|
NMR Database Method
The nuclear magnetic resonance database method enables the identification of the stereochemistry of chiral molecules, especially polyols. It relies on the observation that NMR spectroscopy data depend only on the immediate environment near an asymmetric carbon, not on the entire molecular structure. All stereoisomers of a certain class of compounds are synthesized, and their proton NMR and carbon-13 NMR chemical shifts and coupling constants are compared. Yoshito Kishi's group at Harvard University Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyma ... has reported NMR databases for 1,3,5-triols 1,2,3-triols, 1,2,3,4-tetraols, and 1,2,3,4,5-pentaols.S. Higabayashi, W. Czechtizky, Y. Kobayashi, and Y. Kishi. "Universal NMR Databases for Contiguous Polyols." '' J. Am. Chem. Soc.'' 2003, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Chirality (chemistry)
In chemistry, a molecule or ion is called chiral () if it cannot be superposed on its mirror image by any combination of rotation (geometry), rotations, translation (geometry), translations, and some Conformational isomerism, conformational changes. This geometric property is called chirality (). The terms are derived from Ancient Greek (''cheir'') 'hand'; which is the canonical example of an object with this property. A chiral molecule or ion exists in two stereoisomers that are mirror images of each other, called enantiomers; they are often distinguished as either "right-handed" or "left-handed" by their absolute configuration or some other criterion. The two enantiomers have the same chemical properties, except when reacting with other chiral compounds. They also have the same physics, physical properties, except that they often have opposite optical activity, optical activities. A homogeneous mixture of the two enantiomers in equal parts is said to be racemic mixture, racem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Polyol
In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups (). The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, three and four hydroxyl groups are diols, triols, and tetrols, respectively. Classification Polyols may be classified according to their chemistry. Some of these chemistries are polyether, polyester, polycarbonate and also acrylic polyols. Polyether polyols may be further subdivided and classified as polyethylene oxide or polyethylene glycol (PEG), polypropylene glycol (PPG) and Polytetrahydrofuran or PTMEG. These have 2, 3 and 4 carbons respectively per oxygen atom in the repeat unit. Polycaprolactone polyols are also commercially available. There is also an increasing trend to use biobased (and hence renewable) polyols. Uses Polyether polyols have numerous uses. As an example, polyurethane foam is a big user of polyether polyols. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
NMR Spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic field. This re-orientation occurs with absorption of electromagnetic radiation in the radio frequency region from roughly 4 to 900 MHz, which depends on the isotopic nature of the nucleus and increases proportionally to the strength of the external magnetic field. Notably, the resonance frequency of each NMR-active nucleus depends on its chemical environment. As a result, NMR spectra provide information about individual functional groups present in the sample, as well as about connections between nearby nuclei in the same molecule. As the NMR spectra are unique or highly characteristic to individual compounds and functional groups, NMR spectroscopy is one of the most important methods to identify molecular structures, particularly of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Asymmetric Carbon
In stereochemistry, an asymmetric carbon is a carbon atom that is bonded to four different types of atoms or groups of atoms. The four atoms and/or groups attached to the carbon atom can be arranged in space in two different ways that are mirror images of each other, and which lead to so-called ''left-handed'' and ''right-handed'' versions (stereoisomers) of the same molecule. Molecules that cannot be superimposed on their own mirror image are said to be chiral; as the asymmetric carbon is the center of this chirality, it is also known as a chiral carbon. As an example, malic acid () has 4 carbon atoms but just one of them is asymmetric. The asymmetric carbon atom, bolded in the formula, is the one attached to two carbon atoms, an oxygen atom, and a hydrogen atom. One may initially be inclined to think this atom is not asymmetric because it is attached to two carbon atoms, but because those two carbon atoms are not attached to exactly the same things, there are two different '' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Proton NMR
Proton nuclear magnetic resonance (proton NMR, hydrogen-1 NMR, or 1H NMR) is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the structure of its molecules. In samples where natural hydrogen (H) is used, practically all the hydrogen consists of the isotope 1H (hydrogen-1; i.e. having a proton for a nucleus). Simple NMR spectra are recorded in solution, and solvent protons must not be allowed to interfere. Deuterated (deuterium = 2H, often symbolized as D) solvents especially for use in NMR are preferred, e.g. deuterated water, D2O, deuterated acetone, (CD3)2CO, deuterated methanol, CD3OD, deuterated dimethyl sulfoxide, (CD3)2SO, and deuterated chloroform, CDCl3. However, a solvent without hydrogen, such as carbon tetrachloride, CCl4 or carbon disulfide, CS2, may also be used. Historically, deuterated solvents were supplied with a small amount (typically 0.1%) of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Carbon-13 NMR
