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The field of catalysis, natural products, and polymers has seen remarkable progress in recent years, with new innovations paving the way for breakthroughs in drug discovery, sustainable materials, and industrial applications. Emerging Trends in Catalysis, Natural Products, and Polymers brings together an expansive collection of research highlighting innovative advancements and methodologies in the fields of catalysis, natural product extraction, and polymer science. This book provides a unique opportunity to explore how theoretical and experimental approaches converge to solve modern challenges in organic and materials chemistry. Key topics include the application of Density Functional Theory (DFT) in predicting ruthenium-catalyzed C(sp2)-H activation and the utilization of CuFe2O4 as a supporting catalyst for various organic transformations. Advances in copperand palladium-catalyzed C-N bond formation are also extensively discussed, offering insights into their critical role in the synthesis of pharmaceuticals and fine chemicals. The volume further examines catalytic innovation with a focus on homogeneous and heterogeneous transition metal-catalyzed transfer hydrogenation, Schiff base metal complexes, and green synthetic approaches such as plant-mediated copper nanoparticle synthesis. The exploration of bioactive compounds, including lupane triterpenoids from Diospyros melanoxylon, demonstrates the ongoing integration of natural product research in organic chemistry. The book also delves into the challenges and applications of conducting polymers and the comparative evaluation of organic and inorganic polymers, showcasing their relevance to advanced materials science. This comprehensive work is designed to serve as an invaluable resource for students, researchers, and professionals, offering both theoretical foundations and practical perspectives on emerging trends shaping the future of catalysis, natural products, and polymer chemistry.

Introduction  Natural product scaffolds and heterocyclic ring-based organic compounds are crucial for developing bioactive substances and therapeutic drugs, serving as essential structural units for bioactive molecules and pharmacophores. Numerous experts have worked hard to design and develop organic synthesis, which could make it easier to obtain these crucial organic chemicals. Due to the multistep reactions involving several hazardous chemicals, conventional organic synthesis is neither commercially feasible nor environmentally benign. To overcome these issues, improvisation or developing a new synthetic approach with a superior atom and step economic procedure is always desirable. The biggest challenge in organic synthesis is functionalizing a carbon-hydrogen (C-H) bond in a molecule. This is generally achieved through radical intermediates and catalysis by enzymes or transition metals. The transition metal-catalyzed process is the most popular due to its high chemoselectivity, site-selectivity, and efficiency (Yamaguchi et al., 2012). Inert C-H bonds can be directly functionalized, offering appealing synthetic strategies that enhance both atom and step economy and provide an overall efficiency of multistep synthetic sequences, leading to a sustainable and greener approach. These optimizations provide atom and step-economical methods for synthesizing structurally complicated organic molecules with broad substrate scope and good to exceptional product yields (Ackermann, 2011; Gensch et al., 2016). Direct conversion from the substrate to the desired organic compound without pre-functionalization is attractive and cost-effective. However, it can be quite challenging to selectively functionalize particular C-H bonds due to the inertness of those C-H bonds having similar electronic and bonding properties and the ubiquity of C-H bonds in organic molecules (Sambiagio et al., 2018). Two main techniques have been explored to obtain selectivity in C-H bond functionalization (Brückl et al., 2012). The first is based only on the natural reactivity pattern of an organic molecule. This strategy is highly successful for some heterocycles with at least one specific reactive site due to the presence of heteroatoms. However, it produces inadequate selectivity for most aliphatic and aromatic hydrocarbons. The latter is to direct further functionalization at a particular site using directing groups already present in the molecule (Kuhl et al., 2012). The development of directing groups that effectively control the regioselectivity of C-H functionalization has lately transformed this field, enabling the incorporation of desired groups in unfunctionalized sites (Docherty et al., 2023; Labinger & Bercaw, 2002). Employing directing groups, various functional groups are added to a molecule using this method. Directing groups are crucial for breaking a C-H bond in a transition metal catalysis reaction, where the metal center in the active catalyst complex is usually coordinated with the substrate through a weak interaction with the nearby C-H bond. This interaction is typically not selective; thus, the metal centre may activate numerous C-H bonds on the substrate. However, when a directing group is incorporated into a substrate, the metal center can interact more strongly and regioselectively with a specific region on the substrate as directed by the directing group. This causes selective cleavage

