Aldehydes and Ketones

Carbonyl Compounds: Aldehydes & Ketones

The Magic Double Bond That Changes Everything

Imagine you have a piece of paper. You can fold it once (single bond), or you can fold it twice (double bond). When carbon folds twice with oxygen, something special happens — we get a carbonyl group!

This is our adventure through the world of carbonyl compounds. Think of it like meeting two cousins: Aldehydes and Ketones. They look similar but live in different houses!

What is a Carbonyl Group?

The Heart of Our Story

Picture a seesaw at the playground. One side has a carbon atom (let’s call him Charlie). The other side has an oxygen atom (let’s call her Olivia). They’re connected by a double bond — like holding hands with BOTH hands at once!

    O
    ‖
    C

This C=O is the carbonyl group. It’s the star of our show!

Why is it Special?

Olivia (oxygen) is greedy! She loves electrons more than Charlie does. So she pulls the shared electrons closer to herself. This makes:

• Olivia slightly negative (δ-)
• Charlie slightly positive (δ+)

graph TD
    A["Carbon δ+"] -->|Double Bond| B["Oxygen δ-"]
    C["Electrons pulled toward Oxygen"] --> B

Real Life Example: When you smell vanilla or perfume, you’re smelling molecules with carbonyl groups!

Meet the Two Cousins

Aldehydes: The End-of-the-Line Cousin

What makes an aldehyde?

The carbonyl group sits at the END of the carbon chain. Charlie Carbon is connected to:

• ONE hydrogen atom
• ONE carbon chain (or another hydrogen)

    O
    ‖
H — C — Rest of molecule

Think of it like this: An aldehyde is like a house at the end of a street. The carbonyl is at the edge, with a hydrogen as the mailbox!

Ketones: The Middle-of-the-Road Cousin

What makes a ketone?

The carbonyl group sits in the MIDDLE of the carbon chain. Charlie Carbon is connected to:

• Carbon on BOTH sides (no hydrogen directly attached)

        O
        ‖
Carbon — C — Carbon

Think of it like this: A ketone is like a house in the middle of the street. It has neighbors on BOTH sides!

Naming Aldehydes: The “-al” Ending

How to Name Your New Aldehyde Friends

Naming aldehydes is like giving them a special last name that ends in “-al” (sounds like “owl”).

Step-by-Step Recipe:

1. Count the carbons in the longest chain (including the carbonyl carbon)
2. Use the root name (meth-, eth-, prop-, but-, pent-…)
3. Add “-al” at the end

Examples That Stick

Memory Trick:

• MethAL = 1 carbon + AL
• EthAL = 2 carbons + AL
• PropAL = 3 carbons + AL

graph TD
    A["Count Carbons"] --> B["Find Root Name"]
    B --> C["Add -AL"]
    C --> D["Your Aldehyde Name!"]

Real World:

• Methanal (formaldehyde): Used to preserve specimens in science labs
• Ethanal: Gives green apples their smell!

Naming Ketones: The “-one” Ending

How to Name Your Ketone Friends

Ketones get the special ending “-one” (sounds like “own”).

Step-by-Step Recipe:

1. Count the carbons in the longest chain
2. Number the chain so the carbonyl gets the LOWEST number
3. Use the root name + position number + “-one”

Examples That Stick

Memory Trick:

• PropanONE = 3 carbons + ONE
• ButanONE = 4 carbons + ONE

Why the number? For ketones with 5+ carbons, we need to say WHERE the carbonyl is. “Pentan-2-one” means the carbonyl is on carbon #2.

graph TD
    A["Count Carbons"] --> B["Number Chain - Lowest for C=O"]
    B --> C["Add Position if Needed"]
    C --> D["Add -ONE"]
    D --> E["Your Ketone Name!"]

Real World:

• Propanone (acetone): The main ingredient in nail polish remover!
• Butanone: Used in glues and paints

Physical Properties: How Carbonyl Compounds Behave

Boiling Points: Higher Than Expected!

Remember how Olivia (oxygen) pulls electrons toward herself? This creates a polar molecule. Polar molecules stick to each other better!

The Order:

Alkanes < Aldehydes/Ketones < Alcohols
(lowest)                      (highest)

Why?

• Alkanes: Non-polar, weak attractions
• Aldehydes/Ketones: Polar C=O, medium attractions
• Alcohols: Can form hydrogen bonds, strong attractions

Boiling Point Examples

See the pattern? Same number of carbons, but aldehydes and ketones boil higher than alkanes!

Solubility: Friends with Water?

Small carbonyl compounds (1-4 carbons) dissolve in water. Why?

The polar C=O can form hydrogen bonds with water molecules!

graph TD
    A["Water H-O-H"] -->|Hydrogen Bond| B["C=O in Carbonyl"]
    C["Small Carbonyls"] --> D["Soluble in Water"]
    E["Large Carbonyls 5+ carbons"] --> F["Less Soluble"]

Rule of Thumb:

• Small carbonyls (methanal, ethanal, propanone) = Mix well with water
• Large carbonyls (5+ carbons) = Prefer to mix with oils

Smell and State

Fun Fact: Many perfumes contain aldehydes! Chanel No. 5 was revolutionary because it used synthetic aldehydes to create its famous scent.

Summary: The Big Picture

graph LR
    A["Carbonyl Group C=O"] --> B["Aldehyde"]
    A --> C["Ketone"]
    B --> D["C=O at END"]
    B --> E["Names end in -AL"]
    C --> F["C=O in MIDDLE"]
    C --> G["Names end in -ONE"]
    A --> H["Properties"]
    H --> I["Polar - Higher BP than alkanes"]
    H --> J["Small ones dissolve in water"]
    H --> K["Many have pleasant smells"]

Quick Comparison Table

You Did It!

You now know:

1. Carbonyl group = C=O double bond (polar!)
2. Aldehydes = Carbonyl at the END, names end in “-al”
3. Ketones = Carbonyl in the MIDDLE, names end in “-one”
4. Properties = Higher boiling points than alkanes, small ones dissolve in water

Next time you:

• Remove nail polish (propanone/acetone)
• Smell vanilla (contains aldehydes)
• See preserved specimens (methanal/formaldehyde)

…you’ll know the carbonyl compounds behind the magic!