Formulae Functional Groups And Terminology

Organic Formulae

• **Organic compounds** contain carbon (except metal carbonates, CO₂, CO).
• A **hydrocarbon** contains only hydrogen and carbon atoms.
• The **displayed formula** shows the spatial arrangement of all atoms and bonds.
• In displayed formulae, show **all bonds** between atoms (e.g., O–H bond in alcohols).
• Other representations: **general formula** and **structural formula**.

Homologous Series

• A **homologous series** is a family of organic compounds with the same **functional group** and similar chemical properties.
• The **functional group** is a specific arrangement of atoms responsible for characteristic reactions.
• Key series: **alkanes** (C–C), **alkenes** $(C=C)$, **alcohols** (–OH).
• All members have the same **general formula** and differ by **CH₂**.
• Example: ethanol (C₂H₅OH) and propanol (C₃H₇OH) both have general formula CₙH₂ₙ₊₁OH.

Saturated & Unsaturated Compounds

• **Saturated** compounds have only **single carbon-carbon bonds** (C–C).
• **Alkanes** are saturated; general formula **CₙH₂ₙ₊₂**.
• First three alkanes: methane (CH₄), ethane (C₂H₆), propane (C₃H₈).
• **Unsaturated** compounds contain at least one **carbon-carbon double bond** $(C=C)$.
• **Alkenes** are unsaturated; general formula **CₙH₂ₙ**.
• First three alkenes: ethene (C₂H₄), propene (C₃H₆), butene (C₄H₈).
• Mnemonic: **S**aturated = **S**ingle bonds; **U**nsaturated = do**U**ble bonds.

Naming Organic Compounds: Stems & Suffixes

• The **stem** indicates the number of carbon atoms in the longest chain: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6).
• The **suffix** indicates the functional group: **-ane** (alkane), **-ene** (alkene), **-anol** (alcohol), **-anoic acid** (carboxylic acid).
• Example: C₃H₆ with $C=C$ is **propene**; C₃H₇OH is **propanol**.
• For chains longer than 2 carbons, use a **number** to locate the functional group (e.g., propan-1-ol, but-2-ene).
• Numbering starts from the end that gives the **lowest numbers**.

Naming Carboxylic Acids & Esters (Extended)

• **Carboxylic acids** end in **-anoic acid**; the –COOH carbon is always C1, so no number needed.
• **Esters** are named from the alcohol and carboxylic acid that formed them: **alkyl alkanoate**.
• The alcohol part (C–O single bond) gives the first part (e.g., methyl, ethyl).
• The carboxylic acid part $(C=O)$ gives the second part (e.g., methanoate, ethanoate).
• Example: CH₃COOCH₂CH₃ is **ethyl ethanoate**.

Displayed Formulae Examples

• **Propene**: 3-carbon chain with $a C=C$ double bond between C1 and C2.
• **Propan-1-ol**: 3-carbon chain with –OH on C1.
• **Methyl methanoate**: HCOOCH₃ – alcohol part = methyl, acid part = methanoate.
• Always show all bonds, including C–H and O–H, in displayed formulae.

General structure of an amino acid (example of a displayed formula showing all bonds).