The reactive states of ions: Octatrienes and dimethyl substituted cyclohexadienes

The principal decomposition routes of molecular ions of cis, cis, cis-2,4,6-octatriene, cis, cis, trans-2,4,6-octatriene, trans, cis, trans-2,4,6-octatriene, trans-5,6-dimethyl-1,3-cyclohexadiene and cis-5,6-dimethyl-1,3-cyclohexadiene were studied using ion kinetic spectroscopy. The loss of radicals from [M]⁺· appears to proceed via a ground state, while loss of a neutral molecule appears to involve either complete equilibration of structure within the system or both ground state and excited state pathways.     

SYNTHESIS OF 2-γ-N-(AMINOETHYL)AMINOPROPYL-2-METHYL-6-ALKYL(ARYL,H)-1,3-DIOXA-6-AZA-2-SILACYCLOOCTANES

Some new 2-γ-N-(aminoethyl)aminopropyl-2-methyl-1,3-dioxa-6-aza-2-silacyclooctane and 2-γ-N-(aminoethyl)aminopropyl-2-methyl-6-alkyl(aryl)-1,3-dioxa-6-aza-2-silacyclooctanes have been synthesized from γ-chloropropyldimethoxymethyl silane by ethylenediamine substitution and diethanolamine or N-alkyl(aryl)diethanolamines substitution. The resulting silocanes have been characterized by elemental analyses, IR, and ¹H NMR.     

Antioxidant properties of 2,4-diphenyl-7,8-benzo-5,6-dihydro(4H)selenochromene and 2-<Emphasis Type="Italic">para</Emphasis>-chlorophenyl-4-phenyl-7,8-benzo-5,6-dihydro(4H)selenochromene

The antioxidant properties of 2,4-diphenyl-7,8-benzo-5,6-dihydro(4H)selenochromene and 2-para-chlorophenyl-4-phenyl-7,8-benzo-5,6-dihydro(4H)selenochromene were studied using the initiated oxidation of ethylbenzene and propan-2-ol as model reactions. The antioxidant activity of these compounds was quantitatively characterized by the apparent rate constant of inhibition, fk _in. Addition of 2,4-diphenyl-7,8-benzo-5,6-dihydro(4H)selenochromene to ethylbenzene being oxidized increases the chemiluminescence intensity.     

Reaktionen vonN-Sulfinylverbindungen mit dem 1,2,4-Trithia-3,5-diborolan-Ringsystem und Substitutionsreaktionen am 1,2,4-Trithia-3,5-diborolan und 1,2-Dithia-4-aza-3,5-diborolidin

The reaction of trimethylsilyl- and pentafluorophenyl-N-sulfinylamine respectively with 3,5-dihalogeno-1,2,4-trithia-3,5-diborolanes yields the 1,2-dithia-4-aza-3,5-diborolidines1-3.Tert-butyl-N-sulfinylamine and 3,5-dimethyl-1,2,4-trithia-3,5-diborolane react analogous. OtherN-sulfinylamines however split the disulfane bridge in 3,5-dimethyl-1,2,4-trithia-3,5-diborolane and the 1,4-dithia-2-aza-3,5-diborolidines5A-7(A) are formed. Besides of boroxines, cyclo-2,4,6-trimethyl-1,3-dioxa-5-aza-2,4,6-triboranes and cyclo-2,4,6-trimethyl-1-oxa-3,5-diaza-2,4,6-triboranes are formed as byproducts,8–10 have been isolated. In 1,2,4-trithia-3,5-diborolanes and 1,2-dithia-4-aza-3,5-diborolidines the bromo-atoms can be substituted by alkyl (13, 14), by amino (15–20) and by isothiocyanato groups. The compounds were characterised analytically and spectroscopically (MS; NMR:¹H,¹¹B,¹⁹F,²⁹Si; IR).

