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1.
Delocalized π bond
1) Delocalization II 4 3 keys
In the O 3 molecule, the central atom adopts sp 2 hybridization, as shown in Figure 6-29(a)
.
The sp 2 hybrid orbital of the central O atom and the 2p orbitals of the two ligand O each form a σ bond.
The molecular structure is V-shaped, and the unhybridized 2p z orbital of the central atom has 2 electrons, as shown in Figure 6-29 ( b) as shown
The 2p z orbitals of the two ligands O have single electrons, the bonds are not saturated, and both have the ability to form bonds
.
However, the 2p z orbitals of the two ligands O are far apart and cannot overlap to form a bond
.
Figure 6-29 O 3 molecular center hybridization, molecular structure and delocalized π bond
The delocalized π bond in the O 3 molecule can be understood as a π bond formed by overlapping the p orbitals of two ligand O with the p orbital of the central atom
.
The electrons of the delocalized π bond belong to the entire molecule, and this bond is also called a large π bond
.
SO 2 , HNO 3 , and NO 2 - all have Delocalization Ⅱ 43 bonds, as shown in Figure 6-30
.
SO 2 and NO 2 - are isoelectronic bodies of O 3 , so the three have similar structures and bonds
.
FIG SO 6-30 2 , HN03 .
3 , and NO 2 - T formed delocalized Ⅱ .
4 .
3 bonds
The molecular orbital energy level diagram of Ⅱ 4 3 in O 3 molecule is shown in Fig.
6-31(a).
The combination of 3 pz orbitals forms 3 π orbitals, 1 bonding orbital, 1 antibonding orbital, and 1 non-bonding orbital.
Key track .
Ⅱ .
4 .
3 key on the key molecule is a contribution level, the contribution level of each 1/2 bond OO bond, i.
e.
, O .
3 molecule OO bond in the order of 1.
5 .
It can be seen that O 3 molecules are not as stable as O 2 (the bond level is 2) .
O 3 molecule has no single electron, so O 3 is a diamagnetic molecule .
Fig.
6-31 Molecular orbital energy level diagram and electron arrangement forming bonds of Ⅱ 4 3 and Ⅱ 6 4
The O .
3 is formed Ⅱ molecule .
4 .
3 process can be summarized from the domain π bond-forming conditions are as follows:
(1) Several atoms are as coplanar as possible (the orbits can effectively overlap "side by side")
.
(2) There are orbitals perpendicular to the molecular plane (each orbital participates in the formation of delocalized π bonds)
.
(3) The total number of electrons in the orbital is less than twice the number of orbitals (the contribution of delocalized π bonds to the bond level is not 0)
.
2) Delocalization Ⅱ 6 4 key
In the SO 3 molecule, the central atom S excites a 3s orbital electron to enter the 3d orbital to ensure that there are 3 single electrons in the sp 2 hybrid orbital of S and 2 electrons in the 3pz orbital of the unhybridized central atom; the central S atom The sp 2 hybrid orbital of O and the 2p orbital of the 3 ligand O each form a σ bond, and the molecular structure is an equilateral triangle, as shown in Figure 6-32
.
Figure 6-32 The chemical and molecular structure of the central atom of SO 3 molecule
The 2p z orbitals of the three ligand O in the SO 3 molecule have single electrons, which are parallel to the 3pz orbitals of the central S atom and have the same symmetry.
They can be overlapped side by side to form a delocalized π bond; at the same time, the S atom is excited The electron to the 3d orbital enters the delocalized π bond, SO 3 forms a four-center six-electron delocalized π bond II 6 4 , as shown in Figure 6-33(a) .
The delocalized π bond in the SO 3 molecule can be understood as the p orbitals of the three ligand O overlap each other with the help of the p orbital of the central S atom to form a π bond .
Figure 6-35 Delocalized Ⅱ 6 4 bond in SO 3 and BCl 3 molecules
The energy level diagram of the molecular orbitals in the SO 3 molecule is shown in Figure 6-31(b).
The combination of 4 pz orbitals forms 4 π orbitals, 1 bonded orbital, 1 antibond orbital, and 2 non-bonded orbitals
.
And SO .
3 is similar to, the BCl .
3 , NO .
3 -, CO.
'S .
3 2 - and the like are delocalized Ⅱ .
6 .
4 key
.
Moreover, SO 3 and BCl 3 , NO 3 - and CO 3 2- are mutually isoelectronic bodies
.
In the BCl 3 molecule, B adopts sp 2 hybridization (Figure 6-17).
The three hybrid orbitals are paired with the 3p orbitals of Cl to form a σ bond.
The remaining 2p z orbitals that are not hybridized have electron pairs with Cl.
The 3p z orbitals overlap, so there is a delocalized Ⅱ64 bond in the BCl 3 molecule [Figure 6-33(b)]
.
The formation of the Ⅱ64 bond increases the bond level of BCl 3 and the B-Cl bond in the molecule, alleviates the electron deficiency of B, and improves the stability of the BCl 3 molecule
.