Coupled hydrogen‐bonding interactions between β‐carboline derivatives and acetic acid

In this work, we have analysed the tendency of two β-carboline derivatives, harmane and norharmane, in the formation of hydrogen bonds. We obtained the 1H and 13C NMR spectra of different mixtures of these derivatives with acetic acid (AcOH) in CDCl3. A cyclic 1:3 complex is proposed between harmane and AcOH, while a 1:2 complex is proposed for norharmane. Chemical shifts at temperatures between 233 and 323 K were measured: lowering the temperature produces the same effect as increasing the amount of AcOH in solution. The 13C data confirm a delocalisation of the π electron density towards the pyridinic ring that occurs when AcOH is added. Copyright © 2007 John Wiley & Sons, Ltd.