Intro to Thioesters: Videos & Practice Problems

Thioesters are sulfur analogs of esters, categorized into s-alkyl thioesters and o-alkyl thioesters. The IUPAC naming involves using the thioate modifier for carbon chains with a carbonyl group, while cycloalkanes use the carbo thioate modifier. Common naming employs prefixes based on carbon count, such as "thio" for one carbon (form) and "butra" for four carbons, ending with "ate." Understanding these naming conventions is essential for accurately identifying and working with thioesters in organic chemistry.

Intro to Thioesters Concept 1

Thioesters are important compounds in organic chemistry, serving as sulfur analogs of esters. They can be categorized into two main types: S-alkyl thioesters and O-alkyl thioesters. S-alkyl thioesters, the more common variant, feature a carbonyl group (C=O) that is bonded to a sulfur atom (S), which is further connected to an R group, typically representing a carbon group. This structure is crucial for understanding the reactivity and properties of thioesters.

On the other hand, O-alkyl thioesters differ significantly in their structure. Instead of the traditional carbonyl group bonded to oxygen, they possess a carbon atom double-bonded to sulfur (C=S). This carbon is also single-bonded to an oxygen atom (O), which is then connected to an R group. The distinction between these two types of thioesters is essential for their chemical behavior and applications in various biochemical processes.

In summary, thioesters can exist as either S-alkyl thioesters or O-alkyl thioesters, with S-alkyl thioesters being the more prevalent form. Understanding these structures is fundamental for exploring their roles in organic reactions and biological systems.

Intro to Thioesters Concept 2

Thioesters are a specific class of compounds that share similarities with esters in their nomenclature. When naming thioesters, the carbon chain containing the carbonyl group (C=O) is treated similarly to that of an ester, but with a key distinction: the carbon chain is named as an alkane with a "thioate" modifier. This means that the suffix "-oate" used in esters is replaced with "-thioate" for thioesters.

In cases where the parent chain is a cycloalkane, the nomenclature changes slightly. The appropriate modifier in this scenario is "carbothioate," indicating the presence of the cyclic structure. Additionally, any alkyl group that is attached to the sulfur atom is designated as a substituent and is prefixed with an "S" to denote its connection to sulfur.

For example, if the thioester has a linear carbon chain (represented by the R group), it will simply end with "thioate." Conversely, if the thioester is connected to a cyclopropane ring, the name will incorporate the "carbothioate" modifier, reflecting the cyclic nature of the parent chain.

Understanding these naming conventions is essential for accurately identifying and communicating the structure of thioesters in organic chemistry. As you practice naming various thioesters, keep these guidelines in mind to ensure clarity and precision in your chemical nomenclature.

Intro to Thioesters Example 1

To determine the systematic name of a thioester, it is essential to identify both the parent chain and the substituents correctly. In this example, we start with a carbonyl group, which is integral to the parent chain. The substituent in this case is a sulfur atom bonded to a propyl group, denoted as an S-propyl substituent. The 'S' indicates that the propyl group is attached to the sulfur atom.

Next, we analyze the parent chain, which consists of four carbon atoms. The presence of four carbons indicates that the parent name is derived from butane. To complete the naming process, we modify the parent name by adding the suffix 'thioate' to reflect the thioester functional group. Therefore, the parent name becomes butanethioate.

Combining these elements, the full systematic name for the thioester is S-propylbutanethioate. This name effectively communicates the structure of the compound, highlighting both the substituent and the parent chain.

Provide IUPAC name for following molecule. 

• A. isobutane cyclopentenylthioate
• B. S-isobutyl cyclopentanecarbothioate
• C. S-cyclopentenyl isobutanecarbothioate
• D. S-isobutyl cyclopentenylthioate

Answer: (B)

Intro to Thioesters Concept 3

Thioesters are a specific class of organic compounds characterized by the presence of a carbonyl group (C=O) adjacent to a sulfur atom. When naming thioesters, the carbon chain containing the carbonyl is identified using common name prefixes that correspond to the number of carbon atoms present. For instance, the prefixes are as follows: one carbon is referred to as "form," two carbons as "acet," three as "propion," four as "buty," and five as "valer."

