Functional Groups in Chemistry - Online Tutor, Practice Problems & Exam Prep

Understanding functional groups is crucial in chemistry as they determine the reactivity and properties of compounds. Hydrocarbons, composed solely of carbon and hydrogen, form the basis of organic chemistry. Alkanes are characterized by single carbon-carbon bonds, alkenes by carbon-carbon double bonds, alkynes by triple bonds, and aromatic rings, such as benzene, by alternating double and single bonds in a ring structure. Functional groups without carbonyls (C=O) include alcohols (C-OH), ethers (C-O-C), amines (N-H), alkyl halides (C-X), and thiols (C-SH). In contrast, functional groups with carbonyls include carboxylic acids (C=O-OH), esters (C=O-O-C), amides (C=O-N), aldehydes (C=O-H), and ketones (C=O with carbons on both sides). Recognizing these groups is essential for predicting chemical behavior and understanding molecular interactions.

Functional Groups in Chemistry

Now the functional group represents the part of a molecule that is recognizable and responsible for the compounds reactivity. In this series of videos we're going to go how to identify different functional groups of given compounds. First, we're going to start out with the hydrocarbons. Now hydrocarbons are just compounds containing only carbons and hydrogens, hydro standing for hydrogen and of course carbons for carbons.

If we take a look here, but we have highlighted in red represents that particular functional group. In the first one we have just carbons that are single bonded to one another. We're going to say when we have just a series of carbon single bonded to each other and they're single bonded to hydrogens, this represents what we call an alkane group. So this is an alkane. The chain could get even longer if it wants. So as long as the carbons are single bonded to each other and single bonded to hydrogens, it represents an alkane.

Next we're going to say what's highlighted is 2 carbons. This time they're double bonded to one another. When we're talking about double bonded carbons, this represents an alkene. And then for the third one, we have our carbons triple bonded to each other. When carbons are triple bonded to each other, that's an alkyne. Now you might notice that we have similarities in names. We have alkanes, alkenes and alkynes.

And then finally what we have here is we have a ring with three double bonds within it. This here, we call this a benzene ring, or you may hear it being called an aromatic ring as well. So they're interchangeable terms, benzene ring or aromatic ring. For those of you who plan to go further into chemistry, into organic chemistry, you'll go into greater deaths when it comes to these different functional groups. Now just realize that this first group is only the hydrocarbons. They all have only carbons and hydrogens associated with them.

Functional Groups in Chemistry Example 1

In this example question, it says identify the type of functional group or groups present within the following compound. So here we have a bunch of carbons and hydrogens, so we know that it's a hydrocarbon. Now let's lookout for double bonds and triple bonds because those seem to be big indicators of the different types of hydrocarbons that exist.

If we take a look here, we have these two carbons double bonded to one another. These two carbons double bonded to one another and then here these two carbons triple bonded to one another. Now remember if you have a triple bond between carbons, that represents an alkyne functional group and then here these two double bonded carbon groups represent alkene functional groups.

This structure cannot be seen as an alkane because an alkane possesses only single bonded carbons and hydrogens together. So we wouldn't count that as a unique functional group for this compound. So again, look out for the double bond. Look out for the triple bond. Those are good landmarks to look for when looking at different types of hydrocarbons within any given compound.

Functional Groups in Chemistry

In this video, we'll take a look at the functional groups without carbonyls. Now, a carbonyl group represents a carbon double bonded to an oxygen, so it's represented as C=O. Functional groups without a carbonyl group are recognizable by the presence of sulfur, oxygen, nitrogen, or a halogen. Remember, your halogens are in Group 7A, so they're represented as fluorine, chlorine, bromine or iodine. So a good way to remember this is sun, halogens, sulfur, oxygen, nitrogen and the halogens.

If we take a look down here, we're looking at the what's marked in red. That's kind of like a landmark that helps us to identify that particular functional group. So if we take a look here, if you have a single bonded carbon, so the carbon only has single bonds and it's connected to an OH, that represents an alcohol for the next one. If you have single bonded carbons, alright single body carbons, and they're both connected to the same oxygen making COC, then that is an ether.

For the next one, the landmark is the nitrogen. If we have a single bonded nitrogen connected to hydrogen's then that represents an amine. Now typically you'll see nitrogen could have one hydrogen or two or three hydrogens. Next we have carbon connected to X. What does X represent? Well, X is just a placeholder that represents any of the halogens, fluorine, chlorine, bromine or iodine. So if you have a single bonded carbon here connected to one of the halogens, then we call that an alkyl halid, so it's called an alkyl halid.

Then finally, if you have a single bonded carbon, single bonded carbon that is connected to an SH group, then we call that a thiol O here. These represent the most common types of functional groups that have sulfur, oxygen, nitrogen or halogen, but no carbonyl group. So keep these in mind when you run across them while looking at different functional groups.

Functional Groups in Chemistry Example 2

Here the example question says identify the type of functional group or groups present within the following compound. Remember look for your landmark elements sun or halogens.

If we take a look here, we have an oxygen. We're going to say that oxygen looks like it's connected to what, a carbon here and a carbon here. Those carbons, we don't see double bonds or triple bonds connected to them. So they're just regular single bonded carbons connected to an oxygen.

