Introduction to Organic Chemistry

🧬 What is an Alkane?

Definition:

• Alkanes are structurally simple organic compounds made up solely of carbons (C) and hydrogens (H).

• All atoms are connected by single covalent bonds (C–C and C–H).

• They are a type of hydrocarbon — meaning they contain only hydrogen and carbon.

• Alkanes are saturated compounds — each carbon atom forms the maximum number of bonds (4) possible, usually bonded to other carbons and hydrogens.

Key Points:

• Each carbon in an alkane is tetrahedral (bond angle ≈ 109.5°).

• General formula for alkanes: CₙH₂ₙ₊₂

• Alkanes are relatively unreactive and nonpolar.

🔗 Structure of Alkanes

Alkanes can exist in two main structural forms:

1. Straight Chain (Normal Alkanes)

   • Carbon atoms are joined in a continuous, unbranched chain.

   • Example: n-butane (C₄H₁₀).

2. Ring or Cyclic Alkanes (Cycloalkanes)

   • Carbon atoms are joined in a closed polygonal structure (usually 5 or 6 carbons).

   • Prefix “cyclo–” is added before the name.

   • Example: cyclohexane (C₆H₁₂).

🧩 Representing Organic Structures

Organic molecules can be represented in four main ways:

1. Molecular Formula

   • Shows the total number of atoms of each element.

   • Example: C₄H₁₀

2. Condensed Structure

   • Shows how atoms are grouped, e.g., CH₃CH₂CH₂CH₃.

3. Lewis Structure

   • Displays all bonds and lone pairs explicitly.

   • Shows the connectivity of atoms.

4. Skeletal (Line) Structure

   • Simplified diagram showing bonds between carbon atoms as lines.

   • Hydrogen atoms are implied, not drawn.

   • Steps to draw:

     1. Determine number of carbons.

     2. Draw the carbon skeleton.

     3. Add any non-carbon/non-hydrogen atoms.

⚗ Functional Groups

Definition:
Atoms or groups of atoms bonded in a specific way to the main carbon chain.
They determine the molecule’s chemical behavior and reactivity.
Each functional group follows a general formula and has specific properties.

Halides (Haloalkanes)

• Group 7 elements (F, Cl, Br, I) bonded to carbon chains.

• Prefixes: Fluoro-, Chloro-, Bromo-, Iodo-

• Example: CH₃Cl (Chloromethane)

Ethers

• Oxygen atom linking two carbon chains (R–O–R).

• Suffix: –ether

• Example: CH₃–O–CH₃ (Dimethyl ether)

• Often used as solvents and anesthetics.

Alkenes

• Double-bonded hydrocarbons (C=C).

• More reactive than alkanes due to the π-bond.

• Suffix: –ene

• Shorter bond length than single bonds.

• Example: C₂H₄ (Ethene)

Alkynes

• Triple-bonded hydrocarbons (C≡C).

• Even more reactive than alkenes; less stable.

• Suffix: –yne

• Example: C₂H₂ (Ethyne / Acetylene)

Aromatics

• Special ring structures with alternating double bonds (conjugation).

• Each carbon-carbon bond has equal length.

• Very stable and resistant to reactions.

• Often have distinct smells (like mothballs, cherries, or almonds).

• Example: Benzene (C₆H₆)

Alcohols

• Contain a hydroxyl group (–OH).

• Common in alcoholic beverages.

• Suffix: –ol

• Example: CH₃CH₂OH (Ethanol)

Amines

• Contain nitrogen bonded to one or more carbon atoms.

• Found in proteins and cleaning agents.

• Suffix: –amine

• Example: CH₃NH₂ (Methylamine)

Aldehydes

• Contain a carbonyl group (C=O) at the end of the carbon chain.

• Suffix: –al

• Example: CH₂O (Formaldehyde) — used for embalming and glues.

Ketones

• Contain a carbonyl group (C=O) within the chain (middle carbon).

• Suffix: –one

• Example: CH₃COCH₃ (Acetone) — used in paints, lacquers, and explosives.

Esters

• Contain a COO linkage between two carbon groups (R–COO–R’).

• Suffix: –oate

• Found in fruits, polymers, and polyesters (clothing).

• Example: CH₃COOCH₂CH₃ (Ethyl acetate)

Amides

• Contain a carbonyl (C=O) linked to a nitrogen atom (R–CONH₂).

• Important in proteins (peptide bonds) and nylon polymers.

• Suffix: –amide

• Example: CH₃CONH₂ (Acetamide)

Carboxylic Acids

• Contain the carboxyl group (–COOH).

• Most reactive of all functional groups.

• Found in organic acids and DNA molecules.

• Suffix: –oic acid

• Example: CH₃COOH (Ethanoic acid / Acetic acid)

🧾 IUPAC Naming System

The IUPAC (International Union of Pure and Applied Chemistry) naming rules ensure consistent naming worldwide.

Steps:

1. Identify the parent chain

   • The longest continuous carbon chain determines the base name (meth-, eth-, prop-, but-, etc.).

2. Identify and prioritize substituents

   • Note side chains or functional groups attached to the parent chain.

   • Assign priority based on reactivity.

3. Number the chain

   • Give each substituent/functional group the lowest possible number.

4. Use prefixes for multiples

   • Example: di-, tri-, tetra-, etc.

5. List substituents alphabetically

   • Ignore numerical prefixes when alphabetizing.

6. Combine the name

   • [Position number(s)] + [Substituent name(s)] + [Parent chain] + [Suffix for functional group].

Example:
2-chloropropane → Three-carbon chain (propane) with a chlorine on carbon 2.

🔄 Isomerism (Mentioned in Outline)

Isomers: Compounds with the same molecular formula but different structural arrangements of atoms.

Types:

• Structural isomers: Differ in connectivity (e.g., butane vs. isobutane).

• Stereoisomers: Same connectivity, different 3D orientation (cis/trans).

✅ Summary Chart: Functional Groups and Suffixes