Introduction  Over the past few decades, magnetic nanoparticles (MNPs) have been showing great importance in the field of organic synthetic reactions, catalysis, sensors, biomedicines, environment rehabilitation, etc. (Gawande, M. B. et al., 2013; Del Rio, M. et al., 2022). Numerous research teams have recognized the significance of solid support materials for the creation of environmentally acceptable nano catalysts with high catalytic activity in light of the infinite advantages of MNPs (Sharma, R. K. et al., 2016; Gawande, M. B. et al., 2013; Deng, J. et al., 2011; Nasrollahzadeh, M. et al., 2015; Hudson, R. et al., 2014; Payra, S. et al., 2017; Chng, L. L. et al., 2013; Parandhaman, T. et al., 2017; Zhang, F. et al., 2014; Pourjavadi, A. et al., 2012). Heterogeneous catalysts in organic chemistry are solid catalysts that, while remaining in a distinct phase (usually solid) from the reactants (generally liquids or gasses), promote chemical reactions without being consumed in the process. These catalysts, which have multiple benefits such as ease of separation, recyclability, and selective reactivity, are essential in a variety of industrial processes and laboratory reactions (Lattuada, M. et al., 2007; Jiang, K. et al., 2011). The standard formula for ferrite nanoparticles is MFe2O4, where M is usually divalent metal ion like copper (Cu), zinc (Zn), or nickel (Ni), and iron (Fe) is the common metal (Kazemi, M. et al., 2018). These nanoparticles work very well as heterogeneous catalysts in a variety of chemical reactions because of their special magnetic and electrical characteristics.Because of its special qualities as a catalyst in a variety of processes, copper ferrite (CuFeO4), a mixed-metal oxide, has drawn interest in organic chemistry (Kharisov, B. I. et al., 2019; Zhu, J. et al., 2014; Vannucci, A. K. et al., 2012). It is a spinel-type ferrite that can catalyse a variety of organic transformations because it combines iron and copper in a stable, highly active structure. With benefits including high stability, reusability, and low toxicity, these catalysts are frequently employed in processes like oxidation, coupling, and reduction (Taghavi Fardood, S. et al., 2018). The Figure 1 represents schematic diagram of a reaction where the ferrite nanoparticles as catalyst have been recovered with the aid of an external magnet after the formation of reaction product.

Introduction Metal-catalyzed C–N cross-coupling reactions are powerful synthetic methods for producing both simple and complex organic compounds, including natural products. These methodologies typically involve shorter reaction times and can achieve good to excellent yields with a broad range of reactions, exhibiting high regioselectivity in certain cases. The coupling of carbon and nitrogen to create organic compounds that contain nitrogen, such as urea and amides, is one of the most fundamental chemical reactions and plays a crucial role in human civilization. C–N coupling reactions have significant importance in industry, starting with the production of ammonia (NH3) through the Haber–Bosch process. Molecules containing C–N bonds are prevalent in a variety of organic materials, natural products, pharmaceutical compounds, and agricultural chemicals. This wide applicability makes them crucial chemicals, leading synthetic organic chemists to continuously seek out novel synthetic methods. In recent years, numerous synthetic strategies involving either transition metals or metal-free enzymes and biocatalysts have emerged. Additionally, new technologies, such as electroreduction, have been employed in these C–N coupling processes (Bariwal & Van der Eycken, 2013, Li et al., 2022, Yin et al., 2024, Rahman et al., 2022). Common copper salts/complexes, and diamino ligands Copper is commonly found coordinated by two, three, or four ligands, resulting in linear, trigonal planar, or tetrahedral geometries. Well-known and inexpensive copper halides, such as copper (II) glycinate, copper (II) acetylacetonate (particularly CuI), copper acetates, copper oxide, copper sulfate, and copper triflate salts, are widely used as catalytic systems in C–N bond-forming reactions. Additionally, other complexes such as Cu di-isopropyl salicylate (CuDIPS), copper phthalocyanine, and copper aspirinates have also been employed in these reactions. Copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions are well-established methods for forming triazoles via C–N bonds in one pot. These reactions often involve domino click chemistry and green approach methodologies, leading to the synthesis of biologically important triazoles. Copper salts in combination with diamine ligands are widely used in C–N bond-forming reactions through cross-coupling strategies. Some notable examples of such diamino compounds that can coordinate with copper are illustrated in Figure 1.

