Synthesis and characterization of model compounds for carbazole‐substituted N‐acylated linear polyethylenimine (PEI). Synthesis and 1H‐NMR spectra of N‐acylated diethylamine and N,N′‐dimethyl‐1,2‐ethanediamine containing 9‐carbazolylacetyl, (R,S)‐ or (R)‐2‐(9‐carbazolyl)propanoyl groups

Abstract

AbstractThe synthesis of N,N‐diethyl‐9‐carbazolylacetamide (6), (R,S)‐ and (R)‐N,N‐diethyl‐2‐(9‐carbazolyl)propanamide (7), N,N′‐dimethyl‐N,N′‐di‐(9‐carbazolylacetyl)‐1,2‐ethanediamine (11), and (R)‐N,N′‐dimethyl‐N,N′‐di[2‐(9‐carbazolyl)propanoyl]‐1,2‐ethanediamine (13) is reported. The racemic compound, (R,S)‐2‐(9‐carbazolyl)propanoic acid (2), was resolved by partial crystallization of the diastereomeric salts formed between 2 and (+)‐α‐methylbenzylamine. The 1H‐NMR spectra of 6 and 7 showed magnetic nonequivalence of the chemically equivalent protons of the methyl and methylene groups in 6 and 7 due to partial double bond character of the amide bond. The upfield resonances corresponding to the two sets of methyl and methylene protons were assigned by the aromatic solvent‐induced shift (ASIS) method to the protons anti to the carbonyl oxygen in the conformation of amide bond in 6 and 7. The 1H‐NMR spectra of 11 and (R)‐13 were used to determine the population of anti‐anti, anti‐syn (syn‐anti) and syn‐syn conformers in the structures of these dimer model compounds; the relative conformer populations were 0.45:0.47:0.08 and 0.28±0.02:0.29±0.01:0.43±0.01 in 11 and (R)‐13.