Experimental and computational studies of molecules with close, non-bonded hydrogenehydrogen contacts: common computational methods grossly overestimate some ‘through-space’ NMR scalar coupling constants

摘要

The NMR spinespin scalar coupling constants (J_(HH)’s) of closely contacting, but non-bonded hydrogen atoms in a series of highly strained molecules (including a new in,in-cyclophane made specifically for this study) have been examined both experimentally and computationally. The experimental JHH’s are invariably quite small (0.1-0.6 Hz), but common DFT methods with modest basis sets nearly always overestimate these values, by factors of 10-30, and even with quite large basis sets (up to cc-pVQZ) the JHH’s of two of the molecules are overestimated by a factor of 10 or more. Possible reasons for these discrepancies are discussed.