The Thiol Functional Group

Thiol functional group

Core Concepts

The thiol functional group belongs to a class of organic functional groups that contain sulfur. This article will cover the structure and properties of thiols, as well as the reactions they are a part of.

Topics Covered in Other Articles

What is the Thiol Functional Group?

This group consists of a Sulfur atom bonded to both a Hydrogen atom and an R group. The name thiol refers to the fact that it is, essentially, an alcohol group with a Sulfur atom instead of an Oxygen atom. Thiols, like many Sulfur compounds, have an unpleasant odor. The human nose is so sensitive to thiols that they are often mixed, in low concentrations, with natural gas to make leaks easier to detect.

Quick Facts about the Thiol Functional Group

  • Structure: A Sulfur atom bonded to a Hydrogen atom
  • General Formula: R-SH
  • Atomic weight: 32.073
  • pH: Generally slightly acidic.
  • pKa: Generally around 10.
    • Methanethiol (CH3SH): 10.33
    • Ethanethiol (CH3CH2SH): 10.61

Naming Conventions

The IUPAC naming conventions of Thiols are fairly simple. A thiol’s name is the name of the R group with the suffix thiol. If the placement of the thiol on the R group needs to be specified, the name will have a number indicating its location. If there is more than one thiol, they will be numbered and have a prefix indicating the number of thiols present.

When a thiol is the only functional group on an alkyl chain, its number can go either before the name of the alkyl or before the “-thiol” suffix.

Here are several examples of named thiols:



1,3-butane dithiol




The amino acid Cysteine also contains thiol group:

Thiol Reactions

General Reaction Trends

Thiols often react similarly to alcohols. However, because Sulfur is a larger atom than Oxygen, it is more nucleophilic and polarizable. This means that Sulfur is better at stabilizing negative charges on and next to it.

Formation of Thiols

When a metal hydrosulfide such as LiSH reacts with an alkyl halide such as 2-bromopropane, the result is a thiol and a salt.

Thiol Synthesis

The thiol can then react again with an alkyl halide to form a sulfide, also known as a thioether. The first step in this reaction is the deprotonation of the thiol with a base. This gives the sulfur a negative charge and allows it to perform an SN2 reaction with an alkyl halide.

When thiols react with an oxidizing agent, they form a disulfide. A disulfide is the sulfur analog of a peroxide. Instead of two oxygen atoms bonded together, it consists of two sulfur atoms bonded together.

Example Questions

  1. Which of the following compounds contains a thiol group?

2. Draw the product of the following reaction:

3. Draw structures based on the following names:

a. 2,3-dimethylhexane-3-thiol

b. (E)-pent-2-ene-3-thiol

c. Benzenethiol

Further Reading