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Heptazine
Heptazine, or tri-''s''-triazine or cyamelurine, is a chemical compound with formula , that consist of a planar triangular core group or three fused triazine rings, with three hydrogen atoms at the corners. It is a yellow, weakly fluorescent solid with melting point over 300 °C. It is soluble in organic solvents such as acetonitrile, but is decomposed by water in the presence of light. The name "heptazine" is also used for derivative compounds, which have the three hydrogens substituted by other functional groups. Heptazine oligomers and polymers were discovered in the 19th century but their study has long been hampered by their general insolubility. They are used as flame retardants. Heptazine derivatives have been the object of interest recently for potential applications in electronics materials, explosives, and more. The synthesis of heptazine proper was reported only in 1982. History Berzelius discovered in 1815 that the ignition of mercuric thiocyanate yielded, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Melon (chemistry)
In chemistry, melon is a compound of carbon, nitrogen, and hydrogen of still somewhat uncertain composition, consisting mostly of heptazine units linked and closed by amine groups and bridges (, , , etc.). It is a pale yellow solid, insoluble in most solvents. A careful 2001 study indicates the formula , that consists of ten imino-heptazine units connected into a linear chain by amino bridges; that is, . However, other researchers are still proposing different structures. Melon is the oldest known compound with the heptazine core, having been described in the early 19th century. It has been little studied until recently, when it has been recognized as a notable photocatalyst and as a possible precursor to carbon nitride. History In 1834 Liebig described the compounds that he named melamine, melam, and melon. The compound received little attention for a long time, due to its insolubility. In 1937 Linus Pauling showed by x-ray crystallography that the structure of melon and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyameluric Acid
Cyameluric acid or 2,5,8-trihydroxy-''s''-heptazine is a chemical compound with formula , usually described as a heptazine molecule with the hydrogen atoms replaced by hydroxyl groups ; or any of its tautomers. The substance exists as an equilibrium of 17 tautomers that easily interconvert among each other. Calculations show that the symmetric tri-oxo form (1,4,7-trihydro-2,5,8-trioxo-''s''-heptazine) is the most stable. Therefore, this compound contains amide groups rather than imidic acids. History In 1834 Justus von Liebig described the compounds that he named melamine, melam, and melon. In 1835 Leopold Gmelin prepared novel salts by heating potassium ferrocyanide with sulfur); recognizing their connection to the compounds described by Liebig, he named the salts " hydromelonates" and the corresponding acid " hydromelonic". In the following years Liebig prepared the same salts by other methods, such as by fusing potassium thiocyanate with antimony trichloride, and eventually dete ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydromelonic Acid
Hydromelonic acid, is an elusive chemical compound with formula or , whose molecule would consist of a heptazine molecule, with three cyanamido groups or substituted for the hydrogen atoms. The compound had not been properly isolated as of 2010, due to its tendency to polymerize. However, removal of three protons yields the melonate (formerly hydromelonate) anion , whose salts are stable and have been known since the 19th century. Removal of only two protons yields the divalent hydrogenmelonate anion . History In 1834 Justus von Liebig described the compounds that he named melamine, melam, and melon. In 1835 Leopold Gmelin prepared a potassium salt (later identified as ) by heating potassium ferrocyanide with sulfur); recognizing their connection to the compounds described by Liebig, he named the salt "hydromelonate" and the corresponding acid "hydromelonic". In the following years Liebig prepared the same salt by other methods, such as by fusing potassium thiocyanate with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction, which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds; ionic compounds are held together by ionic bonds; intermetallic compounds are held together by metallic bonds; coordination complexes are held together by coordinate covalent bonds. Non-stoichiometric compounds form a disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, using the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triplet State