     

Mass spectrometric intramolecular cyclization reactions of some 2-N-phenyliminoperhydro-1,3-oxazines

Mass spectrometric fragmentation of four monocyclic and eight condensed skeleton 2-N-phenyliminoper-hydro-1,3-oxazine derivatives have been characterized by metastable ion analysis, collision induced dissociation measurements, exact mass measurements and ion structural studies. Extensive rearrangement reactions, best characterized in terms of intramolecular cyclizations, took place. Namely, when R = H the N-cyclization was almost exclusive whereas in cases where R > H steric reasons rendered the O-cyclization more feasible. Part of the fragmentation of the R = H compounds seemed to occur via the amino form. On the other hand the methane chemical ionization spectra of cis- and trans-anellated 5,6-trimethylene-2-N-phenyliminoperhydro-1,3-oxazines proved that at least some imino structure was present in the gas phase.     

Positive electron impact and chemical ionization mass spectra of some nitramine nitrates

The positive electron impact (EI) and isobutane chemical ionization (CI) mass spectra of six nitramine nitrates were studied with the aid of some accurate mass measurements. In the EI spectra, β fission relative to both the nitramine and nitrate ester is important. In the CI spectra a major ion occurs at [MH – 45]⁺ and was found to be mainly due to [M + 2H ? NO₂]⁺. All of the compounds except N-(2 hydroxyethyl)-N-(2′,4′,6′-trinitrophenyl)nitramine nitrate gave an [MH]⁺ ion. The [MH – 45]⁺ ion in the isobutane CI mass spectra of tetryl is also due to [M + 2H ? NO₂]⁺.     

Ortho effects in organic molecules on electron impact. 14—Concerted and stepwise ejections of SO2 and N2 from N-arylidene 2-nitrobenzenesulphenamides

Unexpected ortho interaction of the nitro group has been noticed during the mass spectral fragmentations of N-arylidene 2-nitrobenzenesulphenamides, where the molecular ions expel SO₂ and N₂ both in concerted and stepwise processes. Loss of a hydrogen or the substituent from this fragment leads to a very abundant ion in all the compounds studied. Based on chemical evidence and linked-scan studies, a 1,2-phenylenetropylium cation structure has been postulated for the [M–SO₂–N₂–H/substituent]⁺ ion.     

Substituent and H/D randomization in the mass spectra of substituted diphenylacetylenic compounds

The mass spectra of several substituted diphenylacetylenes are reported and the [metastable ion]/[daughter ion] ratios for the isomeric chloro- and bromodiphenylacetylenes suggested substituent scrambling in their respective molecular ions. The metastable ion data also indicated equilibration of the chloro substituents in a series of isomeric dichlorodiphenylacetylenes. In addition, the fragmentation patterns for the amino- and nitrodiphenylacetylenes differed somewhat from most other aromatic amino and nitro compounds. The aminodiphenylacetylenes fragment with expulsion of H₂CN from the molecular ion and the expulsion of HCN from the [M – 1]⁺ ion was only a relatively minor reaction. 4-Nitrodiphenylacetylene loses NO from the molecular ion and OH from the [M – NO]⁺˙, whereas the more familiar loss of OH from the molecular ion was not observed. The mass spectra of several deuterated substituted diphenylacetylenes clearly showed extensive (but not complete) H/D equilibration in the molecular ion or some subsequent decomposition ion. Comparative studies between 4-chloro and 4-bromo substituted biphenyl, diphenylacetylene and diphenyldiacetylene indicated similar degrees of H/D randomization, and the results showed that the ? C?C? group did not inhibit the proton equilibration between the two phenyl groups.     

