On the Use of Nuclear Magnetic Resonance for the Detection, Estimation, and Characterization of N-Methyl Groups

Abstract

A useful n.m.r. technique for the detection, estimation, and characterization of N-methyl groups is described. The method depends on the decreased shielding of Nb,,i,-methyl protons when the solvent is changed from deuterochloroform to perdeuteroacetic (PDA) (or acetic) acid t o trifluoroacetic acid (TFA). The decreased shielding results in a downfield shift of the N-methyl resonance of ca. 0.3-1.3 p.p.m. depending on the type of amine. Most N-methyl groups on neutral nitrogen atoms show little movement. For the majority of aliphatic amines in trifluoroacetic acid the NH exchange rate is slow enough a t 38" to permit observation of coupling of H(N) with the N-methyl protons, and thus determination of whether the amine is secondary or tertiary. In some cases information can be obtained about methylene and methine groups attached t o basic nitrogen. In acid solution compounds with basic nitrogen attached to, or part of, an aromatic ring show considerable shift of the aromatic proton resonance signals to lower magnetic field. Combination of the n.m.r. technique with the Herzig-Meyer analysis can also reveal the number of methyl groups attached to neutral nitrogen.

Luciduline: a unique type of Lycopodium alkaloid

“…For personal use only. 5 % solution of deuterium chloride in acetic acid-0-d Selenium Dehydrogenation of Dihydrolucid~iline (5 ml) and allowed to stand at room temperature for Dihydroluciduline (25 mg) was mixed with seleniuni 5 days. The bulk of the solvent was removed under powder (200 mg) and heated in a sealed tube (sealed it1 reduced pressure and a saturated solution (6 ml) of uacuo) at 280-300" for 8 h. The dehydrogenation products anhydrous potassium carbonate in deuterium oxide was were isolated by evaporative distillation directly from the added to the residue.…”

Ceanothus Alkaloids: I. Isolation, Separation, and Characterization

“…All of these methyliinino groups are attached to the basic nitrogen in the molecule a s seen from the 0.79-1.05 p.p.m. downfield shift (Table I) of the N-methyl proton magnetic resonance peak in changing from deuterochloroform t o perdeuteroacetic acid solution (21). This observation was confirmed in the case of ceanothine-A by the preparation of a neutral N-acetyl derivative with n.m.r.…”

Acetylenic esters. II. Further addition reactions with sulfur- and nitrogen-containing compounds

“…In the former solvent, the methylene resonances are distinct a t 4.5 and 3.93 6 (branches of an A2B2 pattern). I n the latter solvent, the CH2 group adjacent to the basic nitrogen (now protonated) suffers a paramagnetic shift (6) and the A2B2 pattern collapses together a t 5.5 6. This, together with other physical data, is consistent with structures XI1 and XIII.…”