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 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.     

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 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 XIII. The structures and energies of mass spectral fragments derived from phosphine-3, diphosphine-4, diphosphine-2 and triphosphine-5

Structures and energies have been calculated, in the MNDO approximation, for PH₃, P₂H₄, P₂H₂, and P₃H₅, for their molecular cations, for all the ions in their mass spectra, and for the corresponding neutral mass spectral fragments. With the exception of the conformation of P₂H₄, which is calculated to be anti rather than gauche, the calculated structures and energies are in good agreement with those found experimentally, where these are known. Appearance potentials have been calculated, and allow deductions to be made concerning fragmentation pathways.     

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.     

An answer to the spiro versus ansa dilemma in cyclophosphazenes: Part I. N3P3Cl4[NH(CH2)3NH]

Structural investigation, mainly by mass spectrometry and X-ray crystallography, of the product obtained from the reaction of propylenediamine and N₃P₃Cl₆ shows it to have a monospiro structure. It is demonstrated that in this case data collected through indirect structural methods such as IR or NMR spectroscopy could not provide a priori the right answer.     

An electrochemical study of redox indicators : Part I. Substituted chrysoidines

The electrochemical oxidation of various substituted chrysoidines was studied by cyclic voltammetry, to determine which have stable oxidation products. Only 4-hydroxy-chrysoidine has a stable product; the apparent oxidation potential is 0.779 V vs. NHE. 4-Methoxy- and 4-ethoxy-chrysoidine rapidly lose methanol or ethanol, respectively, so that the 4-hydroxychrysoidine wave appears on subsequent scans. All the other chrysoidines studied are irreversible. The results indicate that a hydroxy group in the 4-position is necessary for stability; the 4-alkoxychrysoidines can achieve the stable quinoidal structure by cleavage of the alkoxy group after nucleophilic attack.     

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].     

Reductive nitrosylation of tetraoxometallates. Part VIII1. A virtually single step synthesis of azido-nitrosyl derivatives of chromium(I) directly from chromate in aqueous-aerobic media.

Azido-nitrosyl complexes and their derivatives of the types [Cr(NO)(N₃)₅]^3? and [Cr(NO)(N₃)₂(L-L)] [L-L = 2,2′bipyridine (bipy) and 1,10 phenanthroline (phen)] were synthesised directly from chromate ion using hydroxylamine hydrochloride, azide ion and hydroxyl ion and other appropriate ligands virtually in a single step process in an aqueous aerobic medium. The compounds are characterised by IR, molecular weight, molar conductance, magnetic susceptibility, esr and electronic spectral data.     

H NMR, C NMR and mass spectral studies of some Schiff bases derived from 3-amino-1,2,4-triazole

Heterocyclic Schiff bases derived from 3-amino-1,2,4-triazole and different substituted aromatic aldehydes are prepared and subjected to ¹H NMR, ¹³C NMR and mass spectral analyses. ¹H NMR spectra in DMSO exhibit a sharp singlet within the 9.35–8.90 ppm region which corresponds to the azomethine proton. The position of this signal is largely dependent on the nature of the substituents on the benzal moiety. It is observed that the shape, position and the integration value of the signal of the aromatic proton of the triazole ring (⁵C) are clearly affected by the rate of exchange, relaxation time, concentration of solution as well as the solvent used. ¹³C NMR is taken as substantial support for the results reached from ¹H NMR studies. The mass spectral results are taken as a tool to confirm the structure of the investigated compounds. The base peak (100%), mostly the M-1 peak, indicates the facile loss of hydrogen radical. The fragmentation pattern of the unsubstituted Schiff base is taken as the general scheme. Differences in the other schemes result from the effect of the electronegativity of the substituents attached to the aromatic ring.     

Semiempirical molecular orbital studies on the electronic structure of molecules in excited states: The INDO/2-VN— 1 potential model: Part I.

The performance of the V_N—1 potential model at the INDO/2 level of approximation in the calculation of transition energy, singlet—triplet splitting, change in molecular structure, inversion barrier and electron-density distribution in the excited electronic states of a few simple carbonyls is analysed. The method turns out to be reasonably successful in many ways.     

