Molecular fragmentations: Part VII. Structures and energies of mass spectral fragments derived from benzene

Molecular structures and energies have been calculated, using MINDO/3, of the mass spectral ions arising from benzene: (C₆H₆)⁺ (three non-valence isomers); (C₆H₅⁺); (C₅H₃⁺) (four isomers); (C₄H₄)⁺ (three isomers); (C₄H₃)⁺ (two isomers); (C₄H₂)⁺ (four isomers); (C₃H₃)⁺; and (C₂H₂)⁺. Calculations have been made for the conjugate neutral fragments, allowing calculation of appearance potentials, and also for the ion (C₆H₇)⁺.     

Molecular fragmentations: Part VIII. Structures and energies of mass spectral fragments derived from tetraphosphorus trisulphide

Molecular structures and energies have been calculated in the MNDO approximation, for P₄S₃ and its molecular ion P₄S₃⁺, and for the mass spectral fragment pairs: (P₃S₃⁺ + P), (P₃S₂⁺ + PS), (P₃S⁺ + PS₂), (P₂S₃⁺ + P₂), (P₂S₂⁺ + P₂S), (P₂S⁺ + P₂S₂), (P₂S₂), PS₃⁺ + P₃), (PS₂⁺ + P₃S), (PS⁺ + P₃S₂), and (PS⁺ + P₂S + PS). Three distinct energy minima were found for each of P₂S₂⁺ and P₂S₂, and two minima for each of P₂S⁺, P₂S, PS₃⁺, PS₃⁺, PS₂⁺, PS₂, P₃⁺ and P₃. The fragments arising from P₄ and P₄⁺ were also investigated. The structures are discussed in terms of the Jahn—Teller effect, whose predictions are fulfilled without exception.     

Molecular fragmentations: Part V. Structures and energies of mass spectral fragments derived from ethyl acetate

Calculations have been made using MINDO/3 of the structures and energies of four conformations of ethyl acetate, of four isomeric forms of its molecular ion, and of all the fragment and rearrangement ions in the mass spectrum together with those of the corresponding neutral fragments.     

Molecular fragmentations: Part IX. Structures and energies of mass spectral fragments derived from xanthan hydride, 5-amino-1,2,4-dithiazolin-3-thione

Structures and energies have been calculated, in the MNDO approximation, for xanthan hydride (C₂H₂N₂S₃) and its molecular cation, and for the mass spectral fragment ions H₂NCNCS⁺, HNCNCS⁺, CS₂⁺, H₂N₂CS⁺ (two isomers), HN₂CS⁺, S₂⁺, H₂NCS⁺ (three isomers), HNCS⁺ (two isomers), H₃N₂C₂⁺ (four isomers), CS⁺ and HNCS⁺² (two isomers), together with the corresponding neutral fragments.     

Molecular fragmentations: Part I. Structures and energies of molecular fragments derived from formic acid

Molecular geometries and heats of formation are calculated, using MINDO/3, for the following mass-spectral fragment pairs derived from formic acid: X(²A')(HCOOH)⁺; (HCOO)⁺ + H^xxx; (HCO)⁺ + OH; HCO + (OH)⁺; (CO)⁺ + H₂O; (CO₂)⁺ + H₂. The activation energy for the reaction (HCOOH)⁺ → (HCOO)⁺ + H^xxx is 75 kJ mol^?1. A correlation is made of the symmetry classes of the electronic states of (HCOOH)⁺, accessible by single electron excitation, and those of the mass-spectral fragments: it is shown that, despite their closely similar appearance potentials, the ions (HCOO)⁺ and (HCO)⁺ arise from different states of (HCOOH)⁺. The structure of (HCOOH)²⁺ is also reported.     

