Thomas Blumenthal

Cluster Chemistry: XXVIII. Utility of fast atom bombardment mass spectrometry for the characterisation of high molecular weight complexes containing metal clusters

Abstract Fast atom bombardment (FAB) mass spectrometry has been used to obtain spectra of HRu3Au(μ3-S)(CO)9(PPh3), Ru3Au2(μ3-S)(CO)9(PPh3)2 and Ru3Au3(μ3-C12H15)(CO)8(PPh3)3, none of which give metal-containing ions in conventional EI mass spectrometry. All the compounds give molecular (M+) or quasimolecular ([M + 2H]+) ions which fragment by conventional routes.

Cyclization of ortho-cyclopropylphenyl benzamides in gas and liquid phases.

The electron ionization (EI) and collision-induced dissociation (CID) spectra of substituted N-(ortho-cyclopropylphenyl)benzamides 1–7 and N-[ortho-(1-methylcyclopropyl)phenyl]benzamides 8–12 were recorded. In addition to routine bond cleavages, the molecular ions (M+) of 1–12 undergo cyclization into the corresponding 3-aryl-1-alkyl-1-ethyl-1H-benzoxazines and isomeric 5-ethyl-2-oxodibenzoazepines. The presence of a methyl group in the cyclopropyl ring (compounds 8–12) makes the formation of 5-ethyl-2-oxodibenzoazepine less favorable. In accord with mass spectrometric predictions, compound 13 (3-p-tolyl-1-ethyl-1H-benzoxazine) was obtained as a major product of the reaction of N-(ortho-cyclopropylphenyl)-4-methylbenzamide 1 with sulfuric acid. Traces of 5-ethyl-2-oxodibenzoazepine were also detected in gas chromatography-mass spectrometry (GC-MS) analysis of the reaction mixture although the yield was too low to allow its isolation.

The negative ion mass spectra of deprotonated 2,5-diketopiperazines

Abstract Deprotonation of 2,5-diketopiperazine (with HO − ) can occur either on N (position 1(4)) or on carbon (position 3(6)). The two depotonated forms are interconvertible on collisional activation. The major collision-induced fragmentations of (M  H) − ions of substituted 2,5-diketopiperazines are (i) characteristic side-chain losses (e.g. Me . for Ala, PhCH 2 . for Phe, and O  C 6 H 4  CH 2 for Tyr), which identify the particular 2,5-diketopiperazine, and (ii) an unusual loss of RCHO (R is the substituent, e.g. Me for Ala), which involves initial 1,2 migration of R . to the carbon of the adjacent carbonyl group.

Novel inorganic ring systems

Abstract The first cycloalumadisilatriazane system, [ClAl(NMeSiMe2)2NMe]2 (C1), has been prepared. IR and Raman spectra are reported. The molar weight of C1 in benzene and 1H, 13C, 27Al and 29Si NMR spectra are consistent with a nitrogen-bridged dimer which is stereochemically rigid on the NMR time scale near room temperature. Mass spectral evidence is also presented for the dimeric nature of C1 in the gas phase. C1 crystallizes in the triclinic space group P 1 with a 8.2262(7) A, b 9.5147(7) A, c 10.2552(b) A, α 102.655(5)°, β 97.448(5)°, γ 112.088(6)° and Z = 1. The structure was refined to an R value of 0.0303 for 2487 counter-measured, observed X-ray data. The mean AlN bridging distance (1.947(8) A) in the centrosymmetric (AlN)2 ring is much longer than the AlN(cn3) bond (cn = coordination number), 1.803(2) A. A smaller dependence on nitrogen valency was found for the SiN bond lengths; thus the SiN(cn 4) and mean SiN(cn 3) are 1.798(2) and 1.726(14) A, respectively.

The negative ion mass spectra of (M – H) – ions from phenylthiohydantoin derivatives of amino acids

The mass spectra of (M – H)− ions of phenylthiohydantoin (PTH) amino acids show characteristic fragmentations through the side chain (the α-side chain of the original amino acid) which may be used to identify each of the common amino acids. Some of these fragmentations are Leu (C3H8), Ile (CH4, C2H6), Phe (PhH), Tyr (CH2=C6H4=O), Trp (CH2=C8H5N), Ser (CH2O), Thr (MeCHO) and Met (MeSH). The formulae in parentheses represent the neutrals lost.

Fast atom bombardment and electrospray tandem mass spectrometry. Some fragmentation reactions in cyclic nitramines studied using collision-induced dissociation

The initial fragmentation pathways of some cyclic nitramines containing nitroguanidine and/or secondary nitramine groups were identified by fast atom bombardment (FAB) ionization mass spectrometry. Their partially nitrated analogues were analyzed as nitric acid salts using both FAB and electrospray (ES) ionization mass spectrometry. The ES technique gave simple mass spectra dominated by the more diagnostic higher molecular-mass species, which were ideal for tandem mass spectrometry (MS/MS) studies. Fragment-molecule adduct ions of the type [MH + NO2]+ and/or [MH + NO]+ were observed in the FAB spectra in some cases. Fragmentation processes of these and the protonated molecules, together with some fragment ions, were elucidated. The main fragmentation processes were the loss of H2O, NO2 group(s) and to a lesser extent NO. Minor transitions involving ring fragmentations were more favorable for the nitric acid salts than their more highly nitrated analogues.