Double molecule

Pure anhydrous aluminium chloride is a white solid at room temperature. It is composed of double molecules in which a chlorine atom attached to one aluminium atom donates a pair of electrons to the neighbouring aluminium atom thus giving each aluminium the electronic configuration of a noble gas. By doing so each aluminium takes up an approximately tetrahedral arrangement (p. 41). It is not surprising that electron pair donors are able to split the dimer to form adducts, and ether, for example, forms the adduct. 

In the gold(lll) halides (except the fluoride) there is evidence for the formation of double molecules, AujXg (cf. chlorides of iron(III) and aluminium) so that the coordination is brought up to four, but with a planar structure ... 

Raoult observed that many substances dissolved in benzene, nitrobenzene, and ethylene dibromide, gave depressions only half the normal, and this he explained as due to a polymerisation of the solute to double molecules ... 

If the substance shared between two solvents can exist in different molecular states in them, the simple distribution law is no longer valid. The experiments of Berthelot and Jungfleiscli, and the thermodynamic deduction show, however, that the distribution law holds for each molecular state separately. Thus, if benzoic acid is shared between water and benzene, the partition coefficient is not constant for all concentrations, but diminishes with increasing concentration in the aqueous layer. This is a consequence of the existence of the acid in benzene chiefly as double molecules (C6H5COOH)2, and if the amount of unpolymerised acid is calculated by the law of mass action (see Chapter XIII.) it is found to be in a constant ratio to that in the aqueous layer, independently of the concentration (cf. Nernst, Theoretical Chemistry, 2nd Eng. trans., 486 Die Verteilnngssatz, W. Hertz, Ahrens h annulling, Stuttgart, 1909). 

Measurements in this held have been made by Berthelot and Ogier with nitrogen tetroxide Ann. de Chim. et Phys., [v.], 30, 382 (1883)), and with acetic acid ibid., 400), and some calculations with reference to steam have been made by Nernst Verhandl. Deutsch. Phys. Ges., 15, 313) and Levy ibid., 330), who utilised the vapour-pressure measurements of Holborn and Henning Ann. der Physik, (1906), 21 (1907), 22, 23). Wiedemann had previously observed that the specific heats of ethylbromide, ethyl-acetate, and benzene increase with temperature at about the same rate as that of nitrogen tetroxide at 200°. In the case of steam it was assumed that (i.) the polymerisation is to double molecules... 

Benzidine is an aromatic diamine that can be tetrazotised and coupled to two molecules of a coupler such as acetoacetanilide. This gives a yellow disazo pigment that can be regarded as a double molecule of the monoazo pigments described above. The possibilities of making a... 

It is emphasized that the terms excimer2 and exciplex3,4 are reserved here for homomolecular and heteromolecular excited double molecules formed after the act of light absorption by one component in a process of photoassociation, in the absence of spectroscopic or cryoscopic evidence for molecular association in the ground state. Recent findings indicate that excimer (or exciplex) formation may also result from triplet-triplet annihilation,5,8 cation-anion combination7 (doublet-doublet-annihilation), and electron capture by the (relatively stable) dimer (or complex) cation8 these processes are discussed in Section VII. 

Gropp measured the conductivity of liquid and frozen soln. of lithium, sodium, and potassium chlorides. F. Ratig studied the electro-chemical action—vide alkali chlorates. The electrical conductivity of soln. of lithium chloride in several non-aqueous solvents has been investigated. Formic acid as a solvent exerts an ionizing power of the same order of magnitude as water in acetic acid, the lithium chloride seems to be partially associated to double molecules, > and in some solvent,... 

If a second molecule of NaCl is brought near the first, then the opposite charges in the molecules will attract each other and the two molecules will take up the position shown in Figure 6. Here the attraction of the oppositely-charged ions is greater than the repulsive action of the similarly-charged ions, because, in the double molecule,... 

In Section 41 it was shown that attraction between two dipoles in the vapour state can lead to the formation of double molecules. This phenomenon is called association and is observed with water, acetic acid and other substances containing a polar OH group. 

Fig. 6. Struct are of monobasic fatty acid C14Ha9 COOH, showing arrangement of double molecules linked by hydrogen bonds...

Next come structures in which the hydrogen bonds are forming long chains throughout the structure, producing the equivalent not of double molecules but of polymer molecules. The two cases can be... 

Intermolecular forces are repulsive at close range (R < Kmm) and attractive at distant range (R > Rmj Rm n is the position of the minimum of the pair interaction potential). At high enough densities most of the common gases form dimers, also called double molecules or (binary) van der Waals molecules. Higher than binary complexes are expected, too, especially at high densities and temperatures comparable to, or lower than the well... 

Cryoscopic measurements on the acid in benzene, etc., indicate a mixture of single and double molecules. Single molecules of thiocyanie acid may be represented by the formula NsC — SH or S C=NH. Probably the inorganic salts and the esters derived from them have the constitution represented by the first formula. The esters are converted into sulphonic acids and hydrocyanic acid by oxidation,... 

It is probably the presence of unpaired electron spins in the normal oxygen molecules that gives rise to an. interaction between them, somewhat stronger and more definitely directed than ordinary van der Waals forces, that leads to the formation of O (or (O ) ) molecules. These double molecules were discovered by Lewis,44 by the analysis of... 

Benzoic acid and other carboxylic acids have been shown to be associated with double molecules in solution in certain solvents, such as benzene, chloroform, carbon tetrachloride, and carbon disulfide.88 The value 4.2 kcal/mole for the hydrogen-bond energy has been found in this way for benzoic acid and o-toluic acid, and 4.7 kcal/mole for ftZr-toluic acid. 

Salicylic acid forms double molecules in solvents such as benzene and carbon tetrachloride. It has, moreover, been shown by the spectroscopic method (Sec. 12-8) that the double molecule contains no OH groups which are not involved in hydrogen-bond formation. This results from the assumption by the molecule of the following structure ... 

An absorption peak at 6620 cm l has been observed for liquid o-chlorophenol by Errera and Mollet.109 The further decrease in frequency below the value 6910 cm 1 for the trans form of the molecule can be explained by assuming that the liquid contains double molecules with the structure... 

Both normal and mixed carbonates are known. The former is precipitated, as Y2(C03)3 3H O from Y31 solutions by alkali metal carbonates, which in excess dissolve the precipitate to form a soluble hydrated double carbonate. The oxy carbonate is also a double molecule, 3Y2(C(>3)3 2Y(OH>3, formed by action of CCU, upon the hydroxide. 

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