Solvent and Temperature Dependence of NMR Spectral Parameters in 2-Fluoropyridine Solutions

Spin‐echo methods have been used to measure the effects of solvent and temperature on the ¹⁴N and ¹⁹F spectral parameters ${\mathrm{(R}}_{1\mathrm{N}}{\mathrm{,\; R}}_{2\mathrm{F}}^0,\mathrm{and}{J}_{\mathrm{NF}})$ in several 2‐fluoropyridine solutions. These effects were found to depend upon the dielectric constant $\epsilon$ of the solutions, while ${\mathrm{\eta \hspace{0.17em}/\hspace{0.17em}R}}_{1\mathrm{N}}$ , the ratio of visocity to spin–lattice relaxation rate, was found to be approximately constant. Also, with few exceptions $\eta$ tends to increase with increasing $\epsilon$ . Such polarity dependence is found in the effects of temperature as well as of solvent, which supports previous suggestions that the spectral parameters are modified primarily by weak van der Waals‐type molecular association. Instrumental errors are discussed.