And remember, when we have COC, that represents an ether functional group. So here our only functional group within this structure would be our ether.

Functional Groups in Chemistry

We're now going to take a look at the functional groups with carbonyls. Remember, a carbonyl group is just C=O. We're going to say these types of functional groups share some similarities with those without carbonyls. What we have written in red is what that functional group represents. The things around it may change, but as long as you have that portion in red there, that's the functional group.

If we take a look at the first one, we have C=O connected to an OH group that represents what we call a carbasilic acid. So this is a carbacillic acid. For the next one we have C=O connected to O and then connected to AC. That is what we call an Ester. Next we have C=O directly bonded to a nitrogen that is an amide or amide. So both pronunciations are OK. So you might hear it as an amide or an A mind. Same thing.

Next we have AC double bond O connected directly to an H. We call this an aldehyde. And then finally you have AC double bond O with a carbon on each side that represents A ketone. So remember, all of these particular functional groups have the presence of a carbonyl group, and what is marked in red represents that specific functional group.

Functional Groups in Chemistry Example 3

Here we have to identify that type of functional group or groups present within the following compound O . If we take a look look for your carbonyl groups, we have a carbonyl group here. We have a carbonyl group here. Now look to see what they're connected to.

Well, the one on the left, that carbonyl is directly connected to an H. Remember we said if a carbonyl is directly connected to an H, that represents an aldehyde functional group. For the other carbonyl, what is it directly connected to? Well, it's connected to a carbon on this side, but that doesn't tell us much.

It's connected to an OH here because it's connected to an OH. That is also another important functional group, that is a carbasilic acid. So this particular compound possesses 2 carbonyl containing functional groups, one being an aldehyde and one being a carbasilic acid.

Identify the type of functional group(s) present within the following compound. 

• A. amine, ketone
• B. amide, alkene
• C. alkene, ketone
• D. amine, ketone, alkene
• E. alkene, amine

Identify the type of functional group(s) present within the following compound. 

• A. alcohol, ketone
• B. carboxylic acid, alcohol
• C. ether, alcohol
• D. ester, alcohol
• E. ester, ether

Here’s what students ask on this topic:

What are functional groups?

Functional groups are specific groupings of atoms within molecules that have their own characteristic properties, regardless of the other atoms or groups of atoms in the molecule. These groups are responsible for the typical chemical reactions that the molecule undergoes. They are like distinct 'functional' parts of a molecule that define its chemical nature and reactions.

For example, an alcohol group ($-\mathrm{OH}$) in organic compounds makes the molecules polar and capable of forming hydrogen bonds. This group also typically engages in reactions that can transform the molecule into other types of compounds, such as acids or esters. Other common functional groups include carboxylic acids ($-\mathrm{COOH}$), which make compounds acidic, amines ($-\mathrm{NH}2$), which can act as bases, and ketones ($C=O$) which are often involved in energy transfer reactions.

Each functional group has a specific set of properties and reactivity patterns, which allows chemists to predict the behavior of the molecules in which they are found. Understanding functional groups is crucial for studying organic chemistry, as they are foundational to the synthesis and reactions of organic compounds.

How can functional groups be memorized?

Memorizing functional groups can be a daunting task, but there are several strategies you can use to make it easier. One effective method is to create flashcards with the structure of the functional group on one side and its name and properties on the other. This allows for repetitive review and self-testing.

Another approach is to use mnemonics, which are memory aids that help you recall larger pieces of information through simple cues. For example, you might create a memorable phrase where each word starts with the same letter as the functional group it represents.

Grouping similar functional groups together can also help, as you can learn them in sets based on common characteristics, such as all the groups containing oxygen or all the groups that are basic.

Drawing the structures repeatedly can reinforce your memory, as the act of writing helps in retention. Additionally, try to understand the chemical behavior of each functional group, as this conceptual knowledge can help anchor them in your memory beyond rote memorization. Understanding the logic behind the naming and the reactivity of functional groups can make them more intuitive and easier to recall.

How can functional groups be identified?

Functional groups in organic molecules can be identified using a combination of methods, including:

1. Infrared (IR) Spectroscopy: This technique measures the absorption of infrared light by the molecule, which causes vibrations in the bonds. Each functional group has a characteristic absorption pattern or fingerprint in the IR spectrum, which can be used to identify the presence of specific groups.
2. Nuclear Magnetic Resonance (NMR) Spectroscopy: NMR detects the interaction of nuclear spins when placed in a magnetic field. Different functional groups affect the magnetic environment of nearby hydrogen (in ¹H NMR) or carbon atoms (in ¹³C NMR), leading to characteristic shifts in the NMR signals.
3. Mass Spectrometry (MS): MS can provide information about the molecular weight and fragmentation pattern of a compound, which can be indicative of certain functional groups.
4. Chemical Tests: There are various chemical tests that can be performed to identify functional groups. For example, the presence of alkenes can be tested with bromine water, while aldehydes and ketones can be distinguished by their reaction with 2,4-dinitrophenylhydrazine (DNPH).
5. Physical Properties: Some functional groups can be inferred by observing the physical properties of a substance, such as solubility.