Browsing by Author "Perera K. Sarath D"

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    11B NMR Spectroscopy
    (Institute of Chemistry Ceylon, 2023-09) Perera K. Sarath D
    Boron hydrides are known as electron deficient compounds. There are two NMR active isotopes (e.g., 10B and 11B). Boron-11 NMR spectroscopy is widely used to find out molecular structures and exchange processes of boron hydrides.
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    Agostic interaction and metallacycles
    (Institute of Chemistry Ceylon, 2023-06) Perera K. Sarath D
    An interaction that occurs between an unsaturated metal center and a C-H bond of a group attached to that metal center is called an agostic interaction. These interactions are denoted by a half-headed arrow ( ) as given in following examples.
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    Bonding in Organometallic Complexes
    (Institute of Chemistry, 2024-05) Perera K. Sarath D
    Neutral ligands (:L) and monoanionic ligands (X–) donate a pair of electrons or a lone-pair to a vacant orbital in a transition metal centre (M) to form a covalent σ-bond between them. Ligands such as :C≡O, :C≡NR (isonitrile or isocyanide) and :PR3 (tertiary phosphine or phosphite) can donate a pair of electrons to a metal centre to form a σ-bond. These ligands are considered as σ-donors.
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    Diels-Alder Reaction
    (Institute of Chemistry Ceylon, 2023-06) Perera K. Sarath D
    Diels-Alder (D-A) reaction is a (4π+2π) cycloaddition reaction. It is used to generate six-membered rings by combining two π-systems. The key components of this reaction are a conjugated diene (an alkene with two π-bonds) and a dienophile (simple alkene or alkyne). During this concerted reaction, two new sigma bonds are formed and change of two π-bonds into sigma bonds takes place.
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    Dihydrogen Complexes
    (Institute of Chemistry Ceylon, 2024-05) Perera K. Sarath D
    Neutral ligands such as H2 O, NMe3 and PPh3 donate a pair of electrons on the heteroatom to a metal center when coordinate bond is formed. Transition metal hydrides contain at least one M-H bond where a pair of electrons is shared between hydrogen and the metal center. In this article, syntheses and properties of complexes with molecular hydrogen (H2 ) are presented.
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    Elements in Biology
    (Institute of Chemistry Ceylon, 2023-09) Perera K. Sarath D
    Research findings suggest that eleven elements are predominantly present in all biological systems. However, hydrogen, carbon, oxygen and nitrogen correspond to 99% of the total. Hydrogen constitutes 62.8% of the atoms in a human body. The percentage of oxygen, carbon and nitrogen are 25.4, 9.4 and 1.4%, respectively. Other essential elements make up the remaining 1% {sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), sulphur (S) and chlorine (Cl)}. Very large percentages of hydrogen and oxygen arise from the high-water content present in living systems. Regarding our health and well-being, it is important to know about the elements found in biological systems, their functions and the level of toxicity.
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    Introduction to Organometallic Chemistry
    (Institute of Chemistry Ceylon, 2023-09) Perera K. Sarath D
    Organometallic chemistry is a branch of coordination chemistry and deals with compounds which have at least one metal-carbon bond. Since metals are more electropositive than carbon it is considered that the metal-carbon bond is slightly polarised; localizing a small negative charge on carbon and a small positive charge on the metal (i.e., Mδ+–Cδ–). Organic ligands which are coordinated to transition metals can be classified according to (i) hapticity of the ligand and (ii) the number of metal atoms directly bonded to a ligand (i.e., bridging ligands).
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    Introduction to Photochemistry
    (Institute of Chemistry Ceylon, 2024-05) Perera K. Sarath D
    Photochemistry studies light induced chemical reactions and physical processes. Electronically excited molecules are formed by the absorption of suitable radiation in the visible and near ultraviolet region. Naturally occurring phenomena of photochemistry are photosynthesis, phototaxis, photoperiodism, vision and mutagenic effects of light Photochemistry is divided into two processes: - (i) Photophysical process and (ii) Photochemical process.
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    Nucleophilic Attack on Coordinated Ligands
    (Institute of Chemistry Ceylon, 2024-05) Perera K. Sarath D
    Reactions of nucleophiles with transition metal complexes are useful in the preparation of new metal complexes. Unsaturated ligands such as C≡O, isonitriles, olefins, dienes, and arenes are not normally reactive towards nucleophiles. When these ligands or molecules are coordinated to an electron-deficient metal they become activated towards nucleophilic attack. The factors which facilitate nucleophilic attack on a coordinated ligands are (i) formal positive charge on the metal, (ii) coordination of π acceptor ligands, (iii) the metal should be coordinatively saturated. and (iv) high reactivity of the nucleophile
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    Styx Numbers and Rules of Boron Hydrides
    (Institute of Chemistry Ceylon, 2023-06) Perera K. Sarath D
    Boron hydrides are a class of electron deficient compounds that have unusual bonding behavior and form cages and clusters. The electron deficient BH3 is the simplest boron hydride which exists as a dimer B2 H6 (diborane). The structure of B2 H6 contains bridging B-H-B (or BHB) bonds; quite different to those of carbon hydrides.