Halogen substituent

Entry Substituents Halogenation reagent Position Yield (%) Ref. 

Halogen Substituents. Halogen functional groups are readily replaced by nucleophiles, eg, hydroxide ion, especially when they ate attached at the a- or y-position of the pyridine ting. This reaction has been exploited in the synthesis of the insecticide chlorpyrifos [2921-88-2J (43) (42), and the insecticide tiiclopyi [55335-06-3] (44) (14,43). 2,3,5,6-Tetiachloiopyiidine [2402-79-1] reacts with caustic to form the hydioxylated material [6515-38-4], which then can be used to form (44) and (43). 

Reductive ring closure with thionyl chloride led to the introduction of a chloro group in the 5-position. When the 5-position was blocked by a substituent, halogen attack occurred in the 7-position. The mechanism is shown in Scheme 177 (67AHC(8)277>. 

The important role of LU MO in the nucleophilic reactions of saturated hydrocarbons bearing nucleophilic substituents (halogens, alkoxy-, acyloxy-, RSO2O-, etc.) in the molecule has been pointed out 122,123). 

Hine has shown that the relative ability of substituent halogens to enhance trihalo anion formation is... 

The anomeric effect is rather complex and will not be considered in any detail. It occurs when we have a heterocyclic ring (O, N, or S), with an electronegative substituent (halogen, OH, OR, OCOR, etc.) adjacent to the heteroatom, and favours the isomer in which the substituent is axial. Thus, with the first of the... 

With this section, the classification in the Handbook of Heterocyclic Chemistry has been followed thus a general survey of the effect of rings on the reactions of substituents is followed by a survey of the effect of rings on reactions of individual substituents in the order fused benzene rings, C-linked, AMinked, <9-linked, S-linked substituents, halogens, and metals. Substituents attached to cyclic nitrogen and sulfur are dealt with as described below. 

For substituents with —I, +M effects, the orienting effect of such substituents (halogens, alkoxy, thioalkoxy, amino, alkylamino, etc.) is similar to that of alkyl groups. If the substituent is in position 2, further substitution occurs at position 5 if it is in position 3, substitution occurs preferentially at 2, unless the steric requirement forces the incoming substituent to position 5. 

Haloalkanes can be named just like alkanes, with the halogen atom treated as a substituent. Halogen substituents are named fluoro-, chloro-, bromo-, and iodo-. 

Rule 4 in aliphatic substituents, halogen atoms show an inductive effect, decreasing with increasing distance of the halogen from the tri-oxolane ring (Table XI). 

Coupling with phenols is usually effected more easily than coupling with amines, and naphthols couple considerably more readily than hydroxybenzene derivatives. Reactive methylene compounds behave similarly to phenols of the benzene series. Negative substituents (halogen, nitro, sulfo, carboxyl, carbonyl, etc.) accelerate coupling when... 

The remaining chapters are carbodiimides with unsaturated substituents, halogenated carbodiimides, acyl-, thioacyl- and imidoylcarbodiimides, silicon substituted carbodiimides, nitrogen substituted carbodiimides, phosphorous substituted carbodiimides, sulfur substituted carbodiimides, metal substituted carbodiimides, cyclic carbodiimides, polymeric carbodiimides and application of carbodiimides. 

In general, 2- or 3-substituted benzoic acids are monoarylated due to steric interference of the substituent. Halogens other than fluorine are not compatible with the reaction conditions in contrast with the Arl/AgOAc method. 

Other Nitrogen-linked Substituents Halogen Atoms... 

The primary step in reaction of an alcohol with HX is formation of an oxonium complex ROH2+, so that electron-attracting substituents (halogen,... 

Clathrates of [tri-O-thymotide (TOT), brucine, sparteine, 2,2 -dihydroxy-1,1 -binaphthyl-diol] Alkanes, unbranched chiral hydrocarbons, acids and esters bearing small substituents, halogenated hydrocarbons, sulfoxides, phosphine oxides, phosphinates, piperidines [59-64]... 

As for benzene radical cations in solution, substituents containing S and Se deviate from the general trend. Interestingly, also the halogenated benzenes (except CjHsF) follow the same trend as the S- and Se-substituted benzenes, i.e., the ionization potential of the substituent halogen atom rather than the substituent effect as described by the substituent constant governs the ionization potential. 

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