Carbon-13 (C13) nuclear magnetic resonance (most commonly known as carbon-13 NMR spectroscopy or 13C NMR spectroscopy or sometimes simply referred to as carbon NMR) is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR ( NMR) and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. 13C NMR detects only the isotope. The main carbon isotope, does not produce an NMR signal. Although ca. 1 mln. times less sensitive than 1H NMR spectroscopy, 13C NMR spectroscopy is widely used for characterizing organic and organometallic compounds, primarily because 1H-decoupled 13C-NMR spectra are more simple, have a greater sensitivity to differences in the chemical structure, and, thus, are better suited for identifying molecules in complex mixtures. At the same time, such spectra lack quantitative information about the atomic ratios of different types of carbon nuclei, because n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Chemical Shift
In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of a molecule. Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy. Some atomic nuclei possess a magnetic moment (nuclear spin), which gives rise to different energy levels and resonance frequencies in a magnetic field. The total magnetic field experienced by a nucleus includes local magnetic fields induced by currents of electrons in the molecular orbitals (electrons have a magnetic moment themselves). The electron distribution of the same type of nucleus (e.g. ) usually varies according to the local geometry (binding partners, bond lengths, angles between bonds, and so on), and with it the local magnetic field at each nucleus. This is reflected in the spin energy levels (an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Coupling Constant
In physics, a coupling constant or gauge coupling parameter (or, more simply, a coupling), is a number that determines the strength of the force exerted in an interaction. Originally, the coupling constant related the force acting between two static bodies to the " charges" of the bodies (i.e. the electric charge for electrostatic and the mass for Newtonian gravity) divided by the distance squared, r^2, between the bodies; thus: G in F=G m_1 m_2/r^2 for Newtonian gravity and k_\text in F=k_\textq_1 q_2/r^2 for electrostatic. This description remains valid in modern physics for linear theories with static bodies and massless force carriers. A modern and more general definition uses the Lagrangian \mathcal (or equivalently the Hamiltonian \mathcal) of a system. Usually, \mathcal (or \mathcal) of a system describing an interaction can be separated into a ''kinetic part'' T and an ''interaction part'' V: \mathcal=T-V (or \mathcal=T+V). In field theory, V always contains 3 fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Yoshito Kishi
was a Japanese chemist who was the Morris Loeb Professor of Chemistry at Harvard University. He was known for his contributions to the sciences of organic synthesis and total synthesis. Early life and education Kishi was born in Nagoya, Japan and attended Nagoya University, where he obtained both his BS and PhD degrees. He was a postdoctoral research fellow at Harvard University where he worked with Robert Burns Woodward. From 1966 through 1974, he was a professor of chemistry at Nagoya University. Since 1974, Kishi had been a professor of chemistry at Harvard University. Kishi's research has focused on the total synthesis of complex natural products. The accomplishments of his research group include the total syntheses of palytoxin, mycolactones, halichondrins, saxitoxin, tetrodotoxin, geldanamycin, batrachotoxin and many others. Kishi has also contributed to the development of new chemical reactions including the Nozaki–Hiyama–Kishi reaction. Recognition *1999 Imp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Harvard University
Harvard University is a Private university, private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the History of the Puritans in North America, Puritan clergyman John Harvard (clergyman), John Harvard, it is the oldest institution of higher learning in the United States. Its influence, wealth, and rankings have made it one of the most prestigious universities in the world. Harvard was founded and authorized by the Massachusetts General Court, the governing legislature of Colonial history of the United States, colonial-era Massachusetts Bay Colony. While never formally affiliated with any Religious denomination, denomination, Harvard trained Congregationalism in the United States, Congregational clergy until its curriculum and student body were gradually secularized in the 18th century. By the 19th century, Harvard emerged as the most prominent academic and cultural institution among the Boston B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
Kishi, Y
was a Japanese chemist who was the Morris Loeb Professor of Chemistry at Harvard University. He was known for his contributions to the sciences of organic synthesis and total synthesis. Early life and education Kishi was born in Nagoya, Japan and attended Nagoya University, where he obtained both his BS and PhD degrees. He was a postdoctoral research fellow at Harvard University where he worked with Robert Burns Woodward. From 1966 through 1974, he was a professor of chemistry at Nagoya University. Since 1974, Kishi had been a professor of chemistry at Harvard University. Kishi's research has focused on the total synthesis of complex natural products. The accomplishments of his research group include the total syntheses of palytoxin, mycolactones, halichondrins, saxitoxin, tetrodotoxin, geldanamycin, batrachotoxin and many others. Kishi has also contributed to the development of new chemical reactions including the Nozaki–Hiyama–Kishi reaction. Recognition *1999 Imperi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] [Amazon] |
