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|Computer-Assisted Structure Elucidation of Two Isomeric, Highly Symmetrical Helical Molecules||D.R. Carbery, J.P. Lowe, A. Moser, D. Argyropoulos||Download|
Computer-Assisted Structure Elucidation of Two Isomeric, Highly Symmetrical Helical Molecules
David R. Carbery, John P. Lowe, Arvin Moser, Dimitris Argyropoulos
Abstract: Two isomeric, highly-symmetrical helical molecules were synthesized by Rh(I)-catalysed cycloisomerisation of a suitable triyne substrate. The isomers were separated by preparative scale liquid chromatography before 10 mg of each isomer was dissolved with deuterated chloroform and placed in an NMR tube in order to confirm their structures. Here we describe the advanced computation method used for confirming the structures by NMR experiments only.
Due to the presence of molecular symmetry the NMR spectra of the resulting compounds exhibited very few peaks relative to the size of the molecule. That is, half the number of expected signals are observed in the 13C NMR spectrum and, in addition, several of the signals are extremely closely spaced. Moreover the deficient hydrogen content of the compounds resulted in a low number of correlations in the 1H-13C HMBC spectra.
Computer Assisted Structure Elucidation (CASE) together with band-selective versions of the HSQC and HMBC experiments were employed to determine the structures and assign unequivocally the NMR data and thus confirm the new molecules. The final assignment of the two isomeric structures was accomplished by using 1H-1H 2D NOESY experiments.