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HYDROCARBONS 

1. Define each of the following terms
   1. Hydrocarbons

A hydrocarbon is any of a class of organic chemicals made up of only the elements carbon (C) and hydrogen (H). The carbon atoms join together to form the framework of the compound, and the hydrogen atoms attach to them in many different configurations.

1. Isomerism

Isomerism is the phenomenon in which more than one compounds have the same chemical formula but different chemical structures. Chemical compounds that have identical chemical formulae but differ in properties and the arrangement of atoms in the molecule are called isomers.

Describe the various types of isomers

1. Isomerism Types

There are two primary types of isomerism, which can be further categorized into different subtypes. These primary types are Structural Isomerism and Stereoisomerism. The classification of different types of isomers is illustrated below.

1. Structural Isomerism

Structural isomerism is commonly referred to as constitutional isomerism. The functional groups and the atoms in the molecules of these isomers are linked in different ways. Different structural isomers are assigned different IUPAC names since they may or may not contain the same functional group

• Chain Isomerism

• It is also known as skeletal isomerism.
• The components of these isomers display differently branched structures.
• Commonly, chain isomers differ in the branching of carbon
• An example of chain isomerism can be observed in the compound C₅H₁₂, as illustrated below.

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  1. Position Isomerism
• The positions of the functional groups or substituent atoms are different in position isomers.
• Typically, this isomerism involves the attachment of the functional groups to different carbon atoms in the carbon chain.
• An example of this type of isomerism can be observed in the compounds having the formula C₃H₇
  

• 1. Functional Isomerism
• It is also known as functional group isomerism.
• As the name suggests, it refers to the compounds that have the same chemical formula but different functional groupsattached to them.
• An example of functional isomerism can be observed in the compound C₃H₆
  

Vi. Metamerism

• This type of isomerism arises due to the presence of different alkyl chains on each side of the functional group.
• It is a rare type of isomerism and is generally limited to molecules that contain a divalent atom (such as sulfuror oxygen), surrounded by alkyl groups.
• Example: C₄H₁₀O can be represented as ethoxyethane (C₂H₅OC₂H₅) and methoxy-propane (CH₃OC₃H₇).
  1. Tautomerism
• A tautomer of a compound refers to the isomer of the compound which only differs in the position of protons and electrons.
• Typically, the tautomers of a compound exist together in equilibrium and easily interchange.
• It occurs via an intramolecular proton transfer.
• An important example of this phenomenon is Keto-enol tautomerism.
  • Ring-Chain Isomerism
• In ring-chain isomerism, one of the isomers has an open-chain structure whereas the other has a ring structure.
• They generally contain a different number of pi bonds.
• A great example of this type of isomerism can be observed in C₃H₆. Propene and cyclopropane are the resulting isomers, as illustrated below.

• Stereoisomerism

This type of isomerism arises in compounds having the same chemical formula but different orientations of the atoms belonging to the molecule in three-dimensional space. The compounds that exhibit stereoisomerism are often referred to as stereoisomers. This phenomenon can be further categorized into two subtypes. Both these subtypes are briefly described in this subsection.

1. Geometric Isomerism

• It is popularly known as cis-trans isomerism.
• These isomers have different spatial arrangements of atoms in three-dimensional space.
• An illustration describing the geometric isomerism observed in the acyclic But-2-ene molecule is provided below.
  

• 1. Optical Isomerism
• Compounds that exhibit optical isomerism feature similar bonds but different spatial arrangements of atoms forming non-superimposable mirror images.
• These optical isomers are also known as enantiomers.
• Enantiomers differ from each other in their optical activities.
• Dextro enantiomers rotate the plane of polarized light to the right whereas laevo enantiomers rotate it to the left, as illustrated below.
  

Xi. Ionization Isomerism

The compound which give different ions in the solution, although they have same composition, are called ionization isomers and this property is known as ionization isomerism. Compounds which gives different ions in solution although they have same composition are called ionization isomerism. This form of isomerism arises when the counter ion in a complex salt is itself a potential ligand and can displace a ligand which can then become the counter ion.

One example of ionisation isomerism is [Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4.

We can prepare these ionisation isomers in the following method.

[CoBr(NH₃)₅]SO₄→[CoBr(NH₃)₅]²⁺ +SO₄²⁻ = Red−Violet
[CoSO₄(NH₃)₅]Br → [CoSO₄²⁻(NH₃)₅]⁺ + Br⁻  = Red

2. Give the IUPAC names  of the following organic compounds

• C₂H₂

• C₂H₆

• C₂H₄

• C₂H₅OH

3. (a) Write the structural formulae  of the two isomers of  C₄H₁₀

• Give the IUPAC name s of the structures in (a)

4. (i) Describe how  sodium carbonate can be used to distinguish between  a sample of ethanol  from a sample of ethanoic acid  in the laboratory

Ethanol does not react with sodium bicarbonate while ethanoic acid reacts with sodium bicarbonate giving effervescence with evolution of carbon dioxide gas.

• State the observation that would be made  when a piece  of sodium metal is place in a sample of pentanol

If a small piece of sodium is dropped into pentanol, it reacts steadily to give off bubbles of hydrogen gas and leaves a colorless solution of sodium pentoxide

5. Explain how  burning  can be used to distinguish between ethane and ethyne

Because ethene, ethane and ethyne are made up of carbon and hydrogen atoms, they are called hydrocarbons. All three are flammable gases. Their flammability depends on the types of bonds shared by the carbon atoms.

Ethane is the least flammable, while ethene is more flammable and ethyne, also called acetylene, is explosively flammable.

Acetylene or ethyne is favored in welding because it produces a very intense flame. When mixed with oxygen, an acetylene flame can reach temperatures over 6,000 degrees Fahrenheit.

Ethane is colorless and odorless, and its main function is to produce ethene, which is also known as ethylene. Ethylene is also colorless, but some claim that it has a slight musky/sweet smell. People recognize ethylene as the gas that is added to picked, unripe fruit to hasten the fruit’s ripening.