Naslov
13C NMR Spectroscopy of N-Aryl Pyrroles

Autori
Vikić-Topić, Dražen ; Vorkapić-Furač, Jasna ; Williard, Paul ; Mintas, Mladen

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
XIXth European Congress on Molecural Spectroscopy / - , 1989

Skup
XIXth European Congress on Molecural Spectroscopy

Mjesto i datum
Dresden, Njemačka, 04.09.1989. - 08.09.1989

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
N-aryl pyrroles; 13C NMR spectra

Sažetak
The six-bond carbon-fluorine coupling constant in N-(4-fluorophenyl) substituted pyrroles can be related to the molecular conformation via a π – electron conjugation model which follows the cos2Θ law. Using this model the molecular dihedral angles of N-(4-fluorophenyl)-2, 5-dimethylpyrrol and N-(4-fluorophenyl)-2, 5-dimethylpyrrole-3-carbaldehyde (Figure) in solution were found to be similar, amounting to 61-63° to 60-62°, respectively. The crystal geometry of latter was determined by X-ray analysis revealing that aryl and pyrrole rings are twisted toward each other with dihedral angle between the two ring planes of 76.4 (3)°. Ab intio 6-31G calculations (GAUSS 92) have given dehedral angle values of 93° and 87° , respectively. However these dihedral angles are averaged values since librational motion around N-C bond exists, approximately amounting to ± ; ; 30° . It means that energy minimum for rotation is in the range 60-120°. Since six-bond C-F coupling is cos2Θ e dependent only rotamer populations with dihedral angles less than 90° may be observed in 13C NMR. The libration was also analyzed by MM (Insight II) giving fair correspondence with ab initio data. The ab initio analysis of methyl rotation showed negligible diferences in rotational eneries among molecules investigated. Even in the cases where flourine was in ortho position hindered rotation of methyl groups was not proved.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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