Delocalized π‐electrons in 2‐oxazoline rings resulting in negatively charged nitrogen atoms: revealing the selectivity during the initiation of cationic ring‐opening polymerizations |
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Authors: | Thomas Bodner Lisa Ellmaier Verena Schenk Jörg Albering Frank Wiesbrock |
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Affiliation: | 1. Polymer Competence Center Leoben GmbH PCCL, Roseggerstrasse 12, 8700 Leoben, Austria;2. Graz University of Technology, Institute for Chemistry and Technology of Materials, Stremayrgasse 9, 8010 Graz, Austria |
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Abstract: | The inventory of the single‐crystal X‐ray structures of aliphatic and aromatic 2‐oxazolines, namely 2‐nonyl‐2‐oxazoline, 2,2′‐tetramethylenebis(2‐oxazoline) and 2‐phenyl‐2‐oxazoline, reveals significant delocalization of π‐electrons along the N? C? O segment. The delocalization of π‐electrons is stabilized by inductive and resonance contributions of the side‐chains; in 2‐phenyl‐2‐oxazoline, also π‐arene interactions between the benzene ring and the C? N and the C? O bond stabilize the crystalline phase. This delocalization gives a partial negative charge to the nitrogen atom and a partial positive charge to the oxygen atom. The partial negative charge of the nitrogen atom makes this atom the exclusive reaction partner also for highly reactive non‐selective cations, which explains the regioselectivity of electrophilic attacks in cationic ring‐opening polymerizations. Copyright © 2011 Society of Chemical Industry |
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Keywords: | π ‐electron delocalization 2‐nonyl‐2‐oxazoline 2‐phenyl‐2‐oxazoline single‐crystal X‐ray analysis 2,2′ ‐tetramethylenebis(2‐oxazoline) |
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