Chemical correlation of a degradation product of isoherqueinone with S-(–)-ethyl lactate has established that herqueinone and isoherqueinone have the R- and S-configuration respectively at the asymmetric centre in the side-chain; it follows that atrovenetin possesses the R-configuration.
Determination of the molecular structure of B9C2H12AlMe2 by single-crystal X-ray diffraction techniques, shows that the aluminium atom is involved in bonding only to two boron atoms of the B9C2H12 icosahedral fragment: 11B n.m.r. studies suggest that, in solution, the molecule undergoes rapid intramolecular rearrangements.
The crystal and molecular structure of bis-(1,3,5,7-tetramethylcyclo-octatetraenyl)uranium(IV) has been determined; the unusual crystal structure has two types of molecule with different rotomeric configurations around the two dianion rings on a central atom; in one form the methyl groups are approximately staggered and the other eclipsed.
Free silicon and germanium atoms produced in a microwave-sustained helium plasma are detected downstream from the plasma in their ground states by atomic absorption spectroscopy, and reaction of silicon atoms with silane to produce disilane has been found in the flow system.
Rates of exchange at coalescence in d.n.m.r. spectroscopy obtained using approximate equations: (a)kc=(π/√2)Δν and (b)kc=(π/√2)√(Δν2+ 6J2), have been compared with those obtained by complete line shape analysis and have been found to give reliable estimates of free energies of activation within specified limits for coalescing singlets, doublets and AB quartets.
The liberation of p-nitrophenoxide from p-nitrophenyl-α-D-glucopyranoside (1) in alkaline solution involves initial O-1 → O-2 migration of the p-nitrophenyl group to give 2-O-p-nitrophenyl-D-glucose (2), followed by subsequent O-2 → O-3 migration to give the 3-ether (3)[the D-manno-analogues (4 and 5) of (2) and (3) are also formed]; in the final step the 3-ethers are converted into saccharinic acids with the release of p-nitrophenoxide anion.
The purine base in a copper–nucleoside analogue has been shown to possess only one binding site, N(7), indicating that the direction of the co-ordinating orbital on the imidazole nitrogen is not compatibel with the formation of a chelate structure inovolving N(7) and O(6).
Pyrolysis of the vinyl ether adducts obtained by condensation of arylamide oximes and dimethyl acetylene dicarboxylate affords a new class of substituted imidazolinones, probably by a Claisen-type rearrangement with subsequent cyclisation.
The hydrolysis of aryl hydrogen malonates is subject to intramolecular general base catalysis by the ionised carboxyl group; general base catalysis of the hydrolysis of the p-nitrophenyl ester shows unexpectedly complex kinetics, and appears to involve a ketene mechanism.
New evidence for singlet oxygen involvement in the photo-oxidation of amines is presented.
Direct e.s.r. evidence for strong hyperfine interaction with phosphorus, arsenic, or tin atoms β to redical centres is presented, which is linked with the large rate enhancements detected by others when such groups are β to aromatic ring systems; the interaction is shown to be hyperconjugative rather than to involve outer d orbitals.
The hydroxyisopropyldihydrofuranoquinoline alkaloid, platydesmine, has been shown to be an efficient precursor of the furanoquinoline alkaloid, dictamnine, in Skimmia japonica Thunb.
The barrier to internal rotation in N-methylformamide and N-methylacetamide has been shown to be comparable to those in NN-dimethylamides, by n.m.r. lineshape analysis of the N-methyl signals.
Attempted syntheses of 1,5-didehydro[10]annulene derivatives led to an intriguing isomerization which shows that any thermodynamic stability associated with this 10π-electron system is at most comparable to that associated with benzene.
Dehydrobromination of either 1,2-dibromo-1-methylcyclohexane or 1,2-dibromo-4-methylcyclohexane, in a bis-(2-methoxyethyl) ether–sodium methoxide mixture, produces products unusually rich in the exocyclic isomer 3-methylenecyclohexene.
Paramagnetic shifts induced in the 13C n.m.r. spectrum of borneol by tris-(2,2,6,6-tetramethylheptanedionato)praseodymium, Pr(tmhd), have been used in a total assignment; these shifts and those induced by the corresponding europium and terbium complexes agree well with values calculated on the basis that their origin is of a pseudo-contact nature.
The skeletal structures of carboranes, the higher boranes and borane anions, and many transition-metal carbonyl cluster species are related to the number of skeletal bonding electron-pairs they contain; species with n skeletal atoms adopt closo-structures if held together by (n+ 1) pairs, nido-structures if held together by (n+ 2) pairs, and arachno-structures if held together by (n+ 3) pairs of skeletal bonding electrons.
The alkaline cleavage of N-nitroso-N-prop-2-ynylamides (1) and (9) in methanol and the photolysis of alkynone tosylhydrazones (4) and (10) in methanol–sodium methoxide afforded both allenyl and prop-2-ynyl methyl ethers; the site of protonation of diazopropynes and the reactivity of prop-2-ynyldiazonium ions have been investigated.
Spectroscopic (1H n.m.r. and i.r.), electrical conductivity, and chemical evidence indicates that reactions of π-C5H5Fe(CO)2R, π-C5H5Mo(CO)3R, and Mn(CO)5R (R = alkyl or aryl) with SO2 proceed via the intermediacy of the oxygen-bonded sulphinates, which subsequently rearrange to the thermodynamically stable and isolable sulphur-bonded sulphinates.
The synthesis and properties of air-stable hydroborato-complexes, trans-[MA(CO)(R3P)2][M = Ir, Rh; A = BH3(CN), BH4; R3P = tertiary phosphine] are reported; the co-ordination of BH3(CN)–, probably through the –NC group, is the first example of this anion acting as a ligand.
