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Step-Growth Polymerization
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
The sixth row represents the end of the reaction as far as linear polymer is concerned. Of the 10 initial A groups, 1 is still unreacted, but this situation raises the possibility that the decamer shown in row 6 − or for that matter, some other i-mer, including monomer – might form a ring or cyclic compound, thereby eliminating functional groups without advancing the polymerization. Throughout this chapter we will assume that the extent of ring formation is negligible.
Chain-Growth Polymerization
Published in Anil Kumar, Rakesh K. Gupta, Fundamentals of Polymer Engineering, 2018
The generation of small structures (sometimes called microfabrication) is essential to modern technologies like microelectronics and optoelectronics [41,42]. In these applications, one is interested in constructing supramolecular structures utilizing well-defined, low molecular weight building blocks synthesized as above. For this purpose, these building blocks are first functionalized at the chain ends by cyclic pyrrolidinium salt groups and/or tetracarboxylate anions. Self-assembly is defined as the spontaneous organization of molecules into a well-defined structure held together by noncovalent forces. In this case, the functionalized polymer blocks (sometimes called telechelics) are held together by electrostatic forces. On heating this self-assembly, the pyrrolidinium groups (five-ring cyclic compound) polymerize this way, giving a covalent fixation of this assembly.
Synthesis of Molecular Electronic Devices: Towards Molecular Integrated Circuits
Published in Sergey Edward Lyshevski, Molecular Electronics, Circuits, and Processing Platforms, 2018
The cyclic molecules ensure device physics soundness and provide the desired synthesis capabilities. An aromatic hydrocarbon is a cyclic compound with the sp2-hybridized atoms in the ring. This molecule with a delocolized π-electron system has free p-orbitals ensuring conduction of π-electrons. There are some cyclic hydrocarbon molecules that have (4n + 2) πn-electrons, but these molecules are not aromatic because at least one of the carbon atoms within the ring is not sp2-hybridized. For example, cycloheptatriene has six πelectrons; however, one of the seven carbon atoms is the sp3-hybridized and the ring is not planar. The ring must be planar in order for the π-electrons to be delocalized in the ring. The planar structure ensures stability and rigidity. Benzene is the most commonly known aromatic hydrocarbon having six π-electrons with all six carbon atoms sp2-hybridized, and therefore the ring is planar. In particular, the n-system of benzene is formed from six overlapping p-orbitals composing n-molecular orbitals with six π-electrons. In cyclic molecules, carbon atoms can be substituted.Figure 5.2. shows a structural and three-dimensional (3D) view of pyridine, pyrrole, furan, and thiophene. The well-known heterocyclic biomolecules, such as purine and pyrimidine, contain nitrogen and oxygen, seeFigure 5.2.. The derivatives of purine and purimidine can be utilized to synthesize modified nucleotides.
One-pot reactions in the synthesis of thiazolidinone derivatives by nano-Fe3O4–cysteine catalyst
Published in Journal of Sulfur Chemistry, 2022
Halimeh Hajighasemi, Naser Foroughifar, Alireza Khajeh-Amiri, Ebrahim Balali
According to the IUPAC definition, a heterocyclic compound is a cyclic compound with at least one other element, different from C and H in its structure. The first study on heterocyclic compounds dated to the early nineteenth century with isolation of alloxan from uric acid by Brugnatelli and furfural by Doberiner. The first benzothiazole and thiazole rings were reported by Hantzsch in 1879 and 1887, respectively. The importance of this class of heterocyclic compounds was clarified by providing evidence that vitamin B1 has a thiazole structure [1]. This report was the beginning of research on thiazole, and correlated structures.