Mass spectroscopic fragmentation pathways of 1,8-nonadiyne

Cleavage α to triple bonds in straight-chain hydrocabons with only one triple bond is a very minor process. The mass spectrum of 1,8-nonadiyne (mol. wt 120) shows strong peaks at around m/z91, which points to a major fragmentation pathway of cleavage α to triple bonds in straight-chain diynes. This study attempts to explain this paradox. Through-space interaction was indicated through the use of carbon-13 labelling of the terminal carbon atoms in 1,8-nonadiyne, 1,2,8,9-¹³C-1,8-Nonadiyne and 3,7-¹³C-1,8-nonadiyne were prepared to determine which carbon atoms were lost in the process of [M]⁺˙ and [M? 1]⁺ going to m/z91. These two molecules were chosen for ease of synthesis. Low-resolution mass spectra and low-voltage studies determined that a major portion of carbon atoms being lost were from the middle of the carbon chain. This points to a fragmentation pathway that results from through-space interaction of the two terminal triple bonds. It is likely that ionization enhances this through-space interaction of the two triple bonds.     

Reaction of unsaturated phosphonate monoesters with bromo- and iodo(bis-collidine) hexafluorophosphates

Reaction of unsaturated phosphonate monoesters with bromo- and iodo(bis-collidine) hexafluorophosphates are reported to lead to the formation of five- to seven-membered phostones by exo mode cyclizations. When the chains of the unsaturated phosphonate monoesters are substituted in α of the double bond by a dioxolane group endo mode cyclizations are observed. These cyclizations give rise to the formation of 1,2-oxaphosphepane-2-oxide and 1,2-oxaphosphocane-2-oxide.     

The high-valent iron-oxo species of polyoxometalate, if it can be made, will be a highly potent catalyst for C-H hydroxylation and double-bond epoxidation

This study uses density functional theory (DFT) calculations to explore the reactivity of the putative high-valent iron-oxo reagent of the iron-substituted polyoxometalate (POM-FeO4-), derived from the Keggin species, PW12O40(3-). It is shown that POM-FeO4- is in principle capable of C-H hydroxylation and C=C epoxidation and that it should be a powerful oxidant, even more so than the Compound I species of cytochrome P450. The calculations indicate that in a solvent, the barriers, and especially those for epoxidation, become sufficiently small that one may expect an extremely fast reaction. An experimental investigation (by R.N. and A.M.K.) shows, however, that the formation of POM-FeO4- using the oxygen donor, F5PhI-O, leads to a persistent adduct, POM-FeO-I-PhF5(4-), which does not decompose to POM-FeO4- + F5Ph-I at the working temperature and exhibits sluggish reactivity, in accord with previous experimental results (Hill, C. L.; Brown, R. B., Jr. J. Am. Chem. Soc. 1986, 108, 536 and Mansuy, D.; Bartoli, J.-F.; Battioni, P.; Lyon, D. K.; Finke, R. G. J. Am. Chem. Soc. 1991, 113, 7222). Subsequent calculations indeed reveal that the gas-phase binding energy of F5PhI to POM-FeO4- is high (ca. 20 kcal/mol) compared to the corresponding binding energy of propene (ca. 2-3 kcal/mol). As such, the POM-FeO-I-PhF5(4-) complex is expected to be persistent toward the displacement of F5PhI by a substrate like propene, leading thereby to sluggish oxidative reactivity. According to theory, overcoming this technical difficulty may turn out to be very rewarding. The question is, can POM-FeO4- be made?     

Cyclodextrins containing an acetone bridge. Synthesis and study as epoxidation catalysts

Three cyclodextrine derivatives (6A,6D-di-O-(prop-2-one-1,3-dienyl)-alpha-cyclodextrin (1), 6-O-(prop-2-one-1-yl)-alpha-cyclodextrin (2) and 6A,6D-di-O-(prop-2-one-1,3-dienyl)-beta-cyclodextrin (3)) were synthesised and investigated as epoxidation catalysts. The three compounds were synthesised from the corresponding perbenzylated cyclodextrins which were mono- or didebenzylated in the 6-position using Sina?'s method. Reaction with NaH and methallyl chloride in the case of 2, or methallyl dichloride in the case of 1 and 3, followed by dihydroxylation, periodate cleavage and protection group removal gave the target compounds. All three compounds catalysed, in the presence of oxone, the epoxidation of a series of alkenes. Epoxidation was compared to the reaction catalysed by simple ketones and inhibition was studied.     

Photooxygenation of bicyclopropylidene

Upon photooxidation bicyclopropylidene ($\text{1}$) yields spiro[2.3]hexan-4-one ($\text{4}$) and 7-oxatrispiro[2.0.2.1]heptane ($\text{6}$). The formation of these is rationalized. Authentic $\text{6}$ was prepared by epoxidation of $\text{1}$, and $\text{4}$ by isomerization of $\text{6}$.     

Substitution nucleophile radicalaire en chaîne (srn1): 12eme memoire1a (p)-nitrobenzyls disubstitues et fonctionnalises en α

Variously disubstituted and functionalized $\text{p}$-nitrobenzyl substrates 1 and 2 undergo S_RN1 reactions on treatment with a series of nucleophiles, showing the generality of the extension to functionalized substrates and nucleophiles.     

New halogenated monomers and polymers for low loss plastic optical fiber

Abstract

In this paper, theoretical studies about refractive index and attenuation of halogenated and deuterated monomers and polymers are described. Concerning refractive index study, a mathematical model is elaborated to calculate the refractive index of acrylic monomers accurately. Concerning the attenuation in a near infrared (NIR) and visible region, we have shown and quantified that the most important factor of intrinsic absorption in Plastic Optical Fibers (POF) is the presence of C-H bonds. So to reduce attenuation of POF, halogenated and deuterated acrylates and vinyl carbonates are synthesized. Thermal and optical properties of the corresponding homo and copolymers are discussed.     

Synthesis and properties of poly(butylene succinate): Efficiency of different transesterification catalysts

The efficiency of organometal‐ (Ti, Zr, Sn, Hf, and Bi) and metal oxide‐ (Ge and Sb) based catalysts was investigated during the transesterification step of the synthesis of poly(butylene succinate) (PBS). PBS was prepared from succinic acid and 1,4‐butanediol via a two‐stage melt polycondensation process. The catalytic efficiency of the organometal catalysts was as follows: Ti?Zr～ Sn>Hf>Sb>Bi. The germanium and antimony metal oxides displayed desirable catalytic efficiency when were associated with hydroxy acids (lactic acid or glycolic acid), which acted as chelating agents. However, this catalytic system exhibited lower efficiency compared to the titanium system. Furthermore, at high concentrations of hydroxy acids the overall transesterification rate decreased. This effect can be explained by the substitution of PBS hydroxyl end groups by a lactic or glycolic unit, both of which are less reactive during the transesterification reaction. The role of catalytic residues during the storage and processing of PBS was also studied. The reduced viscosity of the PBS samples did not vary when processing at 190 °C from 1 to 10 minutes. However, when stored under ambient conditions, all PBS samples were prone to significant hydrolytic degradation, especially those containing a titanium catalyst. This behavior indicates that zirconium‐ and germanium‐based catalysts could be interesting substitutes for titanium‐based catalysts. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.