Variable-temperature solid-state /sup 13/C CPMAS NMR analysis of meso-tetrapropylporphyrin and of octaethylporphyrin

Journal Article · Wed Aug 17 04:00:00 EDT 1988 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00225a011· OSTI ID:6181079

Frydman, L; Olivieri, A C; Diaz, L E; Valasinas, A; Frydman, B

The high-resolution solid-state /sup 13/C NMR spectra of meso-tetrapropyl- and octaethylporphyrin were recorded with use of the cross-polarization (CP), high-power decoupling, magic-angle spinning (MAS) technique. Doublings in the pyrrole carbon signals of these compounds were ascribed to kinetic solid-state effects involved in the central hydrogen migration. It was found that whereas in meso-tetrapropylporphyrin the positions of the pyrrole carbon signals in the low temperature solution /sup 13/C NMR spectrum are similar to those in the room temperature solid-state NMR spectrum, this is not the case for octaethylporphyrin. In order to characterize the kinetic behavior of these compounds in the solid phase, /sup 13/C CPMAS NMR spectra were recorded at temperatures from slow to fast exchange limits. The changes observed in the spectra were analyzed assuming that the hydrogen migration proceeds between two tautomers of different energies. The shifts that are induced by the aromatic clouds of neighboring molecules were also calculated. With use of these ring current shifts and the low temperature solution chemical shift values, it was possible to obtain kinetic parameters of the solid-state reaction at different temperatures. The implications that the obtained results have for the understanding of the N-H tautomerization process in free base porphyrins are discussed, as well as the relevance that the latter may have for obtaining a mean structure of these compounds. 66 references, 10 figures, 3 tables.

• Research Organization: Universidad de Buenos Aires (Argentina)
• OSTI ID: 6181079
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 110:17; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALKANES
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
DATA
ELECTRONIC STRUCTURE
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
INFORMATION
ISOTOPES
LIGHT NUCLEI
MOLECULAR STRUCTURE
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
SPECTRA
STABLE ISOTOPES