Ortho, para director

Because substitution in toluene occurs primarily at positions ortho and para to methyl we say that a methyl substituent is an ortho, para director... 

Some of the most powerful activating substituents are those m which an oxygen atom IS attached directly to the nng These substituents include the hydroxyl group as well as alkoxy and acyloxy groups All are ortho para directors... 

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 brornination of benzene because bromine is an ortho, para director. Instead, advantage is taken of the powerful activating and ortho, para-directing effects of the fflnino group in aniline. Brornination of aniline yields 2,4,6-tribromoaniline in quantitative yield. Diazotization of the resulting 2,4,6-tribromoaniline and reduction of the diazonium salt gives the desired 1,3,5-tribromobenzene. 

Ortho, para director (Section 12.9) A group that when present on a benzene ring directs an incoming electrophile to the positions ortho and para to itself. 

Anticipating the products of electrophilic aromatic substitution can be more difficult when two or more substituents compete for control. For example, both methyl and methoxy groups are ortho para directors, and compete for control in electrophilic substitution of 2-methylanisole. The reaction product depends on which substituent has the stronger directing influence. 

B — Cl is an ortho, para director. The possible products are 1,3-dichloro-2-nitrobenzene and 2,4-dichloro-1 -nitrobenzene. 

Other substituents are ortho-para-directors, which facilitate attack at these positions. 

Any substituent whose atom attached to the benzene contains a lone pair of electrons is ortho-para directing (but not necessarily a ring activator). Substituents without a lone pair on the atom attached to the ring are likely meta directors (with the exception of alkyl groups and aromatic rings, which turn out to be ortho-para directors). 

The regiochemistry is important. For example, does the reaction follow Markovnikov s rule or is the reaction anti-Markovnikov Or is the substituent a meta-director or ortho-para-director You learned rules such as this for a reason make sure you continually apply them. 

Halogens are the only deactivating substituents that are ortho-para directors. However, they are the weakest of the deactivators. Halogens withdraw... 

All alkyl groups, not just methyl, are activating substituents and ortho, para directors. This is because any alkyl group, be it methyl, ethyl, isopropyl, tert-butyl, or any other, stabilizes a carbocation site to which it is directly attached. When R = alkyl,... 

Two electrophilic aromatic substitution reactions need to be performed chlorination and Friedel-Crafts acylation. The order in which the reactions are carried out is important chlorine is an ortho, para director, and the acetyl group is a meta director. Since the groups are meta in the desired compound, introduce the acetyl group first. 

B-3. All the following groups are activating ortho, para directors when attached to a benzene ring... 

Using the previous information in this section, predicting the position that a second substituent group will take on a benzene ring is easy. For example, the nitration of methyl benzene (toluene) will produce ortho and para nitrotoluene as the main product because the methyl group is an ortho-para director. 

Answer The -OCH, group is an ortho, para director while the ketone function ls a meta director. Thus, to get the desired para arrangement of the groups, the ketone function should be added to B which is a permitted starting material. Let us use procedure X-6 to incorporate the acyl group onto the aromatic ring. 

---