The key difference between thiocyanate and isothiocyanate is that thiocyanate is a functional group in which the alkyl or aryl group is attached through the sulfur atom whereas isothiocyanate is the linkage isomer of thiocyanate in which the alkyl or aryl group is attached through the nitrogen atom.
Thiocyanate and isothiocyanate are functional groups containing carbon, nitrogen, and sulfur atoms. These functional groups have the same connectivity of atoms. That is, the carbon atom is in the middle, while nitrogen and sulfur atoms are attached to its sides. However, the chemical bonding between these atoms is different from each other.
CONTENTS
1. Overview and Key Difference
2. What is Thiocyanate
3. What is Isothiocyanate
4. Side by Side Comparison – Thiocyanate vs Isothiocyanate in Tabular Form
5. Summary
What is Thiocyanate?
Thiocyanate is an anion having the chemical formula –SCN–. It acts as a functional group in many organic compounds. Here, the sulfur atom links with the alkyl or aryl group, while the nitrogen atom is attached only to the carbon atom, which is in the middle of the functional group. Therefore, the sulfur atom has a single bond with the carbon atom, whereas the nitrogen atom has a triple bond with the carbon atom. The sulfur atom forms another single bond with the alkyl or aryl group when forming the organic compound.
Figure 01: Comparison Between Thiocyanate and Isothiocyanate Functional Groups in Organic Compounds
The thiocyanate anion is the conjugate base of thiocyanic acid. Better known examples for compounds containing this anion include ionic compounds, such as potassium thiocyanate and sodium thiocyanate. Phenyl thiocyanate is an example of an organic compound containing thiocyanate functional group. The thiocyanate group is a linkage isomer of the isothiocyanate group. Organic thiocyanate compounds are important as building blocks in synthesizing sulfur-containing organic compounds.
What is Isothiocyanate?
Isothiocyanate is the linkage isomer of thiocyanate functional group. Therefore, the isothiocyanate group also contains carbon, nitrogen and sulfur atoms.
Figure 02: General Structure of Isothiocyanate Group
However, unlike in thiocyanate, when forming an organic compound, the alkyl or aryl group links to this functional group via the nitrogen atom. Here, we can observe a double bond between carbon and nitrogen atoms. There is also a double bond between carbon and sulfur atoms where the sulfur atom is bonded only to the carbon atom.
What is the Difference Between Thiocyanate and Isothiocyanate?
Thiocyanate and isothiocyanate are isomers; they are linkage isomers because they link with alkyl or aryl groups at different points. The key difference between thiocyanate and isothiocyanate is that a thiocyanate is a functional group in which the alkyl or aryl group gets attached through the sulfur atom, whereas isothiocyanate is the linkage isomer of thiocyanate in which the alkyl or aryl group gets attached through the nitrogen atom.
Moreover, there is one triple bond between carbon and nitrogen atoms in the thiocyanate group, while there are no triple bonds between carbon and nitrogen atoms in the isothiocyanate group. Therefore, we can observe a single bond and a triple bond between atoms in the thiocyanate group. There are two double bonds between atoms of the isothiocyanate group. Besides, in the thiocyanate group, the angular geometry can be observed around the sulfur atom while, in the isothiocyanate group, the angular geometry is present around the nitrogen atom.
Below infographic summarizes the difference between thiocyanate and isothiocyanate.
Summary – Thiocyanate vs Isothiocyanate
Thiocyanate and isothiocyanate are isomers; they are linkage isomers because they link with alkyl or aryl groups at different points. The key difference between thiocyanate and isothiocyanate is that a thiocyanate is a functional group in which the alkyl or aryl group is attached through the sulfur atom, whereas isothiocyanate is the linkage isomer of thiocyanate in which the alkyl or aryl group is attached through the nitrogen atom.
Reference:
1. “Thiocyanate.” Wikipedia, Wikimedia Foundation, 28 July 2019, Available here.
2. “Isothiocyanate.” Wikipedia, Wikimedia Foundation, 27 Jan. 2020, Available here.
Image Courtesy:
1. “PhSCN-PhNCS-comparison” (Public Domain) via Commons Wikimedia
2. “Isothiocyanate group” By Fvasconcellos – Own work (Public Domain) via Commons Wikimedia