Amino group ortho effect

A nitro group in the artho or para position to fluonne is known to enhance its replacement by hydroxyl [II, 12] Bromine and iodine are much less prone to hydrolysis under similar conditions The effect is much less pronounced with the meta nitro derivative (equation 11) With o-nitro-p-fluoroaniline, it is the amino group ortho to the nitro group, rather than meia fluorine, that is replaced by hydroxyl (equation 12)... 

As might be expected from a consideration of electronic effects, an amino substituent activates pyrazines, quinoxalines and phenazines to electrophilic attack, usually at positions ortho and para to the amino group thus, bromination of 2-aminopyrazine with bromine in acetic acid yields 2-amino-3,5-dibromopyrazine (Scheme 29). 

E. The Ortho-Effect of the Amino Group and Related Groups... 

It can be seen that lone pair donation creates another favourable resonance form only when electrophilic attack is ortho or para to the amino group. There is a small electron-withdrawing inductive effect... 

Deprotonation of 9 and 10 illustrates this effect in the absence of TMEDA, deprotonation occurs ortho to the more Lewis-basic amino group, while in the presence of TMEDA, the deprotonation occurs ortho to the more electronegative, and therefore more acidifying, MeO group (Scheme 6). ... 

Oxo-, hydroxy and amino groups activate ortho and para positions toward attack by halogens and this far outweighs the deactivating effect of the pyridine nitrogen. Consequently, these compounds are much more reactive than the foregoing examples and this... 

Introduction of Amino Groups The introduction of an amino (-NH2) group (in ortho position) into a benzene ring already having a nitro (-N02) group is one of the simplest and oldest approaches to enhance thermal stability of explosives [35-37]. This is evident from the study of the effect of introduction of amino groups in trinitrobenzene (TNB) [Structure (2.18)] to form monoamino-2,4,6-... 

The second point is somewhat less obvious but is readily illustrated by the synthesis of 1,3,5-tribromobenzene. This particular substitution pattern cannot be obtained by direct bromination of benzene because bromine is an ortho, para director. Instead, advantage is taken of the powerful activating and ortho, para-directing effects of the amino group in aniline. Bromination of aniline yields 2,4,6-tribromoanihne in quantitative yield. Diazotization of the resulting 2,4,6-tribromoaniline and reduction of the diazonium salt gives the desired 1,3,5-tribromobenzene. 

The nitration of aniline in the presence of a large amount of strong sulfuric acid results wholly in the formation of m-nitro-aniline, but the similar nitration of dimethylaniline gives principally a mixture of the ortho- and para-derivatives. Mono-methylaniline stands between aniline and dimethylaniline in respect to the orienting effect of its amino group it yields a considerable amount of the m-nitro- compound—and dimethylaniline is preferred for the preparation of tetryl. Commercial dimethylaniline contains a certain amount of monomethylaniline, from which it is extremely difficult to free it, and this in the manufacture of tetryl is converted in part into 2,3,4,6-tetranitro-phenylmethylnitramine, or m-nitrotetryl, pale yellow, almost white, crystals from benzene, m.p. 146-147.087... 

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