alkene

 FUNCTIONAL GROUP

Many important organic chemistry molecules contain oxygen or nitrogen. It's a good idea to memorize the names and structures of these functional groups, or at least bookmark the page to consult as needed.

Functional groups are groups of atoms found within molecules that are involved in the chemical reactions characteristic of those molecules. Functional groups can pertain to any molecules, but you will usually hear about them in the context of organic chemistry. The symbol R and R' refer to an attached hydrogen or hydrocarbon side chain or sometimes to any group of atoms.

Such a huge number of organic compounds requires organization. They are sorted into organic families defined by functional groups. Functional groups are small structural units within molecules at which most of the compound's chemical reactions occur.
For example, two of the most important families are the alcohols and the carboxylic acids. Their functional groups, the alcohol group and the carboxyl group, respectively, distinguishes them from the rest of the other types of organic compounds.

Important Families of Organic Compounds
Symbolism shown below that you may not understand will be explained later in this topic

Hydrocarbons	Only C and H present
Alkanes	Only single bonds
Alkenes	Double bond(s) between two carbons
Alkynes	Triple bond(s) between two carbons
Aromatic
Alcohols
Ethers
Aldehydes
Ketones
Carboxylic Acids
Esters
Amines
Amides

R, R', and R'' represent hydrocarbon groups (alkyl groups)

The type of properties associated with a compound is different depending on the family it is in. For example, the alkanes have just C-C and C-H single bonds. Since C and H are so alike in electronegativity, they are least able to attract ions or polar molecules, and least able to interact with them. The significance of this will be explained later.

Condensed Structures

To save space and time, condensed structures may be used to simplify the drawing and writing of structural formulas of organic compounds. C-H bonds are understood, and CH₃ means that three hydrogen atoms are bonded to a carbon atom. For example:

CH3 is understood to be

H   | H-C-   |   H

CH3CH2OH is understood to be

H H   | | H-C-C-O-H   | |   H H

CH3OCH2 is understood to be

H   H   |   | H-C-O-C-H   |   |   H   H

Functional Groups and Polar Reactants

When a polar group of atoms, like the OH group or NH group are attached to a carbon, the molecule has a polar site. It may undergo chemical reactions when it attracts polar and ionic reactants, but it will usually be near this functional group. This is why compounds with the same functional group have similar chemical properties, or kinds of reactions. For example, in the amine group, both methylamine and ethylamine give the same kinds of reactions.
CH₃NH₂ + HCl ==> CH₃NH₃⁺ + Cl^{-
methylamine + hydrogen chloride ==> methylammonium ion + chloride ion}

CH₃CH₂NH₂ + HCl ==> CH₃CH₂NH₃⁺ + Cl^{-
ethylamine + hydrogen chloride ==> ethylammonium ion + chloride ion}

Only the NH₂ group of the amines change in the previous two reactions, and it changes the same way in both.

The Symbol R in Structural Formulas

The symbol R, stands for the word radical, and in organic chemistry, represents alkane-like groups. It is sometimes used to simplify equations or to summarize them. For example, to summarize the two equations in the previous sections, you may write:
RNH₂ + HCl ==> RHN₃ + Cl^-

The R takes care of any alkane group that you may substitute in. It takes care of all the equations, including methylamine, ethylamine, propylamine, butylamine, etc. It gives a simpler view of how one group, not just the individual compound, changes into another and how each group affects its properties.

•          Pi bond is the functional group.

•          More reactive than sigma bond.

•          Bond dissociation energies:

Ø  C=C BDE               146 kcal/mol

Ø  C-C BDE                -83 kcal/mol

      Pi bond                   63 kcal/mol  

The explanation;

If we want t o dissociation C double bond change to be C single bond, it will needed energy .

The energy need to dissociation C=C is 146 Kkal/J, and the energy need to dissociation C-C is  -83 Kkal/J. so, the condition to dissociation double bond change to single bond is:

63≤x<83.