Carbonyl Group: Properties & Overview

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  • 0:00 What Is a Carbonyl Group?
  • 0:28 Properties of Carbonyl
  • 1:58 Importance of…
  • 3:48 Why Double Bond a Carbonyl?
  • 4:30 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Carbonyl has many friends in organic chemistry, including aldehyde and ketone. Continue reading to learn about the carbonyl group and find out what makes it so popular.

What Is a Carbonyl Group?

In organic chemistry, a carbonyl group is a functional group where a carbon atom is double bonded to an oxygen atom . A great way to remember that you're dealing with carbonyl is to look at the word itself. 'Carb' reminds you that a carbon atom is needed, while 'O' represents the oxygen atom. Now that we know what carbonyl looks like, let's learn more about its properties.

Properties of Carbonyl

The carbonyl group is found in many other functional groups, from aldehydes and anhydrides to ketones and carboxylic acids, just to name a few. The key point to remember is that whenever you see the formula carbon-oxygen double bond (C=O), you know a carbonyl is present in that functional group.

Another feature of the carbonyl group is its polarity. A polar substance is a compound that carries partial positive and negative charges. Carbonyl's polarity does two things to the property of a compound: increases the melting and boiling points and influences the compound's solubility. Let's tackle how polarity is related to each of these.

First, how does polarity relate to melting and boiling points? Polar compounds use very strong forces to keep the bonds between each atom in the compound strong. As you might suspect, it's hard to break these bonds. If you put a polar compound into a pot and crank up the temperature, the amount of energy required to break the bonds influences the boiling point. The same principle applies to the melting point. But keep in mind that other factors, such as the size of the compound, can affect boiling and melting points as well.

As for polarity and solubility, they're related because of the very simple concept that like dissolves like. Water is polar, and carbonyl is polar, so water dissolves carbonyl. Now that we understand carbonyl's properties, let's focus on its structure.

Importance of Carbonyl's Resonance

Look at these two structures:

One Type of Resonance for the Carbonyl Group

Notice something different about one carbonyl group? That difference is the absence of the double bond. The carbonyl is able to morph into different structures, using the same atoms, carbon and oxygen. In chemistry, this is called a resonance structure. Resonance structures are drawn in a special way to help us understand why the molecule has a positive and negative charge. Here we see how to write a resonant structure for carbonyl:

Complete Resonance Structure of a Carbonyl Group

When you draw these structures, don't forget the double-sided arrow and the brackets. These let people know that the carbonyl can change structures.

You might have noticed that the oxygen atom has dots floating around it with a negative charge sign at the top. Those dots represent lone pairs of electrons, making the oxygen atom electronegative. Lone pair refers to two electrons that can live alone without needing to bond to an atom. Simply put, lone pairs of electrons are independent tough guys.

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