Hans Vermeer

A photoelectron spectroscopic study of keto-enol tautomerism in acetylacetones - a new application of photoelectron spectroscopy☆

Abstract The photoelectron spectra of acetylacetone, 3-methylacetylacetone, and 3,3-dimethylacetylacetone have been recorded over the range of temperature 25–250°C. From the changes in the spectra with temperature the equilibrium constants for the keto ⇋ enol reaction and their temperature dependence have been obtained. The reaction enthalpies derived by means of photoelectron spectroscopy are in good agreement with gas-phase values previously obtained by other methods.

Synthesis and application of precursors of hetero-anthracenes : 2-halo- and 2,2′-dihalodiphenylmethanes and methine substituted derivatives

Abstract In the diphenylmethane series, the synthesis of 2,2′ - diiododiphenylmethane ( 4g ) and the improved synthesis of 2,2′ - dibromodiphenylmethane ( 4e ) are reported. The triphenylmethane derivatives, 2-bromo-, 2-iodo-, 2,2′-dichloro-, 2,2′-dibromo- and 2,2′-diiodotriphenylmethane ( 4f, 4h, 4i, 4j and 4k , respectively) have been prepared. Via an entirely different approach, 1-(2-bromophenyl)- and 1 - (2 - chlorophenyl) - 1 - phenyl - 2,2 - dimethylpropane ( 4m and 4l ) were obtained as derivatives of t-butyldiphenylmethane. Examples are given for the application of the new compounds in the synthesis of 9,10 - dihydro - 9 - heteroanthracenes ( 1, 2 and 3 ) via the formation of the corresponding organometallic derivatives.

10-methyl-9-phosphaanthracene☆

Abstract The synthesis of 10-methyl-9-phosphaanthracene (1b) is described. Its stability is found to be intermediate between that of the unsubstituted parent compound (1a) and of the 10-phenyl derivative (1c). The electronic structure of this new phosphaaromatic system is studied, especially by photoelectron spectroscopy. As inductive and/or conjugative effects of the substituents are shown to be of minor importance, it is concluded that mainly steric effects stabilize the 9-phosphaanthracene system.

On the nature of the “free electron pair” on phosphorus in aromatic phosphorus compounds: The photoelectron spectrum of 2-phosphanaphthalene☆

Abstract The electronic structure of the 2-phosphanaphthalene system has been studied by photoelectron spectroscopy. The assignment of bands in the PE spectra of 2-phosphanaphthalene and 3-methyl-2-phosphanaphthalene has been performed with the aid of two useful generalisations, one pertaining to the energies of the the π ionizations, and the other to the phosphorus n ionization, as well as by calculations using the extended CNDO/S method. The n ionization of the 2-phosphanaphthalenes can be observed as a well separated single band. From the breadth of this n band the “lone pair” is seen to have considerable bonding character resulting from orbital mixing with other σ-orbitals of the molecule. This appears to be the first evidence of appreciable delocalization of ldlone pair” phosphorus electrons in aromatic molecules, which, judging from the breadth of the bands, is almost as large as with pyramidal phosphorus atoms.

On the conformation of unsaturated arsines

Abstract The ground state conformations of dimethylvinylarsine, dimethylphenylarsine, allyldimethylarsine, and benzyldimethylarsine are studied both theoretically and by UV photoelectron spectroscopy. Special emphasis is laid on an elucidation of the various forces, including AsC hyperconjugation, that determine the conformers of these unsaturated arsines.

An investigation of the structure of the so-called phenarsazine : Mass spectroscopical evidence for the thermal formation of phenarsazine

Abstract The structure of Wieland and Rheinheimers “phenarsazine” has been reinvestigated. The proposed aromatic structure 3 is not correct, spectral and chemical evidence showing that this compound is 10,10′-bis(5,10-dihydrophenarsazinyl) 16 . An attempt to synthesize phenarsazine 3 by base-induced hydrogen chloride elimination was unsuccessful. However, mass spectroscopic evidence indicates that phenarsazine is formed by thermal elimination of either hydrogen chloride or methanol from 10-chloro-5,10-dihydrophenarsazine 7 or 10-methoxy-5,10-dihydrophenarsazine 10 , respectively.

On the use of variable temperature photoelectron spectroscopy studying rotational isomerism in tetramethyldiphosphine1,2

Abstract Using variable temperature photoelectron spectroscopy (VTPES), a new assignment of the UV photoelectron spectrum of tetramethyldiphosphine is derived and the equilibrium between its trans and gauche forms is quantitatively studied. The assignment is the same as those of similar hydrazines. The trans isomer is more stable than the gauche by 0.5±0.1 kcal/mol meaning that the populations of each isomer are 60% and 40% at room temperature, respectively and 50% each at 170°C. These results do not confirm the interpretation of electron diffraction data.

On the formation of the so-called arsanthrene

Abstract The structure of Kalbs “arsanthrene oxide” and “arsanthrene” have been reinvestigated. The “arsanth-rene oxide” is monomeric and is therefore properly termed 5,10-epoxy-5,10-dihydroarsanthrene(6). A spectroscopic study of “arsanthrene” revealed that this compound has the dimeric structure 12 corresponding to the photodimer of anthracene. Mechanisms of formation of dimeric “arsanthrene” and the possible dissociation of dimeric “arsanthrene” into its monomer by reaction with a dienophile at elevated temperature are discussed. An attempt to synthesize arsanthrene (7) by dehalogenation of 5,10-dichloro-5,10-dihydroarsanthrene (5) was unsuccessful. The mass spectral fragmentation patterns of some 5,10-dihydroarsanthrenes are recorded.