scholarly journals Sequential C–F bond functionalizations of trifluoroacetamides and acetates via spin-center shifts

Science ◽  
2021 ◽  
pp. eabg0781
Author(s):  
You-Jie Yu ◽  
Feng-Lian Zhang ◽  
Tian-Yu Peng ◽  
Chang-Ling Wang ◽  
Jie Cheng ◽  
...  
Keyword(s):  
Carbonyl Oxygen ◽  
General Strategy ◽  
Computational Approaches ◽  
Formidable Challenge ◽  
Bond Scission ◽  
Spin Center ◽  
Stage Process ◽  
Sequential Generation ◽  
Radical Traps ◽  
Trifluoromethyl Groups

Defluorinative functionalization of readily accessible trifluoromethyl groups constitutes an economical route to partially fluorinated molecules. However, controllable replacement of one or two fluorine atoms while maintaining high chemoselectivity remains a formidable challenge. Here we describe a general strategy for sequential C–F bond functionalizations of trifluoroacetamides and trifluoroacetates. The reaction begins with activation of a carbonyl oxygen atom by a 4-dimethylaminopyridine-boryl radical, followed by a spin-center shift to trigger the C–F bond scission. A chemoselectivity-controllable two-stage process enables sequential generation of difluoro- and monofluoroalkyl radicals, which are selectively functionalized with different radical traps to afford diverse fluorinated products. The reaction mechanism and the origin of chemoselectivity were established by experimental and computational approaches.

scholarly journals Achieving High Performance Molecular Rectification through Fast Screening Alkanethiol Carboxylate-Metal Complexes Electro-Active Unites

2021 ◽  
Author(s):  
Lixain Tian ◽  
Aiqing Fan ◽  
Xi Yu ◽  
Wenping Hu
Keyword(s):  
Metal Complex ◽  
High Performance ◽  
Chemical Space ◽  
Low Cost ◽  
General Strategy ◽  
Device Structure ◽  
Tunneling Model ◽  
Fast Screening ◽  
Formidable Challenge ◽  
Molecular Rectification

Achieving high rectifying performance of molecular scale diode devices through synthetic chemistry and device construction remain a formidable challenge due to the complexity of the charge transport process and the device structure. We demonstrated here high-performance molecular rectification realized in self-assembled monolayer (SAM) based device by low-cost and fast screening the electroactive units. SAMs of commercial available carboxylate terminated alkane thiols on gold substrate, coordinated with a variety of metal ions, structures denoting as Au-S-(CH2)n-1COO-Mm+ (Cn+Mm+), where n=11, 12, 13, 14, 16, 18 and Mm+=Ca2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, were prepared and junctions were measured using a eutectic indiumgallium alloy top contact (EGaIn). The C18+Ca2+ and C18+Zn2+ junctions were found to afford a record high rectification ratio (RR) of 756 at ±1.5 V. Theoretical analysis based on single level tunneling model shows that optimized combination of the asymmetry voltage division, energy barrier and the coupling of carboxylate-metal complex with electrode. Our method described here represent a general strategy for fast, cheap and effective exploration of the metal complex chemical space for high-performance molecular diodes devices.

scholarly journals The crystal structure of 5-(trifluoromethyl)picolinic acid monohydrate reveals a water-bridged hydrogen-bonding network

2020 ◽  
Vol 76 (11) ◽  
pp. 1752-1756
Author(s):  
Naike Ye ◽  
Joseph M. Tanski
Keyword(s):  
Hydrogen Bonding ◽  
Carboxylic Acid ◽  
Picolinic Acid ◽  
Three Dimensional ◽  
Acid Group ◽  
Carbonyl Oxygen ◽  
Hydrogen Bonding Interactions ◽  
Pyridine Nitrogen ◽  
Acid Hydrate ◽  
Trifluoromethyl Groups

The title compound [systematic name: 5-(trifluoromethyl)pyridine-2-carboxylic acid monohydrate], C7H4F3NO2·H2O, is the acid hydrate of a pyridine with a carboxylic acid group and a trifluoromethyl substituent situated para to one another on the aromatic ring. The molecule forms a centrosymmetric water-bridged hydrogen-bonding dimer with graph-set notation R 4 4 (12). Hydrogen-bonding distances of 2.5219 (11) and 2.8213 (11) Å are observed between the donor carboxylic acid and the bridging water acceptor, and the donor water and carbonyl oxygen acceptor, respectively. The dimers are further linked into a two-dimensional sheet via two longer intermolecular hydrogen-bonding interactions between the second hydrogen atom on the bridging water molecule and both a pyridine nitrogen atom and carbonyl oxygen with distances of 3.1769 (11) and 2.8455 (11) Å, respectively. The trifluoromethyl groups extend out the faces of the sheet providing for F...F and C—H...F contacts between the sheets, completing the three-dimensional packing.

scholarly journals Optimization of Energy and Resource Efficiency in a Multistage Drying Process of Phosphate Pellets