1. Introduction With commercial uses ranging from the production of high-quality substances to the manufacture of pharmaceuticals, hydrogenation is an essential step in the formation of organic compounds (Cerveny et al., 1986). There are two main approaches to hydrogenation: direct hydrogenation, which employs pressurized hydrogen gas, and transfer hydrogenation (TH). A versatile and effective approach for producing a large variety of hydrogenated molecules, the TH method entails adding H2 to molecules via an origin other than H2 gas. This approach is increasingly preferred over direct hydrogenation and has recently attracted considerable interest in hydrogenation research. The benefits of the TH method include (i) the elimination of potentially dangerous pressurized hydrogen gas and the complexity of experimental setups, (ii) the accessibility, cost-effectiveness, and ease of use of hydrogen donors, (iii) the potential to recycle the main byproduct, and (iv) the availability and stability of the catalysts employed (Brieger et al., 1974). 1.1. The Historical Context, Core Principles, and Groundbreaking Research on TH (transfer hydrogenation) With a history spanning more than a century, the TH reaction has a rich past. In order to enable hydrogen transfer between equivalent donor and acceptor units, Knoevenagel showed in 1903 that palladium black could efficiently aid in the disproportionation of dimethyl 1,4-dihydro terephthalate into dimethyl terephthalate and cis-hexahydroterephthalate. Three primary types of hydrogen transfer reactions were distinguished by Braude and Linstead: (i) the hydrogen movement within a single molecule; (ii) hydrogen disproportionation, which entails transfer among identical donor and acceptor units; and (iii) TH-dehydrogenation, which takes place between distinct donor and acceptor units. Of them, THdehydrogenation— often just called TH—is the most well-known and often applied sector. Meerwein-Ponndorf-Verley (MPV) reductions, early transition metal-catalyzed reactions, organocatalytic processes, enzyme-catalyzed reactions, heat techniques, and base-catalyzed reactions are among the types of TH reactions that are classified according to the type of catalyst used. The historical context, important research, and underlying ideas of each category will be covered in detail in this section.In 1925, Meerwein et al. independently reported the significant MPV reduction, which were the first TH process involving carbonyl groups. After earning his Ph.D. under Richard Anschütz in Bonn, where he was appointed a professor in 1914, Hans Meerwein (1879–1965) moved to Königsberg in 1922 and then to Marburg. His name is associated with a number of processes and reagents,

1. Introduction Palladium (Pd), which has the atomic number 46, was discovered in 1803 by the English chemist William Hyde Wollaston. It is a well-known transition metal recognized for its versatile catalytic properties in chemical reactions, material sciences, and various industries. The palladium-catalyzed coupling reactions extend beyond the formation of biaryls. Many carbon–carbon, carbon–nitrogen, and carbon–oxygen bond-forming reactions in organic chemistry are facilitated by palladium salts and catalytic systems derived from palladium. Some notable organic reactions that involve palladium include the Mizoroki-Heck reaction, (Biffis et al., 2018, Koranne et al., 2023, Lee et al., 2021) Suzuki-Miyaura coupling, (Zhang et al., 2023) Negishi reaction, (Haas et al., 2016). Stille coupling, (Cordovilla et al., 2015). Sonogashira coupling, (Chinchilla & Najera, 2007) Tsuji-Trost reactions, (Kvasovs et al., 2023). and Wacker catalytic processes. (Zhang et al., 2023) In this chapter, we will focus on the applications of palladium and its salts in C-N bond-forming reactions. 2. Palladium (Pd)-Catalyzed C–N Bond Formation Besides copper, palladium metal is considered as the most widely used metal in organic synthesis. The discovery of cross-coupling reactions catalyzed by palladium(0) complexes in the 1970s was a highly important achievement that substantially changed the strategy of organic chemistry. Best applications of the palladium salts are in enantiolective and new C-N bond forming reactions. Stephen L. Buchwald and John F. Hartwig opened up the catalytic scope of palladium in newer methodologies on C–N bond forming reactions during 1990s, (Ruiz- Castillo & Buchwald, 2016) and henceforth, new methodologies of carbocycles, heterocycles, and simple organic compounds have been created in large scales (Rayadurgam et al., 2021). The mechanisms of palladium-catalyzed C-N cross-coupling reactions are critically discussed in numerous high-quality research journals with different theoretical