Saturated Hydrocarbons

Saturated Hydrocarbons

Saturated hydrocarbons are hydrocarbons consisting of  carbon chains with single bond between them  in which carbon joins with another carbon by single covalent bond e.g Alkanes ( like ethane C₂H₆, propane C₃H₈ )

 

H          H                                              HHH

 

H –   C          C – H                            H – C  –     C –     C – H

 

H        HHHH

 

Alkanese.g Methane (CH₄)

 

The alkanes are aliphatic hydrocarbons.  They form homologous series of saturated hydrocarbons with general molecular formular of CnH₂n+2

 

EVALUATION

1. What is saturated hydrocarbons?
2. Name one example of alkanes.

 

Preparation of  Methane (CH₄)

Methane is prepared in the laboratory by heating ethanoate salt with corresponding alkalis e.g Sodium ethanoate and soda-lime.

 

Physical Properties

1. Methane is a colourless and odourless gas
2. It is slightly soluble in water.
3. It is less dense than air
4. It has no action on litmus paper

 

Chemical Properties.

1. Combustion:- Methane burns in air or oxygen to produce steam, carbon(iv) oxide and a lot of heat CH₄ + 2O₂            2H₂O  +   CO₂.

The general equation of alkanes for combustion is represented as

CxHy(g)   +   ( x + ^y/₄)O₂          ^y/ ₂H₂O(g)   +    xCO₂ (g).

2. Substitutional reaction:- With chlorine gas and bromme gas usually in the presence of ultra’-violet light ( as catalyst).

Uses

1. Methane is used as fuel
2. It is used for making hydrogen gas
3. It is used in making carbon black
4. Used in making carbon (iv) sulphide
5. It is used in making hydrocyanic acid

6          The derivatives of methane e.gtrichloro-methane can be used as anesthetic in surgical operation.  Tetrachloromethane is an organic solvent.

 

Evaluation

1. State four (4) uses of methane
2. Identify two (2) chemical properties of methane.

 

Isomerism

This is the existence of two or more  organic compounds, (isomers) with the  same molecular formula but different structures.

– Isomers are compounds having the same molecular formula but different structural formula.

– As the number of carbon atoms in a molecule increases, the number of isomers also increases, for example, pentane has the following three isomers.

H          H          HHH                             H          H          H          H

 

H          C          C          C          C          C      H              H          C          C          C          C   H

 

H          H          H          H          H                      H          HH

 

Pentame-CH₃(CH₂)₃CH₃                                                 H        C     H

H

2 – methyl butane

H

H –  C  – H

H                        H

H      C          CC     H

H                      H               2,2- dimethyl propane.

H -C – H

H

TYPES OF ISOMERISM

1. Structural Isomerism
2. Stereo Isomerism.

The structural isomerism occurs in organic compound with the same molecular formula but different structural arrangement of the carbon atom.

 

Types of Structural Isomerism

1. Chain isomerism :-This is the kind of isomerism which occurs due to the differences  in  the way by which the carbon atoms are arranged in the chain.

e.g         H        H          H          H                                  H          H          H

 

H-  C  –     C  –       C  –       C – H                             H-         C   –        C   –          C – H

 

H     H H          H                                  HH

H – C – H

Butane

H

2- methyl propane

1. Functional isomerism:- This is the kind of isomerism which due to the difference in     functional group.

e.g            H     H                                                          H          H

 

H-   C  –  C – OH                                                   H   C  –  O-     C-  H

 

H     HHH

Ethanol                                                                        Methoxyl methane.

 

iii.   Positional isomerism:-  This is the kind of isomerism which occurs as a result of the          difference in the way the functional group is positioned.

Example:

H     H                           H          H

 

H       C     CCC   H      H – C –  C =  C –  C – H

 

H     HHHHHHH

But-1-ene                                        But-2- ene

 

2.Stereo Isomerism

Types of stereo isomerism

1. Geometric Isomerism :- This is the existence of compound with the same molecular formula but  different spatial structural formula.

