Intro to Redox Reactions - Online Tutor, Practice Problems & Exam Prep

Redox reactions, or oxidation-reduction reactions, involve the transfer of electrons between reactants. In organic chemistry, oxidation increases carbon-oxygen bonds, while reduction increases carbon-hydrogen bonds. For example, oxidizing an alcohol leads to an aldehyde and then a carboxylic acid, increasing carbon-oxygen bonds from one to three. Conversely, reducing a carboxylic acid decreases carbon-oxygen bonds and increases carbon-hydrogen bonds, transitioning to an aldehyde and then to an alcohol. Understanding these transformations is crucial for grasping organic reaction mechanisms and pathways.

Identifying Redox Reactions Concept 1

In this video, we're going to talk about redox reactions, first from a General Chemistry perspective and then from an organic chemistry perspective. Recall that redox reactions, also known as oxidation-reduction reactions, involve the transference of an electron or electrons between reactants. This is our general chemistry definition of a redox reaction. In organic chemistry, it's a little bit different. Here, redox reactions involve increasing or decreasing the oxygen or hydrogen amount on a molecule. When we talk about oxidation, oxidation involves increasing the number of carbon-oxygen bonds on the molecule. If we're talking about reduction, that involves increasing the number of carbon-hydrogen bonds on the molecule.

If we take a look here at oxidation versus reduction, we're going to see that on the far left side, we have a hydrocarbon, in the form of methane, and then on the far right side, we have carbon dioxide. Notice that they're both grayed out. That's because we don't really deal with these two types of compounds when we're talking about oxidation versus reduction. We're going to focus on the middle portion, where we're going from an alcohol to what looks like an aldehyde to a carboxylic acid. That's the portion that we care about in terms of organic chemistry.

Now here, we can oxidize a hydrocarbon to our alcohol, and notice that we had no carbon-oxygen bonds initially, but our first oxidation step creates our first carbon-oxygen bond, applicable for alcohols. If we continue with our oxidation process, we started with one carbon-oxygen bond, and now we have two because we're double-bonded to that oxygen. This section here stands for aldehydes and ketones. If we continue oxidizing, we get to a carboxylic acid, and we go from having two carbon-oxygen bonds to now three. If we continued further, we would get carbon dioxide, which has four carbon-oxygen bonds. However, we do not concern ourselves with that portion because it does not represent an organic molecule for us.

Going the opposite way with reduction, we start out with the carboxylic acid, then move over to the aldehyde or ketone section. Here we notice that we go from three carbon-oxygen bonds to just two. Not just that, but we're increasing the number of carbon-hydrogen bonds. Initially, we had only one carbon-hydrogen bond, and now we're back to two. Continuing onward, instead of having two carbon-oxygen bonds, we have three, and we're at the alcohol phase. If we continued, we would have four carbon-hydrogen bonds. Again, we're not concerned with the extremes in this image; we don't concern ourselves with hydrocarbons or carbon dioxide. We operate in the highlighted section in the middle, between alcohols, aldehydes and ketones, and carboxylic acids.

Intro To Redox Reactions Example 1

Determine if the following reaction represents an oxidation or reduction reaction. If we take a look here, we're going to say that we have, as far as we can see, 1 carbon-oxygen bond, and we have 1 carbon-hydrogen bond here. Now here this is just a regular carbon-carbon bond, and this is just a regular carbon-carbon bond, so we don't look at those. Now we're focusing on this carbon because we can see that it undergoes a change here. So that's where we're focusing on it. So we're going to say here we're starting out with 1 carbon-oxygen and 1 carbon-hydrogen. If we come over here, what's happened? Well, we can see that this carbon, which is still the same carbon here, has lost its carbon-hydrogen bond. So it has 0 of those now. And now instead of being connected to oxygen just once, it's now connected to it twice. So we have increased the number of carbon-oxygen bonds. And we know when we do that, that's a sign of oxidation. So here we'd say that this reaction represents an oxidation reaction. We have an alcohol that's been oxidized into a ketone product.

Determine if the following reaction represents an oxidation, reduction or neither.

• A. oxidation
• B. reduction
• C. neither

Determine if the following reaction represents an oxidation, reduction or neither.

• A. oxidation
• B. reduction
• C. neither

Here’s what students ask on this topic:

What is a redox reaction in organic chemistry?

In organic chemistry, a redox reaction involves the transfer of electrons, leading to changes in the oxidation state of molecules. Oxidation refers to the increase in the number of carbon-oxygen bonds, while reduction involves an increase in the number of carbon-hydrogen bonds. For example, oxidizing an alcohol (R-OH) can lead to the formation of an aldehyde (R-CHO) and further oxidation can produce a carboxylic acid (R-COOH). Conversely, reducing a carboxylic acid decreases the carbon-oxygen bonds and increases the carbon-hydrogen bonds, transitioning to an aldehyde and then to an alcohol.

How do you identify oxidation and reduction in organic molecules?

In organic molecules, oxidation is identified by an increase in the number of carbon-oxygen bonds. For example, converting an alcohol (R-OH) to an aldehyde (R-CHO) or a carboxylic acid (R-COOH) involves oxidation. Reduction, on the other hand, is identified by an increase in the number of carbon-hydrogen bonds. For instance, reducing a carboxylic acid (R-COOH) to an aldehyde (R-CHO) and then to an alcohol (R-OH) involves reduction. These changes are crucial for understanding reaction mechanisms and pathways in organic chemistry.

What are the steps involved in the oxidation of an alcohol in organic chemistry?

The oxidation of an alcohol in organic chemistry typically involves several steps. First, the alcohol (R-OH) is oxidized to an aldehyde (R-CHO), which involves the formation of a carbon-oxygen double bond. This is the first oxidation step. If oxidation continues, the aldehyde can be further oxidized to a carboxylic acid (R-COOH), which involves the formation of an additional carbon-oxygen bond. Each step increases the number of carbon-oxygen bonds, moving from one in the alcohol to two in the aldehyde and three in the carboxylic acid.

What is the difference between oxidation and reduction in organic chemistry?

In organic chemistry, oxidation and reduction refer to changes in the number of carbon-oxygen and carbon-hydrogen bonds. Oxidation involves an increase in the number of carbon-oxygen bonds. For example, oxidizing an alcohol (R-OH) to an aldehyde (R-CHO) and then to a carboxylic acid (R-COOH) increases the carbon-oxygen bonds from one to three. Reduction, on the other hand, involves an increase in the number of carbon-hydrogen bonds. For instance, reducing a carboxylic acid (R-COOH) to an aldehyde (R-CHO) and then to an alcohol (R-OH) increases the carbon-hydrogen bonds.

Why are hydrocarbons and carbon dioxide not typically considered in organic redox reactions?

Hydrocarbons and carbon dioxide are not typically considered in organic redox reactions because they represent the extremes of oxidation and reduction. Hydrocarbons, like methane (CH₄), have no carbon-oxygen bonds, while carbon dioxide (CO₂) has four carbon-oxygen bonds. Organic redox reactions usually focus on the intermediate stages, such as alcohols, aldehydes, ketones, and carboxylic acids, where the changes in carbon-oxygen and carbon-hydrogen bonds are more relevant to organic reaction mechanisms and pathways.