The structure of nitrogen atoms in amines, like nitrogen atoms in ammonia molecules, is connected with hydrogen or hydrocarbon radicals in three-SP hybrid orbits, forming a pyramid, leaving a SP3 hybrid orbit occupied by solitary electrons. If a amine has three different groups, there should be a pair of enantiomers (see the mapping phenomenon):
However, due to the low activation energy required by the solitary electrons in the flip amine molecule, the enantiomers could not be separated.
The experimental results show that the amine and ammonia molecule has a pyramid structure, the nitrogen atom is SP3 hybridization, and the bond angle is about 109 degrees. In the amine molecule, the three-SP3 hybrid orbits overlap with the s-orbitals of the hydrogen atom or the hybrid orbits of the carbon atoms to form Three 6 keys, leaving a pair of solitary pairs of electrons occupying the fourth SP3 orbit at the apex of the prism.
Aniline is also a pyramid-shaped structure, but the h-n-h bond angle is larger, is 113.9 degrees, n-n-h plane and benzene plane intersection angle of 38 degrees.
If there are three different groups of nitrogen atoms in the amine molecule, it has the chiral property and there should be a pair of enantiomers in theory.
Since the energy barrier between the two enantiomers is quite low, about 21kj/mol, it can be rapidly converted to each other at room temperature, in fact, such enantiomers have not yet been segmented.
In quaternary ammonium salts, the four SP3 orbits of nitrogen are all used to bond, and if there are four different groups of nitrogen atoms, there are enantiomers. For example: The methylation of iodine-benzyl propyl phenyl amine is divided into right and left optical isomers.