Isomerization Of Molecular Ions Research Articles

Characteristics Of The GC-MS Mass Spectra Of Terpenoids (C10H16)

The terpenoids, sometimes referred to as isoprenoids, are a large and diverse class of naturally occurring organic chemicals similar to terpenes, derived from five-carbon isoprene units assembled and modified in thousands of ways. Most are multicyclic structures that differ from one another not only in functional groups, but also in their basic carbon skeletons. These lipids can be found in all classes of living things, and are the largest group of natural products. The features of mass spectra of mono-, bi- and tri-cyclic terpenoids: 1-isopropyl-4-methyl-1, 3-cyclohexadiene (I) terpilene; 1-methyl-4-(1-methylethylidene)-1- cyclohexene (II) terpinolene; 4-methyl-3-(1-methylethylidene)-1-cyclohexene (III); 1,5,5-trimethyl 3-methylene-1-cyclohexene (IV); 2,6,6-trimethylbicyclo\\\\\\\\\\\\\\ [3.1.1]-2-heptene (V) ii -pinene; 2,2,6-trimethylbicyclo [3.1.1]-2-heptene (VI) i¢ -pinene; 2,2-dimethyl-3-methylenebicyclo [2.2.1]-heptane (VII) camphene;1-isopropyl-4-methylbicyclo [3.1.0]-2-hexene (VIII) i¢ -thugene; 5-isopropyl-2-methylbicyclo [3.1.0]-2-hexene (IX) ii -thugene; 1-methyl-6-(1-methylidene) bicycle [3.1.0] hexane (X); 3,7,7-trimethylbicyclo [4.1.0]-3-heptene (XI) i¤ -3-carene; 4,7,7-trimethylbicyclo [4.1.0]-2-heptene (XII) (+)-4-carene; 3,7,7- trimethylbicyclo [4.1.0]-2-heptene (XIII) (+)-2-carene; 1,7,7-trimethyltricyclo [2.2.1.0(2.6)]-heptane (XVI) tricyclene; 1,3,3-trimethyltricyclo [2.2.1.0(2.6)]- heptane (XVII) cyclofenchene extracted from natural raw materials and comprising a number of drugs were investigated. The mass spectra for: cyclohexene- 3-(tretbutyl) peroxide (XIV) and 3-isopropyl-1-cyclohexene (XV) were investigated as well. It was established that the mass spectra of these compounds are absolutely identical in mass values of peaks of fragment ions, where their relative intensities have minor differences. In the spectra of all compounds the observed characteristic ions were [M-CH (CH3)2] and [M-CH (CH3)2 –H2]. The latter has a structure with m/z 91 that is attributed to pathing. All fragment ions correspond to even-electron cations. The identity of mass spectra of the studied tepenoids is explained by isomerization of molecular ions, similar to isomerization of terpenes in chemical transformations under the action of acids, also under the influence of other catalysts, temperature and light

Differentiation and electron ionization‐induced isomerization of 4,5‐Bis(alkylthio)‐1,3‐dithiole‐2‐thiones and 1,2‐dithiole‐3‐thiones

AbstractThe electron impact ionization mass spectra of 4,5‐bis(alkylthio)‐1,3‐dithiole‐2‐thiones and their 1,2‐dithiole‐3‐thione isomers were studied by accurate mass measurements and linked scans. The relative abundance of ions formed following the extrusion of S2, CS or CS2 allows an unambiguous isomer differentiation. Isomerization of molecular ions was studied by means of metastable ion analysis and collision‐induced dissociation. The order of reactivity was analogous to that observed in isomerization under photochemical conditions.

ChemInform Abstract: Isomers and Isomerization of Molecular Ions: The Formation of Stable Ion‐Neutral Complexes During Unimolecular Dissociation

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Fragmention behaviour of ω-functionalized allenes and their isomeric acetylenes under electron impact. Study on the isomerization of molecular ions and structural assignment of heteroatom migration related to a McLafferty-type rearrangement by CAD-MIKE spectrometry

CAD-MIKE Spectra of ions (1)–(6) are discussed. The main fragmentation pathway, loss of an ethylenic fragment leading to C4H5X+˙ ion, has been confirmed to proceed via a McLafferty-type rearrangement by comparison of the CAD-MIKE spectra of this ion to those of model structures. It is further shown, by means of kinetic-energy-release measurements (T values), that the investigated isomeric species do not interconvert after electron impact to an appreciable extent.