Basic concepts of organic chemistry

Welcome to Core Organic Chemistry!

Welcome! You are about to dive into one of the most exciting parts of Chemistry. Organic chemistry is the study of carbon compounds. Since carbon is the building block of life, you are basically studying the chemistry of you, as well as everything from the fuel in cars to the medicines in your cabinet.
Don't worry if this seems like a lot of new words at first—think of it like learning the grammar of a new language. Once you know the rules, you'll be able to read and "build" molecules with ease!

1. Representing Organic Molecules

In organic chemistry, we use different ways to draw the same molecule. Each has a specific purpose. Let's look at the ways to show butane or ethanol.

Types of Formulae

• General Formula: The simplest algebraic way to describe a whole "family" of chemicals (a homologous series). For example, all alkanes follow the rule \( C_nH_{2n+2} \).
• Structural Formula: This gives the minimum detail needed to show how atoms are arranged. For example, butane is CH₃CH₂CH₂CH₃.
• Displayed Formula: This is the "full map." It shows every single atom and every single bond. Tip: Always remember to draw every 'H' atom in a displayed formula, or you might lose marks!
• Skeletal Formula: This is the "chemist’s shorthand." We remove all 'C' and 'H' labels from the main chain. A carbon atom sits at every "corner" or end of a line. It’s much faster to draw once you get the hang of it!

Quick Review:
- Molecular Formula: Just the count (e.g., \( C_4H_{10} \)).
- Empirical Formula: The simplest ratio (e.g., \( C_2H_5 \)).

Key Takeaway:

Different formulas tell us different things. Use displayed when you need to see every bond, and skeletal for complex structures to keep things tidy.

2. Naming Compounds (IUPAC Rules)

To prevent confusion, chemists worldwide use IUPAC rules to name molecules. It’s like giving every molecule a unique first name, middle name, and surname.

The First Ten Alkanes

You need to know these prefixes by heart. They tell you how many carbons are in the main chain:

1. Meth- (1)
2. Eth- (2)
3. Prop- (3)
4. But- (4)
5. Pent- (5)
6. Hex- (6)
7. Hept- (7)
8. Oct- (8)
9. Non- (9)
10. Dec- (10)

Memory Aid: To remember the first four, try: Monkeys Eat Peeled Bananas (Methane, Ethane, Propane, Butane).

How to name a molecule:

1. Find the longest continuous carbon chain (this is your "parent" name).
2. Identify any functional groups (like -OH for alcohols).
3. Number the carbons so the functional group has the lowest possible number.
4. Name any side chains (alkyl groups like methyl -CH₃ or ethyl -C₂H₅) and list them alphabetically.

Example: 2-methylbutan-1-ol tells us there are 4 carbons (butan), an alcohol group on the 1st carbon (-1-ol), and a methyl group on the 2nd carbon (2-methyl).

3. Important Terminology

Organic chemistry has its own vocabulary. Here are the "must-know" terms:

• Homologous Series: A family of compounds with the same functional group. Each member differs by a \( CH_2 \) group. Think of it like a family where everyone has the same last name but is a different height.
• Functional Group: The "business end" of the molecule. It’s the part responsible for how the molecule reacts (e.g., \( C=C \) in alkenes).
• Aliphatic: Carbons joined in straight chains, branched chains, or non-aromatic rings.
• Alicyclic: An aliphatic compound arranged in a ring.
• Aromatic: Compounds containing a benzene ring (a special hexagon of carbons).
• Saturated: Contains only single bonds (like alkanes).
• Unsaturated: Contains at least one multiple bond, like a \( C=C \) double bond or a benzene ring.

Did you know? The term "saturated" means the molecule is "full" of hydrogen. It can't take any more because every carbon is already using its four bonds to the max!

4. Isomerism

Structural Isomers are molecules that have the same molecular formula but a different structural arrangement.
Think of it like an anagram: the words "LISTEN" and "SILENT" have the same letters, but they mean different things because the letters are in a different order.

Example: Both butane and 2-methylpropane have the formula \( C_4H_{10} \), but one is a straight chain and the other is branched. They have different physical properties, like boiling points!

Key Takeaway:

Structure determines function. Even if the atoms are the same, how you connect them changes the chemical's personality.

5. Reaction Mechanisms: How Bonds Break

A reaction mechanism shows the "step-by-step" journey of electrons during a reaction. When a covalent bond breaks, it is called fission.

Types of Bond Fission

1. Homolytic Fission: The bond breaks evenly. Each atom from the bond takes one electron. This creates two radicals.
Analogy: Two friends sharing a Kit-Kat bar—each takes exactly one stick.
2. Heterolytic Fission: The bond breaks unevenly. One atom takes both electrons, becoming a negative ion, while the other gets none and becomes a positive ion.
Analogy: One person takes both sticks of the Kit-Kat, leaving the other friend with nothing.

Radicals and Curly Arrows

• Radical: An extremely reactive species with an unpaired electron. We show this with a dot (e.g., \( Cl• \)).
• Curly Arrows: These are used to show the movement of a pair of electrons.
- The tail starts where the electrons are (a bond or a lone pair).
- The head points to where the electrons are going.
Don't worry if this seems tricky! Just remember: the arrow always follows the electrons, not the atoms.

Common Mistake to Avoid: Drawing a curly arrow from an atom. Electrons live in bonds or lone pairs, so the arrow must start there!

Summary of Reaction Concepts:

• Homolytic = Radicals (equal split).
• Heterolytic = Ions (unequal split).
• Curly arrows = Electron pair movement.