Template effects on the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine and their arsenic elimination reaction

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene as the chiral template was employed to promote the asymmetric cycloaddition reaction between 3,4-dimethyl-1-phenylarsole and diphenylvinylphosphine. It has been proven that the chiral template incorporating napthylamine is more efficient than the benzylamine based analogue as evidenced by the drastic improvement in stereoselectivity and reaction rate. However, when no chiral template was employed, trans-[PdI₂(3,4-dimethyl-1-phenylarsole)₂] reacted with trans-[PdI₂(diphenylvinylphosphine)₂] producing a structurally novel diiodo complex, as a result of an interesting selective cleavage of one As-C bond in the norbornene skeleton and subsequent rearrangements within the skeletal framework. The molecular structure of the diiodo product has been confirmed by X-ray crystallography. Structural analysis showed that in addition to the normal As-P five-membered ring, there is one new five-membered ring containing As-O bond being formed during the course of the reaction along with another seven-membered ring incorporating a hydroxy group.     

A Quantum Chemical Study of N14 Cluster

Ab initio molecular orbital theory and density functional theory have been employed to study N₁₄ cluster with low spin at the HF/6-31G*, B3LYP/6-31G*, B3PW91/6-31G*, BP86/6-31G*, and BHLYP/6-31G* levels of theory. Twelve isomers were studied, including one previously investigated cage molecule. The most stable isomer of N₁₄ is a C _2h -symmetric molecule that contains two separated five-membered nitrogen rings connected by a —N=N—N=N— bridge. The second, third, and fifth most stable isomers each have one five-membered nitrogen ring. The theoretical results suggest that the five-membered nitrogen ring gives rise to a particularly stable structural unit, and the more side chains that the five-membered nitrogen ring links with, the less stable the structure will become.     

Consecutive Fragmentation Mechanisms of Protonated Ferulic Acid Probed by Infrared Multiple Photon Dissociation Spectroscopy and Electronic Structure Calculations

Protonated ferulic acid and its principle fragment ion have been characterized using infrared multiple photon dissociation spectroscopy and electronic structure calculations at the B3LYP/6-311?+?G(d,p) level of theory. Due to its extensively conjugated structure, protonated ferulic acid is observed to yield three stable fragment ions in IRMPD experiments. It is proposed that two parallel fragmentation pathways of protonated ferulic acid are being observed. The first pathway involves proton transfer, resulting in the loss of water and subsequently carbon monoxide, producing fragment ions m/z 177 and 149, respectively. Optimization of m/z 177 yields a species containing an acylium group, which is supported by a diagnostic peak in the IRMPD spectrum at 2168?cm^?1. The second pathway involves an alternate proton transfer leading to loss of methanol and rearrangement to a five-membered ring.     

The question of cyclic versus acyclic ions: The structure of [C10H12]+˙ gas phase ions

The extent of isomerization of acyclic and cyclic gas phase radical cations of composition [C₁₀H₁₂]⁺˙ has been investigated by using collisionally activated dissociation spectroscopy. Both electron and charge exchange ionizaiton were employed to form the ions with various internal energies. The [C₁₀H₁₂]⁺˙ ions investigated consisted of ionized phenylbutenes, ring-substituted methyl derivatives of allylbenzene and phenylpropene, 1-methyl-2-isopropenylbenzene, benzylcyclopropane, phenylcyclobutane, tetralin and 1-methylindan. The 1-methylindan and tetralin radical cations are the most stable of the C₁₀H₁₂ isomeric radical ions. The [C₁₀H₁₂]⁺˙ formed from acyclic olefins having the double bond in conjugation with the aromatic ring retain the initial structure to a significant extent. However, ions derived from olefins with the double bond out of conjugation with the benzene ring preferentially cyclize to stable five- and six-membered cyclic ions. Ring opening of small-ring cyclic ions, such as ionized benzylcyclopropane and phenylcyclobutane, occurs, followed by ring closure to the tetralin radical cation.     

Electron ionization-induced loss of a methyl radical from 1-cyclopropyl-4-substituted-1,2,3,6 tetrahydropyridine derivatives

The electron ionization mass spectra of 1-cyclopropyl-4-substituted-1,2,3,6-tetrahydropyridine derivatives are characterized by a base peak corresponding to [M-15]⁺. Evidence is presented to support a fragmentation process involving an initial cyclopropyl ring opening of the parent cyclopropylaminyl radical cation followed by intramolecular transfer of a hydrogen atom from the ring carbon atoms α to nitrogen to the primary carbon-centered radical and finally a fragmentation step proceeding by loss of a methyl radical and formation of a stable N-ethenyldihydropyridinium ion, the [M-15]⁺ fragment.     

