Visionneuse

Date_TXT

Germany : Springer, 2020

Auteur

Jean Demaison, Natalja Vogt

Sujet

Molecules ; Molecular Hamiltonian ; Molecular Mechanics

Type de document

Livre

Description :

The introduction is first a summary of the history of the field of molecular structure determination. Then, the goal of the book is explained and an abstract of the different chapters is given.
The structure of a molecule (molecular geometry, electron density distribution, flex- ibility) contains the features responsible for its physical and chemical properties. In other words, molecular geometry is required to explain molecular behavior. This is particularly important in biochemistry. There is indeed considerable evidence that odors, enzymatic activity, etc., are all subject to stereochemical control.
Molecule (from new latin molecula = small mass) is the smallest unit, consisting
of groups of atoms, into which a substance can be divided without a change in its chemical structure (Oxford dictionary).
Although the concept of molecular structure was developed during the nineteenth century, Franklin (1774) devised an experiment permitting to determine the size of the oleic acid molecule using what would be later called a Langmuir monolayer, i.e., a one-molecule thick layer of oil spread onto a surface of water.
In 1808, John Dalton’s experiments showed that matter consisted of elemen- tary particles, or atoms. These atoms combine in fixed relative proportions to form molecules (Proust 1806). The first attempt to explain the structure of the molecules is the electrostatic theory of Davy (1812) around 1806 and later Berzelius (1814). Group of atoms are bound together by electrostatic attraction. In 1834, Dumas (1837) has shown that this theory is not applicable to organic molecules. But it was Avogadro (1811), who made the distinction between molecule and atom.
In 1858, Couper (1858) and, then, Kekulé (1865) were the first to state that carbon is tetravalent and to form a concrete idea of molecular structure. However, Butlerov (1861) was the first to use the term “chemical structure” and he restated, clarified, and enlarged upon the ideas of Couper and Kekulé. von Bayer (1885) published his theory of ring strain whose main conclusion is that bond angles may deviate from the tetrahedral value of 109° 28r. In 1874, the concept of tetrahedral carbon was simultaneously introduced by Le Bel (1874) and Van’t Hoff (1874). In 1873, van der Waals (1873) proposed his famous equation describing the behavior of real
gas and first published in his dissertation. It was used to determine the radius of molecules (van der Waals radius for atoms). However, the existence of molecules was contested by reputed scientists such as Ernst Mach and Marcellin Berthelot until the experimental work of Perrin (1913) on the Brownian motion.