and experimentally proven methods (Beletskaya & Averin, 2021). However, the most acceptable mechanistic pathway to reaction products in these Pd-catalyzed reactions involving palladium is illustrated in Scheme 1. The process begins with the formation of a palladium complex through the reaction of an aryl halide (which can be aliphatic, heteroaryl, or functionalized alkenes/alkynes), a palladium salt, and amino nucleophiles. In the presence of a suitable base, the loosely bonded halide or any leaving groups are eliminated, leading to the formation of a palladium (IV) complex. This complex then undergoes reductive elimination, resulting in stable aminated aryl, heteroaryl, alkyl, or functionalized alkenes/ alkynes. Additionally, a more generalized reaction mechanism is presented in a circular pathway format, highlighting the bonding approaches, rearrangements, intermediate formations, and the final release of target compounds, as depicted in Scheme 1. The involvement of higher valence organo-palladium complexes in such catalytic transformations have been well established (Hickman & Sanford, 2012).

Introduction  Schiff base ligands (also called azomethines) were first revealed by German chemist Hugo Schiff in 1864. They are synthesized through a straightforward condensation reaction between an amine and a carbonyl compound (aldehyde or ketone). This reaction forms a characteristic imine group (>C=N-) while eliminating a water molecule as a byproduct. Schiff bases are highly versatile and serve as ligands for various transition metals, forming complexes with applications in catalysis, material science, and medicinal chemistry. Their ease of synthesis, tunable structure, and ability to stabilize metal centers make them valuable in both academic research and industrial processes (Cozzi, 2004). They can form stable complexes with almost all metal ions, offering various coordination geometries. Their flexibility makes them valuable in catalysis, medicinal chemistry, and materials science, with wide applications across these fields. Schiff base metal complexes exhibit exceptional catalytic performance in various high-temperature reactions (>100 °C), even under humid conditions. These complexes are widely employed in catalytic processes, such as oxidation, reduction, carbon-carbon bond formation, polymerization, and asymmetric synthesis (Zoubi et al., 2016). Recently, interest in olefin polymerization has increased due to their ability to catalyze the formation of commercially significant branched and linear polyethylenes. Their versatility, structural tunability, and high stability make them ideal for such applications, offering pathways to develop advanced materials with tailored properties for industrial and commercial use. Schiff base complexes thus remain central to modern catalysis research. These complexes have shown great potential in producing polymers with tailored properties, making them highly valuable in industrial applications. Schiff base complexes have gained attention for their catalytic roles, particularly in the reduction of ketones to alcohols and the alkylation of allylic substrates. These complexes, typically coordinating with metal ions, facilitate crucial organic transformations by stabilizing intermediates, offering an efficient and selective route for various chemical reactions. Schiff base complexes enable controlled ring-opening polymerization of cycloalkenes at low temperatures, offering precise molecular weight regulation without side reactions. In contrast, traditional catalysts like tungsten, molybdenum, or ruthenium with alkylating agents require high temperatures and lack molecular weight control, making Schiff bases more efficient for polymerization. The oxidation of hydrocarbons catalyzed by Schiff base complexes has garnered significant academic and industrial interest. These metal complexes are studied for their ability to facilitate efficient and selective oxidation reactions, offering insight into their catalytic activity and potential applications in chemical processes and industrial oxidation technologies. The ring-opening of large cycloalkanes is challenging due to their stability, but Schiff base complexes of cobalt(II) and chromium(III) effectively catalyze these reactions. These complexes enhance metal center reactivity and stabilize intermediates, enabling efficient cleavage of cyclic structures and expanding possibilities for catalytic transformations in synthetic and industrial chemistry. These complexes not only facilitate the process but also exhibit important enantioselectivity, creating them valuable catalysts in asymmetric synthesis and fine chemical production. Chiral Schiff base complexes have emerged as versatile and efficient catalysts in various organic transformations, particularly in asymmetric synthesis. Schiff bases derived from salen and binaphthyl frameworks are effective in Michael addition reactions, offering high enantioselectivity and catalytic efficiency. While transition metal complexes

