Organic Chemistry : Introduction 2

Organic Reaction
In this topic, we will study about chemical reaction mechanism, so we will understand and be able to predict the result after the reaction of organic substance.

Bond forming
 1. Each of the atom use one electron to make one covalent compound.
 2. One of the atom use two electron to make one covalent compound.

Bond Cleavage
 1. Homolytic - Each atom gets one electron resulting "Free Radical"
 2. Heterolytic - When one atom has its EN more than another's, two electrons go to that atom, resulting one cation and one anion.


Stability of Intermediate
Carbon can be bonded with hydrogen or alkyl (commonly written as "R" - an alkane with one hydrogen taken away... to bond with this carbon instead.) Remember than alkyl has carbons, whose EN is more than hydrogen's, making it wants to give electrons to others since there are many electrons around carbons.
This concludes that the more alkyls carbon connects to, the more electrons likely to go into that carbon atom.
1. Carbon Radical = Carbon that lost 1 electron from 8 to 7. >> It needs 1 more electron>> want R = more R bonded with, more stability.
2. Carbonbocation (+) = Carbon that lost 2 electron from 8 to 6. >> It needs 2 more electrons >> want R = more R bonded with, more stability.
3. Carbonion (-) = Carbon that has full 8 electrons. >> It does not need anymore electrons >> hate R = more R bonded with, less stability.


Inductive Effect
All atoms do not have the same EN. Some are high while some are low. Also some atoms mat be an ion. This makes electrons likely to be found in different possibility in each point.
 - If the electrons are dense or have - ion, it donates electron. For example, Alkyl (with the same reasons above.)
 - If the atom have high EN valve, it withdraws electrons. For example, -O-H (Oxygen wants an electron.)
This can affect
1. Polarity. Electrons might flow some ways more often or not.
2. Stability & Reaction. Molacule with somewhere lots of electrons coming close has less stability - harder to do chemical reaction.
3. Acid. The less stability of bond connecting hydrogen, the more hydrogen flow away, therefore stronger acid.
4. Base. The higher density of the electrons around the atom, the more - charge there is, the more protons that want come stick with, therefore stronger base.


Resonance
Resonance is the state that there is an odd number of pi-electron pairs, running all way around molecule cycles or always switching between some different atoms. Rssonance makes molecule more stable.

 Reference : BCC M.5 Chemistry Book.