Ring preferential

Hydrogenation of 2-naphthol can proceed at either ring with the general tendency to reduce the unsubstituted ring preferentially. The ratio R of... 

In a study aimed at the identification of products of free radical reactions with polystyrene- and aromatic-based PEMs using model compounds, Hiibner and Roduner observed the addition of free radicals to the aromatic rings, preferentially in the ortho position to alkyl- and RO-substituents (in polystyrene- and aromatic-based PEMs, the para position is blocked by the presence of the sulfonic acid group). This study demonstrated the combined ortho-activation by these substituents and the meta-directing effect... 

Chlorine can be substituted onto an aromatic ring in the presence of a catalyst, such as ferric chloride. FeClj. nr aluminum chloride. AlClj. The simplest case would be chlorination of benzene. Substitution of a second Cl onto the ring preferentially goes to the para position, but the ortho and mela isomers can he formed with (he latter least favored. If the chlorination... 

Reaction of a nitro-substituted aryl halide with a good nucleophile leads to nucleophilic aromatic substitution. Methoxide will displace fluoride from the ring, preferentially at the positions ortho and... 

The so-called anomeric effect, ie. that polar substituents X attached to a carbon a to a heteroatom Y (Y = O, N) in a six-membered ring preferentially reside in the axial position, has been shown to be solvent-dependent [82, 83, 217, 282-286], In general, the position of an anomeric equilibrium shifts in favour of the equatorial anomer with increasing solvent polarity. The anomeric effect is thought to be the result of either molecular orbital interactions, which stabilize the axial conformer, or electrostatic interactions, which destabilize the equatorial conformer [82, 282],... 

Five- and six-membered ring hemiacetals and hemiketals are common configurations of many sugars. Ribose, which forms a part of the structure of RNA, closes to form a five-membered ring preferentially. 

In early work, Sachs383 found that certain naphthalene derivatives, such as naphthylamines and naphthols, are aminated in the aromatic ring, preferentially at the 5-position, when melted with sodamide. This reaction, however, has greater importance for the preparation of amino derivatives of certain N-heterocycles.384 385... 

Following the dipole moments presented, quaternary alkylations on nitrogen take place readily. But unlike pyridine, both quinoline and isoquinoline heterocyclic nitrogen promote the reaction with nucleophiles. What is more, electrophilic substitution takes place much more easily than in pyridine, and the substituents are generally located in carbocyclic ring preferentially in the more activated positions of the benzene ring, with a positional selectivity in the case of quinolines in the order of C8 > C5 > other positions. 

When an alkyl group is attached to a benzene ring, preferential fragmentation occurs at a benzylic position to form a fragment ion of the formula m/e... 

It was not until the period from 1920 to 1930 that the size of the rings was definitively determined by the English carbohydrate research group at Birmingham. This group eventually was led by W. Norman Haworth. These researchers found that the hexoses formed six-membered rings preferentially... 

The action of peracids on substituted 2-(2-pyridyl)benzothiazoles attacks their pyridine ring preferentially subsequent cleavage of the thiazole ring results in 2-(l-oxido-2-picolinamido)benzenesulphonic acids. In contrast, pertrifluoroacetic acid oxygenates the nitrogen of the thiazole ring."... 

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