Mass spectra of new heterocycles: XVI. Electron impact study of alkyl 5-aminothiophene-2-carboxylates

Electron impact mass spectra of alkyl 4-alkoxy-5-amino-3-methylthiophene-2-carboxylates were studied for the first time. These compounds, except for 4-(1-ethoxyethoxy) and 4-(ferrocenylmethoxy) derivatives, give rise to a stable molecular ion whose decomposition follows three pathways. The main fragmentation pathway of the molecular ion is elimination of alkyl radical from the 4-alkoxy group, the second pathway involves expulsion of alkoxy group from the ester moiety, and the third pathway is decomposition of the thiophene ring. The molecular ions of 4-(1-ethoxyethoxy)thiophenes decompose mainly via elimination of ethyl vinyl ether molecule with formation of [M–VinOEt]⁺ · odd-electron ion, and fragmentation of the latter follows general pathways. In the mass spectra of 4-(ferrocenylmethoxy)thiophenes the most abundant are ferrocenylmethyl ion with m/z 199 (I _rel 100%) and fragment ions derived therefrom.     

Electron-impact induced fragmentation of some natural products containing bis-2,2-dimethylchromene and bis-2,2-dimethylchroman ring systems

Derivatives of eriostoic and eriostemoic acids (II and III) and their tetrahydro analogs (VI and IX) which contain the bis-2,2-dimethylchromene and the bis-2,2-dimethylchroman ring systems respectively, fragment subsequent to electron-impact in characteristic fashion. The former yield mass spectra dominated by the loss of a methyl radical from their molecular ions while the latter exhibit preferential fragmentation of the heterocyclic ring system. In particular the hydrogen transfer process accompanying elemination of C₄H₇ from the parent ion of bis-2,2-dimethylchromans was investigated by deuterium labeling studies. Fragment ions containing the bis-2,2-dimethylchroman ring undergo further fragmentation by the loss of C₄H₈ rather than C₄H₇. An unusual elimination of CH₅ (accompanied by the appropriate metastable ion) from the molecular ions of the 3,5-dinitrobenzoate esters (XIV and XV) was observed in their mass spectra.     

Symmetry of chloronium ions from ionic reaction of chlorine, chlorine monofluoride gas, and chlorine monofluoride complex with terminal alkenes

Ionic chlorination of 1H,1H,7H-perfluorohept-1-ene (2) and heptafluoropropyl trifluorovinyl ether (4) with chlorine monofluoride (ClF) gas in aprotic solvent; and alkenes 2, 1H-perfluorohept-1-ene (3E), and 4 with chlorine (Cl₂) in protic solvent were investigated. Regiochemical data from SN₂-like ring-opening of the intermediate was used to predict the symmetry of the chloronium ion. The chloronium ions from perfluorohydroalkene 2 with two terminal hydrogens were found to be unsymmetrical with positive charge localized on the terminal carbon. However, reaction of ClF_(g) with 3E containing a single terminal fluorine atom gave data suggesting a symmetrical chloronium ion. Alkene 4 contains a heptafluoropropyl ether group that stabilizes positive charge on the number-2 carbon and it is reactive enough to give products with the sluggish ClF complex generated in situ. Reactive eletrophiles ClF_(g), Cl_2(g), or the less reactive ClF complex, give an unsymmetrical chloromium ion with charge localized on the internal number-2 carbon.     

Mass spectrometric behaviour of simple oxazolidines under electron impact and chemical ionization

The 70 eV electron impact mass spectra of 33 differently substituted oxazolidines were studied to determine the effect of substituents and the existence of the ring—chain tautomeric equilibrium on the decomposition of the molecular ions. Most of the fragmentations can be rationalized to start as the cleavage initiated by the radical site at nitrogen. Isomeric compounds showed different spectra and were easily differentiated. The position of the ring—chain equilibrium could be located only roughly. The chemical ionization mass spectra of the compounds were also recorded, with ammonia, isobutane, acetone or methane as reagent gas. Methane was the only reagent gas that promoted extensive fragmentation of the protonated molecules. However, no information about the position of ring-chain tautomerism was obtained under these conditions. Analogously to other related five-membered heterocycles, the oxazolidines reacted under acetone chemical ionization conditions to afford [M + CH₃CO]⁺ adduct ions. These adducts were stable, however, and unlike those of 1,3-dioxolanes and 1,3-oxathiolanes, they did not decompose and form stable oxonium ions.     