1. Introduction Hydrogenation plays a vital role in the transformation of organic compounds, making it essential for synthesizing fine chemicals and pharmaceuticals. This process is widely utilized in both laboratories and for industrial applications (Andersson et al., 2008). Typically, two approaches are used for hydrogenation: traditional one involves direct hydrogenation using pressurized hydrogen gas, and the other relies on transfer hydrogenation (TH), which involves addition of hydrogen into a molecule from a non-H2 sources (Johnstone et al., 1985). The use of high-pressure hydrogen gas, however, demands significant investment in infrastructure, making it less economically feasible for developing a sustainable hydrogenation industry. In contrast, TH has gained increasing attention due to its sustainability, particularly when employing hydrogen donors derived from biomass, such as alcohols and organic acids, which are abundant, cost-effective, and easy to handle instead of using non-renewable H2 gas for reduction of CO2 (Becattini et al., 2021) (Figure 1). 2. Historical Background and Classification The hydrogen transfer process has a rich history spanning over a century. In 1903, Knoevenagel first demonstrated that palladium black effectively promoted the disproportionation of dimethyl 1,4-dihydroterephthalate into dimethyl terephthalate and cis-hexahydroterephthalate, in which hydrogen transfer was occurred between identical molecules (identical donor and acceptor) (Knoevenagel et al., 1905). This pioneering work established the foundation for hydrogen transfer reactions. Braude and Linstead later categorized these reactions into three distinct types (Braude et al., 1954):

Introduction  Before 1800, it was believed that organic compounds could only be synthesized by living organisms, not possible in the laboratory. Friedrich Wohler successfully synthesized the first organic compound urea in the laboratory. Recently, synthetic organic chemistry has been a well-established science to construct derivative or new compounds, which have been utilized in the fields of medicine, food, clothing, nutrition, polymers, plastic, highly durable materials, and high energy fuels, that are beneficial to humans, and society. To achieve faster organic transformations, many advancements have been made, as a result, catalysts have been taken into account, which provides an alternate faster path for the reaction by lowering the activation energy. The catalysts play a very crucial role in achieving organic transformations more efficiently, affordably, and with higher yields in less time. Additionally, the catalyst which is environment-friendly and easily recoverable after completion of the process, would be beneficial in both economic and ecological ways (Trost, 1991). The utilization of nanoparticles as catalysts in organic transformations is more advantageous over conventional catalysts because of lower catalyst loadings, and high performance of the reaction in heterogenous phase. The large surface area of nanoparticles is responsible for high reactivity towards organic transformations. Till now, many nano-dimension metals like gold (Au), silver (Ag), platinum (Pt), and palladium (Pd) efficiently utilized to catalyze organic transformations (Muskan et al., 2022). The ever-growing demand for productive and sustainable catalytic systems has driven the utilization of transition metal nanoparticles as catalysts in organic conversions (Pathak et al., 2024). Among these, copper-based nanoparticles have shown great potential as catalysts due to their large surface area and variable oxidation states, which enable them to function as both oxidizing and reducing agents, effectively replacing traditional palladium catalysts (Pathak et al., 2024). Copper-based nanoparticles having specific physicochemical properties, varying in size, porosity, surface/volume ratio, and shape can also be synthesized through different physical, chemical, and biogenic methodologies. Most physical and chemical methods are considered toxic, have huge energy demands, and have high-temperature demands. In contrast, biogenic methods are simple and non-toxic. The biogenic procedure can be done by using microbes, fungi, algae, plants, extracts, etc. This chapter provides insights into various aspects of the biogenic synthesis of copper-based nanoparticles using plants and multiple catalytic applications in recent organic transformations.

