Organic Chemistry

Organic Chemistry is the study of organic compounds.

Organic compounds are compounds which contain the element carbon. Most organic compounds also contain hydrogen. Organic compounds which contain carbon and hydrogen only are known as hydrocarbons.

Organic compounds may also contain other elements such as chlorine, nitrogen, oxygen, etc.

Do note that there are some exceptions. Carbon monoxide (CO), carbon dioxide (CO₂), calcium carbonate (CaCO₃), etc are not classified as organic compounds even though they contain carbon.

In this post, we will look at the following basic fundamentals when it comes to organic chemistry:

• Homologous Series
• Functional Group
• Naming of Organic Compounds
• Formulae

A) Homologous Series

A homologous series refers to a family of organic compounds with the same general formula and similar chemical properties.

Do note that some textbooks defined homologous series as a family of organic compounds with the same functional group and similar chemical properties. This sounds a bit off considering that alkanes homologous series does not contain any functional group.

The homologous series covered in GCE O-Level Pure Chemistry syllabus (and other Sec 4 IP Chemistry syllabus) in Singapore are: Alkanes, Alkenes, Alcohols and Carboxylic Acids.

Organic compounds in the same homologous series have the following characteristics:

• Represented by a General Formula
• Regularly increasing relative molecular masses from one member to the next member
• Can be prepared by similar methods
• Gradual change in physical properties from one member to the next member
• Similar chemical properties
• Same functional group (except alkanes homologous series)

B) Functional Group

A functional group is defined as an atom or a group of atoms that gives a molecule its characteristic properties.

All molecules containing the same functional group will behave similarly towards the same chemical reagents, i.e. they have the same chemical properties.

Following are some homologous series and their functional groups that are covered in the Pure Chemistry syllabus:

• Alkanes – Do not have any functional groups. There are only C-C and C-H covalent bonds in the molecule.
• Alkenes – Contain the carbon-carbon double bond, C=C.
• Alcohols – Contain the hydroxyl group, -OH.
• Carboxylic acids – Contain the carboxyl group, -COOH.

C) Naming of Organic Compounds

The naming of organic compound is divided into three parts:

Part 1: Length of the parent chain i.e. the number of carbon atoms in the longest continuous (unbroken) chain [also known as the Prefix]

Prefix	meth-	eth-	prop-	but-
Number of carbon atoms in molecule	1	2	3	4

Part 2: Functional Group found in main parent chain [also known as the Suffix]

Homologous series	alkane	alkene	alcohol	carboxylic acid
Suffix	-ane	-ene	-ol	-oic

Part 3: Side group that are attached to the main parent chain [also known as Substituent]

Substituent	-Cl	-Br	-I	-CH3
Name of side group	chloro	bromo	iodo	methyl

 

For example, ethene is an alkene with two carbon atoms per molecule.

For example, propanol is an alcohol with three carbon atoms per molecule.

D) Formulae

They are four types of formulae that we can use to represent a particular organic compound. This also means that you will be tested in Chemistry examinations on all four types of formulae which are:

• Empirical  formula which is the simplest whole no. ratio of atoms of each element
• Molecular formula which is the total no. of atoms of each element in each molecule
• Structural formula which shows how atoms are arranged in the molecule
• Full Structural formula which shows all the bonds between atoms in a molecule

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends.

Do stay tuned to the upcoming posts as we will be looking at more key concepts in Organic Chemistry as well as some GCE O-Level Pure Chemistry and Sec 4 IP Chemistry examination questions.

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