Proton transfer reaction in N‐methyl‐2‐hydroxy‐Schiff bases

Abstract

The structure of two ortho‐hydroxy N‐methyl Schiff bases as well as the selfcondensation product of 2‐(N‐methyliminomethyl)‐phenol are determined by X‐Ray crystallography and by ab initio DFT, on B3LYP/6‐31G** level, calculations. Electronic coupling between acidic and basic centres of the molecules, especially effective in the proton transfer structure, is discussed on the basis of detailed analysis of differentiation of bond lengths both in aromatic and chelate rings. Consequences of this coupling on the intramolecular hydrogen bonding and proton transfer process are discussed.

Specific Features of Intramolecular Proton Transfer Reaction in Schiff Bases

“…Similar result (47 %) was found [16] in the crystal structure of proton transfer form of 2-(N-methyliminomethyl)-4,6-dichlorophenol by the analysis the geometry of chelate ring. In both approaches the standard single, double and aromatic bond lengths were applied [17].…”

Solid-State and Solution Structural Studies of 4-{[C(E)]-1H-Azol-1-ylimino)methyl}pyridin-3-ols

“…1 for atom numberings) of all four compounds 1 -4 in (D 6 )DMSO solution, and analysis of the chemical shifts (see Table 4) led to the conclusion that only the hydroxyimino form A exists in all cases in the solvent (D 6 )DMSO. Except for 2, the 4-{[C(E)]-(1H-azol-1-ylimino)methyl}pyr-idin-3-ols were not soluble in CDCl 3 .…”

“…4 J(2',5') = 1.4, HÀC(2')); 8.14 (d, 3 J(5, 6) = 5.1, HÀC(6)); 7.92 (t, 3 J(4',5') = 1.4, HÀC(5')); 7.81 (d, HÀC (5)); 7.13 (t, HÀC(4')). 13 C-NMR (CD 3 A C H T U N G T R E N N U N G OD): 155.2 (C(3)); 150.3 (CH=N); 141.2 (C(6)); 140.3 (C(2)); 138.0 (C(2')); 129.6 (C(4')); 127.6 (C(4)); 122.8 (C(5)); 113.6 (C(5')).…”

“…13 C-NMR (CD 3 A C H T U N G T R E N N U N G OD): 155.2 (C(3)); 150.3 (CH=N); 141.2 (C(6)); 140.3 (C(2)); 138.0 (C(2')); 129.6 (C(4')); 127.6 (C(4)); 122.8 (C(5)); 113.6 (C(5')). Anal.…”

A Multinuclear Magnetic Resonance Study of Intramolecular Hydrogen Bonding in Some Schiff and Schiff–Mannich Bases in Solution and in the Solid State

“…However, the position of the most diagnostic C-2 signal confirms the existence of weak hydrogen bonding in the solid state. Comparison of bond lengths derived from X-ray measurements [5,6] suggests that for the compounds investigated we can expect the NH bond lengths to be close to 1.7 Å for the coumarine derivative and a little bit longer for the Schiff base BS. This conclusion is in accord with the available X-ray data [1] where the N-H distance was estimated to be 1.69 Å for the coumarin derivative and 1.65 Å for BS.…”