 

e.g  CH₃CH₃

C  =  C                                                                                      CH₃               H

C = C

H H   Cis but-2-ene                                  H                CH₃    Trans-but-2-ene

 

1.  Optical Isomerism:- They have different configuration and they rotate plane polarized        light e.g.                             H                                              H

 

CH₃ – C – COOH                                HOOC – C – CH₃

 

OH                                                           OH

IUPAC NOMENCLATURE

In IUPAC nomenclature, every name of organic compound consists of a ROOT, SUFFIX and PREFIX names.

 

ROOT NAME

Name of the parent alphatic hydrocarbon with the longest carbon chain in a molecule .

 

SUFFIX NAME

Name of the principal functional group substituents on the longest carbon chain in a molecule.

 

PREFIX NAME

Name of the other substituents on the longest carbon chain which are not functional group e.g 1- chloroethan – 1- ol.

1- chloro = Prefix

ethane = root

-1- ol Suffix

 

RULES FOR IUPAC NOMENCLATURE

1. Select the longest continuous carbon chain as parent hydrocarbon.
2. Number the longest carbon chain. Starting from the end that gives lowest possible number to the suffix and then the prefix.
3. Indicate the other substitents by prefixes, preceded by number to show their position on the carbon chain.
4. If the same alky or other substituents group occur more than once as side chain show how many are present by using prefix di,tri, tetra, etc. and indicate by various number the position of each group on the longest carbon chain.
5. If there are several different alkyl groups attached to the present chain, name them in order of increasing size or in alphabetical order.

 

H           H          H

 

C –           C –           C – H

 

H                      H                         2 methyl propane

H -C – H

 

H

 

H    HHHH

 

H     C    CCCC   H                                             2- methyl pentane

 

H     HHH

 

H   C   H

 

H

 

 

H   HHH        CH₃C₂H₅  HH

 

 

H –        C –  C –  C-    C  –     C  –      C  –    C –   C  – H

 

H    HHH        C₃H₇    H       HH

3,3,-diethyl – 4- methyl 1-5 propyl octane.

 

6. If there are halogens together with alkyl groups attached to the parent chain, name the halogen first in alphabetical order and the alkyl group as explained earlier.

 

H    Cl

1- bromo-2- chloro propan-2-ol.

H      C –   C-  OH

 

Br   CH₃

Evaluation

Name the following compounds.

 

1a.        H   HH

 

H – C  – C  –  C  – H

 

H   HH

 

1. CH₃CHClCH₂OH

 

2. List the rules for IUPAC Nomenclature.

 

WEEKEND ASSIGNMENT

1. The structure of 1,2,3-trichloro-2-methyl butane is

 

1. a) CH3 H       H         H                   b)                       Cl        Cl        Cl         H

 

H-    C  –    C    –   C  –   C – H                H- C    –  C  –     C –       C – H

 

ClCl        H     HClClCl         H

 

 

 

1. c) ClClCl H                          d)                                   H       HHH

 

H –  C-       C-        C  –   C  – H                                      H –  C –      C –        C-      C – H

 

H H – C- H    HH                                               HHH

H – C- H

 

H                                                                                           H

2. Which of these compounds exhibits resonance ?

(a) Ethanol                   (b) Ethane        (c) Benzene      (d) Ethyne.

3. The solubility of alkane in organic solvent is due to presence of its

(a) polar molecule                 (b) non-polar molecule  (c) Low melting points  (d) low freezing            points.

4. Which of these is alkane member?

(a) Ethene                (b) Pecane        (c )Propyne        (d) Butanol

5. The root in the organic compound below is:

 

H     HH

 

H- C –  C –     C –   H

 

H     H      OH.

 

(a) Propane                 (b) Propan-1-ol            (c ) Propanol       (d) hydrogen

 

THEORY

1. Write briefly on the following:
2. Cracking
3. Isomerism
4. Homologous Series
5. Stereo Isomerism
6. Optical Isomerism.
7. Name the following compound
8. CH₂(OH)CH(OH)CH₂OH
9. C₂H₄CL₂

 

See also

ALKYNES

UNSATURATED HYDROCARBONS

SIMPLE MACHINE

AIR AND COMBUSTION

AN ALKALI