Molecular Structure of the Complex of Octano-8-lactam with Magnesium Bromide

Abstract

Octano‐8‐lactam forms a complex with magnesium bromide, which could be of importance in elucidating the mechanism of anionic polymerization of the lactam initiated by Grignard compounds. The complex was obtained in pure form and analyzed using thermal analysis (DSC and TGA), multinuclear NMR and IR spectroscopy. Analysis of 1H, 13C, 14N and 15N NMR spectra, relaxations and PGSE measurements, as well as IR spectra and well‐corresponding theoretical calculations, showed that six molecules of octano‐8‐lactam and one MgBr2 molecule form a complex with high symmetry. Two different forms of the complex were found, one of them strongly predominating.

Role of magnesium complexes in the anionic polymerization of hexano-6-lactam

“…This also indicates the existence of an interaction between carbonyl groups of N-BtHL with magnesium bromide. 13 C NMR spectra of 5 wt% solutions of free N-EAA and N-BtHL in CDCl 3 were measured at 300 K. As we did not find suitable solvents in which corresponding complexes with MgBr 2 remains stable, required NMR spectra were measured in solid state. Signal assignment of the resulting solution and solid-state 13 C NMR spectra are presented in Figures 5 and 7.…”

“…13 C NMR spectra of 5 wt% solutions of free N-EAA and N-BtHL in CDCl 3 were measured at 300 K. As we did not find suitable solvents in which corresponding complexes with MgBr 2 remains stable, required NMR spectra were measured in solid state. Signal assignment of the resulting solution and solid-state 13 C NMR spectra are presented in Figures 5 and 7. Signal of carboxyl group of N-EAA in the complex is significantly shifted to lower field (170.92 ppm) compared with free N-EAA (169.16 ppm), which reflects substantial decrease in electron density around carboxyl carbon (Fig.…”

“…6). In addition, in 13 15 N NMR spectrum of the complex MgBr 2 (N-EAA) 4 in solid state at 300 K. Solution 13 C NMR and solid-state 13 C CP/MAS NMR spectra of N-BtHL and its complex with MgBr 2 are shown in Fig. 7.…”

“…7. As the molecules of N-BtHL involved in the complex formation are substantially larger as compared with previously introduced N-EAA, corresponding 13 C NMR spectra are rather complicated and individual signals became to overlap. Nevertheless signal assignment is possible and resulted NMR spectra can be qualitatively analyzed.…”

“…In this complex all the six molecules of HL have almost exactly equivalent positions, the carbonyl oxygen atoms forming coordination bonds to the magnesium atom and the amide protons being bound by predominantly electrostatic bonds to the bromine atoms [9]. Similarly, octano-8-lactam differed from HL by the occurrence of cis as well as transoid conformation of the amide group [10][11][12], forms a highly symmetrical complex [13] with MgBr 2 .…”