Application of NMR spectroscopy of chiral association complexes. 8—Rotation about the C(sp2)–C(aryl) Bond in 2,6–disubstituted benzamides

The barrier to rotation about the C(sp²)? C(aryl) single bond in non-planar benzoyl compounds was investigated using N,N-dimethyl, N,N-tetramethylene and N,N-diisopropyl derivatives of 2,4,6-trimethylbenzamide and 2,6-dimethoxybenzamide and N,N-dimethyl derivatives of the corresponding thiobenzamides. Their ¹H and ¹³C NMR spectra were determined and assigned and the splittings in the ¹H spectra due to the addition of the optically active shift reagent (+)-Eu(hfbc)₃, are discussed. The free enthalpy of activation was calculated from the coalescence temperature of the ortho-methyl or -methoxyl signals and from a line-shape analysis. An exact equation for the determination of the rate constant at coalescence and a valid approximation which includes the line-width are presented. A distinct effect of the size of the N-substituent on the barrier to rotation in 2,6-dimethoxybenzamides was observed, while the π values for the 2,4,6-trimethylbenzamides studied are practically identical.     

The mass spectra of some 2,1,3-benzothiadiazoline and 2,1,3-benzothiadiazine 2,2-dioxides

Although the behaviour of 1H, 2H-2,1,3-benzothiadiazoline 2,2-dioxide is similar to that of sulphoxides in the mass spectrometer in losing a molecule of SO₂, the 1,3-dimethyl derivative loses the radical SO₂H. In addition the radical CH₃SO₂ is lost in a one step process that must involve a methyl migration. The radical SO₂H is also lost from 2,1,3-benzothiadiazine 2,2-dioxides methylated in the 3-position and the hydrogen involved is shown to originate from this methyl group by deuterium labelling. The mass spectra of other 2,1,3-benzothiadiazine 2,2-dioxides are also discussed.     

Chemical ionization desorption mass spectrometry of some quaternary ammonium salts

The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]⁺ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH₃? CH₃]^+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation.     

The fragmentation of ortho-methoxyphenyl-2-propanone oximes and related compounds–further examples of an ortho-effect

An [M ? 31]⁺ ion was a prominent fragment in the mass spectra of three ortho-methoxy-phenyl-2-propanone oximes and is shown to be due to the expulsion of a methoxyl radical from the molecular ion as a result of an ortho-effect. In contrast, an [M ? 31]⁺ ion was absent from the spectra of a structurally related ketone and a hydroxylamine, and was not observed in the spectra of meta- and para-methoxyphenyl-2-propanone oximes.     

Dynamic 1H NMR Study of Aryl-Nitrogen Single Bond and Carbon-Carbon Double Bond Rotational Energy Barriers in Two Highly Functionalized Pyranopyrimidines

 The reactive 1:1 intermediate produced in the reaction between 2,6-dimethylphenyl isocyanide and dimethyl acetylenedicarboxylate was trapped by N,N′ -dimethylbarbituric acid to yield the isomeric products dimethyl 7-(2,6-dimethylphenylamino)-1,3-dimethyl-2,4-dioxo-4H-pyrano[3,2-d]pyrimidine-5,6-dicarboxylate and dimethyl (E)-2-((2,6-dimethylphenylamino)-(1,3-dimethyl-2,4,6-trioxo-pyrimidine-5-ylidene)-methyl)-but-2-enedioate in a nearly 1:1 ratio and an overall yield of 85%. Dynamic effects were observed in the ¹H NMR spectra of these compounds and were attributed to restricted rotation around the aryl-nitrogen single bonds and the polarized carbon-carbon double bond.     

Mechanistic study of the decomposition reactions of azobenzene

The electron impact-induced fragmentation of azobenzenes and its d₁, d₂, d₅, d₁₀, and ¹⁵N analogues was studied by mass Spectrometry and ion kinetic energy spectroscopy. The main fragment ions found in the mass spectrum of azobenzene are due to two parallel stepwise processes from the molecular ion: the expulsion of N₂ and two hydrogen radicals producing an ion at m/z 152 having possibly a biphenylene radical cation structure and loss of C₆H₅? and N₂. Except in the elimination of two hydrogen atoms from [M ? N₂]^+· ions, hydrogen scrambling between the phenyl rings does not feature in azobenzene upon electron impact.     

