Organic Compounds: Structural, Formulas & Stereochemistry

Structural formula of an organic compound is the graphical representation of the arrangements of the atoms of the molecule in a three-dimensional space where chemical bonding is also depicted implicitly or explicitly. There are various different ways of depicting the structural formulas of organic compounds. Lewis structure, Condensed structural formula and skeletal formula are some of the methods used widely to represent and understand the spatial arrangement of atoms in the organic molecules.

Key Terms: Organic Compounds, Lewis Structures, Structural formulas, Condensed structural formula, Skeletal formula, Stereochemistry

Read More : Concepts in Chemistry

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What is an Organic Compound?

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Organic compounds fundamentally are those chemical compounds that contain any kind of carbon-hydrogen bond. Carbon has a fascinating property called catenation that allows it to quickly form bonds with any given elements it interacts with. The specific branch of chemistry that deals with properties, synthesis, reactions etc. of such organic compounds is called Organic Chemistry.

Organic and Inorganic Compounds

Organic compounds can be natural or synthetic. Natural organic compounds are those which are directly extracted from natural resources such as petrochemicals. These compounds do not occur in a large quantity in the earth strata but they are a fundamental chemical constituent of living beings. On the other hand, synthetic ones are synthesized using the known reactions of other compounds. There are certain examples of organic compounds like ethanol and insulin which are manufactured using microorganisms.

The video below explains this:

Organic Compound Detailed Video Explanation:

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Structural Representation of Organic Compounds

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Structural formula of an organic chemical compound is the graphical representation of the arrangements of the atoms of the molecule in a three-dimensional space. The chemical bonding is also shown implicitly or explicitly. Structural formulas give a more comprehensive geometric representation of the molecular structure of the organic compound. Thus, we can easily distinguish between the chemical compounds with the same chemical formulas but different structural orientations. 

Organic Compounds structural representation

Structurally the organic compounds can be depicted in different ways:

• Lewis structures
• condensed structure formulas
• Bond-line structural formula

Lewis Structures

Lewis structure or Lewis dot structures are flat graphical representations that show atom connectivity and lone pair or unpaired electrons. It is not a three-dimensional structure. This formula is usually used for small organic molecules. Here, each of the lines represents two electrons of a single bond while two or three parallel lines between pairs of atoms represent double and triple bonds respectively. All the non-bonded paired or unpaired electrons or any other charges are also indicated.

Lewis dot structure of Water 

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Condensed Structural Formula

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The condensed structural formula is a typographic system arose to describe organic structures in a line of text. It is a convenient way of representing simple chemical structures however, its use is limited while representing the cyclical molecules.

Eg: CH₃CH₂OH (ethanol)

Here, parentheses are also used to show multiple identical groups, usually indicating attachment to the nearest non-hydrogen atom on the left when appearing within a condensed structural formula.

Eg: (CH₃)₂CHOH or CH(CH₃)₂OH (2- propanol)

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Skeletal Formula

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Skeletal formulas are another standard way of representing complex organic molecules. Here, the carbon atoms are implied to be located at the vertices or corners and end of the line segments rather than being indicated with the letter ‘C’. Hydrogen atoms attached to carbon atoms are not indicated. However, the hydrogen atoms attached to atoms other than carbon atom must be mentioned explicitly. Here, each of the carbon atoms is thought to be associated with hydrogen atoms to give the carbon atom its four bonds. 

Skeletal formula of Isobutanol (CH₃)₂CHCH₂OH

Read Also: Carbonyl Compounds

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Stereochemistry: 3D Representation of Organic Molecules

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There are several ways to represent the three-dimensional structure of the organic molecules. These three-dimensional arrangement of atoms in a molecule is called stereochemistry. 

Stereochemistry in Skeletal Formula

The chirality of an organic compound can be represented by Natta Projection method. Here, solid wages showcase bonds pointing above the plane of the paper while dashed wages are indications of bonds pointing below the plane.

Skeletal formula of Strychnine

Unspecified Stereochemistry

Wavy single bonds represent unspecified stereochemistry or sometimes a mixture of isomers.

Fructose

The above diagram shows the fructose molecule with a wavy bond to HOCH₂ group. The wavy bond represents the bond of unspecified characteristics.

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Things to Remember

• Organic compounds are those chemical compounds that contain any kind of carbon-hydrogen bond. 
• The catenation property of the carbon atoms allows the formation of organic compound formation.
• Structure formula refers to the graphical representation of the arrangements of the atoms of the molecule in a three-dimensional space. 
• Lewis structures are two-dimensional flat graphical representations that show atom connectivity and lone pair or unpaired electrons. 
• Each line represents two electrons of a single bond while two or three parallel lines between pairs of atoms represent double and triple bonds respectively.
• Condensed structural formula is a typographic system used to describe organic structures in a line of text. It is of limited use in representing cyclical structures.
• In the case of skeletal formula, the carbon atoms are implied to be located at the vertices or corners and end of the line segments while “C” is never written. However, the hydrogen atoms are indicated.

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