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  Structures of Hydrocarbons, Chemistry tutorial

Structures of Hydrocarbons:

PURPOSE

  •  To illustrate methods for alkanes from their 3 dimensional models. 
  •  To write the names of alkanes from their structural formulas. 
  •  To build models of isomers of alkanes. 
  •  To write structural methods for cycloalkanes and haloalkanes.  

Discussion: 

The saturated hydrocarbons represent a group of organic compounds created of carbon and hydrogen. Alkanes and cycloalkanes are termed saturated hydrocarbons since their carbon atoms are attached via only single bonds. In every kind of alkane, each carbon atom has 4 valence electrons and must always have 4 single bonds.

To study more about the 3-dimensional structure compounds, it is useful to make models using a ball-and-stick model kit. In the kit are plastic (or wooden) balls and sticks that symbolize characteristic components and chemical bonds correspondingly in organic compounds.

Table:  Elements and Bonds Represented in the Organic Model Kit

Colour

Element

Number of Bonds

Black

 carbon

4

White

hydrogen

1

Red

oxygen

2

Yellow

nitrogen

3

Green

 chlorine

1

Blue

bromine

            1

The 1st model to construct is methane, CH4, a hydrocarbon consisting of 1 carbon and 4 hydrogen atoms. The model of methane illustrates the 3-dimensional figure, a tetrahedron, approximately a carbon atom.

227_Molecular Formulafor.jpg

To symbolize this model on paper, its form is flattened, and the carbon atom is exposed connected to 4 hydrogen atoms. This kind of method is termed a total structural formula. Though, it is more suitable to utilize a shortened version termed a condensed structural formula. To inscribe a condensed method, the hydrogen atoms are collection through their carbon atom. The number of hydrogen atoms is written as a subscript. The whole structural method and the condensed structural formula for C2H6 are given away below:

1661_complete structural foemula.jpg

Naming Alkanes:

The names of alkanes all end by -ane. The names of organic compounds are depend on the names of the alkane family.

Table:  Names of Some Organic Compound

Name

Formula 

  Name

Formula

Methane

  CH4

Hexane

CH3CH2CH2CH2CH2CH3

Ethane

CH3CH3

Heptane

CH3CH2CH2CH2CH2CH2CH3

Propane

CH3CH2CH3

Octane

CH3CH2CH2CH2CH2CH2CH2CH

Butane

CH3CH2CH2CH3

Nonane

CH3CH2CH2CH2CH2CH2CH2CH2CH3

Pentane

CH3CH2CH2CH2CH3

Decane

CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Constitutional isomers:

Constitutional isomers are symbolized when a molecular formula can stand for two or more different structural (or condensed) formulas. One structure can't be transferred to the other through no breaking and shaping bonds. The isomers have diverse physical and chemical properties. One of the causes for the huge array of organic compounds is the phenomenon of isomerism.

Cycloalkanes:

In a cycloalkane, and alkane has a cyclic or loop structure. There are no finish carbon atoms. The structural method of a cycloalkane shows all of the carbon and hydrogen atoms. The condensed formula collections the hydrogen atoms through each of the carbon atoms. Another type of notation termed the geometric structure is often utilized to depict a cycloalkane through showing simply the bonds that draw the geometric shape of the compound. For instance, the geometric shape of cyclopropane is triangle, and the geometric shape of cyclobutane is square. Instances of the different structural formulas for cyclobutane are exposed beneath.

1054_Cycloalkanes.jpg

Haloalkanes: 

In haloalkanes, a halogen atom such as chlorine (Cl) or bromine (Br) replaces a hydrogen atom of an alkane or a cycloalkane. 

561_Haloalkanes.jpg

Experimental procedures  

Using an organic model kit, construct a ball-and-stick model of the following molecules. Draw the three-dimensional shape of the molecules and write the complete structural formulae and condensed formulae for all the isomers if any. Be sure to name all compounds.

(I)  alkanes  

A) Methane, CH4                                B) Ethane, C2H6                                    C) Propane, C3H8

D) Butane, C4H10                      E) Pentane, C5H12                     F) Hexane, C6H14

(II) cycloalkanes

G) Cyclopropane, C3H6      H) Cyclobutane, C4H8                    I) Cyclopentane, C5H10

J) Cyclohexane, C6H12

(III) haloalkanes

K)  1,2-dichloropropane                  L) Bromoethane                M) Dibromopropane

N)  1,2-dichlorocyclopentane         O) 2- methylpropane

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