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Preparation of 1° Amines: Hofmann and Curtius Rearrangement Overview01:07

Preparation of 1° Amines: Hofmann and Curtius Rearrangement Overview

In the presence of an aqueous base and a halogen, primary amides can lose the carbonyl (as carbon dioxide) and undergo rearrangement to form primary amines. This reaction, called the Hofmann rearrangement, can produce primary amines (aryl and alkyl) in high yields without contamination by secondary and tertiary amines.
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
Structure of Amines01:19

Structure of Amines

The hybridized nitrogen atom in amines possesses a lone pair of electrons and is bound to three substituents with a bond angle of around 108°, which is less than the tetrahedral angle of 109.5°. However, the C–N–H bond angle is slightly larger at 112°, with a carbon–nitrogen bond length of 147 pm. This carbon–nitrogen bond length of of amines is longer than the carbon–oxygen bond of alcohols (143 pm) but shorter than alkanes’ carbon–carbon bond (154 pm). These aspects are illustrated in Figure...
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR01:15

¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR

The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
NMR Spectroscopy Of Amines01:19

NMR Spectroscopy Of Amines

In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is broad and...
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...

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[External stimulus-responsive conformational alterations of aromatic amides].

Iwao Okamoto1

  • 1Laboratory of Organic Chemistry, Showa Pharmaceutical University, Tokyo, Japan. iokamoto@ac.shoyaku.ac.jp

Yakugaku Zasshi : Journal of the Pharmaceutical Society of Japan
|December 3, 2009
PubMed
Summary

Aromatic amides can switch between molecular structures, enabling control over molecular function. This conformational change, influenced by external stimuli, is key for developing advanced molecular switches and devices.

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Area of Science:

  • Molecular Chemistry
  • Supramolecular Chemistry
  • Materials Science

Background:

  • Molecular structure and conformational changes are critical for controlling molecular function, particularly in molecular switches and devices.
  • While most molecular switches require high activation energy for structural changes, some biological systems utilize conformational preferences to regulate bioactivity.
  • Aromatic amides exhibit unique conformational properties, with secondary amides typically favoring trans conformations, while N-methylation promotes cis conformations.

Purpose of the Study:

  • To investigate the conformational alteration of aromatic amides in response to external stimuli.
  • To explore the potential of these stimuli-responsive aromatic amides in the development of molecular switches and functional molecules.

Main Methods:

  • Investigated conformational changes in N-phenyl-N-quinonyl amides based on the redox state of the quinonyl group.
  • Examined conformational alterations in N-methyl pyridylamides influenced by solvent acceptor ability and acid addition.
  • Studied the folding and unfolding behavior of N-methylated pyridylamide oligomers.

Main Results:

  • N-phenyl-N-quinonyl amides demonstrated conformational changes correlated with the redox state of the quinonyl moiety.
  • N-methyl pyridylamides exhibited conformational alterations in response to solvent properties and acid presence.
  • N-methylated pyridylamide oligomers displayed distinct folding and unfolding characteristics.

Conclusions:

  • Aromatic amides can be designed to alter their preferred conformation in response to specific external stimuli.
  • These stimuli-responsive conformational changes in aromatic amides offer promising applications for molecular switches and functional materials.