In the naming convention for thioesters, the prefix is combined with the "thio" prefix to indicate the presence of sulfur, and the suffix "ate" is used to complete the name. Therefore, the general structure for naming a thioester involves identifying the alkyl group attached to the sulfur as a substituent, similar to the IUPAC naming system. The final name will reflect the number of carbons in the thioester chain, prefixed by "thio," and suffixed with "ate."

For example, a thioester derived from a three-carbon chain would be named "thio-propionate," indicating the presence of a propionyl group and a sulfur atom. Understanding this naming system is essential for accurately identifying and communicating about thioesters in chemical contexts.

Intro to Thioesters Example 2

In organic chemistry, thioesters are a class of compounds that contain a sulfur atom bonded to an acyl group. To name a thioester, it is essential to identify the substituents and the parent chain correctly. In this case, the thioester has a sulfur atom attached to a phenyl group, which is derived from benzene. When benzene acts as a substituent, it is referred to as a phenyl group.

The naming process begins with identifying the sulfur substituent, which in this case is designated as "S-phenyl." Next, we determine the parent chain, which consists of two carbon atoms. The prefix for a two-carbon acyl group is "acet," and since we are dealing with a thioester, we add the suffix "-ate" to complete the name.

Combining these elements, the common name for this thioester is S-phenylthioacetate. This name reflects both the substituent and the structure of the compound, providing a clear understanding of its composition.

Provide common name of following thioester. 

• A. S-butyl pentanethioate
• B. S-pentyl thiobutyrate
• C. O-butyl valeratethioate
• D. S-butyl thiovalerate

Answer: (D)

Draw a structure for pentyl benzothioate.

• A.
• B.
• C.
• D.

Answer: (A)

Here’s what students ask on this topic:

What are thioesters and how are they different from regular esters?

Thioesters are sulfur analogs of esters, where the oxygen atom in the ester is replaced by a sulfur atom. In a typical ester, the structure is R-CO-O-R', where a carbonyl group (C=O) is bonded to an oxygen atom, which is further bonded to an alkyl or aryl group. In thioesters, the structure is R-CO-S-R', where the carbonyl group is bonded to a sulfur atom instead of oxygen. This substitution of sulfur for oxygen gives thioesters different chemical properties compared to regular esters, such as increased reactivity due to the larger atomic radius and lower electronegativity of sulfur.

How do you name thioesters using IUPAC nomenclature?

In IUPAC nomenclature, thioesters are named similarly to esters but with specific modifiers. For a linear carbon chain with a carbonyl group (C=O), the name ends with 'thioate.' For example, if the parent chain is a cycloalkane, the name ends with 'carbothioate.' The alkyl group attached to the sulfur is named as a substituent with an 'S-' prefix. For instance, if you have a thioester with a cyclopropane ring, it would be named as 'cyclopropanecarbothioate.' The general format is: S-alkyl group + parent chain + thioate or carbothioate.

What is the common naming system for thioesters?

The common naming system for thioesters uses prefixes based on the number of carbons in the carbon chain. For example, one carbon is 'form,' two carbons are 'acet,' three carbons are 'propion,' and four carbons are 'butra.' The name includes a 'thio' prefix and ends with 'ate.' The alkyl group attached to the sulfur is named as a substituent, similar to IUPAC naming. For example, a thioester with three carbons and an ethyl group attached to sulfur would be named 'S-ethyl propionthioate.'

What are the types of thioesters and which one is more common?

Thioesters are categorized into two types: S-alkyl thioesters and O-alkyl thioesters. S-alkyl thioesters have a structure where the carbonyl group (C=O) is bonded to a sulfur atom, which is further bonded to an alkyl group. O-alkyl thioesters have a structure where the carbonyl group is bonded to a sulfur atom, which is bonded to an oxygen atom, and then to an alkyl group. S-alkyl thioesters are more common than O-alkyl thioesters.

Why are thioesters more reactive than regular esters?

Thioesters are more reactive than regular esters primarily due to the presence of sulfur instead of oxygen. Sulfur has a larger atomic radius and lower electronegativity compared to oxygen, which makes the carbon-sulfur bond weaker and more susceptible to nucleophilic attack. This increased reactivity is particularly important in biochemical processes, such as the formation and breakdown of acetyl-CoA in metabolic pathways.