Molecules ortho

Troscompt N, Faure A, Wiesenfeld L, Ceccarelll C, Valirrai P (2009) Rotatiraial excitation of formaldehyde by hydrogen molecules ortho-H2CO at low tranpraature. Astron Astrophys... 

In such tables, typical chemical shifts are assigned to standard structure fragments (e.g., protons in a benzene ring). Substituents in these blocks (e.g., substituents in ortho, meta, or para positions) are assumed to make independent additive contributions to the chemical shift. These additive contributions are listed in a second series of tables. Once the tables are defined, the method is easy to implement, does not require databases, and is extremely fast. Predictions for a molecule with 50 atoms can be made in less than a second. On the other hand, it requires that the parent structure and the substituents are tabulated, and it considers no interaction... 

It is also to he noted that ortho and para substitution often occur together in the same molecule, so that the group R enters the para and also both the ortho positions thus both aniline and phenol on bromination readily give symmetric (2,4,6) tribromo-compounds (p. 165), while both toluene and phenol on nitration readily give the symmetric trinitro-derivatives (p. 170). 

Quite apart from isotopes, it has been shown that under ordinary conditions hydrogen gas is a mixture of two kinds of molecules, known as ortho- and para-hydrogen, which differ from one another by the spins of their electrons and nuclei. 

Excluding the phenomenon of hyperconjugation, the only other means by which electronic effects can be transmitted within saturated molecules, or exerted by inductive substituents in aromatic molecules, is by direct electrostatic interaction, the direct field effect. In early discussions of substitution this was usually neglected for qualitative purposes since it would operate in the same direction (though it would be expected to diminish in the order ortho > meta > para) as the cr-inductive effect and assessment of the relative importance of each is difficult however, the field effect was recognised as having quantitative significance. ... 

Figure 5.18 Nuclear spin statistical weights (ns stat wts) of rotational states of various diatomic molecules a, antisymmetric s, symmetric o, ortho p, para and rotational, nuclear spin...

All other homonuclear diatomic molecules with / = for each nucleus, such as F2, also have ortho and para forms with odd and even J and nuclear spin statistical weights of 3 and 1, respectively, as shown in Figure 5.18. 

Phtha/k anhydride is the most important type of dibasic acid derivative ki alkyd preparation because of its low cost and the excellent overall properties it imparts to the reski. The anhydride stmcture allows a fast esterification to form half-esters at relatively low reaction temperatures without hberatkig water, thereby avoiding the danger of excessive foaming ki the reactor. However, skice the two carboxyl groups of phthaUc anhydride are ki the ortho position to each other on the benzene ring, cycHc stmctures may and do occur ki the reski molecules. 

This addition is general, extending to nitrogen, oxygen, carbon, and sulfur nucleophiles. This reactivity of the quinone methide (23) is appHed in the synthesis of a variety of stabili2ers for plastics. The presence of two tert-huty groups ortho to the hydroxyl group, is the stmctural feature responsible for the antioxidant activity that these molecules exhibit (see Antioxidants). 

A hydroxyl group is situated ortho to a carboxyl group which as a bidentate ligand is terminally metallized on the fiber when aftertreated with dichromate. An example is Alizarine Yellow GG [584-42-9] (50) (Cl Mordant Yellow 1 Cl 14025). Cr(III) has a coordination number of six, and therefore normally two dye molecules of the sahcyhc type are chelated to the metal ion. 

Aromatic compounds may be chlorinated with chlorine in the presence of a catalyst such as iron, ferric chloride, or other Lewis acids. The halogenation reaction involves electrophilic displacement of the aromatic hydrogen by halogen. Introduction of a second chlorine atom into the monochloro aromatic stmcture leads to ortho and para substitution. The presence of a Lewis acid favors polarization of the chlorine molecule, thereby increasing its electrophilic character. Because the polarization does not lead to complete ionization, the reaction should be represented as shown in equation 26. 

D C Red No. 36 (27) is an unsulfonated pigment. It contains no groups capable of salt formation and is thus insoluble direcdy on coupling. Its chlorine group ortho to the azo group results in a stericaHy hindered molecule with low solubiUty and excellent light stabiUty. The unsulfonated dyes Citms Red No. 2 (8) and D C Red No. 17 (20) are insoluble in water but soluble in aromatic solvents. 

Insoluble sulfonated pigments are made from colorants that contain a sulfonic acid group that is easily converted into an insoluble metal salt. In most cases, the sulfonic acid group is ortho to the diazo further reducing the solubilizing characteristics of the sulfonic grouping. The shade of these products is affected by the metal incorporated into the molecule and the physical characteristics of the colorants. D C Red Nos. 7 (19b) and 34 (26) are insoluble sulfonated pigments. 

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