Methoxy triethylene glycol terminated alkanethiol monolayers self-assembled on Au and Ag have recently been found to exhibit a striking difference in protein resistance, which has been interpreted in terms of the transition of the ethylene glycol tails from a helical to an all-trans conformation (Harder, P.; Grunze, M.; Dahint, R.; Whitesides, G. M.; Laibinis, P. E. J. Phys. Chem. 1998, 102, 426−436. Wang, R. L. C.; Kreuzer, H. J.; Grunze, M. J. Phys. Chem. 1997, 101, 9767−9773). To gain further arguments in favor of such a conformational transition, we undertake a search for the lowest energy monolayer configurations on Au and Ag by combining the methods of stochastic global search and static energy minimization. The conformational and intermolecular contributions to the monolayer lattice energy are calculated using a classical atomistic force field fitted to ab initio MP2 level calculation results for 1,2-dimethoxyethane. It is found that in the lowest energy monolayer configuration on Au the methoxy triethylene glycol tails really assume a helix-like conformation, with the three constituent O−C−C−O bond sequences being in the trans−gauche−trans form. The helical conformation is mainly stabilized by the intra- and intermolecular electrostatic interactions between the ethylene glycol units. In the Ag-supported monolayer, characterized by a perceptibly higher packing density, the helical conformer loses its stability due to conformational strains and becomes less favorable than a nearly planar all-trans conformer. The calculation results provide support to the view that the origin of the gauche effect observed in poly- and oligo(ethylene glycols) is in the influence of a polar environment and not in intrinsic properties of the ethylene glycol unit.

Oxidative C-O coupling of pyrazolones with N-hydroxy compounds of different classes (N-hydroxyphthalimide, N-hydroxybenzotriazole, oximes) was achieved; both one-electron oxidants (Fe(ClO 4 ) 3 , (NH 4 ) 2 Ce(NO 3 ) 6 ) and two-electron oxidants (PhI(OAc) 2 , Pb(OAc) 4 ) are applicable, and the yields reach 91%. Apparently, the coupling proceeds via the formation of N-oxyl radicals from N-hydroxy compounds. One of the N-oxyl intermediates, the diacetyliminoxyl radical, was found to be exclusively stable in solution in spite of being sterically unhindered; it was isolated from an oxidant and used as a new reagent for the synthesis and mechanism study. The products of C-O coupling of pyrazolones with N-hydroxyphthalimide can be easily transformed into aminooxy compounds, valuable substances for combinatorial chemistry.

For the stable germylene, N,N'-di-tert-butyl-1,3-diaza-2-germacyclopent-4-en-2-ylidene, 2, the Raman line for the cyclic C=C stretching mode is strongly enhanced and shifted to longer wavelength, compared with that in reference compounds. The enhancement and frequency shift are even greater than those found for the corresponding stable silylene 1. These results, along with NMR evidence and theoretical calculations, suggest that the aromatic electron delocalization is even greater in the germylene than that in the silylene.

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