Mechanism of the sulfurisation of phosphines and phosphites using 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride)

Contrary to a previous report, the sulfurisation of phosphorus(III) derivatives by 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride) does not yield carbon disulfide and cyanamide as the additional reaction products. The reaction of xanthane hydride with triphenyl phosphine or trimethyl phosphite yields triphenyl phosphine sulfide or trimethyl thiophosphate, respectively, and thiocarbamoyl isothiocyanate which has been trapped with nucleophiles. The reaction pathway involves initial nucleophilic attack of the phosphorus at sulfur next to the thiocarbonyl group of xanthane hydride followed by decomposition of the phosphonium intermediate formed to products. The Hammett rho-values for the sulfurisation of substituted triphenyl phosphines and triphenyl phosphites in acetonitrile are approximately -1.0. The entropies of activation are very negative (-114+/-15 J mol-1 K-1) with little dependence on solvent which is consistent with a bimolecular association step leading to the transition state. The negative values of DeltaS(not equal) and rho values indicate that the rate limiting step of the sulfurisation reaction is formation of the phosphonium ion intermediate which has an early transition state with little covalent bond formation. The site of nucleophilic attack has been also confirmed using computational calculations.     

Unusual metalloporphyrins : thorium and uranium complexes of octaethylporphyrin.

The action of thorium or uranium tetrachloride with octaethylporphyrin [(oep)H₂] affords the dichlorometal (IV) complexes [M(IV)(oep)Cl₂, L_n] (M(IV) = Th or U, L = benzonitrile, tetrahydrofuran or pyridine). Spectral properties of these complexes are in good agreement with a cis octa-coordination.     

Gravimetric determination of the abundance ratio of zirconium and hafnium, based on the in situ thermal decomposition of K(4)[(Zr,Hf)(C(2)O(4))(4)].5H(2)O

Careful heating of K(4)[(Zr,Hf)(C(2)O(4))(4)].5H(2)O results in a two-step thermal decomposition which can be written as: K(4)[(Zr,Hf(C(2)O(4))(4)].5H(2)O --> K(4)[(Zr,Hf)(C(2)O(4))(4)] --> {2K(2)CO(3)+(Zr,Hf)O(2)}. The weight-ratio of the successive decomposition products depends on the abundance ratio of Zr and Hf, and forms the basis for the present method of gravimetric determination.     

Solution-state conformations of 2-fluoro-, 2-chloro- and 2-bromo-acetophenone: a dipole moment and kerr effect study

Experimental dipole moments and infinite-dilution Kerr constants for 2-fluoro-, 2-chloro and 2-bromo-acetophenone (CH₃COC₆H₄X; X = F, Cl, Br) as solutes in CCl₄ at 25°C are analysed, yielding the following effective dihedral angles and percentage abundances of the less stable XO-cis conformers: X = F, 10 ± 10°, 5 ± 5%; X = Cl, 40 ± 5°, 10 ± 5%; and X = Br, 65 ± 10°, 25 ± 10%.     

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.     

Photophysical studies of uranyl complexes: VIII. Luminescence spectra of UO2SO4 · 312H2O and two polymorphs of bis(urea) uranyl sulfate

The photoluminescence spectra of hydrated and anhydrous uranyl sulfates have been studied under conditions of high resolution at cryogenic temperatures. All uranyl sulfate systems were found to yield nonequivalent spectra: the energies for the electronic and vibronic origins were found to vary with the system, and certain uranyl vibrational frequencies exhibited a dependence on environment. These differences must reflect the various ways in which the uranyl centers are linked by the bridging sulfate groups, as this linking is the main difference between the various structures.     

Synthesis,Structure and Biological Activity of 5-Benzyl-4-amino-1,2,4- triazole-3-thione Schiff Base

A novel Schiff base was synthesized via 5-benzyl-4-amino-1,2,4-triazole-3-thione with 3-phenoxy-benzaldehyde under refluxing. The structure was characterized by elemental analysis, IR, 1H NMR, ESI-MS and single-crystal X-ray diffraction. This compound crystallizes in monoclinic, space group P21 /c with a = 16.0289(16), b = 5.8022(6), c = 20.542(2), β = 95.667(2)o, C22 H18 N4 OS, Mr = 386.46, V = 1901.1(3)3, Z = 4, Dc = 1.347 g/cm3, F(000) = 804, μ = 0.191 mm-1, the final R = 0.0453 and wR = 0.1307 for 2456 observed reflections with I 2σ(I). The crystal packing of the compound is stabilized by classical intermolecular N–H···S hydrogen bonds. Furthermore, the biological activity to four vegetable pathogens has been tested. The title compound exhibited good fungicidal activities to Gibberlla nicotiancola.