M. Hamdan

Reactions of 3-carbomethoxy-2-aza-1,3-butadiene derivatives with dienophiles

Abstract The reactions of 1,1-diphenyl-3-carbomethoxy-2-aza-1,3-butadiene derivatives la-e (on C4 : H,H or H,CH3 or H,C6H5, both E and Z isomers), and of the C4 unsubstituted 1 -phenyl-1-ethoxy analogue 2, were studied with a number of electron-rich and electron-poor dienophiles, with results showing that la-e give heterocycloadducts in Diels-Alder reactions with electron-poor dienophiles. Michael adducts were obtained from the EtAlCl2 catalyzed reactions of these compounds with dimethyl acetylendicarboxylate. Compound 2 gave heterocyclic adducts as well but behaved like a nucleophile, at least in the case of the reactions with dimethyl acetylendicarboxylate and ethyl propynoate: these reactions afforded 2-azatrienes as Michael adducts that gave pyridine derivatives upon heating. The synthesis of the new 1-ethoxy-2-aza-1,3-butadiene 2 is also reported.

Differentiation between isomeric 1-aminocyclo-propane- 1 - carboxylic acid derivatives by means of chemical ionisation and mass selected collision induced dissociation

Abstract Chemical ionisation in ammonia and in methane, electron impact ionisation and mass selected collision induced dissociation involving 10 1-aminocyclopropane- 1 -carboxylic acid derivatives are reported. The data presented, exhibit a number of qualitative differences which are attributed to the different isomeric structures of the investigated precursors. Competition between protonation and addition reaction channels which yield MH+ and [M + NH4]+ in ammonia, chemical ionisation and the different internal excitation experienced by ions formed in chemical ionisation, and by electron impact, are two experimental observations which the present work seeks to underline.

Electronic and vibrational transitions observed in collisions between C+2 and He

Abstract Electronic and vibrational transitions among the low-lying doublet and quartet states of C+2 ions are investigated by means of high resolution collision spectroscopy. The presented translational energy spectra of 3 keV C+2 ions scattered off a He target clearly show a number of excitation/de-excitation transitions, the lowest of which is centred at ∼ ±0.35 eV. Assignment of this transition to C+2 (X4Σ−g, ν = 2 ↔ ν = 0) is based on the existing ab initio configuration interaction (CI) calculations. The observation of this and other similar transitions is the first experimental evidence which shows that vibrationally excited C+2 (X4Σ−g) ions formed by electron impact can live for at least a few microseconds (ion transit time between the ion source and the target cell).