Organic Chemistry : Alkene

Alkene is similar to alkane. The only one difference is one of the bond between carbons are double, not single. This makes the number of Hydrogen atom twice of number of carbons. (CnH2n). Below is the alkene, with 6 carbon, called Hexene.

http://www.green-planet-solar-energy.com/alkene.html

However, as an example shown above, the position of double bond can be at many possible places. This gives the isomerism of alkene depending on double bond, which is important when we are learning how to call its name.

IUPAC Name
The difference of alkene and alkane is
- when we are finding the longest carbon chain, the chain we choose MUST contain the double bond.
- when we are numbering in order the carbon in the chain, the number we give to carbons with double bond must be as low as possible, regardless to any other brunches.
- The last word "alkene" such as "Hexene" must also tell where the double bond is. E.g. Hex-3-ene tells that the double bond is at third carbon. (see picture above.)
- When we look at the double bond, two carbons here are connected with other alkyls or hydrogens. Some maybe big or some maybe small. If the bigger ones are at the same side, use prefix "cis". If they are opposite, use "tran".

http://www.elmhurst.edu/~chm/vchembook/209cistrans.html

 Reference : BCC M.5 Chemistry Book.

Organic Chemistry : Alkane

Alkanes & Cycloalkanes

Hydrocarbon is an organic substance containing only carbon (C) and hydrogen (H). Alkanes is the hydrocarbon that every covalent bond is a single bond.
If it is a chain, this makes the  number of H = 2 times of the number of C +2 , or written C(n)H(2n+2).
If it is a cycle (called cycloalkanes), this makes the  number of H = 2 times of the number of C , or written C(n)H(2n).

Here is a few examples and their names.

http://www.u-helmich.de/che/12/03-oc/klassen/alkane/alkane01.jpg
http://www2.chemie.uni-erlangen.de/projects/vsc/chemie-mediziner-neu/kohlenwasserstoffe/bilder/cycloalkane.gif


Name

There are common name and IUPAC name. Common name is used for small and simple alkanes. However, IUPAC one is formal, official, and need to be used for complicated alkanes. We will know IUPAC name only since common name can be found every where while IUPAC should be found and used in HERE.

http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry

Number of carbons	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	20	30
Prefix	Meth	Eth	Prop	But	Pent	Hex	Hept	Oct	Non	Dec	Undec	Dodec	Tridec	Tetradec	Pentadec	Eicos	Triacont

Now we know methane = CH4, Dodecane = C12H26.

1. Find the longest chain or cycle of carbon. Other alkyls (alkanes connectting) and atom are now considered as a brunch from chain/cycle.
2. Number orderly that longest one. Now we know what carbon we are talking about by the number.
3. However, there are somethimes many ways to number and find lostlest one. Use the one that the brunch appears as fast as possible when we numbered.
Ex. If 6-carbon chain with two methyls each at carbon 3 and 5 from left to right. We must numder from right to left since this makes the brunch appears at second carbon (from right), not third (from left).

4. We need to call all the brunches in alphabet order with number to indicate their positions. For example, for picture above, brunched are 18-bromo-12-butyl-11-chloro-4,8-diethyl-5-hydroxy-15-methoxytricos-6,13-dien-19-yne-3,9-dione. (Name of brunch are difficult, well, just need to remember...)

5. then end with longest chain/cycle. For example, 23 =


Physical Properties

Table of alkanes

Alkane	Formula	Boiling point [°C]	Melting point [°C]	Density [g·cm3] (at 20°C)
Methane	CH4	-162	-183	gas
Ethane	C2H6	-89	-182	gas
Propane	C3H8	-42	-188	gas
Butane	C4H10	0	-138	gas
Pentane	C5H12	36	-130	0.626(liquid)
Hexane	C6H14	69	-95	0.659(liquid)
Heptane	C7H16	98	-91	0.684(liquid)
Octane	C8H18	126	-57	0.703(liquid)
Nonane	C9H20	151	-54	0.718(liquid)
Decane	C10H22	174	-30	0.730(liquid)
Undecane	C11H24	196	-26	0.740(liquid)
Dodecane	C12H26	216	-10	0.749(liquid)
Icosane	C20H42	343	37	solid
Triacontane	C30H62	450	66	solid
Tetracontane	C40H82	525	82	solid
Pentacontane	C50H102	575	91	solid

Density
Bigger Molecule, higher density.

Melting and boiling points
Both are higher when the molecule are bigger. This is because Alkane has no polar, so the bond between molecule are London, which depends on mass.

Melting (blue) and boiling (pink) points of the first 14 n-alkanes in °C
http://en.wikipedia.org/wiki/Alkane

Polarity
As alkane have no polar or charge, so it is not solutable in water for sure.

Reaction
- Alkanes can be "cracked" into smaller pieces by add hydrogen and catalyst (which fixes the hydrogen not to move so it can bump... or do the reaction easier.)
- Hydrogen in alkanes can be replaced by other halogen atom.
- Alkanes can be made by add Hydrogen to alkenes or alkynes.

  http://www.nature.com/nature/journal/v455/n7211/images/nature07369-f1.2.jpg

Same for cycloalkanes.

 Reference : BCC M.5 Chemistry Book.

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.

Organic Chemistry : Introduction 1

Isomerism

Isomer molecules are molecules that all have the same number and exact types of atoms, but have different way of forming in molecules.

1. Structural Isomer

The position or bonding is different. Thus, it is easy to notice.

2. Stereo Isomer

Same bonding and position, but in the different directed angles such as mirror to another (called Optical.)

Types of Hydrocarbons

according to bondings

1. saturated : all bonds are sigma.

2. unsaturated : some bonds are pi.

according to structures

1. Aliphatic Hydrocarbon : uncyclic carbon chain.

2. Alicyclic Hydrocarbon : cyclic carbon chain.

3. Aromatic Hydrocarbon : cyclic carbon chain with Resonance.

4. Heterocyclic : cyclic carbon chain with some other atoms in the cycle.

according to functional groups

We can classify them in many many many .... manyyyyy functional groups.

 Reference : BCC M.5 Chemistry Book.