Irradiation of the 13C satellite (1% natural abundance) of the NMR 1H signals yield NOE effects on the spatially close hydrogens of the same isotopomer but not on the hydrogens of the 99% isotopomer having only 12C atoms. In a DPFGSE-NOE sequence the latter signals are completely cancelled and it is possible, therefore, to detect NOE effects experienced by isochronous lines that would not be otherwise observable. This allows the structural assignments of symmetric isomers to be unambiguously obtained. Examples are reported for the cases of the cis and trans dimethylstilbene, cis and trans stilbeneoxide, 2,5- and 3,4-dimethylthiophene, 1,8- and 1,5-dimethylnaphthalene, syn and anti 1,2-bis(2-methyl-1-naphthyl)benzene, 1.3-cyclooctadiene and cycloheptatriene.
L. Lunazzi , A. Mazzanti (2004). A New NMR Approach for the Assignment of Symmetric Isomers. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 12155-12157 [10.1021/ja047887+].
A New NMR Approach for the Assignment of Symmetric Isomers
LUNAZZI, LODOVICO;MAZZANTI, ANDREA
2004
Abstract
Irradiation of the 13C satellite (1% natural abundance) of the NMR 1H signals yield NOE effects on the spatially close hydrogens of the same isotopomer but not on the hydrogens of the 99% isotopomer having only 12C atoms. In a DPFGSE-NOE sequence the latter signals are completely cancelled and it is possible, therefore, to detect NOE effects experienced by isochronous lines that would not be otherwise observable. This allows the structural assignments of symmetric isomers to be unambiguously obtained. Examples are reported for the cases of the cis and trans dimethylstilbene, cis and trans stilbeneoxide, 2,5- and 3,4-dimethylthiophene, 1,8- and 1,5-dimethylnaphthalene, syn and anti 1,2-bis(2-methyl-1-naphthyl)benzene, 1.3-cyclooctadiene and cycloheptatriene.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
