¹ H‐NMR‐Studien zur Rotationsisomerie im Vinylcyclopropan‐System, I Eine modifizierte Karplus‐Kurve

Abstract

rn Mit Hilie von Modellverbindungen wird eine modifizierte Karpius-Kurve fur die Diederwinkel-Abhangigkeit der vicinalen H,H-Kopplungskonstanten uber die C-C-Einfachbindung zwischen Dreiring und Doppelbindung im Vinylcyclopropan abgeleitet. Die Beziehung 3J ~ 5.0 -1.8 cos 0 f 4.3 cos 2 wird den experimentellen Befunden am besten gerechl. CNDO/2-Rechnungen bestiitigen dieses Ergebnis. 1H-n.m.r. Studies on the Rotational Isomerism in the Vinylcyclopropane System, I A Modified Karplus-Curve Using model compounds, a modified Kurplus-curve for the angular dependence of the vicinal H,H coupling constant over the single bond between three membered ring and double bond in vinylcyclopropane is derived. The relation 3J = 5.0 -1.8 cos Q' + 4.3 cos 2 CP fits the experimental data best. CNDO/2 calculations confirm this result. rn Dank der Abhiingigkeit vicinaler H,H-Kopplungskonstanten vom Torsionswinkel @ (1)1.2) hat die NMR-Spektroskopie unsere Kenntnisse iiber Rotationsisomere (Rotamere) in offenkettigen gesattigten und ungesattigten Verbindungen wesentlich erweitert. Die Konformationen substituierter Athane3-Q, Propene7. 8) und Buta-diene9) sind in zahlreichen Arbeiten untersucht worden. H b 1 2 1) M. Karplrrs, J. chem. Physics 30, 11 (1959).

Proton magnetic resonance studies of sym-oxepin oxide

“…Exchange broadening of the !H NMR spectrum of 1 was not observed at temperatures up to 116 °C;2 hence, a method independent of the 1 NM R time scale was sought to detect the possible Cope rearrangement in the sy/M-oxepin oxide system. The specific generation of i>'w-2,7-dideuteriooxepin oxide (9) or of sym-4,5-dideuteriooxepin oxide (10) would provide a means to detect the Cope rearrangement via the scrambling of the deuterium labels, 9 +± 10 (Scheme I). The labeling experiment would not rely on the observation of fluxional behavior of the NMR spectrum and, thus, could detect a Cope rearrangement proceeding at a rate much slower than that measured for the analogues 2 and 3.…”

“…The overlap of the es and ct*cn orbitals is expected to be markedly reduced for cases where the cyclopropane is syn fused to the azo linkage; the participation of the cyclopropane is predicted and observed to be correspondingly reduced. Ample precedent thus indicated that the anti-fused epoxide of the dideuterioazo compound 8 would participate in a nitrogen extrusion reaction (A¡ » A4, Scheme I), selectively generating s>ro-2,7-dideuteriooxepin oxide (9). By dissolution of 8 in DCC13 at ambient temperatures2 we expected to observe loss of nitrogen (8 -* 9) followed by the establishment of the equilibrium 9 <=> 10, now, due to isotopic labeling, no longer a degenerate Cope rearrangement.…”

“…. (9) A sample was kindly provided by Dr. W. T. Borden and Y. C. Toong. Later a literature preparation appeared: D. Mackay, C. W. Pilger, and L. L. Wong, J. Org.…”

Conformational analysis of 2-(carboxycyclopropyl)glycine agonists of glutamate receptors in aqueous solution using a combination of NMR and molecular modelling experiments and charge calculations

“…Indeed, if one makes the assumption that the ring exists in a single conformation it is possible to test Karplus-type equations. [33][34][35][36] A comparison between theory and experiment was made by using information from a variety of conformationally rigid angles encountered in the cyclopropyl ring of L-CCG-I and L-CCG-IV.…”

Synthesis and Dimerization of Bicyclo [4.4.1] undec‐1 (11)‐ene, a Bridged trans‐Cycloheptene

“…spectrum reveals no signal for a vinylic proton, but the presence of a one-proton doublet ( J = 11.5 Hz) at 0.98 ppm. This points to a proton on an otherwise fully substituted cyclopropane ring, joined to a tertiary carbon atom with a proton in exclusive or predominating trunsoid conformation [21], i.e. a structure unit 21.…”