Berzelius structures

Dalton s work on relative weights, multiple proportions, and the atomic theory did not have an immediate effect on chemists of his day. Dalton s ideas did provide a framework for determining the empirical formula of compounds, but his table of relative weights was not accurate enough to give consistent results. Many scientists still debated the existence of atoms in the second half of the nineteenth century. Still, little by little, the atomic theory was adopted by chemists as a valid model for the basic structure of matter. While Dalton continued his life as a humble tutor in Manchester, other chemists used Dalton s ideas to establish the atomic theory. Foremost among these was Jons Jacob Berzelius (1779-1848) of Sweden, the foremost chemical authority of the first half of the nineteenth century. 

Daltons atomic concept not only created and illuminated the numerical relations of composition it also created the possibility of molecular structure. Dalton himself defended his use of circular symbols for his atoms against the literal symbols of Berzelius because the circles allowed spatial representation. Berzelius symbols, he wrote. 

Jince the time of Berzelius, chemists have proposed structures for the amorphous, black substance known as humic acid. In the past 150 years, much experimental work has appeared on the nature of humic acid, most of it based on classical chemical and microbiological studies. Very little information about the molecular structure of humic add has resulted from these studies however. Some of the problems plaguing investigators in this field have been (a) variation in the source of humic acid, (b) variation in the definition of humic fractions of soil and coal, (c) lack of crystallinity of the samples, (d) uncertainty of molecular weight measurements, (e) variation in extraction techniques, and (f) variation in elemental composition. The little unambiguous information that exists today is based on extensive degradation of the humic acid polymer and represents only a small fraction of the total molecule. 

A history of ether and etherification is a welcome, and now rare, focus on an individual compound.72 It covers work by Berzelius, Gerhardt, Hennell, Kolbe, Liebig, and of course Williamson. Acetoacetic ester has received detailed historical notice in a biography,73 as have salicylic acid and the salicylates.74 Apart from natural products, few heterocyclic substances have been recently the subject of historical enquiry. An impressive exception is that of pyrrole, a simple molecule explored by Dippel, Reichenbach, Runge and others, and manufactured by Du Pont.75 There is also an account of the structural problems posed by piperidine.76 Accounts have been given of the discovery of aniline from crystallin (a product of the thermal decomposition of indigo),77 of the history of phenol over the last two centuries,78 and of organic nitrates and their uses in medicine.79... 

Regioselectivity in the formation of regioisomers is also observed in electrophilic aromatic substitution reactions. In the case of monosubstituted benzene derivatives, there are three possible regiosomeric products that form at different rates, based on the mechanism of the reaction (see Figure 13). see also Berzelius, Jons Jakob Chirality Dalton, John Davy, Humphry Molecular Structure Scheele, Carl Wohler, Friedrich. 

The term polymer was introduced by Berzelius in 1833. These are materials comprised of huge molecules that have very high molecular weight, and are composed of a large number of repeating units named mers. A proper comprehension of the structure of polymers did not come into view until the second decade of the twentieth century. Previously, these compounds were considered... 

Heteropolyacids similarly form a group of compounds in which it has only just been possible to give the correct stoichiometric composition, after the structural principles had become better known by X-ray analysis. The best-known heteropolyacid is actually phosphomolybdic acid, in fact the test for phosphate ions with ammonium molybdate leads to the formation of the well-known, slightly soluble ammonium phosphomolybdate discovered by Berzelius, gross composition after drying, (NH4)3P04.i2Mo03. 

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