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The reaction mechanism of the Biginelli reaction is a series of bimolecular reactions leading to the desired dihydropyrimidinone. [14]According to a mechanism proposed by Sweet in 1973 the aldol condensation of ethylacetoacetate 1 and the aryl aldehyde is the rate-limiting step leading to the carbenium ion 2.
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Biginelli's first known scientific work, in which he was a co-author of his mentor Icilio Guareschi, was focused on synthesis and reactivity of chlorobromonaphthalene. [10] [11] Already in the University of Florence, Biginelli described a three-component reaction between urea, aldehyde, and ethyl acetoacetate, which was at first incorrectly interpreted as one leading to the formation of alpha ...
The structure of Earth can be defined in two ways: by mechanical properties such as rheology, or chemically. Mechanically, it can be divided into lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core. Chemically, Earth can be divided into the crust, upper mantle, lower mantle, outer core, and inner core. [6]
Under the Manichaean view of the universe, the world is formed by ten layers of heaven and eight layers of the Earth. The separated top section depicts paradise, below it are the sun (right) and moon palaces, which are shown in two circles. Then the ten layers of heaven, where angels and the twelve zodiac signs are included.
Another argument for the impossibility of circular realizations, by Helge Tverberg, uses inversive geometry to transform any three circles so that one of them becomes a line, making it easier to argue that the other two circles do not link with it to form the Borromean rings. [27] However, the Borromean rings can be realized using ellipses. [2]
The Dymaxion map projection, also called the Fuller projection, is a kind of polyhedral map projection of the Earth's surface onto the unfolded net of an icosahedron.The resulting map is heavily interrupted in order to reduce shape and size distortion compared to other world maps, but the interruptions are chosen to lie in the ocean.
such double bonds and circles never join; there are no rings with three double bonds, since they are always represented by circles; moreover, the number of circles in the graph is maximized; when a ring with a circle is adjacent to a ring with two double bonds, an arrow is drawn from the former to the latter ring.