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1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation
A S Antonov1,2, A F Pozharskii1, P M Tolstoy2
1Department of Organic Chemistry, Southern Federal University, Zorge str. 7, 344090 Rostov-on-Don, Russian Federation.
Methoxy groups on ortho-arylketimines significantly boost nitrogen basicity, influencing protonation sites. This impacts hydrogen bonding and rotation dynamics in protonated naphthalene derivatives.
Area of Science:
- Organic Chemistry
- Supramolecular Chemistry
- Computational Chemistry
Background:
- Investigating the structural and protonation properties of ortho-arylketimines derived from 1,8-bis(dimethylamonio)naphthalene.
- Understanding the influence of methoxy substituents on the electronic and steric properties of these molecules.
Purpose of the Study:
- To elucidate the structure and protonation behavior of ortho-arylketimines with varying methoxy groups.
- To explore the stabilization mechanisms of neutral and protonated species.
- To determine the effect of methoxy groups on basicity and rotational dynamics.
Main Methods:
- Solution-state Nuclear Magnetic Resonance (NMR) spectroscopy in acetone, DMSO, and MeCN.
- Solid-state X-ray diffraction analysis.
- Gas-phase Density Functional Theory (DFT) calculations.
Main Results:
- Stabilization of neutral E-isomers via intramolecular C=N-H···OMe hydrogen bonds.
- Electron-donating methoxy groups enhance imino nitrogen basicity, leading to proton abstraction from the naphthalene core.
- Experimental evidence for hydrogen bonding involving the protonated dimethylamino group and the imine nitrogen.
- Methoxy group number and position significantly influence the rotation rate of the NH2+ fragment in dicationic forms.
Conclusions:
- Methoxy substituents play a crucial role in dictating the protonation pathways and structural preferences of ortho-arylketimines.
- Intramolecular hydrogen bonding contributes to the stability of neutral imine isomers.
- The electronic effects of methoxy groups are key to understanding the observed basicity and dynamic behavior.
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