Hybrid orbital function and molecular orbital function, structural formula

In the last article, I mentioned a brief history of organic chemistry and a hybrid orbital function.

 

Introduction to organic chemistry, history and hybrid orbital functions
https://biostudy.tistory.com/189

Introduction to organic chemistry, history and hybrid orbital functions

The link above is a link to the article.

Now that we have mentioned the sp3 hybrid orbital function, we will now talk about the sp2 hybrid orbital function.

The most famous sp2 hybrid orbital function is the ethylene structure.

 

H2C-CH2 structure

Three Sp2 hybrid orbital There is one 2p orbital that is not hybridized, so there are three sp2 making a plane perpendicular to the p orbital, each at 120 degrees.

I hurriedly drew it with paint

 

 

In this way, you can think of the p orbital as the y-axis, and the sp2 hybrid orbitals as the xz plane.

Therefore, the sp2 hybrid orbitals have a vertical relationship with the p orbitals, and the three sp2 orbitals in the xz plane have 120 degrees to be far from each other.

 

This is the viewpoint as seen from the y-axis

When each carbon of ethylene meets each other, a strong sigma bond is formed by the bond of sp2-sp2.

In addition, not only sigma bonds but also pi bonds are formed on the side, so sp2-sp2 sigma bonds and 2p-2p pi bonds form double bonds between four covalent electrons and carbon.

 

 

Here, the bonding angle of H-C-H is 117.4 degrees, the bonding length of C-H is 108.7 pm, and the bonding strength is 464 kJ/mol (111 kcal/mol).

In addition, the bonding angle of H-C-C is 121.3 degrees, the length of C-C bonding is 133.9 pm, and the bonding strength is 728 KJ/mol (174 kcal/mol).

For reference, the C-C bond length of ethene is 154pm, and the bond strength is 377KJ/mol.

The C-C double bond has a strong bond strength and a short bond length because four electrons instead of two electrons bond the nucleus to each other.

In addition, double bonds can be said to be stable because of their small bonding reactivity.

Also, H-C-C is 121.3 degrees, which is approximately 4 degrees larger than the H-C-H coupling angle.

Suppose you are sitting in the subway and the next person is sitting by a very large person.

Then, of course, your body is supposed to be pushed, which is the same for this reason.

The hybrid function of acetylene and sp is similar.

 

 

This time in three-dimensional space, the p orbital exists vertically on the y-axis and z-axis

You can think of the sp orbital on the x-axis.

Therefore, when forming an acetylene molecule, the two sp hybrid orbitals form hydrogen and sigma bonds.

Thus, one sigma bond and two pi bonds are formed.

By comparing the hybrid orbital functions of sp3, sp2, sp

The bond length is in the order of sp3>sp2>sp, sp3 is a single bond, sp2 is a double bond, sp is a triple bond.

Also, the bonding strength or bonding angle is sorted in the order of sp3<sp2<sp.

In addition, there are s fraction, s orbital fraction, which only needs to know the value of 1/n+1 in sp(n).

For sp3, it is calculated as 1/3+1 = 0.25
 
Moving to the molecular orbital function and explaining the molecular orbital function, the molecular orbital function is called MO, Molecular orbital, and is a combination of atomic orbital functions unique to each atom in the formation of a covalent bond.

This means that it describes the region of space that is easiest to find electrons in a molecule.

 

You only need to know LUMO and HOMO, ignoring Diene, EDG, etc.

HOMO refers to the most energetic orbital among orbitals filled with electrons, and LUMO refers to the highest orbital among orbitals without electrons.

As the number of nodes increases, the energy increases, so you only need to know that degree.

The chemical structure roughly has a condensed structure and a skeletal structure.

 

reduced structure formula

This expression method is called a reduced structure formula.

 

skeletal structure

This structure is called a skeletal structure.

Scientists are very cumbersome with simple repetitive tasks, so only elements other than C and H are marked, and only these skeletons remain.

As a rule, carbon always has a tetravalence, so you need to count the number of double bonds and crossing lines to derive how many hydrogens and carbons in the molecule, and thus the molecular formula.