| These designs are inspired by six molecules associated in some way with this department. Four have historical significance, and two originate from recent research. The theme is not just of the molecule itself but of the behaviour of the electrons associated with them. It is these electrons that define the shapes of molecules and their properties such as colour, aromaticity and reactivity. This latter is illustrated by the characteristic reaction of a steroid, a species very much associated with Sir Derek Barton and the principles of conformational analysis. The aromatic organometallic molecule ferrocene is associated with another departmental Nobel laureate, Sir Geoffrey Wilkinson. Two examples of more recent vintage illustrate the properties of ionic liquids and how the concept of aromaticity can be combined with that of chirality and topology. The artwork is created by fusing these chemical themes with quantum mechanical theories of the behavour of electrons as inspired by mathematics and physics. | ||
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This is the chloride salt of the dyestuff mauveine-A discovered by William Perkin in 1856 and now recognised as a member of the phenazinium class of aromatic molecules. In 1853 Perkin had become a student in the Royal college of chemistry, the predecessor to the current department. He went on to found the first fine organic chemicals company in the world with R&D as its innovative core. The artwork depicts the "highest occupied molecular orbital" (the HOMO). Its partner in colour is the "lowest unoccupied molecular orbital" (the LUMO). The excitation of an electron from the first to the second energy level is what gives this compound its remarkably intense purple hue. | |
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Monastral blue is a copper phthalocyanine and the highest volume pigment ever produced (you may have some in the clothes you are wearing now). It was discovered in the 1930s by ICI, but its structure and remarkable chemical properties were established by Sir Patrick Linsted in the chemistry department here. This fruitful collaboration between industry and our department was very much the forerunner of the modern research model. The artwork depicts the most stable π molecular orbital, which is the orbtal associated with the aromaticity of the ligand surrounding the central metal and which is now recognised as comprising a flat, 18π-electron system. | |
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This is a 2,3 substituted molecule related to cholestanol, one of the family of steroids. Sir Derek Barton in the 1940s and 1950s used such molecules and their reactions to demonstrate the principles of conformational analysis. The natural bond orbitals shown here illustrate how antiperiplanar alignment of the two substituents naturally leads to the otherwise mysterious reaction resulting in the formation of a species known as an epoxide. Such understanding was crucial to the development of synthetic routes to the first contraceptive drugs and to rational methods for inventing new reactions. | |
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Ferrocene is another class of organometallic compound. In 1952 Sir Geoffrey Wilkinson and Robert Woodward proposed a structure for it combining the concept of aromatic ligands with (a different) 18-electron rule for valence shells in transition metals. This heralded in a new era of understanding how transition metals bond, insights which led inter alia, to the development of new classes of highly effective catalysts. The artwork illustrates the most stable ferrocene molecular orbital, of the nine associated with those seminal 18 electrons. | |
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Whereas Monstral above is a member of the tetraphyrin family (haemoglobin and chlorophyl are examples of molecules containing similar rings), one can expand the motif to an octaphyrin, as here. This molecule has the shape of a lemniscate (the name for the ∞ sign or figure eight), and was discovered in the department to exhibit the topology of a doubly-twisted Möbius band for the π-electrons with the unusual property of writhe (shared with e.g. a cyclic DNA double-helix). Such molecules exhibit molecular chirality as members of the class of twisted (and writhing) and very unflat aromatic rings. The artwork shows the most stable π-molecular orbital, which takes the topological form of a torus link. | |
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| Ionic Liquids are a class of solvent/reaction media composed entirely of ions and unlike molten salts they are normally liquid below 100°C. They exhibit a number of highly desirable physical properties, including vanishing vapour pressure, a large liquid range and favourable solvation behavior. Imperial college has been at the forefront of research exploring the properties of these systems. The artwork depicts the molecular orbital interaction of benzene (π-HOMO) with the LUMO of a 1,3-dimethyl imidazolium chloride ion-pair of a typical ionic liquid. This π-π* interaction is stabilized by the presence of the chloride anion, playing an important role in the preferential solvation of aromatic molecules over n-alkanes and aiding separation processes. | | |
April, 2013.