Organic Chemistry: Types of Formulae

Organic Chemistry is a very important component in A-Level H2 Chemistry and is about 40% weightings for Cambridge A-Level Higher 2 (H2) Chemistry in Singapore.

From my experience in conducting weekly A-Level JC H2 Chemistry tuition classes for close to two decades, i realised that many are having problem in mastering Organic Chemistry because of their poor fundamentals. One of them is knowing the different types of formulae to be used in examination when asked.

In the video below, i will be sharing with you the most common formulae in Organic Chemistry such as:

• Molecular Formula
• Empirical Formula
• Structural Formula (Condensed Structural Formula)
• Displayed Formula (Full Structural Formula)
• Skeletal Formula
• Stereochemical Formula

Length of video: 4.05 mins

Link to video: http://www.youtube.com/watch?v=MAL6pqvPmvQ

Empirical Formula

• Simplest formula that shows the ratio of number of atoms of the elements present in one molecule

Molecular Formula

• Shows the actual number of atoms of the elements present in one molecule

For example, the empirical formula and molecular formula for lactic acid is CH₂O and C₃H₆O₃.

Condensed Structural Formula

• Shows how the constituent atoms of a molecule are joined together with minimal detail using conventional groups
• All the atoms attached to a particular carbon atom are written immediately after that carbon atom

For example, the condensed structural formula for lactic acid is CH₃CH(OH)CO₂H and that for 2-methylpropene is CH₂C(CH₃)₂.

Full Structural Formula (Displayed Formula)

• Detailed structure of a molecule showing the relative placing of atoms and the number & type of bonds between them
• One of the common mistake students often made is the omission of O-H bonds for the hydroxyl functional group
• For ring structures (including benzene rings), all the C and H atoms (and their related bonds) can be omitted
• the following symbols are used to represent the cyclohexane ring and benzene ring respectively

Skeletal Formula

• Simplified organic formula by removing hydrogen atoms from alkyl chains, leaving just the carbon skeleton and associated functional groups
• Each C-C bond in the carbon skeleton is a line (each end is a carbon atom)
• Double and triple lines indicate double and triple bonds respectively

• Note that skeletal or partial skeletal structures are acceptable in student’s answers where they are unambiguous.

Stereochemical Formula:

• Shows the three-dimensional spatial arrangement of bonds, atoms and groups around a key part of a molecule (usually a stereochemical centre)
• Solid wedges indicate bonds to an atom pointing out of the plane of the paper
• Dashed wedges or hashed lines indicate bonds to an atom pointing into the plane of the paper
• Normal straight lines indicate bonds on the plane of the paper

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.

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PS: Under related articles below, there are several blog post discussions and questions related to Organic Chemistry. You can also do a keyword search using the search box at the top right hand corner.

Related Articles:

• Determining Molecular Formula from Empirical Formula
• Organic Chemistry: Total Number of Stereoisomers
• Organic Chemistry: Constitutional (Structural) Isomerism
• Organic Chemistry: Introductory Topics
• Organic Chemistry: Isomerism in Organic Compounds

Sean Chua

Winners Education Centre Pte. Ltd.

Many know me as the Ten Year Series book author for JC A-Level H2 Chemistry and O-Level Pure Chemistry. My 19+ years of coaching experience (since 1999) with more than 1500 students from 180+ JCs and Secondary Schools has allowed me to understand the true reasons why students are not able to perform well in Chemistry. Most importantly, my strength lies in using everyday analogies (even grandmothers can understand!) to simplify abstract concepts. Also, my teaching methodology has been designed to be fun, enjoyable and effective for my students.

If you want to have an enjoyable time learning Chemistry and being motivated to excel in Chemistry, contact me today at 9828 7357