15 N NMR spectroscopy 28 —solvent effects on the 15 N 13 C coupling constants of amides, imides, ureas and polypeptides

The 15 N 13 C coupling constants of 15 N‐enriched acetamide, N ‐acetylglycine anilide, phthalimide, α,α′‐bisphthalimido‐ p ‐xylene, N ‐methyl‐ N ′‐phenylurea, poly‐ L ‐alanine and poly‐ L ‐valine were measured in various solvents. It was found that the 15 N 13 C coupling constants depend largely on the nature of the solvent. Increasing acidity leads to higher one‐bond and lower two‐bond coupling constants. A change of concentration does not have any influence on the 15 N 13 C couplings while a large increase in temperature leads to a slightly lower 1 J (NC). It is concluded that solvent effects may limit the use of 15 N 13 C coupling constants for the elucidation of solvent‐induced conformational changes.