Intramolecular easily polarizable hydrogen bonds with 1-piperidine carboxylic acids

Add time:07/30/2019    Source:sciencedirect.com

IR spectra are plotted from C5H10N(CH2)nCOOH, n = 1–4, in DCCl3 solutions. From the carboxylic bands, information is obtained on whether the proton is present at the carboxylic group or at the N atom. Furthermore, an IR continuum indicates the presence of easily polarizable hydrogen bonds, With 1-piperidine acetic acid, the proton is found at the N atom. Intermolecular asymmetrical O- …H+N hydrogen bonds are formed, which are not easily polarizable. With the substances n = 2–4, intramolecular OH …N ⇌ O- … H+N bonds are found with the proton distributed between the O and N atoms. A double minimum energy surface is present in these bonds. A strong IR continuum indicates that these hydrogen bonds are easily polarizable. With increasing concentration, the weight of the polar proton boundary structure O- …H+N increases. As explained in detail, this is due to interaction effects between these hydrogen bonds. These interaction effects do not occur with the substance n = 4, since they are hindered by the hydrocarbon skeleton. In the case of intermolecular OH …N ⇌ O-…H+N bonds, the IR continua show structures in the region 3200-1800 cm-1. These structures of the continua are not observed with the in OH…N⇌O-…H+N hydrogen bonds.

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