Seven- and Eight-Membered Ring Conformations of Phosphorus Containing Heterocycles

Synthesis and Conformation of Chiral Eight-Membered 12H-Dibenzo[d,g][1,3,2]dioxaphosphocins1

“…The downfield signal is further split by five-bond J coupling to phosphorus ( 5 J HP = 2.2 Hz). The magnitude of the observed geminal coupling constant and the observation of five-bond coupling of the downfield proton signal to phosphorus are consistent with a boat−chair conformation in solution, vide ante (Figure ). ,− …”

“…Studies on the conformation of the 12 H -dibenzo[ d,g ][1,3,2]dioxaphosphocin ring have appeared only within the past 10 years. Quite recently, several reviews have appeared on the subject. ,− The commonly accepted nomenclature to describe the conformation of eight-membered rings is used herein; namely the boat−chair ( C s symmetry), boat−boat ( C s symmetry), twist-boat ( C 1 symmetry), and twist ( C 2 symmetry), which are abbreviated BC, BB, TB, and T, respectively. − Arshinova has noted that the boat conformer ( C 1 symmetry; abbreviated B) should also be considered as it is commonly found in the solid state. − The B conformation represents a highly distorted TB geometry about halfway between the symmetric C 2 T and BB geometries . The B conformation is characterized by a C aromatic −O−P−O torsion angle of 0° …”

Neutral Pentacoordinate and Hexacoordinate Germanium(IV) Complexes: Valence Expansion At Gemanium By Transannular Bonding Of Selenium in an Eight-Membered Ring1

“…Conformation in the Solid-State and Solution Dimethylgermanium Derivative. The commonly accepted nomenclature to describe the conformation of eight-membered rings is used herein; namely the boat−chair ( C S symmetry), boat−boat ( C S symmetry), twist-boat ( C 1 symmetry), and Twist ( C 2 symmetry), which are abbreviated BC, BB, TB, and T, respectively. − Arshinova has noted that the boat conformer ( C 1 symmetry; abbreviated B) should also be considered as it is commonly found in the solid state (Figure ) . The B conformation represents a highly distorted TB geometry about halfway between the symmetric C 2 T and BB geometry .…”

Steric Consequences on the Conformation of Medium-Sized Rings: Solution NMR, Solid-State Crystallographic, ab Initio Molecular Orbital Calculations, and Molecular Mechanics Studies on Substituted Eight-Membered Organosilicon Ring Systems1

“…The originally observed dependence for the geminal 2 J HCH coupling constant of the C(12)-geminal protons in substituted 5,6,7,12-tetrahydrodibenzo[ a , d ]cyclooctenes with ring conformation − was extended to probe the conformation of 12 H -dibenzo[ d , g ][1,3,2]dioxaphosphocins in solution. 6e,f,8a,b The observation of a geminal coupling constant of −12 to −13 Hz in 12 H -dibenzo[ d , g ][1,3,2]dioxaphosphocins is consistent with a BC (or BB) conformation with the exocyclic substituent on phosphorus assuming a pseudoequatorial placement, whereas TB and B conformations were associated with coupling constants ranging from −14 to −19 Hz 8b. Arbusov et al further applied this probe to the 12 H -dibenzo[ d , g ][1,3,2]dioxasilocin ring system .…”

“…In a recent study, Arbusov et al suggested a BC conformation for 2 in solution and dismissed consideration of the BB conformation based upon arguments that suggest a high ground-state energy for this conformation 6f,, However, recent NMR spectral and crystallographic studies have shown evidence for the BB conformer in certain 12 H -dibenzo[ d , g ][1,3,2] dioxaphosphocins. − The BB conformation has been observed in the solid-state for certain 12 H -dibenzo[ d , g ][1,3,2]dioxametallocins. − …”