Analysis of 2D Maps Based on Similarity in DFT-Calculated vs Experimental 13C–15N Spin Couplings for a Representative Sample of Conformationally Rigid and Structurally Fixed Nitrogen-Containing Organic Compounds

Abstract

In this work, we carried out an extended verification of the ¹³C–¹⁵N spin–spin coupling constants as a new structural indicator of nitrogen-containing organic compounds. In this regard, we performed a quantum-chemical calculation (B3LYP with basis set 6-311++G(2df,2p)) for a representative sample of 193 spin–spin couplings for the currently known literature experimental data on them in the conformationally rigid and structurally fixed compounds. Comparison of theoretical couplings with experimental ones shows a statistically significant good to excellent agreement. A parallel analysis of the variability of the calculated values of ¹³C–¹⁵N spin bonds with the variability of experimental data within groups of related compounds turned out to be practically useful. The approach developed can be used to quite reasonably determine the signs of spin–spin coupling constants ¹³C–¹⁵N. It can also provide important additional information for assigning ¹³C peaks in cases where this cannot be done using standard NMR spectroscopy techniques.