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Alders are trees that compose the genus Alnus in the birch family Betulaceae. The genus includes about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few species extending into Central America, as well as the northern and southern Andes.
In organic chemistry, the Diels–Alder reaction is a chemical reaction between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene derivative. It is the prototypical example of a pericyclic reaction with a concerted mechanism. More specifically, it is classified as a thermally allowed [4+2] cycloaddition with Woodward–Hoffmann symbol [π4s + π2s]. It was first described by Otto Diels and Kurt Alder in 1928. For the discovery of this reaction, they were awarded the Nobel Prize in Chemistry in 1950. Through the simultaneous construction of two new carbon–carbon bonds, the Diels–Alder reaction provides a reliable way to form six-membered rings with good control over the regio- and stereochemical outcomes. Consequently, it has served as a powerful and widely applied tool for the introduction of chemical complexity in the synthesis of natural products and new materials. The underlying concept has also been applied to π-systems involving heteroatoms, such as carbonyls and imines, which furnish the corresponding heterocycles; this variant is known as the hetero-Diels–Alder reaction. The reaction has also been generalized to other ring sizes, although none of these generalizations have matched the formation of six-membered rings in terms of scope or versatility. Because of the negative values of ΔH° and ΔS° for a typical Diels–Alder reaction, the microscopic reverse of a Diels–Alder reaction becomes favorable at high temperatures, although this is of synthetic importance for only a limited range of Diels–Alder adducts, generally with some special structural features; this reverse reaction is known as the retro-Diels–Alder reaction.
Kurt Alder was a German chemist and Nobel laureate.
Alnus incana, the grey alder, tag alder or speckled alder, is a species of multi-stemmed, shrubby tree in the birch family, with a wide range across the cooler parts of the Northern Hemisphere. Tolerant of wetter soils, it can slowly spread with runners and is a common sight in swamps and wetlands.
In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity". The resulting reaction is a cyclization reaction. Many but not all cycloadditions are concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic. As a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile.
The Aza-Diels–Alder reaction is a modification of the Diels–Alder reaction wherein a nitrogen replaces sp2 carbon. The nitrogen atom can be part of the diene or the dienophile.
Roman Zarubin is a Russian sprint canoeist who has competed since the late 1990s. He won seven medals at the ICF Canoe Sprint World Championships with a gold, three silvers, and three bronzes.
Ognjen Filipović is a Serbian sprint canoer who competed for Serbia and Montenegro and later Serbia. He won six medals at the ICF Canoe Sprint World Championships with two golds, a silver K-4 200 m: 2007 for Serbia), and three bronzes.
Sergey Kalesnik is a Soviet-born Belarusian sprint canoeist who competed from the late 1980s to the late 1990s. He won six medals at the ICF Canoe Sprint World Championships with three golds and three silvers.
Arnaud Hybois is a French sprint canoeist who has competed since the late 2000s. He has won six medals at the ICF Canoe Sprint World Championships with three golds, a silver and two bronze.
Donald "Don" Cooper is a New Zealand canoe sprinter who competed in the early to mid-1970s. At the 1972 Summer Olympics in Munich, he was eliminated in the semifinals of the K-1 1000 m and the repechages of the K-2 1000 m event. Four years later in Montreal, Cooper was eliminated in the semifinals of the K-1 1000 m event.
Roderick Fitzgerald Gavin is a New Zealand sprint canoeist who competed in the late 1970s. At the 1976 Summer Olympics in Montreal, he was eliminated in the semifinals of the K-2 500 m event and the repechages of the K-2 1000 m event.
John Leonard is a New Zealand sprint canoeist who competed in the late 1970s. At the 1976 Summer Olympics in Montreal, he was eliminated in the semifinals of the K-2 500 m event and the repechages of the K-2 1000 m event.
Declan Burns is an Irish canoe sprinter who competed from the mid-1970s to the late 1980s. At the 1976 Summer Olympics in Montreal, he was eliminated in the repechages of both the K-2 500 m and the K-4 1000 m events. Four years later in Moscow, Burns was eliminated in the repechages of the K-1 500 m event. At his third and final Summer Olympics in Seoul, he was eliminated in the semifinals of the K-2 1000 m event.
John MacDonald is a New Zealand sprint canoeist who competed in the late 1980s and early 1990s. He was eliminated in the semifinals of the K-4 1000 m event at the 1988 Summer Olympics in Seoul. Four years later in Barcelona, he was eliminated in the semifinals of both the K-1 500 m and K-1 1000 m events.
Stephen Richards is a New Zealand sprint canoeist who competed in the late 1980s and early 1990s. He was eliminated in the semifinals of the K-4 1000 m event at the 1988 Summer Olympics in Seoul. Four years later in Barcelona, he was eliminated in the semifinals of the same event.
Dmitry Torlopov is a Kazakhstani sprint canoeist who has competed since the mid-1990s. At the 1996 Summer Olympics in Atlanta, he was eliminated in the repechages of the K-2 500 m event and the semifinals of the K-4 1000 m events. Twelve years later in Beijing, Torpolov was eliminated in the semifinals of both the K-1 500 m and the K-1 1000 m event.
The retro-Diels–Alder reaction is the reverse of the Diels–Alder (DA) reaction, a [4+2] cycloelimination. It involves the formation of a diene and dienophile from a cyclohexene. It can be accomplished spontaneously with heat, or with acid or base mediation.
In organic chemistry, the hexadehydro-Diels–Alder (HDDA) reaction is an organic chemical reaction between a diyne and an alkyne to form a reactive benzyne species, via a [4+2] cycloaddition reaction. This benzyne intermediate then reacts with a suitable trapping agent to form a substituted aromatic product. This reaction is a derivative of the established Diels–Alder reaction and proceeds via a similar [4+2] cycloaddition mechanism. The HDDA reaction is particularly effective for forming heavily functionalized aromatic systems and multiple ring systems in one synthetic step.
The United States Bridge Championships (USBC) is a yearly competition held to select either one or two teams that will represent the United States at international competition for the game of contract bridge. The general conditions of contest used by the United States Bridge Federation can be found here. There are multiple events in the USBC including Open, Women, Seniors, and Mixed divisions. This article contains information about the Open division in which anyone of any age or gender can compete.
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