Dorothy Z. Denney

A reconsideration of the mechanism for the aromatic version of radical nucleophile displacement reactions

Abstract A review of the literature and new experimental data indicate that aromatic radical anions containing leaving groups react with nucleophiles by a bimolecular displacement process.

INHIBITION OF PSEUDOROTATION IN SOME MONOCYCLIC PENTAOXYPHOSPHORANES

Abstract Phosphoranes were prepare by allowing 2,4,8,10-tetra-tert-butyl-6-(2,2,2,trifluoroethoxy)-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, the analogous ethoxy compound, 2,4,8,10-tetra-tert-butyl-6-(2,2,2,-trifluoroethoxy)-dibenzo[d,f][1,3,2]dioxaphosphepin and the analogous compound without tert-butyl groups to react with trifluoroethyl benzenesulfenate. The first three phosphoranes showed significant barriers to intramolecular ligand reorganization, 14–16 kcal/mole. The phosphorane without the tert-butyl groups had a barrier too low to measure. These observations are discussed in terms of steric inhibition of pseudorotation.

Fluoromethoxydiazirine and fluoromethoxycarbene

Abstract 3-Fluoro-3-methoxydiazirine was synthesized in ~35% overall yield in a two-step procedure that eschews elemental fluorine.

CONFORMATION OF EIGHT-MEMBERED DIOXATHIASILOCIN HETEROCYCLES IN SOLUTION

Abstract The dibenzo[d,g][1,3,6,2]dioxathiasilocin derivatives 3a-f were prepared by the reaction of the thiobisphenols 1a-b with the corresponding dichlorosilanes 2a-e using triethylamine as an acid acceptor. The free energy of activation for ring inversion of the 2,4,8,10-tetra-tert-butyl-substituted 3a was determined by variable temperature 1H NMR to be 13.9 kcal/mol. The 1H NMR spectral data of 3a requires that the ring conformer possess a σ plane of symmetry passing through the silicon and bridging sulfur atoms. In the variable temperature 1H NMR spectra of the 2,4,8,10-tetramethyl-substituted 3b no evidence was observed for the slowing of ring inversion at-55oC, suggesting that the energy of activation for ring inversion is less than 10.9 kcal/mol. The 1H NMR spectral data of 3e-f indicates the presence of equilibrating conformational isomers. The results of this study supports the suggestion that steric factors are a major contributor to the barrier of ring inversion for the dibenzo-[d, g][1,3,6,2]...

Structure, bonding and lattice dynamics of tri- and tetraphenyltin derivatives as studied by Mössbauer and multinuclear NMR spectroscopy

Abstract The structure and bonding properties of a number of closely related tetraphenyltin- and triphenyltin chloride compounds have been studied by the 119Sn Mossbauer effect and multinuclear NMR spectroscopy. The comparison of liquid and solid state 13C and 119Sn NMR spectra and of glassy solution matrix and neat solid state Mossbauer spectra provides information about the extent of intermolecular association effects in these compounds. The results indicate that all materials with the exception of (p-CF3Ph)3SnCl are adequately described as monomeric solids with tetrahedral geometry around the metal atom. For the latter compound spectroscopic evidence for the presence of a five-coordinated tin species is presented.

SOME CHEMISTRY OF 2,8-DIOXA-5-AZA-1-PHOSPHABICYCLO[3.3.0] OCTANE AND 2,10-DIOXA-6-AZA-1-PHOSPHABICYCLO[4.4.0] DECANE. FURTHER EVIDENCE FOR THE BIPHILIC INSERTION MECHANISM

Abstract 2,8-Dioxa-5-aza-1-phosphabicyclo[3.3.0] octane, 1, and 2,10-dioxa-6-aza-1-phosphabicyclo[4.4.0] decane, 2, both react with diethyl peroxide to give phosphoranes containing two ethoxy groups. The reactivities of 1 and 2 towards diethyl peroxide are very different. The reaction of 1 at 0°C in methylene chloride is complete after 7 days whereas 2 and diethyl peroxide in methylene chloride require 30 days at room temperature for 89% reaction. The opposite reactivity of 1 and 2 are found in their reactions with diphenyl disulfide. These data strongly support a direct insertion by phosphorus into the oxygen-oxygen bond of the peroxide. Compounds, 1 and 2 were allowed to react with trifluoroethoxy benzenesulfenate and 1,1,1,3,3,3-hexafluoroisopropoxy benzenesulfenate. Dioxyphosphoranes were formed in all cases. The structures of these materials are discussed. Products of condensation reactions of 1 and 2 were also obtained and structural features are noted.

The carbon-13 nuclear magnetic resonance spectra of four eudesmane sesquiterpenols

Abstract The 13 C NMR spectra of geosmin, selina-4(14),7(11)-diene-99-ol and two dihydroeudesmol isomers have been obtained and the individual resonances assigned. Several different empirical correlations developed by others have been combined in simple calculations to predict chemical shift values for sesquiterpenols of the eudesmane group.

Concerning the mechanism of displacement of nitro groups from activated aromatic systems

Abstract The photostimulated reactions of p-nitrobenzophenone and p-nitrobenzonitrile with a variety of nucleophiles have been investigated. Displacement of the nitro group is observed in all cases. The rates of the reactions were measured by FT-IR. The rates were slowed by substances such as sulfur, air, Galvinoxyl and p-benzoquinone. In several cases rates of loss of starting material were monitored by quenching the reaction mixtures and isolating product and starting material. These reactions also showed inhibition of their rates in the presence of inhibitors. These results indicate that the reactions are chain processes. It is concluded that the substrates are converted into their corresponding radical anions which then react with the nucleophiles in a bimolecular displacement reaction. The alternate mechanism, which involves dissociation of the radical anions, is precluded because they are known not to dissociate.

Preparation and structural studies of a number of heterocyclic phosphoranes

Abstract A series of monocyclic five-membered ring containing trivalent phosphorus compounds with oxygen, nitrogen and sulfur bonded to phosphorus, in various combinations has been allowed to react with trifluoroethyl and 1,1,1,3,3,3-hexafluoroisopropyl benzenesulfenates. In some cases, pentacoordinated phosphorus compounds resulted. These materials have been studied by various NMR techniques. The same trivalent phosphorus compounds were allowed to react with 3,4-(bistrifluoromethyl)1,2,dithiete. In some cases phosphoranes were formed and they were also studied by NMR.

The stability and electronic structure of diphenylcobalticiniummethyl carbonium ion

Abstract The cobalticinium group, because of its strongly electron-withdrawing inductive, field and resonance effects greatly decreases the stability of a carbonium ion in the α-position of a side chain. The stability constant of C5H5Co+C5H4(C6H5)2C+, (I) has been determined spectrophotometrically in 80–96% sulfuric acid: pKR−15.3 ± 0.3. The relative stabilities for R(C6H5)2C+ are: cobalticinium, 1; H, 102; phenyl, 5 × 108; ferrocenyl 1016. Compound I, however, shows a lower sensitivity to changes in solvent acidity than would be predicted by the HR scale. Proton and 13C NMR spectra of I in ClSO3H/D2SO4 indicate delocalization of the positive charge onto the phenyl groups comparable to that of (C6H5)2CH+ and C6H5)3C+ and delocalization to a much lesser extent onto the cobalticinium group.