Solid-State Reaction of Poly(1,6-di-N-carbazolyl-2,4-hexadiyne) with Electrophiles

Abstract

^(13)C cross-polarization/magic angle spinning (CP-MAS) NMR at 50.36 MHz reveals that the reaction of the crystalline polymer poly-N-dicarbazolyl-2,4-hexadiyne (poly-DCH) with the electrophilic reagents liquid bromine, gaseous chlorine, and nitric acid fumes results in the formation of covalent bonds in the polymer. Spectra have been obtained both of the products formed as well as of model compounds, and factors influencing the quantitative interpretation of peak intensities have been taken into consideration. The observed disappearance of peaks from carbon atoms either bonded to or adjacent to bromine atoms is due to a dipolar interaction not averaged to zero by magic-angle spinning. The NMR results show that the initial anisotropic reaction is a selective attack of the bromine at the 3,6 positions of the aromatic rings of the carbazole moiety, resulting in a polymer with four Br/repeat unit. At higher bromination levels electrophilic addition to the multiple bonds in the backbone occurs. Other evidence suggests that the triple bond may react preferentially, resulting in formation of a mixed polyacetylene for products of composition poly-DCH(Br_(6.0)). The reaction of poly-DCH with nitric acid fumes appears to result in substitution at the 3,6 positions of the carbazole ring. In contrast, exposure of poly-DCH to chlorine gas most likely effects both electrophilic substitution and addition in the carbazole sidechains.