The crystal and molecular structure ofexo-1,7-dichloro-8,8,9,9,10,10-hexafluoro-3,4-benzotricyclo[5.3.0.02,6]decene-3

The crystal structure of the title molecule has been determined by single crystal X-ray diffraction method. The molecule crystallizes in the orthorhombic space group Pbca with unit-cell dimensions a = 21.872(8), b = 11.815(6), c = 10.785(6) Å, and Z = 8. The structure has been solved by MULTAN and refined by least-squares calculations to R = 7.62% for 2088 reflections measured by a diffractometer. The molecule has the exo configuration. The central cyclobutane ring is nearly planar. The two five-membered rings are of the envelope conformation. The dihedral angle between the cyclobutane ring and the terminal five-membered ring is 75.5° and that between the cyclobutane ring and the other five-membered ring is 62.2°.     

Time resolved absorption and resonance Raman spectroscopic studies of the oxidation of benzidine in aqueous solution

We report a time resolved resonance Raman study of transient radicals produced in the pulse radiolytic oxidation of benzidine in aqueous solution. The intense and structured transient absorption in the 400–470 nm region, observed at microsecond times in the acidic medium, is attributed to the benzidine radical cation. The Raman spectrum, observed by excitation in resonance with this absorption, exhibits eight prominent bands which are assigned to planar phenyl vibrations. The ring breathing mode (v₁) at 844 cm^-1 is most highly resonance enhanced, indicating an overall expansion of the ring CC bonds in the excited state. The interring CC bond, with partial double bond character, is characterized by an intense (v₁₃) Raman band at 1335 cm^-1. The frequency of the in-phase v_7a CN stretching vibration is 1540 cm^-1. These frequencies and the presence of weak bands attributable to non-planar phenyl vibrations indicate the radical to be slightly non-planar. The pK_a for the proton loss from the radical cation is 10.87, four units higher than for the aniline radical cation. At high pH the observed transient has a broad and structureless absorption at ∽ 380 nm. It is identified from its resonance Raman features as the 4(4′aminophenyl)anilino radical formed by proton loss from the radical cation. The interring CC bond is characterized by a Raman band at 1292 cm^-1, indicating it to be a single bond. The structure of this neutral radical is highly nonplanar, with little conjugation between the two ring systems so that electronic excitation is primarily confined to the anilino moiety. The acidic and basic forms of the radical react rapidly in second order processes to produce products which absorb strongly at, respectively, 360 and 410 nm.     

Radical reactions of a stable N-heterocyclic germylene: EPR study and DFT calculation

The first radical adducts of a stable N-heterocyclic germylene were investigated. Novel radical species were produced from a variety of precursors and studied by EPR spectroscopy. DFT (B3LYP) calculations of radical adducts of different (C, Si, Ge) unsaturated N-heterocyclic divalent species with phenoxyl radical show that in the radicals studied the unpaired electron is delocalized over the five-membered ring and the spin density on the central atoms decreases in the following order: C > Si > Ge. These trends can be understood in terms of zwitterionic structure of radical adducts.     

Spectra and structure of small ring compounds: Part XXX. Microwave spectrum of 1,1-difluoro-1-silacyclopent-3-ene

The microwave spectrum of 1,1-difluoro-l-silacyclopent-3-ene has been recorded from 26.5 to 40.0 GHz. Only A-type transitions were observed. The R-branch assignments have been made for the ground state and the first three excited states of the ring puckering vibration. It is shown that the five-membered ring structure is planar from the values of the components of the dipole moment, as well as from the value of the inertial defect as a function of the ring puckering quantum number. From the relative intensity measurements, it is concluded that the first excited state of the ring puckering vibration has a frequency of 38 ±7 cm^?1 and that the vibration is nearly harmonic. The components of the dipole moment were determined by the Stark effect to be μ_a = 2.02 ±0.06 D, μ_b = 0, and μ_c = 0.0 ±0.09 D. All of the observed data are consistent with a molecule of C_2v symmetry and the possible reasons for this structure are discussed.     

