests no chemical equilibrium (Giacomelli et al, 1994) at least in this short temperature range.…”

Inter‐ and intramolecular hydrogen bonds in polyamines: variable‐concentration1H‐NMR studies

“…1 H‐NMR chemical shifts and signal strengths are very sensitive to hydrogen‐bond formation. In almost all cases, formation of a hydrogen bonds shifts the 1 H‐NMR signal downfield 36. Hydrogen bonds and the concurrent fast proton exchange contribute to widening of the resonance signal 37 .…”