Molecular fragmentations: Part II. Structures and energies of molecular fragments derived from formamide and its molecular cation

Molecular geometries and heats of formation have been calculated, using MINDO/3, for mass spectral fragment pairs (A⁺ + B) derived from formamide. There are five stable isomeric forms of the molecular ion: [H₂NC(OH)]⁺, (H₃NCO)⁺, [HNC(OH₂)]⁺, [NCH(OH₂)]⁺, and (NCOH₃)⁺ (in order of increasing

, but no isomer (H₂NCHO)⁺. There are three isomeric forms of (M—H)⁺: (H₂NCO)⁺ (HNCOH)⁺, and (NCOH₂)⁺: the only stable form of (M—2H)⁺ is (NCOH)⁺. Other (A/B)⁺ fragment pairs calculated are (CO/NH₃)⁺, (HCO/NH₂)⁺, (H₂O/HCN)⁺, (H₂O/HNC)⁺ [HO^. + (HCNH)⁺], and [HO^. + (H₂NC)⁺]. The structure of the doubly charged ion M²⁺ is also reported.     

Molecular fragmentations: Part IV. The mass spectral fragmentation of carbon tetrachloride

MINDO/3 calculations have been made of the molecular structures and energies of seven isomeric forms of the molecular cation (CCl₄)⁺, of the mass spectral fragment pairs:

and also of a number of neutral fragment pairs. Reaction energy profiles have been calculated for two fragmentations of (CCl₄)⁺, into [(CCl₂)⁺ + Cl₂], and into [(CCl₃)⁺ + Cl^?], in the latter of which the reaction proceeds via a rather stable intermediate; for the fragmentation of three electronic states of (CCl₃)⁺ into [(CCl₂)⁺ + Cl^?], where the ground singlet state and first triplet state of (CCl₃⁺ yield the ground doublet state of (CCl₂)⁺, but the first excited singlet of (CCl₃)⁺ yields the first excited doublet of (CCl₂)⁺ ; and for the fragmentation of the ground state of (CCl₃)⁺ into [(CCl)⁺ + Cl₂].     

Molecular fragmentations: Part VI. Structures and energies of the valence isomers of benzene,and their molecular cations and anions

Molecular structures and energies have been calculated, in the MINDO/3 approximation, for neutral singlets and triplets, and for molecular cations and anions of benzene and seven of its valence isomers.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 5. The4 N-cyclohexyl derivative

Summary Metal ion complexes of the thiosemicarbazone,⁴ N-cyclohexyl-2-[1-(2-pyridinyl)ethylidene]hydrazinecarbothioamide (HL4CH), have been prepared and spectrally characterised. Both the size of the cyclohexyl-group attached at⁴N as well as the⁴N hydrogen affect the stoichiometry and stereochemistry of the isolated complexes. The large cyclohexyl-group evidently causes the isolation of [Fe(HL4CH) (L4CH)H₂O](ClO₄) instead of the expected [Fe(L4CH)₂]ClO₄[Co(L4CH)Br] instead of [Co(HL4CH)Br₂], and [Ni(L4CH)Br] instead of [Ni(HL4CH)₂Br₂]. The presence of the hydrogen at⁴N presumably hinders the deprotonation of HL4CH on complex formation since [Cu(HL4CH)Cl₂] was isolated rather than [CuLCl], which occurs when the thiosemicarbazone has⁴N with two alkyl groups or incorporated in a ring. Further, although we prepared [Ni(L4CH)Br], complexes of this stoichiometry are planar and diamagnetle when⁴N does not have a hydrogen(s) attached to it rather than tetrahedral and paramagnetic as has been found for the present complex.     

