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RESEARCH PRODUCT

Through-space spin-spin coupling in acetylenic systems. Ab initio and DFT calculations

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Abstract: We have investigated, by means of ab initio and DFT calculations, the magnitude of through-space spin-spin couplings ( J CH and J HH ) in CH/π bonded van der Waals dimers involving acetylene, and in a structurally related covalent compound (4-ethynylphenanthrene). Within regions where the interaction is stabilizing J HH couplings are very small (< 0.1 Hz) for all complexes. In the acetylene-methane complex J CH is also very small, whereas in the acetylene-benzene complex and the acetylene dimer it shows a relatively large dependence on the tilt angle from the T-shaped arrangement, for which the smallest values are calculated, to a parallel slipped arrangement where J CH is ca. 0.5 Hz. The relative magnitude of through-space couplings in 4-ethynylphenanthrene and a tilted acetylene-benzene dimer, featuring the same internuclear arrangement as in model dimers, are compared. Keywords: Through-space coupling, NMR, ab initio , DFT. Introduction Although spin-spin coupling is normally considered as a signature of covalent bonding, several cases have been known for a long time where non-negligible couplings are observed between nuclei (notably