In quantum mechanics, a triplet is a quantum state of a system with a spin of quantum number =1, such that there are three allowed values of the spin component, = −1, 0, and +1. Spin, in the context of quantum mechanics, is not a mechanical rotation but a more abstract concept that characterizes a particle's intrinsic angular momentum. It is particularly important for systems at atomic length scales, such as individual atoms, protons, or electrons. Almost all molecules encountered in daily life exist in a singlet state, but molecular oxygen is an exception. At room temperature, O2 exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state. This makes it kinetically nonreactive despite being thermodynamically one of the strongest oxidants. Photochemical or thermal activation can bring it into the singlet state, which makes it kinetically as well as thermodynamically a very strong oxidant. __TOC__ Two spin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystal Structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns that repeat along the principal directions of Three-dimensional space (mathematics), three-dimensional space in matter. The smallest group of particles in the material that constitutes this repeating pattern is the unit cell of the structure. The unit cell completely reflects the symmetry and structure of the entire crystal, which is built up by repetitive Translation (geometry), translation of the unit cell along its principal axes. The translation vectors define the nodes of the Bravais lattice. The lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called ''lattice parameters'' or ''cell parameters''. The symmetry properties of the crystal are described by the con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resonance (chemistry)
In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or ''canonical structures'') into a resonance hybrid (or ''hybrid structure'') in valence bond theory. It has particular value for analyzing delocalized electrons where the bonding cannot be expressed by one single Lewis structure. Overview Under the framework of valence bond theory, resonance is an extension of the idea that the bonding in a chemical species can be described by a Lewis structure. For many chemical species, a single Lewis structure, consisting of atoms obeying the octet rule, possibly bearing formal charges, and connected by bonds of positive integer order, is sufficient for describing the chemical bonding and rationalizing experimentally determined molecular properties like bond lengths, angles, and dipole moment. Howev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nelson J
Nelson may refer to: Arts and entertainment * ''Nelson'' (1918 film), a historical film directed by Maurice Elvey * ''Nelson'' (1926 film), a historical film directed by Walter Summers * ''Nelson'' (opera), an opera by Lennox Berkeley to a libretto by Alan Pryce-Jones * Nelson (band), an American rock band * ''Nelson'', a 2010 album by Paolo Conte People * Nelson (surname), including a list of people with the name * Nelson (given name), including a list of people with the name * Horatio Nelson, 1st Viscount Nelson (1758–1805), British admiral * Nelson Mandela, the first black South African president Fictional characters * Alice Nelson, the housekeeper on the TV series ''The Brady Bunch'' * Dave Nelson, a main character on the TV series ''NewsRadio'' * Emma Nelson, on the TV series ''Degrassi: The Next Generation'' * Foggy Nelson, law partner of Matt Murdock in the Marvel Comic Universe * Greg Nelson, on the American soap opera ''All My Children'' * Harriman Nelson, on the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ramachandra S
Rama (; ), Ram, Raman or Ramar, also known as Ramachandra (; , ), is a major deity in Hinduism. He is the seventh and one of the most popular ''avatars'' of Vishnu. In Rama-centric traditions of Hinduism, he is considered the Supreme Being. Rama is said to have been born to Kaushalya and Dasharatha in Ayodhya, the ruler of the Kingdom of Kosala. His siblings included Lakshmana, Bharata (Ramayana), Bharata, and Shatrughna. He married Sita. Though born in a royal family, their life is described in the Hindu texts as one challenged by unexpected changes such as an exile into impoverished and difficult circumstances, ethical questions and moral dilemmas. Of all their travails, the most notable is the kidnapping of Sita by demon-king Ravana, followed by the determined and epic efforts of Rama and Lakshmana to gain her freedom and destroy the evil Ravana against great odds. The entire life story of Rama, Sita and their companions allegorically discusses duties, rights and social ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray Crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their crystallographic disorder, and various other information. Since many materials can form crystals—such as salts, metals, minerals, semiconductors, as well as various inorganic, organic, and biological molecules—X-ray crystallography has been fundamental in the development of many scientific fields. In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences among various mat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linus Pauling
Linus Carl Pauling (; February 28, 1901August 19, 1994) was an American chemist, biochemist, chemical engineer, peace activist, author, and educator. He published more than 1,200 papers and books, of which about 850 dealt with scientific topics. ''New Scientist'' called him one of the 20 greatest scientists of all time, and as of 2000, he was rated the 16th most important scientist in history. For his scientific work, Pauling was awarded the Nobel Prize in Chemistry in 1954. For his peace activism, he was awarded the Nobel Peace Prize in 1962. He is one of five people to have won more than one Nobel Prize (the others being Marie Curie, John Bardeen, Frederick Sanger and Karl Barry Sharpless). Of these, he is the only person to have been awarded two unshared Nobel Prizes, and one of two people to be awarded Nobel Prizes in different fields, the other being Marie Curie. Pauling was one of the founders of the fields of quantum chemistry and molecular biology. His contributions t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