Molecular fragmentations: Part III. Structures and energies of the transition states in the rearrangement and decomposition of formamide molecular cations

MINDO/3 calculations have been made for the activation enthalpies, and the transition state structures for the following equilibria between isomers of the formamide molecular cation, M⁺: (NCOH₃)⁺ ? (NCHOH₂)⁺ ? (HNCOH₂)⁺? (H₂NCOH)⁺? (H₃NCC)⁺ for the following equilibria between the isomers of (M-H)⁺: (NCOH₂)⁺ ? (HNCOH)⁺ ? (H₂NCO)⁺ and for seven decomposition reactions of general type: M⁺ → (M-H)⁺ + H^? Rate constants have been deduced using calculated enthalpies of activation, and estimated A factors. All the processes are symmetry-allowed.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 4. The 3-piperidinyl derivative

Summary Metal ion complexes of the thiosemicarbazone, 3-piperidinyl-3-thiocarboxylic acid-2-[1-(2-pyridyl)ethylidene]hydrazide (HLpip) have been prepared and spectrally characterized. HLpip coordinates both as the deprotonated ligand (i.e., pyridylN, azomethineN, and thione sulphur) and the neutral ligand (i.e., pyridylN and azomethineN) with the sulphur possibly weakly coordinating in [Ni(HLpip)₂](BF₄)₂. All three preparative cobalt(II) salts yielded cobalt(III) cationic complexes. The nickel(II) and copper(II) chloride salts gave [M(Lpip)Cl] solids while complexes involving the neutral ligand were prepared with the corresponding bromide salts. Significant differences in the spectral properties of the various complexes are observed when compared to other thiosemicarbazones prepared from 2-acetylpyridine.     

Strained heterocyclic systems. VIII. The mass spectral fragmentations of some arylquinolines and quinoline N-oxides

High resolution mass spectra of compounds 1—8 were investigated. For the quinolines (1–3) the absence of major peaks other than M⁺ and (M-1)⁺ reflects the stability of those systems. The N-oxides (4–6) all exhibit major peaks at M⁺, (M-16)⁺, and (M-17)⁺. In addition, 4 shows prominent fragmentations reflecting loss of hydrogen and carbon monoxide. The pathways are related to the geometries of the N-oxides; deuterated compounds (7–8) aided these assignments.     

Hydrazones derived from thiooxamohydrazides and 3-formyl-4-hydroxycoumarin: synthesis, structures, and fragmentation

Novel hydrazones were obtained from thiooxamohydrazides and 3-3-formyl-4-hydroxycoumarin. According to data from NMR spectroscopy and X-ray diffraction, the coumarin fragment in the compounds obtained exists as 4-hydroxycoumarin or chromane-2,4-dione. When dissolved in dimethyl sulfoxide, these hydrazones undergo fragmentation into derivatives of 1,3,4-thiadiazole and 4-hydroxycoumarin.     

Strained heterocyclic systems. VII. The mass spectral fragmentations of dihydrocycloalka[b]quinolines and quinoline N-Oxides

High resolution mass spectra of compounds 1-6 were investigated. The quinolines ( 1-3 ) all exhibit a prominent (M-1)⁺ peak and subsequent loss of HCN. These processes are consistent with azatropylium ion intermediates. The N-oxides ( 4-6 ) all exhibit major peaks at (M-16)⁺; the abundance of the latter is related to the geometry of the molecule. The four-membered ring compounds (3 and 6) give more complex spectra, which reflect the influence of the fused strained ring.     

Small elemental clusters. I. The structures of Be2, Be3, Be4, and Be5

The geometries and energies of beryllium clusters up to Be₅ are examined using ab initio molecular orbital theory. Allowances are made for electron correlation with Møller—Plesset perturbation theory to fourth order. Correlation is found to have a dramatic effect on the relative energies of the several structures examined for Be₄ and Be₅. Furthermore, the effect of d-type basis functions on the correlation energy results in an increased binding energy for the clusters. Be₂ is only weakly bound. For Be₃, the best estimate of the binding energy is 6 kcal/mole for the singlet equilateral triangle. Be₄ is tetrahedral in its ground state and the estimated binding is 56 kcal/mole. The best structure for Be₅ is a singlet trigonal bipyramid, and the binding energy is 88 kcal/mole at the highest level of theory used.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 2. The4 N-dimethyl derivative

