A Level Chemistry Revision: Organic Chemistry – Introduction To Organic Chemistry

by Lucy Bell-Young

Organic chemistry is somewhere between inorganic chemistry and biochemistry. While it focuses on carbon-based substances, it isn’t concerned with the biological processes that produce many of the organic compounds that it studies.

When revising for organic chemistry as part of your chemistry A level, you’ll also need a proper foundation in inorganic chemistry. For example, you’ll need to know about both the chemical and physical properties of various organic compounds. You’ll also spend a significant amount of time mastering how to name regular organic compounds, like alkanes.

In fact, naming and classifying organic compounds are the two main topics in organic chemistry. You must understand the IUPAC principles behind the standard nomenclature, such as the positions of the functional groups, and master how organic compounds are classified based on their functional groups. 

What is Organic Chemistry?

As the name suggests, organic chemistry is mainly concerned with organic substances. It’s the study of the molecular structure, physical and chemical properties, reactions, and synthesis of organic compounds or compounds that are carbon-based.

These compounds contain carbons that are covalent-bonded with other carbon atoms and elements. Most of these carbons can form chains and cyclical structures. Many of them form isomers or compounds that have the same chemical formulas, but different positions of carbons, elements, or functional groups in the structure.

Brief History

The historical origin of organic chemistry can be traced back to Friedrich Wohler’s 1828 discovery, when he synthesised urea. He was able to produce this substance from inorganic compounds, namely the salts potassium cyanate and ammonium sulphate. The process was later named Wohler’s synthesis.

Wohler’s discovery was a turning point in the scientific understanding of how organic compounds are created. Before this discovery, scientists believed in the concept of vitalism. Vitalism proposed that organic substances were endowed with a “vital force” from living organisms.

However, urea is an organic substance that naturally occurs as a component of urine. Therefore, Wohler’s synthesis disproved the idea of vitalism. This paved the way for the scientific study of organic compounds as a separate discipline from organic chemistry and biochemistry.

What Are the Differences Between Organic Chemistry and Biochemistry?

Organic chemistry has many similarities with biochemistry in that both disciplines are concerned with organic chemicals. However, organic chemistry doesn’t include the study of biological processes when looking at organic chemicals. It also has special focus on specific types of organic compounds, such as hydrocarbons and alcohols.

Here are the major differences between organic chemistry and biochemistry:

  • Organic chemistry is focused on investigating the various chemical and physical properties of organic substances, with the main aim being to synthesise these substances or create new useful compounds from them.
  • Biochemistry is primarily concerned with the way organic compounds and biomolecules function in living biological systems. Although biochemistry is mainly focused on organic substances, the discipline is only focused on those substances that have direct functions in living organisms.
  • Organic chemistry is concerned with studying the chemical and physical behaviours of organic substances for their industrial and commercial applications. From fuel to synthetic fibres, organic chemistry is at the forefront.
  • Biochemistry also has some industrial applications. However, it’s more about understanding how chemical reactions in biological processes work, such as protein synthesis. Consequently, it has several applications in medicine and pharmaceutical science.

What Are the Topics in Organic Chemistry?

The topics studied in organic chemistry have some overlaps with both biochemistry and inorganic chemistry. For instance, you need to know how to balance chemical equations based on the molarity of the reactants.

In organic chemistry, you’ll also study several complex organic compounds that have some roles in metabolic processes. Here are the main topics and sub-topics in organic chemistry that you need to explore when revising for exams:

  • The hydrocarbons: These include naming the alkanes (straight-chain hydrocarbons), the alkenes (hydrocarbons that contain double bonds), and the alkynes (hydrocarbons that contain triple bonds).
  • Functional groups: These include the various hydrocarbon-based chains or cyclic compounds that contain other elements and functional groups. These are the haloalkanes and haloarenes, the alcohols, the ethers, the aldehydes, the ketones, the carboxylic acids, the carboxylates, the esters, the acyl groups, the acyl halides, the acid anhydrides, the amines, the amides, the nitriles, and the cyclic compounds.
  • Ions: These are the cations and anions of organic compounds. They include the hydrons and the parent hydride cations.

How Are Organic Compounds Classified?

Organic compounds are classified on their compositions, molecular structures, and functional groups. In each category of organic compounds, there are several different examples, but they all share some common chemical and physical properties. 

For example, many organic compounds have functional groups that define their chemical and physical properties. Most of these compounds are derived from hydrocarbons. 

Here are some of the major classifications of organic compounds:

The Hydrocarbons

These compounds are composed of only carbon and hydrogen atoms.

  • Alkanes: Alkanes are hydrocarbons with straight chains of carbon atoms that have hydrogen atoms attached. The simplest example is methane, which only has one carbon atom in it.
Methane structure
  • Alkenes and alkynes: These are the hydrocarbons that have double (alkenes) and triple (alkynes) bonds.
Ethene and ethyne structures
  • The aromatics: These hydrocarbons contain hydrocarbon rings. The simplest example is benzene. The structural formula for benzene can be written in several ways:
Structural formula of Benzene

Functional Groups

These are defined by the special types of molecular groups attached to hydrocarbon derivatives.

  • Amines: These are organic compounds with an amine (from ammonia) functional group. One or more hydrogens of ammonia are replaced by an alkyl group. Below are some examples of amines. They have the general structure of R–CO–NR′R″.
General structure of the amines
  • Alcohols: These have the R-OH structure. They have a hydroxyl functional group (-OH) attached to an aliphatic substituent. 
Alcohols R-OH structure
  • Ethers: These have the structure of R-O-R’. The oxygen is attached to either two alkyl or two aryl groups. 
Structures of multiple ethers
  • Alkyl halides: These are also known as haloalkanes because one or more hydrogens of alkane are replaced by a halogen. Below are some examples of alkyl halides:
Alkyl halides structures
  • Thiols: These organic compounds have the generalised form R−SH. The sulphur is attached to an alkyl or other types of organic substituents. Examples include:
Generalised form of thiols
  • Aldehydes: These have the generalised form R-CHO. The carbonyl centre is double bonded with oxygen. These are examples of aldehydes:
  • Ketones: Ketones have the structure R2C=O. The carbon is covalently bonded with oxygen and attached to two hydrocarbon radicals.
Ketones structure
  • Carboxylic acids: Their general formula can be written as R−COOH. They include amino acids and fatty acids.
  • Amides: These contain atoms of nitrogen that are bonded with the carbon of the carbonyl group. Amides can be derived from the reactions between ammonia and carboxylic acids.

For more A level chemistry resources to help you revise and for information on studying chemistry A level, check out our A Level Chemistry Resources hub.


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