Reactivity and Orientation in Mono

Benzenes and even substituted benzenes are organic compounds that come under the category of hydrocarbons. They have a planar ring-like structure and have 6 carbons connected with hydrogens. There are 3 double bonds and 3 single bonds in total, and have lone pairs of electrons in their structure. The lone pairs of electrons keep moving from one carbon atom to the other. When the hydrogen atom is replaced by a functional group, the formation of new benzyl compounds takes place. Some examples of the compounds generally formed are toluene, aniline, etc. They can be substituted in two ways: mono substitution and disubstitution. 

        Toluene     Aniline

What is a Benzene ring or benzene nucleus? 

Benzene is an organic compound with the formula C6H6. It is composed of 6 carbon atoms and has a single hydrogen atom connected with each one of them. It is one of the basic petrochemicals. Benzene nucleus is often considered an aromatic compound because of the continuous pi bonds that are cyclic. Aromatic compounds are said to have a good smell or aroma, which is one of their physical properties that helps in their physical detection. 

 Benzene

Monosubstituted Benzenes: Reactivity and Orientation

Benzenes that have a single substituent place in their structure, one functional group can be added to them. The prefix in the name of benzene is decided on that very basis. Toluene, Anisole and Aniline are some of the most common examples of monosubstituted benzenes. 

Reactivity

Reactivity of this organic compound greatly depends on the functional group attached to the benzene ring. However, the functional groups that help in increasing the reactivity of benzene are known as the activating functional groups, and the ones that slow down the reactivity of benzene are called the deactivating groups. 

When an incoming electrophile attacks, they can further be classified into categories of directors:

• Ortho and para directors: Directors that increase the density of electrons at the ortho and the para positions are called ortho and para directors.

• Meta directors: Directors that increase the density of electrons at the meta position are called meta directors. 

When we consider monosubstituted benzenes, we can take the example of aniline. Aniline has an NH2 group placed in the place of a hydrogen atom. This changes its name to aminobenzene. 

Substitution reactions are generally those chemical reactions in which one functional group replaces the other. For example, para substitution reaction, monosubstitution in benzene reaction, etc. 

The nitro group is said to be the deactivating group, as it shifts the electron density to the meta position. It is the most common deactivating group in the study of Benzene Nucleus. 

A Benzene nucleus has 6 C-C bonds and each of those C is attached to one H. The orientation is like this:

• 6 Carbons are arranged in the benzene nucleus 

• 1 functional group is attached to one C at the place of one replaced hydrogen atom 

The structure stays very much the same, and the only difference that takes place is the changing of one hydrogen atom with a functional group. 

Disubstituted Benzene: Reactivity and Orientation

The disubstituted benzenes are the benzene nuclei that have two substituents in place of two out of six hydrogen atoms in their structure. The places and positions of these substituents are quite decided and predefined in the case of disubstituted benzenes. 

Whether the ultimate effect on the benzene nucleus will be activating or deactivating is decided by the cumulative influence of both the substituents. Depending on these influences, the disubstitution benzene orientation can be of two types:

• Cooperative: The compounds that have a cooperative orientation are way easier to predict than the antagonistic or the non-cooperative ones. A point that must be noted about this orientation is that if there are two different sites that are favoured, substitution will occur at the place where there is less hindrance by the ortho groups. The site that has more or a high hindrance by the ortho groups, would definitely not be favoured. 

• Non-Cooperative: They are comparatively more difficult to predict than the cooperatively oriented disubstituted benzenes. If the substituents are identical to one another, the symmetry will help to reach a better conclusion. The product determining influence is exerted by the charge stabilisation due to the presence of non-bonding electrons.

Reactivity of disubstituted benzene depends on the functional groups attached to them and their additive effect on the entire benzene nucleus. 

Conclusion

Benzene nucleus substitution reaction is important for the study of the behaviour of benzene and the possible combinations of functional groups with them, resulting in new compounds. Benzene is useful in various industries such as chemical, industrial and construction industries. It is used in making asphalt that is used for construction purposes. Monosubstituted and disubstituted benzenes have different reactivity rates, which depend on their substituents.