Mechanism of 1,3-migration in allylperoxyl radicals: computational evidence for the formation of a loosely bound radical-dioxygen complex

The three pathways postulated for 1,3-migration of the peroxyl group in the allylperoxyl radical (1a), a key reaction involved in the spontaneous autoxidation of unsaturated lipids of biological importance, have been investigated by means of quantum mechanical electronic structure calculations. According to the barrier heights calculated from RCCSD(T)/6-311+G(3df,2p) energies with optimized molecular geometries and harmonic vibrational frequencies determined at the UMP2/6-311+G(3df,2p) level, the allylperoxyl rearrangement proceeds by fragmentation of 1a through a transition structure (TS1) with a calculated DeltaH++(298 K) of 21.7 kcal/mol to give an allyl radical-triplet dioxygen loosely bound complex (CX). In a subsequent step, the triplet dioxygen moiety of CX recombines at either end of the allyl radical moiety to convert the complex to the rearranged peroxyl radical (1a') or to revert to the starting peroxyl radical 1a. CX shows an electron charge transfer of 0.026 e in the direction allyl --> O(2). The dominant attractive interactions holding in association the allyl radical-triplet dioxygen pair in CX are due chiefly to dispersion forces. The DeltaH(298 K) for dissociation of CX in its isolated partners, allyl radical and triplet dioxygen, is predicted to be at least 1 kcal/mol. The formation of CX prevents the diffusion of its partners and maintains the stereocontrol along the fragmentation-recombination processes. The concerted 1,3-migration in allylperoxyl radical is predicted to take place through a five-membered ring peroxide transition structure (TS2) showing two long C-O bonds. The DeltaH++(298 K) calculated for this pathway is less favorable than the fragmentation-recombination pathway by 1.9 kcal/mol. The cyclization of 1a to give a dioxolanyl radical intermediate (2a) is found to proceed through a five-membered ring transition structure (TS3) with a calculated DeltaH++(298 K) of 33.9 kcal/mol. Thus, the sequence of ring closure 1a --> 2a and ring opening 2a --> 1a' is unlikely to play any significant role in allylperoxyl rearrangement 1a --> 1a'. In the three pathways investigated, the energy of the transition structure is predicted to be somewhat lower in either heptane or aqueous solution than in the gas phase. Although the energy lowering calculated for TS1 is smaller than the calculated for TS2 and TS3, it is very unlikely that the solvent effects may reverse the predicted preference of the fragmentation-recombination pathway over the concerted and stepwise ring closure-ring opening mechanisms.     

The molecular structure of trans- and cis-bicyclo-[4.3.0]nonane in the gas phase,studied by electron diffraction and molecular mechanics

The structure and conformations of trans- and of cis-bicyclo[4.3.0]nonane have been studied in the gas phase. Molecular mechanics calculations applying the force field of Ermer and Lifson were used to obtain geometrical constraints, vibrational amplitudes and perpendicular vibrational corrections. The vibrational parameters were corrected for the large amplitude motion of the five-membered ring. The refinement for the trans-isomer confirms completely the predictions of the force field calculations. Although a stable solution could not be obtained for the cis-compound there is no contradiction between experiment and model calculations. The cyclohexane ring in both isomers is found to have a distorted chair conformation. In the cis-isomer it is flattened along the junction and more twisted in the other part. For the trans-compound the reverse is true.The following structural parameters r_g, r_α-structure) are put forward, (a) trans-compound: C₂-symmetry, _r(C-C)_av = 1.536 Å. Average bond angle and average torsion angle in the cyclohexane ring are 110.2° and 58.1°, respectively. The connection angle, defined as the angle between the planes bisecting C6-C1-C5-C9 and C2-C1-C5-C4, is 180°. (b) cis-compound: no symmetry, r(C-C)_av = 1.536 Å. Average bond and torsion angles in the cyclohexane ring are 112.2° and 52.3°, respectively. The connection angle is 124.8°.A comparison is made with structures of related compounds.     

Generation of Chloropolyfluoromethylene-1-indanyl Cations and Their Isomerization into Chloropolyfluoromethylindenyl Cations

Chlorooctafluoro-3-methylene-1-indanyl, 3-(chlorofluoromethylene)heptafluoro-1-indanyl, and 2- and 3-(dichloromethylene)heptafluoro-1-indanyl cations were generated from the corresponding dihalomethyleneindans in the system SbF₅-SO₂ClF. Isomerization of these cations yields thermodynamically more stable polyfluoromethylindenyl cations with chlorine atoms in the five-membered ring.     

