Infrared Spectra of Cyanoacetaldehyde (NCCH2CHO): A Potential Prebiotic Compound of Astrochemical Interest

Cyanoacetaldehyde (NC? CH₂CH?O) and its isomer, cyanovinylalcohol (NC? CH?CH? OH), as possible components of the interstellar medium, comets, or planetary atmospheres, exist in equilibrium in the gas phase, although the latter compound is very much in the minority (2 %). The recording and analysis of the gas‐phase infrared spectrum of the former compound within the 4000–500 cm^?1 spectroscopic range and the potential presence of the latter isomer, which could be vital for their detection in these media, are reported. CCSD(T) and G4 high‐level ab initio methods, as well as density functional theory calculations, predict the existence of two stable rotamers of cyanoacetaldehyde. The global minimum has a structure with an unusual O‐C‐C‐C dihedral angle (150°) that falls between the antiperiplanar (180°) and anticlinal forms (120°). The second rotamer, which is about 4.0 kJ mol^?1 less stable in terms of free energy, has a planar structure that corresponds to the synperiplanar form (O‐C‐C‐C dihedral angle: 0°). The absorption vibrational bands of the two aldehyde rotamers that are present in the mixture lead to a spectrum with a very complex structure in the region of deformation movements, in which several low‐intensity bands overlap. A complete and unambiguous assignment of the experimental spectrum has been achieved by using the calculated harmonic and anharmonic vibrational frequencies.     

Structural revision and absolute configuration of lateritin

‘Lateritin’ (1), a morpholine-2,5-dione (depsipeptide), was reinvestigated for its structure and absolute configuration. On the basis of thorough 1D and 2D NMR and mass spectrometrical analyses, the structure of 1 was revised to be identical with beauvericin (8) and confirmed that beauvericin (8) is the trimeric lactone of ‘lateritin’ (1). The absolute configuration was determined by acidic hydrolysis, followed by application of Marfey’s method, menthyl ester derivatization, and GC–MS analysis. In addition, the specific optical rotation values of the hydrolysis products were compared with those of available standards.     

Multinuclear alkylaluminium macrocyclic Schiff base complexes: influence of procatalyst structure on the ring opening polymerisation of epsilon-caprolactone

Two remote dialkylaluminium centres supported by a macrocyclic Schiff base ligand exhibited beneficial cooperative effects, whilst aluminoxane-type bonding proved to be detrimental to activity for the ring opening polymerisation of epsilon-caprolactone.     

Solid-state structures and solution studies of novel cyclopentadienyl mercury compounds

New mercury cyclopentadienyl complexes Hg(eta1-Cp')Cl have been prepared by the reaction of HgCl2 and the appropriate KCp' salts or by the transmetalation of HgCl2 with ZnCp'2 (Cp'=C5Me4H, 1; C5Me4But, 2; C5Me4SiMe3, 3; C5H4SiMe3, 4). By contrast, only the SiMe3-substituted bis(cyclopentadienyl) derivatives, Hg(C5Me4SiMe3)2 (5) and Hg(C5H4SiMe3)2 (6), can be isolated by the above synthetic procedures and the appropriate ratio of reagents or from HgCp'Cl and KCp'. Solution NMR studies reveal nonfluxional behavior of the SiMe3-substituted complexes 3, 5, and 6. X-ray studies of the solid-state structures show that the six compounds contain eta1-Cp' ligands, with linear or almost linear C-Hg-Cl or C-Hg-C coordination environments. The two HgCp'2 compounds, 5 and 6, have the expected insular structures, but the HgCp'Cl derivatives show supramolecular associations by means of weak secondary Hg...Cl interactions. Thus, the HgCp'Cl compounds 1, 3, and 4 form three different polymeric chain structures with typically two Hg...Cl interactions of 3.04-3.46 A per mercury. By contrast, 2 forms a tetramer, [Hg(C5Me4SiMe3)Cl]4, with a cubelike arrangement of four Hg and four Cl atoms. Density functional theory has been used to investigate the electronic structure of the compounds.