scholarly journals Beyond strain release: Delocalisation-enabled organic reactivity

2021 ◽  
Author(s):  
Alistair Sterling ◽  
Russell Smith ◽  
Edward Anderson ◽  
Fernanda Duarte
Keyword(s):  
Total Synthesis ◽  
Driving Force ◽  
Strain Energy ◽  
Building Blocks ◽  
Equivalent Strain ◽  
Bond Breaking ◽  
Polymer Science ◽  
Activation Barriers ◽  
Key Factor ◽  
Strain Release

Strain energy has long been recognised as a fundamental driving force for organic reactions. However, the release of strain alone is an insufficient predictor of reactivity, as seen in the equivalent strain energies but disparate reactivity of cyclopropane and cyclobutane. Here we show that electronic delocalisation is a key factor that operates alongside strain release to boost reactivity, significantly lowering the energy required for bond-breaking in cyclopropanes, cycloalkynes and cycloalkenes. Consideration of thermodynamic and delocalisation parameters explains the relative rates of reaction of molecules containing these functional groups, leading to a ‘hierarchy of delocalisation’ and a rule-of-thumb model that accurately predicts activation barriers. The implications of these principles are demonstrated in the context of the reactions of strained building blocks commonly encountered in total synthesis, medicinal chemistry, polymer science and bioconjugation.

Factors Affecting Molecular Self-Assembly and Its Mechanism

2012 ◽  
Vol 9 (1) ◽  
pp. 43 ◽  
Author(s):  
Hueyling Tan
Keyword(s):  
Self Assembly ◽  
Building Blocks ◽  
Molecular Engineering ◽  
Molecular Structures ◽  
Polymer Science ◽  
New Approach ◽  
Factors Affecting ◽  
Dna Structures ◽  
Self Assembling ◽  
Wide Range

Molecular self-assembly is ubiquitous in nature and has emerged as a new approach to produce new materials in chemistry, engineering, nanotechnology, polymer science and materials. Molecular self-assembly has been attracting increasing interest from the scientific community in recent years due to its importance in understanding biology and a variety of diseases at the molecular level. In the last few years, considerable advances have been made in the use ofpeptides as building blocks to produce biological materials for wide range of applications, including fabricating novel supra-molecular structures and scaffolding for tissue repair. The study ofbiological self-assembly systems represents a significant advancement in molecular engineering and is a rapidly growing scientific and engineering field that crosses the boundaries ofexisting disciplines. Many self-assembling systems are rangefrom bi- andtri-block copolymers to DNA structures as well as simple and complex proteins andpeptides. The ultimate goal is to harness molecular self-assembly such that design andcontrol ofbottom-up processes is achieved thereby enabling exploitation of structures developed at the meso- and macro-scopic scale for the purposes oflife and non-life science applications. Such aspirations can be achievedthrough understanding thefundamental principles behind the selforganisation and self-synthesis processes exhibited by biological systems.

scholarly journals Non-Enzymatic Desymmetrization Reactions in Aqueous Media

Symmetry ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 720
Author(s):  
Satomi Niwayama
Keyword(s):  
Natural Products ◽  
Total Synthesis ◽  
Functional Groups ◽  
Organic Compounds ◽  
Recent Progress ◽  
Aqueous Media ◽  
Building Blocks ◽  
Organic Reactions ◽  
Environmentally Benign ◽  
Enzymatic Desymmetrization

Symmetric organic compounds are generally obtained inexpensively, and therefore they can be attractive building blocks for the total synthesis of various pharmaceuticals and natural products. The drawback is that discriminating the identical functional groups in the symmetric compounds is difficult. Water is the most environmentally benign and inexpensive solvent. However, successful organic reactions in water are rather limited due to the hydrophobicity of organic compounds in general. Therefore, desymmetrization reactions in aqueous media are expected to offer versatile strategies for the synthesis of a variety of significant organic compounds. This review focuses on the recent progress of desymmetrization reactions of symmetric organic compounds in aqueous media without utilizing enzymes.

Total Synthesis of Woodrosin I. Part 1. Preparation of the Building Blocks and Evaluation of the Glycosylation Strategy.