Summary Metal ion complexes of the thiosemicarbazone,N-dimethyl-2-[1-(2-pyridinyl)ethylidene]hydrazinecarbothioamide (HL4DM) have been prepared and characterized spectrally. HL4DM coordinates primarily as the deprotonated tridentate ligand (i.e., pyrïdylN, azomethineN, and thione sulphur). In contrast to related thiosemicarbazones, oxidation to cobalt(III) does not occur during complex formation with cobalt(II) halides. Oxidation does occur on reflux with ethanolic Co(BF₄)₂, but we isolated a planar cobalt(II) complex as well. Only with the tetrafluoroborate salts of cobalt(II) and nickel(II) are complexes isolated containing the neutral thiosemicarbazone. Square planar [Ni(L4DM)X]complexes where X=Cl, Br, and OH have been isolated and e.s.r. spectra of a 1% Cu/Ni complex are compared to the results of other workers.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 3. The 3-hexamethyleneimine derivative

Summary Metal ion complexes of the thiosemicarbazone, 3-hexamethyleneimine-3-thiocarboxylic acid-2-[1-(2-pyridyl)-ethylidene]hydrazide (HLhexim) have been prepared and spectrally characterized. HLhexim coordinates primarily as the deprotonated tridentate ligand (i.e., pyridylN, azomethineN, and thione sulphur). The air oxidised cobalt(III) complex, [Co(LHexim)₂] (BF₄), was isolated from the preparation with cobalt(II) tetrafluoroborate, but other cobalt(II) salts yielded tetrahedral cobalt(II) compounds. Planar nickel(II) and copper(II) complexes were isolated from preparations with halide salts. Significant differences in the spectral properties of the various complexes are observed when compared to other thiosemicarbazones prepared from 2-acetylpyridine.     

Carbodications. I. The structures and energies of C4H isomers

At high levels of ab initio theory (6-31G*//4-31G), the most stable C₄H isomer is indicated to be the nonplanar cyclobutadiene dication ( 1a ); the planar form, 1b , is indicated to be 7.5 kcal/mol less stable. The second most stable C₄H isomer, the methylenecyclopropene dication, is indicated to prefer the perpendicular ( 2a ) over the planar ( 2b ) arrangement by 7 kcal/mol. The “anti van't Hoff” cyclo-(HB)₂C?CH₂ system ( 4 ), isoelectronic with 2 , also prefers the perpendicular conformation ( 4a ), and retains the C?C double bond. The linear butatriene dication ( 3 ) is the least stable C₄H species investigated. The perpendicular (D_2d) arrangement ( 3a ), permitting double allyl cationlike conjugation, is preferred over the planar D_2h form ( 3b ) by 26 kcal/mol. The heat of formation of the most stable form of C₄H, 1a , is estimated to be 623–640 kcal/mol. This species should be thermodynamically stable toward dissociation into smaller charged fragments.     

Transition metal ion complexes of thiosemicarbazones derived from 2-acetylpyridine. Part 1. The4N-methyl derivative

Summary A series of metal ion complexes of the thiosemicarbazone,N-methyl-2[1-(2-pyridinyl)ethylidene]-hydrazinecarbothioamide (HL4M) has been prepared and spectrally characterized. HL4M coordinates either as a neutral bidentate ligand (i.e., pyridyl N and imine N) or as deprotonated tridentate ligand (i.e., pyridyl N, imine N and thiol sulphur). The cobalt(II) salts yield hexacoordinated cobalt(III) cations, and an isoelectronic species, [Ni(L4M)₂], has been formed from Ni(C₂H₃O₂)₂. The remaining nickel(II) complexes involve the neutral ligand, as do two of the three copper(II) complexes. HL4M possesses a weaker ligand field and has less covalency in its bonding than related thiosemicarbazones that possess anN-dialkyl-function.