Formation Of Ionic Bond

This video is describe about Formation of ionic bond.

   

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Aliphatic Compounds

      Aliphatic compounds are open-chain or acyclic compounds. [ Greek - aliphos ( fat, oil ) ]                      

Acyclic meaning:        
          Acyclic compound with a linear structure, rather than a cyclic one. An open-chain compound having no side chains.
          Aliphatic compounds are otherwise known as non-aromatic compounds. Aliphatic compounds can be saturated joined by single bonds (alkanes) or unsaturated with double bonds (alkenes) or triple bonds (alkynes).

            
              In organic chemistry alkane or paraffin is a saturated hydrocarbon. Alkanes contain only two elements carbon and hydrogen. In alkane all of the carbon-carbon bonds are single bonds. Each carbon atom forms four bonds and each hydrogen atoms form a single bond. Alkane general chemical formula   C_nH_{2n+2 .}

 Alkanes
Methane :

     Paraffins are the saturated hydrocarbons. Main source of paraffins is mineral oil or petroleum. The simplest paraffin is methane CH_{4. Methane contain one atom of carbon and four atoms of hydrogen. It is a alkane mainly occurs in natural gas. Methane is a product of organic decay in swamps and marshes, the gas obtained by the action of bacteria, this method of formation of natural gas given rise to the name "marsh-gas" for methane.}

_{Structure of methane:}

        Methane is a tetrahedral molecule with 4 equivalent C - H bonds. The molecular formula of methane is CH_4.   SP^{3  hybridization.}

^{Properties of methane:}

• Water insoluble.
• Methane is a colourless, odourless and non-poisonous gas.
• Methane is quite soluble in ethanol and ether.
• Melting point - 90.7 K
• Boiling point - 109 - 113 K.
• Liquid methane does not burn unless subjected to high pressure.
• Gas at room temperature.
• It burns with a non-luminous flame in air or oxygen, forming carbon dioxide and water.

                            CH₄     +     2O₂     →     CO₂     +     2H₂O

Substitution reaction of methane:

                 In a substitution reaction, a functional group in a particular chemical compounds is replaced by another group.

                A good example of a substitution reaction is the photochemical chlorination of methane forming methyl chloride.

                            CH₄     +     Cl₂     →     CH₃Cl     +     HCl

                                                              (methyl chloride)

                A mixture of  methane and chlorine is exposed to sunlight, that time substitution reaction occurs. But the reaction doesn't stop here, all four hydrogen atoms in methane are successively replaced by chlorine atoms.

                           CH₄     +     Cl₂     →     CH₃Cl     +     HCl

                                                           (methyl chloride)

                           CH₃Cl     +     Cl₂     →     CH₂Cl₂     +     HCl

                                                            (Methylene chloride)

                           CH₂Cl₂     +     Cl₂     →     CHCl₃     +     HCl

                                                                   (chloroform)

                           CHCl₃     +     Cl₂     →     CCl₄     +     HCl

                                                             (carbon tetrachloride)

             Methane react with chlorine, the hydrogen atoms are replaced, and chlorine atoms take their place. This type of reaction is known as substitution reaction. The atom or group that has replaced the hydrogen atom is called the substitution and when a substituent atom or group is replaced by some other atom or group, the reaction is referred to as a replacement reaction. It should be noted that in substitution or replacement reaction there is no change in structure.

             Methane reacts with bromine in the presence of UV light to form bromomethane.

                         CH₄     +     Br₂     →     CH₃Br     +     HBr

                                                         (bromo methane)

             Methane reacts explosively with gaseous fluorine. The initial reaction is possible.

                         CH₄     +     2F₂     →     C     +     4HF

Mechanism:

Step 1 :

Initiation Step :

UV light breaking a bromine molecules into free radicals.