Quantum-Chemical Investigation of Reaction Mechanism of 2-R-4-Oxo-5,6-Benzo-1,3,2-Dioxaphosphorinanes with Chloral and Fluoral

Abstract

Reaction of 2-R-4-oxo-5,6-benzo-1,3,2-dioxaphosphorinanes I with chloral leading to formation of seven-membered heterocycles - 1,4,2-dioxaphosphepines is characterized by the high degree of stereoselectivity. We investigated the model reactions of 2-R-4-oxo-1,3,-dioxaphosphorin-5-enes with CX₃CHO by PM3 and ab initio methods in STO-3G, 3-21G, 6-31G*, MP2/6-31G* basis set and also DFT method (B3LYP).     

Mass spectra of linear and branched methyl(vinyl)siloxanes

The mass spectra of some linear and branched methyl(vinyl)siloxanes Me₃SiOSi(Me)(R)(OSiMeVin) _n Y (R=Vin, OSiMe₃; Y=OSiMe₃, Cl;n=0–2) were studied. The regularities of their fragmentation and an anomalously high probability of elimination of the ethylene molecule to form the stable 1,3-dioxa-2,4,6-trisilacyclohexane skeleton were revealed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 113–115, January, 1999.     

Efficient Synthesis of New Pyrimido[5′,4′:5,6]pyrano[2,3-d]pyrimidine-2,4,6(1H,3H)-triones via the Tandem Intramolecular Pinner–Dimroth Rearrangement,and Their Antibacterial Activity

Synthesis of new 8-alkyl-5-aryl-1,3-dimethyl-5,7-dihydro-2H-pyrimido[5′,4′:5,6]pyrano[2,3-d]- pyrimidine-2,4,6(1H,3H)-triones by the high yield reaction of 7-amino-5-aryl-1,3-dimethyl-2,4-dioxo-1,3,4,5- tetrahydro-2H-pyrano[2,3-d]pyrimidine-6-carbonitriles with aliphatic carboxylic acids in the presence of POCl3 is presented. It is probable that synthesis of these new products proceeds via the tandem intramolecular Pinner–Dimroth rearrangement. The products are characterized by FT-IR, ¹H, and ¹³C NMR spectra and evaluated for their antibacterial activity against gram +ve bacteria (Staphylococcus aureus and Staphylococcus epidermidis) and gram–ve bacteria (Escherichia coli and Pseudomonas aeruginosa) using the disc diffusion method.

     

13C NMR study of isoxazolines and isoxazolidines in the thiophene and benzo[b]thiophene S-oxide and S,S-dioxide series

The ¹³C NMR spectra were recorded for isoxazolines and isoxazolidines from 2,4,6-trimethylbenzonitrile oxide or α-phenyl-N-phenyl nitrone as dipolarophiles with the thiophene and benzo[b]thiophene S-oxide and S,S-dioxide series. The effects of the isoxazoline or isoxazolidine groups are not very different. Owing to the electronegativity of the oxygen atom, the main influence arises from the regioselectivity of the addition to the carbon atoms located at the α or β position from SO or SO₂.     

The mass spectrometric fragmentation of n-benzylacetamide

The low energy mass spectra of N-benzylacetamide have been recorded. The major fragmentations of the molecular ion are similar to those observed in the acetanilide spectrum. In addition, the secondary dissociation of the [C₆H₅CH₂NH]⁺ ion by loss of HCN is shown to occur with transfer of the -N–H hydrogen to the ring.     

Optimization of Oxidative Method for Synthesis of 1,3-Diformyl-2,4,6-triethylbenzene

Oxidation of 1,3-diformyl-2,4,6-triethylbenzene with chromium anhydride in diluted H₂SO₄ to form 1,3-di(hydroxymethyl)-2,4,6-triethylbenzene was studied.