Electronic effects of heterocyclic ring systems as evaluated with the aid of13C and15N NMR chemical shifts and NBO analysis

H. Neuvonen, F. Fülöp, K. Neuvonen, A. Koch, E. Kleinpeter

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The electronic effects of the 5- and 6-membered heterocyclic rings on the C=N-N unit of five different hydrazone derivatives of pyridine-2-, -3- and -4-carbaldehydes, pyrrole-2-carbaldehyde, furan-2- and -3-carbaldehydes and thiophene-2- and -3-carbaldehydes have been studied with the aid of 13C and 15 NMR measurements together with the natural bond orbital (NBO) analysis. As model compounds are used the corresponding substituted benzaldehyde derivatives. The polarization of the C=N unit of the hydrazone functionality of the heteroaryl derivatives occurs in an analogous manner with that of phenyl derivatives. The electron-withdrawing heteroaryl groups destabilize and the electron-donating groups stabilize the positive charge development at the C=N carbon while the effect on the negative charge development is opposite. The 15N NMR chemical shift of the C=N and C=N - N nitrogens and the NBO charges at C=N - N unit can be correlated with the replacement substituent constants σ of the heteroaryl groups. 13C NMR shifts of the C=N carbon of N,N-dialkylhydrazones of the heteroarenecarbaldehydes can be correlated with a dual parameter equation possessing the polar substituent constant σ* of the heteroaryl group and the electronegativity of the heteroatom as variables.

Original languageEnglish
Pages (from-to)173-184
Number of pages12
JournalJournal of Physical Organic Chemistry
Volume21
Issue number3
DOIs
Publication statusPublished - Mar 2008

Fingerprint

Chemical shift
chemical equilibrium
Nuclear magnetic resonance
Derivatives
Hydrazones
orbitals
nuclear magnetic resonance
hydrazones
rings
electronics
Carbon
Thiophenes
Electronegativity
Electrons
carbon
furans
pyrroles
thiophenes
pyridines
electrons

Keywords

  • C NMR
  • Atomic charges
  • Heteroaryl groups
  • Hydrazones
  • Replacement substituent constants

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Electronic effects of heterocyclic ring systems as evaluated with the aid of13C and15N NMR chemical shifts and NBO analysis. / Neuvonen, H.; Fülöp, F.; Neuvonen, K.; Koch, A.; Kleinpeter, E.

In: Journal of Physical Organic Chemistry, Vol. 21, No. 3, 03.2008, p. 173-184.

Research output: Contribution to journalArticle

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