The Perlin effect in 2-halocyclohexanones and 2-halocyclohexanethiones

Abstract

The Perlin effect is an NMR phenomenon observed in six-membered rings and it is referred to as 1JC−Hax < 1JC−Heq. In the present work, the influence of halogens (F, Cl and Br) at position 2 in cyclohexanones and cyclohexanethiones is theoretically evaluated on the one-bond C2H2 coupling constants, i.e. on the Perlin effect. An important hyperconjugative interaction (πC=Y → σ*C-H, Y = O and S) operating in the studied systems seems to play a significant role for the observed 1JC−Hax < 1JC−Heq behavior. In addition, the Lewis contribution (JLewis) dominates the Fermi Contact term (JFC), which plays the major role for the overall one-bond CH coupling constant. Compared to the gas phase, this behavior was found to be insensitive to implicit solvents (DMSO and water).