Introduction 1.1. Definition and Significance of Natural Products Natural products are chemical compounds or substances derived from living organisms in nature. These diverse sources, including plants, animals, fungi, and microorganisms, produce a wide range of chemical structures and functions. The significance of natural products lies in their diverse biological activities and potential applications in therapeutics, agriculture, and various industries. Natural products have been used for centuries in traditional medicine and continue to serve as the foundation for many modern pharmaceuticals, providing templates for the development of synthetic analogues and novel drugs. Their complexity and unique structural features often translate into high biological activity, making them valuable in the discovery of new therapeutic agents. Furthermore, natural products are generally perceived as safer and more environmentally friendly compared to synthetic chemicals, contributing to their appeal in numerous applications. 1.2. Historical Perspective on the Use of Natural Products The use of natural substances has a long history, with evidence of their application in ancient civilizations such as Egypt, China, India, and Greece. Traditional medical systems, including Ayurveda, Traditional Chinese Medicine, and Indigenous practices, have utilized plants, animals, and minerals to treat various ailments. These early practices laid the foundation for the systematic investigation of natural products and their medicinal potential. One of the earliest documented uses of natural products in medicine is the Ebers Papyrus, an ancient Egyptian text from around 1550 BCE (Packard, 1931). Similarly, ancient Indian texts, such as the Charaka Samhita and the Sushruta Samhita, describe the use of plant-based medicines in Ayurvedic tradition. The scientific investigation of natural products gained momentum in the 19th century, with the isolation of pure compounds, including morphine, quinine, and penicillin. 1.3. Current Trends and Applications Natural products are invaluable in various industries, serving as a rich source of bioactive compounds for drug development, sustainable agriculture, and functional food products. Many modern medicines, such as the anticancer drug paclitaxel and the antimalarial artemisinin, are derived from natural sources. These naturally-derived compounds often possess unique structures and mechanisms of action that are difficult to replicate synthetically.

1. Introduction  Among the innumerable gifts of nature, plants, animals and minerals have been the basis of treatment of human diseases. Generally it is either of prebiotic origin or originating from microbes, plants or animal sources. More likely they are the natural expression of the increase in complexity of organisms. Beside animals, plants are one of the most important sources of natural products. From the very beginning of their existence, man has acquainted himself with plants and used them in a variety of ways throughout the ages. In search of food and to cope successfully with human sufferings, ancient man began to distinguish those plants suitable for nutritional purposes from others with definitive therapeutic action. Some plants are widely used as food while others showed beneficial effects against various human sufferings such as injuries and diseases. This relationship has grown between plants and man, and many plants have come to be used as drugs. The use of plant as a drug can be divided broadly into five periods. The early period covers the Indian, Chinese, Sumerian, Egyptian and Assyrian civilizations followed by the Greco-Roman, Arabian, Medieval and modern periods (Buchnman, 1980). Among ancient civilisations, India has been known to be rich repository of medicinal plants as the forest in India is the principal repository of large number of medicinal and aromatic plants, which are largely collected as raw materials for manufacture of drugs and perfumery products. About 8,000 herbal remedies have been codified in Ayurveda. The Rigveda (5000 BC) has recorded 67 medicinal plants (Chopra et al., 1956), Yajurveda 81 species and Atharvaveda (4500-2500 BC) 290 species. Charak Samhita (700 BC) and Sushrut Samhita (200 BC) had described properties and uses of 1100 and 1270 species, respectively (Kirtikar & Basu, 1918; Baquar, 1989) in compounding of drugs and these are still used in the classical formulations, in the Ayurvedic system of medicine. Before the availability of synthetic drugs, medicinal plants were used as the most primary source of medicine and continue to provide the mankind with new remedies for many diseases. These were used in crude forms like expressed juice, powder, decoction or infusion. As the plant have specialized biochemical capabilities they are able to synthesize and accumulate a vast array of primary and secondary chemical constituents or phytochemicals (Ghazanfar, 1994). Phytochemicals are responsible for metabolic activities and used for defense purpose. They are produced by specific biochemical pathways, which occur inside the plant cells. Due to their physical characteristic and chemical properties these chemical constituents are highly beneficial to the mankind and most importantly in primary health care. The first chemical substance isolated from plants was benzoic acid (Figure 1) discovered in 1560. The potent pain-killer, morphine (Figure 1) was separated from the dried latex of Papaver somniferum L. (opium) by F. W Serturner (1783-1814). The bioactive molecule, ephedrine (Figure 1) is one of the most potent plant based medicine and was isolated from Ephedra sinica (Ma huang). It was used in the form of various salts to combat bronchial asthma (Tang & Eisenbrand, 1992). Reserpine (Figure 1) an indole alkaloid, obtained from the roots of Indian plant, Rauwolfia serpentina, was used to treat hypertension. Taxol (Figure 1) is a diterpenoid first isolated from the stem bark of pacific Yew, Taxus brevifolia and used against ovarian for the treatment of ovarian cancer.

