Ortho and para directing

XY is just a single atom XY is ortho and para directing. 

CHO, -COOH, -CONH, -CN, -NO, -SO3H, and the chief ortho and para directing groups are ... 

Resonance effects are the primary influence on orientation and reactivity in electrophilic substitution. The common activating groups in electrophilic aromatic substitution, in approximate order of decreasing effectiveness, are —NR2, —NHR, —NH2, —OH, —OR, —NO, —NHCOR, —OCOR, alkyls, —F, —Cl, —Br, —1, aryls, —CH2COOH, and —CH=CH—COOH. Activating groups are ortho- and para-directing. Mixtures of ortho- and para-isomers are frequently produced the exact proportions are usually a function of steric effects and reaction conditions. 

Methoxylation of 2,5- and 2,3-dibromopyrazines provides the basis for a comparison of ortho and para direct deactivation (Section II, E, 2, e) in the mono-methoxy derivatives such as 198 and 199. Pyrazine derivatives are discussed in Sections II, C and II, D. 

Ortho- and Para-Directing Activators Alkyl Groups... 

The nitroso group, — N = Op is one of the few nonhalogens that is an ortho- and para-directing deactivator. Explain by drawing resonance structures of the carbocation intermediates in ortho, mela, and para electrophilic reaction on nitrosobenzene, C<3Hs N = 0. 

The hydroxyl group is a strongly activating, ortho- and para-directing substituent in electrophilic aromatic substitution reactions (Section 16.4). As a result, phenols are highly reactive substrates for electrophilic halogenation, nitration, sulfonation, and lTiedel-Crafts reactions. 

The curved arrows show how one resonance structure relates to another. Notice that the formal negative charge is located on the ortho and para positions, exactly where reaction takes place most quickly. Other ortho- and para-directing groups include —NH2, —Cl, and —Br. All have an atom with a lone pair of electrons next to the ring, and all accelerate reaction. 

Explain why ortho- and para-directing groups accelerate electrophilic substitution on the benzene ring and identify such groups (Section 18.8). 

You have read earlier that aniline is a resonance hybrid of five structures. Where do you find the maximum electron density In these structures Ortho- and para-posltlons to the -NHg group become centres of high electron density. Thus -NH group Is ortho and para directing and a powerful activating group. 

Although electron-donating substituents activate the ring towards electrophilic attack, they are both ortho and para directing, and an electrophilic... 

As predicted by electron density difference plots (see text). o,p = ortho- and para-directing (relative to silicon) m = meta-directing (relative to silicon). 

In the rabbit, phenol gives rise to catechol and quinol. Hydroxyquinol is a minor metabolite of catechol but not of quinol, and neither quinol nor resorcinol is further oxidized to trihydric phenols.126 Aniline and its derivatives do not undergo meta substitution, but give rise to ortho- and para-directed hydroxylation products only.122... 

Ortho and Para Directing Groups. In general the common rules of orientation regarding intermoleaular acylation can be extended to the... 

The HRP-catalyzed polymerizations were preferentially ortho and para directing, resulting in branched polymeric materials, which were intractable and had poor electrical properties. However, SBP-mediated synthesis of polyaniline at 1°C in either aqueous or partially organic solvents resulted in low branching and ortho-coupled polyaniline at pH higher than 3.0. SBP actually outperforms HRP in terms of stability and is now used in numerous biotechnological applications [51]. 

---