ChemInform ◽  
2003 ◽  
Vol 34 (18) ◽  
Author(s):  
Alois Fuerstner ◽  
Fabien Jeanjean ◽  
Patrick Razon ◽  
Conny Wirtz ◽  
Richard Mynott
Keyword(s):  
Total Synthesis ◽  
Building Blocks

Crack Driving Force in Anisotropic Media due to Non-Elastic Deformation

2004 ◽  
Vol 261-263 ◽  
pp. 75-80
Author(s):  
G.H. Nie ◽  
H. Xu
Keyword(s):  
Elastic Deformation ◽  
Driving Force ◽  
Strain Energy ◽  
Elastic Stress ◽  
Complex Function ◽  
Crack Driving Force ◽  
Special Cases ◽  
Degree Of Anisotropy ◽  
Minimum Strain Energy ◽  
Orthotropic Media

In this paper elastic stress field in an elliptic inhomogeneity embedded in orthotropic media due to non-elastic deformation is determined by the complex function method and the principle of minimum strain energy. Two complex parameters are expressed in a general form, which covers all characterizations of the degree of anisotropy for any ideal orthotropic elastic body. The stress acting on the long side of ellipse can be considered as a crack driving force and applied in failure and fatigue analysis of composites. For some special cases, the resulting solutions will reduce to the known results.

Effects of Weld Strength Heterogeneity on Crack Driving Force in Stress and Strain Based Design Scenarios

2014 ◽  
Author(s):  
Stijn Hertelé ◽  
Noel O’Dowd ◽  
Matthias Verstraete ◽  
Koen Van Minnebruggen ◽  
Wim De Waele
Keyword(s):  
Driving Force ◽  
Large Scale ◽  
Limit State ◽  
Weld Strength ◽  
Force Response ◽  
Crack Driving Force ◽  
Key Factor ◽  
Weld Properties ◽  
Girth Welds ◽  
Strain Hardening Behavior

Weld strength mismatch is a key factor with respect to the assessment of a flawed girth weld. However, it is challenging to assign a single strength mismatch value to girth welds, which are generally heterogeneous in terms of constitutive behavior. The authors have recently developed a method (‘homogenization’) to account for weld strength property variations in the estimation of crack driving force response and the corresponding tensile limit state. This paper separately validates the approach for stress based and strain based assessments. Whereas homogenization is reliably applicable for stress based assessments, the strain based crack driving force response is highly sensitive to effects of actual heterogeneous weld properties. The sensitivity increases with increased weld width and decreased strain hardening behavior. For strain based design, a more accurate methodology is desirable, and large scale testing and/or advanced numerical modeling remain essential.

Stereocontrolled construction of key building blocks for the total synthesis of amphoteronolide B and amphotericin B

1987 ◽  
Vol 109 (7) ◽  
pp. 2205-2208 ◽  
Author(s):  
Kyriacos C. Nicolaou ◽  
R. A. Daines ◽  
J. Uenishi ◽  
W. S. Li ◽  
D. P. Papahatjis ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Amphotericin B ◽  
Building Blocks

ChemInform Abstract: Stereocontrolled Construction of Key Building Blocks for the Total Synthesis of Amphoteronolide B and Amphotericin B.

ChemInform ◽  
1987 ◽  
Vol 18 (33) ◽  
Author(s):  
K. C. NICOLAOU ◽  
R. A. DAINES ◽  
J. UENISHI ◽  
W. S. LI ◽  
D. P. PAPAHATJIS ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Amphotericin B ◽  
Building Blocks

Motivation-Based Teaching Practices

2013 ◽  
Vol 4 (1) ◽  
pp. 56-60
Author(s):  
Anissa Khaldi
Keyword(s):  
Instructional Practices ◽  
Present Article ◽  
Language Learners ◽  
Driving Force ◽  
Teaching Practices ◽  
Important Variable ◽  
Learning Goals ◽  
Final Part ◽  
Key Factor ◽  
Shed Light

One of the factors that have been found to significantly influence EFL language learners’ success is motivation. It is said that it provides a strong impetus to initiate learning and, at the same time, a driving force to sustain the long, often tiring process of learning. Hence, it is crucial for instructors to consider how to foster this important variable. The present article argues that motivation can be stimulated through a number of teaching practices. It will set out to review some research concerning motivation along with its different components. Moreover, the article will explain how motivation helps learners pursuit their challenging learning goals in the path of success. The bulk of the final part will be devoted to some of the instructional practices that teachers may use so as to get learners motivated as well as sustain their motivation. Finally, the conclusion of this article will also shed light on the idea that although motivation is a key factor for success, it is not the only variable that EFL instructors should seek to take into account. There are other variables that can be held responsible for successful learning.

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