Conformational analysis of alkylated biuret and triuret: Evidence for helicity and helical inversion in oligoisocyanates

Authors
Roth, J O'Leary, DJ Wade, CG Miller, D Armstrong, KB Thoburn, JD
Citation
J. Roth et al., Conformational analysis of alkylated biuret and triuret: Evidence for helicity and helical inversion in oligoisocyanates, ORG LETT, 2(20), 2000, pp. 3063-3066
Citations number
19
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANIC LETTERS
ISSN journal
15237060 → ACNP
Volume
2
Issue
20
Year of publication
2000
Pages
3063 - 3066
Database
ISI
SICI code
1523-7060(20001005)2:20<3063:CAOABA>2.0.ZU;2-Z
Abstract
[GRAPHICS] The conformations of several oligoisocyanates have been investigated by NMR in order to study the onset and dynamics of helicity in polyisocyanates. P entaethylbiuret and hexaethyltriuret were found to adopt turns and helices in solution. For hexaethyltriuret, symmetric and asymmetric helices are pre sent. Not only is an interconversion of these forms observed (Delta G(SA)do uble dagger = 9.3 +/- 0.4 kcal/mol) but also a reversal of helicity (Delta G(PM)double dagger = 9.0 +/- 0.4 kcal/mol). The coalescence pattern for the latter process provides direct evidence for a concerted, conrotatory helic al inversion.