The NMR study of long-range spin–spin coupling: Peculiarities of molecular structure of N-vinylpyrazole derivatives

• The 1H NMR spectra of 1-vinylpyrazole have been analyzed.
• Analysis of LRSSC indicates the existence of rotary cis–trans-isomerism.
• Identification of the signals is achieved by transformation of the spectrum by paramagnetic additive.

The 1H NMR spectra of 1-vinylpyrazole and its 4-bromosubstituted derivative have been studied. The suppression of spin–spin coupling is rationalized by alteration of relaxation time of nuclei (interacting according to spin–spin mechanism) in samples containing paramagnetic ions. The analysis of long-range spin–spin coupling allows deducing the inference about effective population of both S-trans(N-2)- and S-cis(N-2)-conformations in molecules of 1-vinylpyrazole derivatives.