Vapor phase GC-IR identification of regioisomeric N-methoxybenzyl-4-substituted-2,5-dimethoxyphenethylamines (NBOMe)

Gas chromatography with vapor phase infrared spectroscopy can distinguish the common NBOMe drugs 25I-NBOMe and 25B-NBOMe from their 3- and 4-methoxybenzyl isomers, even though their mass spectra are nearly identical and only reveal the halogen. Specific infrared absorption bands indicate the position of the methoxy group on the benzyl ring: a band at 1608 cm⁻¹ is unique to the 4-methoxy isomer, while the 2-methoxy isomer shows a band at 1593 cm⁻¹ and the 3-methoxy isomer at 1597/1598 cm⁻¹. Asymmetric aryl-O stretching frequencies also shift with substitution position. The overall shape and relative intensities of multiple bands allow clear identification of each isomer in both drug series.

Study at a glance

Abstract

Abstract The common NBOMe drugs of abuse, N-(2-methoxybenzyl)-4-iodo-2,5-dimethoxyphenethylamine (25I-NBOMe) and N-(2-methoxybenzyl)-4-bromo-2,5-dimethoxyphenethylamine (25B-NBOMe), can be differentiated from their corresponding 3- and 4-methoxybenzyl isomers by gas chromatography with vapor phase infrared spectroscopy. The mass spectra for these regioisomeric compounds are essentially identical providing only the identity of the halogen but no specific ions to identify the methoxy group position on the benzyl aromatic ring. The bands from single ring model compounds 2C-B, 2C-I, and all three positional methoxy substituted benzylamines were used to assign each vapor phase absorption band to either the halogenated 2,5 dimethoxybenzene ring or the methoxybenzylamine ring. A pair of aromatic ring stretching bands reflect the position of methoxy group substitution on the benzyl aromatic ring. The 1608 cm−1 band is specific for the two regioisomeric 4-methoxy-benzylamine isomers and this band occurs at 1593 cm−1 for the 2-methoxy isomer in both the 25I and 25B series and shifts to1597/1598 cm−1 for 3-methoxybenzyl 25I and 25B. Asymmetric aryl-O stretching frequencies shift with a change in methoxy substitution around the benzyl aromatic ring (Ring 2) and occur at 1237/1238 cm−1 for ortho, 1261 cm−1 for meta, and 1246 cm−1 for the para isomers. The overall shape and relative intensities of numerous bands in the vapor phase spectra provide clear identification for the individual methoxybenzyl isomers for the 25I-NBOMe and 25B-NBOMe series.