Intro to Thioesters - Online Tutor, Practice Problems & Exam Prep

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

Hey, everyone. So let's take a look at the introduction to thioesters. Now we're going to say thioesters themselves are sulfur analogs of esters. And we're going to say there are two types of them. We have our s alkyl thioester, which is the common one.

If we take a look at the image to the right, we're going to say this represents an s alkyl thioester. As we can see, it has a carbonyl group. This carbonyl group is connected to a sulfur, which in turn is connected to an r group. In this case, this r group represents a carbon group. Then we have our O alkyl thioester, which would be this one.

Notice the differences. Now we no longer have our typical carbonyl group where it is carbon double bonded to oxygen. Instead, we have carbon double bonded to sulfur. Then that carbon is single bonded to an oxygen, which in turn is single bonded to an r group and an alkyl group. Now we're going to say here that these s thioesters, which again are the first image, are also known as thioesters.

So just remember, when we're talking about these thioesters, they can either be in the form of an s alkyl thioester, or they can be in the form of an o alkyl thioester. The first one is the more common version of these two possibilities.

Intro to Thioesters Concept 2

Hey, everyone. So in this video, we're going to talk about the IUPAC naming when it comes to our thioester. Now here we're going to say it's similar to ester nomenclature. We're going to say the carbon chain with the carbonyl group, so C≡O, is named as an alkane with a thioate modifier. And we're going to say if the parent chain is a cycloalkane, then we're going to use carbothioate modifier.

And we're going to say the alkyl group attached to sulfur, it's named as a substituent with an S prefix. So here we're going to have our S prefix with our substituent. We have our parent and then we modify the ending. So if we're taking a look here, we have our thioesters. We're going to say here our R group represents a chain.

Because it's not a ring, it's just going to have the modifier ending of thioate. Here we have our carbonyl connected to sulfur connected to another R group, a carbon group. But let's say that we are connected to a ring. So let's say we're connected to this cyclopropane ring. Because that cyclopropane ring is there, remember, if parent chain is a cycloalkane, we're going to use carbothioate modifier.

So this would become carbothioate modifier ending. Alright. So these are the basic steps when it comes to the nomenclature of our thioesters. Now let's click on the next video and start putting it to practice when it comes to naming these different types of thioesters.

Intro to Thioesters Example 1

In this example question, it says, provide the systematic name for the following thioester. Now, if we take a look here, we have our carbonyl group. Remember, this carbonyl group is going to form the part of the parent chain, and we're going to say that this sulfur with this R group, this R chain here represents our substituent. We're going to say it has 1, 2, 3, so this is a propyl chain connected to sulfur. Remember, we name it as an S substituent.

So this would be S-propyl. And that's an S. Looks like a 5, but it's an S. And then we're going to say when it comes to our parent name, we have 1, 2, 3, 4 carbons that are part of the parent chain. Four carbons is butane.

And then here, remember, our modifier 'n' will become a thioate, so this would be butanethioate. So the name of this thioester would be S-propylbutanethioate.

Provide IUPAC name for following molecule. 

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

Intro to Thioesters Concept 3

Hey, everyone. So let's take a look at common naming in reference to thioesters. Now here we're going to say that the carbon chain with the carbonyl group, so C=₂O, is named using common name prefixes. Now, the number of carbons determines our prefix. So one will be form, 2 would be acid, 3 would be propion, 4 would be butra, and 5 would be valer.

Now, here we're going to say that the prefix would have a thio prefix and it would have an -ate suffix. And we'd say that the alkyl group attached to sulfur is named as a substituent, the same as we have done with IUPAC naming. So here, in terms of the naming system, it would be S-substituent thio, the prefix would be based on the number of carbons within the thioester, and then we end with -ate. Alright. So this is the setup when it comes to common naming for thioesters.

Now that we know the basic idea, let's click on the next video and put our rules to work. We're going to start naming thioesters using the common naming system.

Intro to Thioesters Example 2

Hey everyone. So here it says, provide a common name for the following thioester. If we take a look here, we can see that our s substituent is this sulfur with this benzene ring. Now here, remember when benzene is a substituent, it's no longer called Benzene, it's called Phenyl. So it's going to be an S substituent, so this would be S-phenyl.

Next, we're going to say, the prefix that we use is thiol. And if we look at this, we would say that the number of carbons that are part of the parent chain are 1, 2, 2 carbons. Remember, that would mean that the prefix would be "acid," and then we end it with "ate." So the name of this thioester will be S-phenylthioacetate. So that would be our final answer.

Provide common name of following thioester. 

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

Draw a structure for pentyl benzothioate.

• A.
• B.
• C.
• D.

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.