Sunday, October 27, 2019

Bruice Organic Chemistry Notes #4

This post is the continuation of this post. Here, I will explain from number 7 to 16. 

7. HOW SINGLE BONDS ARE FORMED IN ORGANIC COMPOUNDS
To visualize how the single bonds are formed, let we study that based on methane case. Methane (CH4) has 4 covalent C-H bonds. There are so many ways to represent methane such as based on the perspective formula, ball-stick model, space-filling model, and electronic potential map.


The model from the perspective formula lets the reader knows the 3-dimensional structure of a molecule on a paper easily by sketching it using wedges and dashes which the central atom is always assumed to be in the plane of the paper. A bond with wedges is drawn to visualize the bond that is projected out of the plane of the paper toward the viewer, while the bond with the dashes, projected back from the paper away from the viewer.

Ball-stick model visualizes the structure of the molecule that the ball shows the atoms as spheres and the bond as sticks. While the space-filling model is a model that can visualize the relative size of the atoms or molecules to understand an important point if needed. For the electronic potential map, we have discussed this before in the previous post.

From those model as the representation of a molecule, we can see the bonds that connect atom to atom. In the case of methane, the atom Carbon only has 2 unpaired valence electrons, so how this atom can make up to 4 bonds? So the answer of how the single bonds are formed is through HYBRIDIZATION.

Hybridization is a concept proposed by Linus Pauling in 1931. Basically, the theory is created to simplify the understanding of how bonds formed. So, The hybridization of the hybrid orbital theory comes to make things fit to give us a very good picture of the bonding in organic compounds.

Simply, hybridization is a concept of mixing orbitals or combining orbitals. So to make the bond, one s and 3 p orbitals are all combined into 4 equal orbitals. This hybridization for a single bond is called sp3 orbital, so it contains one part s and 3 parts p orbitals.


An important thing about single bond in methane is the angle formed. As it is sp3 orbitals, the orbitals move as far from each other that the most stable angle they can fit is 109.5 degree which then form a regular tetrahedron.


While, below is the bond in ethane.


Another important thing that will differentiate between single bond and other bonds is the length of carbon-carbon bond, in single bond, the length is 1.54 Armstrong.


Look also at the electrostatic potential map, the color shows there is no specific electronegativity difference.

8. HOW A DOUBLE BOND IS FORMED: THE BONDS ETHENE
The example of a compound with double bond is ethene. As it has double bond connected 2 carbons, it has only 3 atoms bonded. Then, the hybridization needed is sp2, as only 1 s orbital with 2 p orbitals are mixed to form 3 bonds, so 1 p orbital is not needed and becoming the unhybridized p orbital.


Next, I will discuss about these parts below. See you!

9. HOW A TRIPLE BOND IS FORMED: THE BONDS IN ETHYNE
10. THE BONDS IN THE METHYL CATION, THE METHYL RADICAL, AND THE METHYL ANION
11. THE BONDS IN AMMONIA AND IN THE AMMONIUM ION
12. THE BONDS IN WATER
13. THE BOND IN A HYDROGEN HALIDE
14. HYBRIDIZATION AND MOLECULAR GEOMETRY
15. SUMMARY HYBRIDIZATION, BOND LENGTHS, BOND STRENGTH, AND BOND ANGLES
16. DIPOLE MOMENTS OF MOLECULES


Reference
Bruice, P. Y. 2017. Organic Chemistry Eighth Edition. England: Pearson Education Limited.

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