Introduction  Polymers are mostly distinguished from metals by their property of inability to conduct electricity. Because of the insulating properties, polymers find advantages for many applications of plastics. However with the discovery of poly sulphur nitride [(SN)x], which acts as super-conductor at low temperature the evolution of conducting polymers began in 1975. After two years the linear conjugated organic polymer polyacetylene treated with gaseous bromine or Iodine found to have metallic properties. Some examples of conducting polymers are polyaniline, polypyrrole and polythiophene etc. Conducting polymers are organic polymer, possesses the magnetic, electronic, electrical properties, mechanical properties, and processibility etc. These properties are most commonly related to the conventional polymer. The transformation of polymer from insulator to conductor is called doping. For example: the effect of conductivity due to the absorption of I2 into polyacetylene is analogous to the effect of doping of arsenic, boron, and phosphorus into silicon to make semiconductor. Doping and undoping can be achieved in conducting polymers by an alternate route of electrochemical oxidation and reduction. Doping includes either the removal of electrons from or addition of electron to the conjugated backbone of conducting polymers. Doping is therefore of two types: Oxidative doping (p-type): In this case, the polymer backbone carries a positive charge due to removal of an electron by ordinary oxidation. Examples of p-doped conductive polymers are polyacetylene, polyaniline, polypyrroles etc. The p-doping causes oxidation of the polymer backbone to form cations. When these cations move along the polymer backbone in an electrical field, the polymer is electrically conductive. Reductive doping (n-type): the polymer backbone acquires negative charge by receiving electrons. Ex: Polyacetylene can be n-doped by alkali metals but these are less explored because they are very much sensitive towards atmospheric air than specific undoped type polymer. According to the principle of electroneutrality, doped conducting polymer needs counter ion to balance the opposite charges in the polymer backbone. These counterions are called dopant. Some common examples of dopants are usually small anions e.g. Cl-, I-, and SO4 2-. However poly-electrolyte like p-toluene sulphonic acid can act as the dopant. The process by which the doped polymer loses its charges and becomes an insulator is called undoping. For a doped conducting polymer with isolated small anions as dopants, undoping is accompanied by the loss of the dopant. Undoping causes the conductive polymer to lose its electrical conductivity and useful optical properties.

1. Introduction Organic polymers are large, chain-like molecules made up of repeating structural units (monomers) that are primarily carbon-based. These polymers are found both in nature and can be synthesized in labs, and they form the basis of many materials we use daily. Here are some main types of organic polymers (Harris, F. W., 1981). 2. Natural Organic Polymers These are polymers found in nature. Examples include: • Proteins: Polymers made up of amino acid monomers, serving as the building blocks for tissues and enzymes in organisms. • Nucleic Acids: DNA and RNA, which are composed of nucleotide monomers, store genetic information in cells. • Polysaccharides: Carbohydrate polymers like cellulose (found in plant cell walls), starch (energy storage in plants), and glycogen (energy storage in animals). • Natural Rubber: Derived from latex in plants, primarily from the rubber tree (Hevea brasiliensis). 3. Synthetic Organic Polymers These are human-made polymers produced through chemical synthesis. Common examples include: • Polyethylene: A plastic used in bags and containers, made from ethylene monomers. • Polystyrene: Used in packaging, insulation, and disposable cutlery, made from styrene monomers. • Polyvinyl Chloride (PVC): A durable polymer used in pipes, cables, and construction, made from vinyl chloride monomers. • Nylon and Polyester: Common synthetic fi bers used in textiles.