Structure of Aniline

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In aniline, the c-N bond length is 1.41 A, while that of cyclohexylamine is 1.47 A, indicating the existence of partial π bonds between N and C.

Aryl N distance

In aniline, the c-N bond length is 1.41 A, while that of cyclohexylamine is 1.47 A, indicating the existence of partial π bonds between N and C. The C(aryl)-NH2 distance in aniline is highly sensitive to substituent effects. The distance is 1.34 A in 2,4, 6-trinitrophenylamine and 1.44 A in 3-methylaniline.

 

The pyramid is changed

The amine in aniline is a slightly pyramidal molecule with nitrogen hybridization between SP3 and SP2. Nitrogen is described as having high P properties. The amino group in aniline is flatter (i.e., it is a "shard pyramid") than the amino group in aliphatic amines because of the conjugation of lone pairs with aryl substituents. The observed geometry reflects a compromise between two competing factors: 1) The stability of n-lone pair electrons in significant S-characteristic orbitals favors pyramiding (s-characteristic orbitals have lower energy), and 2) the delocalization of n-lone pair electrons into aromatic rings favors planeness (lone pairs in pure P orbitals overlap best with orbitals in benzene π systems).

 

Consistent with these factors, substituted anilines with electron-donating groups are more pyramidal, while substituted anilines with electron-withdrawing groups are more planar. In parental aniline, lone pairs are about 12% s characters corresponding to sp7.3 hybridization. (For comparison, alkyl amines usually have lone pair electrons in orbitals close to SP3.)

 

The pyramidal Angle between c-N bond and h-N-H Angle bisector is 142.5°. [14] For comparison, in the more intense pyramidal methylamine, the value is about 125°, while formamide has an Angle of 180°.

 

diazotization

Aniline and its ring - substituted derivatives react with nitrite to form diazonium salts. Through these intermediates, the amine groups can be converted to -OH, -CN or halides by the Sandmeyer reaction. The diazo salt can also react with NaNO2 and phenol to produce a dye called benazophenol in a process called coupling. The conversion of aromatic primary amines to diazonium salts is called diazotization. In this reaction, the primary aromatic amine reacts with sodium nitrile and 2 moles of HCl, which is called an ice-cold mixture because the temperature used is 0.5 °C, and it forms a benzendiazonium salt as the main product as well as water and sodium chloride.

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