                            Cl - Cl      →     Cl●     +     ●Cl

                            [Cl₂       →     2Cl●]

Step II

Propagating Steps :

                          CH₄     +     Cl●     →     CH₃●     +     H-Cl 

                          CH₃●     +     Cl₂     →     CH₃Cl     +     Cl● 

Step III

Terminating Steps:

                         Cl●     +     Cl●             →     Cl₂

                         Cl●     +      CH₃●        →     CH₃Cl

                        CH₃●     +     CH₃●      →     CH₃CH₃

Comparison of cis-trans with E/Z

  Z   ==>  Cis isomer
  E   ==>  Trans isomer

The comparison of E-Z and Cis- Trans is suitable for above type of  isomers only. Not in all isomers. For example.

E/Z notation

E   ==>  Entgegen ( German word ). Two groups of higher priority are on opposite sides of double bond.
Z   ==>  Zusammen ( German word ). Two groups of higher priority are on same sides of double bond.
Example :

       Now we start with the cis isomer, the left end of the double bond has C and H. By the CIP priority rules, C is higher priority than H. ( Due to its higher atomic number ). In cis isomers the right end of the double bond also the same priority. Since the two priority groups are both on the same side of the double bond. Therefore this is (z) 2- butene.
        Now we look at the trans isomer, the higher priority group are on the opposite sides of the double bond. Therefore this is (E) 2- butene.

Example:

Stereoisomerism

                   Isomers which have the same molecular formula and same structure but differ in the arrangement of atoms or groups in space. There are two types of stereoisomerism.

• Geometric isomerism
• Optical isomerism.

Geometric Isomerism:

         Isomers which arise due to the different spatial arrangement of atoms or groups around double bond or in cyclic compounds. In organic chemistry geometric isomerism otherwise known as cis/trans isomerism. Generally such isomers contain double bond , which cannot rorate, and also one form cannot be readily converted into the other form without breakage of a bond. cis and trans isomers occur both organic molecule and inorganic coordination complexes.

Example:

     The identical groups lying on the same side, the diastereomers is referred to as cis. In Latin cis means ' on the same side '

     The identical groups lying on the opposite side, the diastereomers is referred to as trans. In Latin trans means ' across ' or 'on the other side'.

     Disubstituted cyclic compounds can also exist in two different forms.

Example:

Coordination Complexes.

                     In coordination complexes cis isomers in which similar ligands are closer together and trans isomers in which similar ligands are opposite together. Not all coordination compounds have geometric isomers.

Example:

Two isomers of squar planar Pt(NH₃)Cl_2.

Cis isomer used in anti-tumor activity.

Trans isomer does not exhibit any anti-tumor activity.

 

Isomerism

         Compounds having same molecular formula but possessing different properties. This phenomenon is known as isomerism. There are two types of isomerisms.
                        ( i ) Structural isomerism.
                       ( ii ) Stereoisomerism.

Structural isomerism:
         Isomers which have the same molecular formula but differ in their structures. It is otherwise known as constitutional isomerism. It is opposed to stereoisomeris. Different types of structural isomers are given below.

• Position isomerism.
• Chain isomerism.
• Functional isomerism.

Position isomerism:

         In position isomerism a functional group or other substituents changes position on a parent ( main carbon chain ) structure. It is otherwise known as regioisomerism.

Example:

Chain isomerism:

        Chain isomers differ in the structure of their chain ( carbon skeleton ). It is otherwise known as skeletal isomerism.

Example:

But pentane  C₅H₁₂  has three isomers.

Functional isomerism:

           Isomers have the same molecular formula but different functional groups are known as functional isomerism.

Example:  C₃H₆O 

Example: C₂H₆O

 CH₃ – O – CH₃    diethyl ether.

Carbon-oxygen-carbon chain functionality is called Ether.

 CH₃ CH₂ – O – H Ethanol.

Carbon-oxygen-hydrogen functionality is called Alcohol.

Cannizzaro Reaction

                             The cannizzaro reaction is a redox reaction. Two molecules ( aliphatic and aromatic aldehydes ) of an aldehyde are reacted to produce a alcohol and carboxylic acid in the presence of strong base.

   a  -   Keto aldehydes give the product of an intramolecular disproportionation in excellent yields.

Mechanism :

NaOH Na ⁺    +  OH ^–   

 

^{Nucleophilic addition of OH- to aldehyde.}

The Crossed cannizzaro reaction, uses formaldehyde as reducing agent.