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3376 ◽  
Author(s):  
Valery Meshalkin ◽  
Vladimir Bobkov ◽  
Maksim Dli ◽  
Vincenzo Dovì
Keyword(s):  
Quality Indicators ◽  
Energy Savings ◽  
Dynamic Programming Algorithm ◽  
Programming Algorithm ◽  
General Strategy ◽  
Sintering Process ◽  
Multi Stage ◽  
Operational Variables ◽  
Stage Process

The roasting of phosphate pellets is an energy-intensive process the optimization of which can give rise to considerable efficiency improvements. To this purpose, the mathematical modeling and the computer-aided simulation of a multi-stage process of phosphate pellets roasting have been developed. This process includes drying, dissociation reaction of carbonates and a sintering process in a moving, dense, multilayer mass of phosphate pellets in a special horizontal grate apparatus. A theoretical model for the physical-chemical processes of a mass of phosphate pellets moving in a multistage process and subject to external operation variables (i.e., temperatures and flowrates of the drying gas at different positions of the conveyor length) has been developed. By letting these control variables vary over suitable ranges limited by technical constraints, it is possible to construct an algorithm that minimizes the overall energy consumption subject to the attainment of the required quality indicators of the pellets. Therefore, the set of constraints includes bounds on both the operational variables and quality indicators of the final product. A dynamic programming algorithm subject to suitable penalty functions for avoiding constraints violation has been used. The results obtained show that the scientifically based operation described in this paper achieves the goal of attaining considerable energy savings while assuring the quality of the finished pellets. Furthermore, the results highlight the convenience of extending the general strategy developed in this article to other chemical energy engineering processes.

Electron diffraction detection of ordliking in annealed PbTe thin film

1990 ◽  
Vol 48 (4) ◽  
pp. 1018-1019
Author(s):  
Karimat El-Sayed
Keyword(s):  
Thin Film ◽  
Electron Diffraction ◽  
Lead Telluride ◽  
Structural Basis ◽  
Face Centered Cubic ◽  
X Ray ◽  
Polycrystalline Thin Films ◽  
Stage Process ◽  
Diffraction Patterns ◽  
Face Centered

Lead telluride is an important semiconductor of many applications. Many Investigators showed that there are anamolous descripancies in most of the electrophysical properties of PbTe polycrystalline thin films on annealing. X-Ray and electron diffraction studies are being undertaken in the present work in order to explain the cause of this anamolous behaviour.Figures 1-3 show the electron diffraction of the unheated, heated in air at 100°C and heated in air at 250°C respectively of a 300°A polycrystalline PbTe thin film. It can be seen that Fig. 1 is a typical [100] projection of a face centered cubic with unmixed (hkl) indices. Fig. 2 shows the appearance of faint superlattice reflections having mixed (hkl) indices. Fig. 3 shows the disappearance of thf superlattice reflections and the appearance of polycrystalline PbO phase superimposed on the [l00] PbTe diffraction patterns. The mechanism of this three stage process can be explained on structural basis as follows :

Process \'prǎ|,ses\n: The Action of Moving Forward Progressively from One Point to Another on the Way to Completion

1979 ◽  
Vol 44 (1) ◽  
pp. 3-30 ◽  
Author(s):  
Carol A. Pruning
Keyword(s):  
Process Model ◽  
Communicative Behaviors ◽  
Adult Level ◽  
Remedial Programs ◽  
Stage Process ◽  
The Way

A rationale for the application of a stage process model for the language-disordered child is presented. The major behaviors of the communicative system (pragmatic-semantic-syntactic-phonological) are summarized and organized in stages from pre-linguistic to the adult level. The article provides clinicians with guidelines, based on complexity, for the content and sequencing of communicative behaviors to be used in planning remedial programs.

Suicide on the Indian Subcontinent

Crisis ◽  
2002 ◽  
Vol 23 (3) ◽  
pp. 104-107 ◽  
Author(s):  
Murad M. Khan
Keyword(s):  
Sri Lanka ◽  
Mental Health Professionals ◽  
Indian Subcontinent ◽  
Interpersonal Relationship ◽  
Public Health Problem ◽  
Elderly Subjects ◽  
Important Public Health Problem ◽  
Policy Makers ◽  
Formidable Challenge ◽  
Causative Factors

Summary: The Indian subcontinent comprises eight countries (India, Pakistan, Bangladesh, Nepal, Sri Lanka, Afghanistan, Bhutan, and the Maldives) and a collective population of more than 1.3 billion people. 10% of the world's suicides (more than 100,000 people) take place in just three of these countries, viz. India, Sri Lanka, and Pakistan. There is very little information on suicides from the other four countries. Some differences from suicides in Western countries include the high use of organophosphate insecticides, larger numbers of married women, fewer elderly subjects, and interpersonal relationship problems and life events as important causative factors. There is need for more and better information regarding suicide in the countries of the Indian subcontinent. In particular, studies must address culture-specific risk factors associated with suicide in these countries. The prevention of this important public health problem in an area of the world with myriad socio-economic problems, meager resources, and stigmatization of mental illness poses a formidable challenge to mental health professionals, policy makers, and governments of these countries.

Sign in / Sign up

Export Citation Format

Share Document