Interpreting 2h J (F,N), 1h J (H,N) and 1 J (F,H) in the hydrogen‐bonded FH–collidine complex

Ab initio EOM‐CCSD calculations were performed to determine 19 F, 1 H, 19 F, 15 N and 1 H, 15 N spin–spin coupling constants in model complexes FH–NH 3 and FH–pyridine as a function of the F—H and F—N distances. The absolute value of 1 J (F,H) decreases and that of 1h J (H,N) increases rapidly along the proton‐transfer coordinate, even in the region of the proton‐shared F—H—N hydrogen bond. In contrast, 2h J (F,N) remains essentially constant in this region. These results are consistent with the recently reported experimental NMR spectra of FH–collidine which show that 1h J (H,N) increases and 1 J (F,H) decreases, while 2h J (F,N) remains constant as the temperature of the solution decreases. They suggest that the FH–collidine complex is stabilized by a proton‐shared hydrogen bond over the range of experimental temperatures investigated, being on the traditional side of quasi‐symmetric at high temperatures, and on the ion‐pair side at low temperatures. Copyright © 2002 John Wiley & Sons, Ltd.