Mass spectrometry of systems containing a group IVB—transition metal bond : I. The phenyl- and pentafluorophenyl- silicon, -germanium and -tin derivatives of pentacarbonylmanganese

The 70 eV mass spectra of the series Ph_3?n(C₆F₅)_nMMn(CO)₅ (n = 0 to 3 and M = Si, Ge or Sn) and Ph₃PbMn(CO)₅ have been examined and the proposed fragmentation schemes are supported by the observance of the appropriate metastable ions. Most of the total ion current is carried by metal-containing ions, particularly those containing just a Group IV metal. In all cases the initial fragmentation is by the loss of one or more carbonyl groups from the molecular ion, followed, except in the case of the fully fluorinated silicon derivatives, by the cleavage of the metal—metal bond. The fragmentation of the remainder of the molecule is then controlled by the nature of M and the number of pentafluorophenyl groups, the silicon derivatives showing a greater abundance of ions formed by the cleavage of the CC, CH or CF bonds in the aromatic ring, in contrast to the tin and lead derivatives which fragment almost exclusively by the cleavage of the metal—carbon bond. The formation of metal fluoride species plays an important part in the fragmentation of the pentafluorophenyl derivatives and becomes more important as the Group IV metal becomes heavier, while except for Ph₃PbMn(CO)₅ the abundances of the ions resulting from the migration of a complete aromatic ring from one metal to the other remain essentially constant. However, some of the observed changes in the fragmentation modes are not readily predicted on the basis of the expected variation in the relative metal—carbon or metal—metal bond strengths since these appear to be more dependent on the stabilities of the radical species or on the ion species formed. The tin—metal molecular bond dissociation energies in Ph₃SnMn(CO)₅ and Ph₃SnFe(CO)₂Cp were found to be 61 ± 8 and 54 ± 9 kcal mol^?1, respectively.     

<Emphasis Type="Italic">Ab initio</Emphasis> study of hydrogen bond complexes of ring compounds containing the H<Subscript>2</Subscript>N-C=Y moiety with water

Ab initio calculations, including natural charge population and natural resonance theory analyses, have been carried out to study the two-way effects between hydrogen bonds (H-bonds) and the intramolecular resonance effect by using the H-bonded complexes of ring compounds containing the H₂N-C=Y moiety (C=Y bond is contained in the six-membered or five-membered rings) with water as models. The amino groups in the four monomers of ring compounds (FAYs, Y represents the heavy atoms in the substituent groups, =CH, =N, =SiH, and =P, respectively) can all serve as H-bond donors (HD) and H-bond acceptors (HA) to form stable H-bonded complexes with water. The HD H-bond and resonance effect enhance each other (positive two-way effects) whereas the HA H-bond and resonance effect weaken each other (negative two-way effects). The resonance effect in FAY(1) (C=Y bond is contained in the six-membered rings) is weaker than that in formamide, and those in FAY(2) and FAY(3) (C=Y bonds are contained in the five-membered rings). The two-way effects between H-bond and resonance effect exist in the H-bonded complexes of ring compounds containing the H₂N-C=Y moiety with water.      

Mass spectra of 2,3-polymethylene-3,4-dihydroquinazolin-4-ones with substituents at C9

Summary The main fragments in the mass spectra of the 2,3-polymethylene-3,4-dihydroquinazolin-4-one with six- and seven-membered alicyclic rings are formed by the decomposition of ring C through the stage of the cleavage of the C₉-C₁₀ bond, while the compound with a five-membered ring ejects a hydrogen atom.A hydroxy group at C₉ initiates the appearance of fragments due to the initial cleavage of the C₂-C₉ bond. In the spectra of the halogen and acetoxy derivatives the fragmentation of the alicyclic ring is suppressed and the main fragmentation pathway is the splitting out of the substituent. The hypothesis of the protonation of the N₁ nitrogen atom has been adopted to explain the stability of a number of the ions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 180–187, March–April, 1979.     

A new approach to a vitamin D ring C/D building block from the Hajos dione, involving epoxide opening at the more substituted carbon atom

A new approach to a trans-hydrindane building block for 1α,25-dihydroxyvitamin D₃ (calcitriol) synthesis from the Hajos dione has been developed. The α,β-unsaturated carbonyl group in the Hajos dione has been protected and the carbonyl group in the five-membered ring has been used for the side chain attachment. Key steps in the six-membered ring transformation include: reduction of the carbonyl group, stereoselective epoxidation of the double bond in the allylic alcohol, opening of the epoxide at the more substituted carbon atom and regioselective deoxygenation.