Search results for "LOAD"

Heterocycles from α-aminonitriles.

2014

Owing to their various modes of reactivity, α-aminonitriles represent versatile building blocks for the construction of a wide range of nitrogen heterocycles. The present Concept article focuses on synthetic methodologies using their bifunctional nature which is the basis of their reactivity as α-amino carbanions and as iminium ions. Reactions exclusively taking place on either the amine or on the nitrile moiety will not be considered.

A DFT study of the role of Lewis acid catalysts in the mechanism of the 1,3-dipolar cycloaddition of nitrile imines towards electron-deficient acrylo…

2012

Abstract The role of the Mg complex formation in the reaction rate and regioselectivity of the 1,3-dipolar cycloaddition (13DC) reactions of nitrile imines (NIs) towards electron-deficient methacryloylpyrazolidinones has been theoretically studied using DFT methods at the B3LYP/6-31G * level. These 13DC reactions have an asynchronous concerted mechanism with a low polar character, displaying a high C regioselectivity induced by a steric repulsion between the phenyl substituent present at the C3 carbon of the NIs and the pyrazolidinone appendage present in the methacryloyl derivative, which increases with the formation of the bulky Mg–methacryloylpyrazolidinone complex. Solvent effect has be…

[2+2+2] Cycloadditions of Alkynylynamides - A Total Synthesis of Perlolyrine and the First Total Synthesis of “Isoperlolyrine”

2011

The total syntheses of the carboline alkaloids perlolyrine and "isoperlolyrine" are reported. Key-steps of the syntheses are Negishi coupling reactions on alkynylynamides and their metal-catalyzed [2+2+2] cycloadditions with nitriles to form the β- and γ-carboline cores. The choice of the catalyst strongly affects the β/γ ratio. Spectroscopic features of the γ-isomer are distinctly different from those of the naturally occurring isoperlolyrine.

The Participation of 3,3,3-Trichloro-1-nitroprop-1-ene in the [3 + 2] Cycloaddition Reaction with Selected Nitrile N-Oxides in the Light of the Exper…

2021

The regioselective zw-type [3 + 2] cycloaddition (32CA) reactions of a series of aryl-substituted nitrile N-oxides (NOs) with trichloronitropropene (TNP) have been both experimentally and theoretically studied within the Molecular Electron Density Theory (MEDT). Zwitterionic NOs behave as moderate nucleophiles while TNP acts as a very strong electrophile in these polar 32CA reactions of forward electron density flux, which present moderate activation Gibbs free energies of 22.8–25.6 kcal·mol−1 and an exergonic character of 28.4 kcal·mol−1 that makes them irreversible and kinetically controlled. The most favorable reaction is that involving the most nucleophilic MeO-substituted NO. Despite P…

A DFT study for the regioselective 1,3-dipolar cycloadditions of nitrile N-oxides toward alkynylboronates

2003

Abstract The mechanism for the 1,3-dipolar cycloaddition of benzonitrile oxide toward ethynyl and propynylboronate has been studied by using density functional theory (DFT) at B3LYP/6-31G* level. These cycloadditions are concerted [3+2] processes. The presence of the two oxygens on the boronic ester precludes the participation of the boron atom on [3+3] processes. The two regioisomeric channels associated to the formation of the isoxazoles bearing the boronic ester unit on the 4- or 5-positions have been characterized. The B3LYP/6-31G* activation parameters are in acceptable agreement with the experiments, allowing to explain the factors controlling these regioselective cycloadditions.

Experimental and theoretical push-pull Chemo- and regioselectivity in 1,3-Dipolar cycloaddition reactions: the case of benzotriazepin-5-one with mesi…

2007

A novel heterocyclic compound 3-mesityl-5-methyl-4,5,11,11a-tetrahydro-6H-[1,2,4]oxadiazolo [5,4-b][1,3,4]benzotriazepin-6-one 4 has been synthesised by a 1,3 dipolar cycloaddition (13DC) reaction of 1,3,4-benzotriazepin-5-one 1 with mesitylnitrile oxide 3. The reaction, beside its synthetic interest, has shown to be completely chemo- and regioselective. The structure of the compound was determined by X-ray crystallography and analysed by spectral methods (NMR and mass spectrometry). The molecular mechanism for the reaction has been studied using quantum mechanical calculations at the B3LYP/6-31G* theory level. Two mechanisms are possible for the formation of the cycloadduct 4. The first on…

Deciphering the Macroeconomic Effects of Internal Devaluations in a Monetary Union

2020

We study the macroeconomic effects of internal devaluations undertaken by a periphery of countries belonging to a monetary union. We find that internal devaluations have large and positive output effects in the long run. Through an expectations channel, most of these effects carry over to the short run. Internal devaluations focused on goods markets reforms are generally more powerful in stimulating growth than reforms aimed at moderating wages, but the latter are less deflationary. For a monetary union with a periphery the size of the euro area's, the countries at the periphery benefit from internal devaluations even at the zero lower bound (ZLB) of the nominal interest rate. Nevertheless,…

Probabilistic Analysis of Non-Local 1-D Continuum under Random Load

2008

PENGARUH BEBAN, KOMPENSASI DAN LINGKUNGAN KERJA TERHADAP DISIPLIN KERJA KARYAWAN

2020

This study aims to determine whether the workload, compensation and partial and simultaneous work environment of employee work discipline at PT. Bank Rakyat Indonesia (Persero) Tbk Manokwari Branch Office. 
 This type of research is associative quantitative research. The sample used in this study was 53 respondents with a sampling technique using Nonprobability Sampling. Data collection uses observation, interviews, and questionnaires.
 The results of this study prove that work is significant for employee work discipline, significant compensation for employee work discipline, and work environment significantly affects employee work discipline. Simultaneously the workload, compensa…

A Novel Technique Using Polytetrafluoroethylene Tape to Solve Screw Loosening Complication in Implant-Supported Single Crowns

2020

This study aimed to analyze a novel technique to make screws with greater untightening resistance and to solve screw loosening in implant-supported single crowns. Thirty grade IV titanium straight abutments were screwed onto 30 external hex implants using grade IV titanium screws (30 Ncm). They were exposed to cyclic loading (300,000 cycles, 200 N). Samples were divided into 4 groups (15 samples per group): new screws (SCREW group) (control), reused screws (rSCREW group), new screws wrapped with polytetrafluoroethylene (PTFE) tape (PTFE group), and reused screws wrapped with PTFE tape (rPTFE group). Reverse torque values (RTVs) were recorded with a digitally calibrated implant motor. Mean R…