Mass spectrometry of onium compounds. XXIII—ionisation potentials in the structural assignment of [M – N2] ions from diazo-oxides

The ionisation potential shows that fulven-6one is formed pyrolytically from o-benzo-diazo-oxide. Appearance potential measurements show increasing pyrolytic contribution to the [M – N₂] species with increase in ion source temperature.     

Sodium 2-mercaptoethanesulfonate in reversible adduct formation and water solubilization

Sodium 2-mercaptoethanesulfonate (MESNA, coenzyme M) forms 1:1 covalent adducts with highly pi-electron deficient heterocycles. The addition is caused by the thiol function, and the adducts become water soluble as sulfonates. 1H NMR spectroscopy has been used to obtain information about electronic and steric effects on the equilibria between 2-pyrimidinones and their 1:1 MESNA adducts. The adducts are potential prodrugs for biologically interesting 2-pyrimidinones.     

N-quaternary compounds—IXL : Circular dichroism of α-trimethylammonio aldehydes

(S)-α-Trimethylammonio aldehydes have been synthesised over several steps from corresponding amino acids. The dichroic carbonyl absorption can be rationalised in terms of the Octant Rule with the assumption of a preferred conformation. The chiroptical properties of intermediate α-phthalimido aldehydes have also been investigated.     

Regioselectivity in reactions of alkynylmetal complexes with pyrimidinones

Regioselectivity is observed in $\text{1}\text{1}$-adduct formation between phenylethynyltriisopropoxytitanium and 2(1/H)-pyrimidinones; the new carbon-carbon bond is formed at C(4). In contrast the 3,4- and 3,6-dihydro products are formed together from the corresponding magnesium and lithium reagents, but from the magnesium compound the major product is the 3,6-dihydro isomer. Ethynylmagnesium bromide gives equimolar amounts of the 3,4- and 3,6-dihydro isomers. Dehydrogenation of the products gives the alkynylated aromatic heterocycles.     

N-quaternary compounds. Part LIX. Facile synthesis of 3-vinyl-4(3H)-pyrimidinethiones

3-Vinyl derivatives of 4(3H)-pyrimidinethiones have been prepared from 2,3-dihydrothiazolo[3,2-c]pyrimidinium derivatives through ring-opening by a strong base such as potassium t-butoxide in DMF. The pyrimidinium derivative is initially prepared from 4(3H)-pyrimidinethiones. 3-Vinyl-4(3H)-pyrimidinethiones are also formed by the ready decarboxylation of 2,3-dihydrothiazolo[3,2-c]pyrimidinium-3-carboxylates. In the mass spectrometer the nature of the volatile species was elucidated by means of appearance potentials and fragmentation patterns.     

Crystal structures and magnetic properties of 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes

Four new copper(II) complexes of formula [Cu(2)(tppz)(dca)(3)(H(2)O)].dca.3H(2)O (1), [Cu(5)(tppz)(N(3))(10)](n)() (2), [[Cu(2)(tppz)(N(3))(2)][Cu(2)(N(3))(6)]](n)() (3), and [Cu(tppz)(N(3))(2)].0.33H(2)O (4) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and dca = dicyanamide anion] have been synthesized and structurally characterized by X-ray diffraction methods. The structure of complex 1 is made up of dinuclear tppz-bridged [Cu(2)(tppz)(dca)(3)(H(2)O)](+) cations, uncoordinated dca anions, and crystallization water molecules. The copper-copper separation across bis-terdentate tppz is 6.5318(11) A. Complex 2 is a sheetlike polymer whose asymmetric unit contains five crystallographically independent copper(II) ions. These units are building blocks in double chains in which the central part consists of a zigzag string of copper atoms bridged by double end-on azido bridges, and the outer parts are formed by dinuclear tppz-bridged entities which are bound to the central part through single end-on azido bridges. The chains are furthermore connected through weak, double out-of-plane end-on azido bridges, yielding a sheet structure. The intrachain copper-copper separations in 2 are 6.5610(6) A across bis-terdentate tppz, 3.7174(5) and 3.8477(5) A across single end-on azido bridges, and from 3.0955(5) to 3.2047(7) A across double end-on azido bridges. The double dca bridge linking the chains into sheets yields a copper-copper separation of 3.5984(7) A. The structure of 3 consists of centrosymmetric [Cu(2)(tppz)(N(3))(2)](2+) and [Cu(2)(N(3))(6)](2)(-) units which are linked through axial Cu.N(azido) (single end-on and double end-to-end coordination modes) type interactions to afford a neutral two-dimensional network. The copper-copper separations within the cation and anion are is 6.5579(5) A (across the bis-terdentate tppz ligand) and 3.1034(6) A (across the double end-on azido bridges), whereas those between the units are 3.6652(4) A (through the single end-on azido group) and 5.3508(4) A (through the double end-to-end azido bridges). The structure of complex 4 is built of neutral [Cu(tppz)(N(3))(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper separation of 3.9031(15) A. The magnetic properties of 1-4 have been investigated in the temperature range 1.9-300 K. The magnetic behavior of complexes 1 and 4 is that of antiferromagnetically coupled copper(II) dimers with J = -43.7 (1) and -2.1 cm(-)(1) (4) (the Hamiltonian being H = -JS(A).S(B)). An overall ferromagnetic behavior is observed for complexes 2 and 3. Despite the structural complexity of 2, its magnetic properties correspond to those of magnetically isolated tppz-bridged dinuclear copper(II) units with an intermediate antiferromagnetic coupling (J = -37.5 cm(-)(1)) plus a ferromagnetic chain of hexanuclear double azido-bridged copper(II) units (the values of the magnetic coupling within and between the hexameric units being +61.1 and +0.0062 cm(-)(1), respectively). Finally, the magnetic properties of 3 were successfully analyzed through a model of a copper(II) chain with regular alternating of three ferromagnetic interactions, J(1) = +69.4 (across the double end-on azido bridges in the equatorial plane), J(2) = +11.2 (through the tppz bridge), and J(3) = +3.4 cm(-)(1) (across the single end-on azido bridge).     

Ionisation potentials in structure analysis of isomeric nitrones,oxaziranes, O-ether oximes and acid amides

Comparative studies of the ionisation potentials and the mass spectra of some isomeric nitrones, oxaziranes, O-ether oximes and acid amides gave no evidence for hermally-induced isomerisation in the mass spectrometer. Characteristic differences in the electron-impact-induced fragmentation patterns are discussed.     

Mass spectrometry of some triphenylcyclopropenium salts. Competition between dimerisation and adduct formation

The triphenylcyclopropenium chloride, bromide and iodide evaporate in the mass spectrometer mainly as the covalent cation-halide adduct, the fluoroborate as the corresponding fluoride adduct and boron trifluoride. In addition di-3,3′-triphenylcyclopropene is formed, presumably via triphenylcyclopropenyl radicals.