The structures of acetylacetone,trifluoroacetyl-acetone and trifluoroacetone

The molecular geometries of three structurally related compounds have been determined by electron diffraction in the gas phase. Acetylacetone, which exists primarily as the enol tautomer, was found to have a planar symmetric ring with the following r_g values: C₁-C₂ = 1.405± 0.005 Å, C₂-C₄ = 1.510± 0.005 Å, C-O = 1.287± 0.006 Å, C-H = 1.090± 0.010 Å, ∠C₂C₁C₃ = 118.3 ± 1.8°, ∠C₁C₃O₁ = 123.2± 1.7°, ∠C₁C₃C₅ = 122.0± 1.2°, and ∠CCH = 110.2 ± 2.1°. A model in which the enol proton is in the ring plane located symmetrically between the oxygen atoms is in best agreement with the diffraction data. The structure of trifluoroacetylacetone is similar to that of acetylacetone. The r_g values for this compound are C₁-C₃ = 1.4164 ± 0.006 Å, C₃-C₅ = 1.511 ± 0.021 Å, C₂-C₄ = 1.536 ± 0.018 Å, C-O = 1.270 ± 0.008 Å, C-H = 1.088 ± 0.039 Å, C-F = 1.340 ± 0.005 Å, ∠C₂C₁C₃ = 117.2 ± 1.8°, ∠C₁C₂O₂ = 123.6 ± 1.7°, ∠C₁C₃C₅ = 118.1 ± 2.3°, ∠C₁C₂C₄ = 123.0 ± 1.4°, ∠CCH = 109.0± 4.8°, and ∠CCF = 110.6± 0.8°. The r_g values for the trifluoroacetone are: C₁-C₂ = 1.481 ± 0.019 Å, C₁-C₃ = 1.562 ± 0.011 Å, CO = 1.207 ± 0.006 Å, C-H = 1.089 ± 0.024 Å, C-F = 1.339 ± 0.003 Å, ∠C₂C₁O = 122.0 ± 1.1°, ∠C₃C₁O = 116.8 ± 0.7 °, ∠CCH = 105.0 ± 2.2 °, and ∠CCF = 110.7 ± 0.3°. The significance of the error estimates is discussed briefly.     

Tandem mass spectrometry methods for definitive protein identification in proteomics research

Optimized procedures have been developed for the addition of sulfonic acid groups to the N-termini of low-level peptides. These procedures have been applied to peptides produced by tryptic digestion of proteins that have been separated by two-dimensional (2-D) gel electrophoresis. The derivatized peptides were sequenced using matrix-assisted laser desorption/ionization (MALDI) post-source decay (PSD) and electrospray ionization-tandem mass spectrometry methods. Reliable PSD sequencing results have been obtained starting with sub-picomole quantities of protein. We estimate that the current PSD sequencing limit is about 300 fmol of protein in the gel. The PSD mass spectra of the derivatized peptides usually allow much more specific protein sequence database searches than those obtained without derivatization. We also report initial automated electrospray ionization-tandem mass spectrometry sequencing of these novel peptide derivatives. Both types of tandem mass spectra provide predictable fragmentation patterns for arginine-terminated peptides. The spectra are easily interpreted de novo, and they facilitate error-tolerant identification of proteins whose sequences have been entered into databases.     

Electrolytic reduction of 3-carbethoxyquinoline

Two well-defined one-electron waves are observed on the polarograms for the reduction of 3-carbethoxyquinoline in 95% aqueous ethanol containing 1 M ammonium acetate. During macroscate electrolysis at a potential on the plateau of either wave, the ratio of the heights of the waves remains equal to one. Polarographic and voltammetric evidence is presented that the first wave represents a reversible one-electron reduction to a radical which rapidly dimerizes; and the second wave represents an irreversible one-electron reduction of the initially formed radical. The reduction mechanism suggested by the electrochemical evidence is verified by the isolation of dimeric products from controlled-potential electrolysis at the top of the first wave and the isolation of 1,4-dihydro-3-carbethoxyquinoline at the top of the second wave. The chemical characteristics of the dimeric products are discussed.     

Der Reaktionsmechanismus der allgemeinen Säure-Basen-Katalyse der Mutarotation der Glucose, 9. Mitt.: Die Katalyse der Mutarotation der Glucose durch Essigsäure

Ohne Zusammenfassung1.–8. Mitt.:Hermann Schmid, Mh. Chem.94, 1206 (1963);95, 454, 1009 (1964);Hermann Schmid undGünther Bauer, Mh. Chem.95, 1781 (1964); Mh. Chem.96, 583, 1503, 1508, 1510 (1965).     

Identification of N-methylpyrazole analog isomers by 13C NMR

Using several N-methyl pyrazole analogs the utility of ¹³C nmr in determining isomeric structures was examined. The chemical shift assignments of the pyrazole carbons and thus the isomeric structures were determined using a combination of proton coupled and proton decoupled ¹³C nmr spectra.     

Vergleichende Untersuchungen zur Struktur von 4‐Dimethylaminopyridin‐Addukten

Comparative Structural Studies on 4‐Dimethylaminopyridine‐Adducts Lewis acid‐base adducts of the type dmap—MMe₃ (M = Al 1 , Ga 2 , In 3 , Tl 4 ) as well as dmap—AlCl₃ ( 6 ) and dmap—Al(t‐Bu)₃ ( 7 ) were synthesized by reaction of MR₃ with 4‐dimethylamino‐pyridine (dmap) whereas dmap—AlH₃ ( 5 ) was obtained from AlH₃·Et₂O. 1 — 7 were characterized by means of NMR (¹H, ¹³C{¹H}) and mass spectrometry and elemental analysis. In addition, their solid state structures were determined by single crystal X‐ray diffraction studies. A comparison of the structural parameters reveales the influence of both electronic (Lewis acidity of the group 13 atom) and steric interactions on the structure and stability of as prepared Lewis acid‐base adducts.     

A highly efficient olefin metathesis initiator: improved synthesis and reactivity studies

The synthesis of ligand 8, required for the preparation of catalyst 4c has been optimised. Ligand exchange studies indicate that biphenyl-based alkylidene 4c initiates considerably faster than its unsubstituted analogue 4a. The performance of 4c in ring-opening cross metathesis reactions involving substrates containing unprotected chelating atoms is also reported.