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CIE iGCSE Co-ordinated Sciences-C11.2 Naming organic compounds- Study Notes- New Syllabus

CIE iGCSE Co-ordinated Sciences-C11.2 Naming organic compounds – Study Notes

CIE iGCSE Co-ordinated Sciences-C11.2 Naming organic compounds – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.

Key Concepts:

Core

  • Name and draw the displayed formulas of:
    (a) methane and ethane
    (b) ethene
    (c) ethanol
  • State the type of compound present, given a chemical name ending in -ane, -ene or -ol, or from a molecular formula or displayed formula

Supplement

  • Name and draw the structural formulas and displayed formulas of unbranched:
    (a) alkanes
    (b) alkenes, including but-1-ene and but-2-ene (not cis/trans) containing up to four carbon atoms per molecule

CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics

Displayed Formulas of Simple Organic Compounds

(a) Methane and Ethane (Alkanes)

1. Methane (\(\mathrm{CH_4}\))

  • Molecular formula: \(\mathrm{CH_4}\)
  • Type: Alkane (saturated hydrocarbon)
  • Displayed formula:

2. Ethane (\(\mathrm{C_2H_6}\))

  • Molecular formula: \(\mathrm{C_2H_6}\)
  • Type: Alkane (saturated hydrocarbon)
  • Displayed formula:

(b) Ethene (Alkene)

  • Molecular formula: \(\mathrm{C_2H_4}\)
  • Type: Alkene (unsaturated hydrocarbon — contains a C=C double bond)
  • Displayed formula:

(c) Ethanol (Alcohol)

  • Molecular formula: \(\mathrm{C_2H_6O}\)
  • Type: Alcohol (contains the functional group –OH)
  • Displayed formula:

Key Idea:

  • Alkanes (e.g. methane, ethane) have only single bonds → saturated compounds.
  • Alkenes (e.g. ethene) have at least one double bond → unsaturated compounds.
  • Alcohols (e.g. ethanol) contain the –OH functional group.

Example :

Which compound listed above is unsaturated and why?

▶️ Answer/Explanation

Step 1: Unsaturated compounds contain at least one C=C double bond.

Step 2: Among methane, ethane, ethene, and ethanol, only ethene has a C=C bond.

Final Answer: Ethene is unsaturated because it contains a carbon–carbon double bond.

Identifying the Type of Compound from Name or Formula

The type of organic compound can be recognised from its name ending, molecular formula, or displayed formula.

1. Compounds Ending in –ane

  • Names ending in –ane indicate an alkane.
  • Alkanes are saturated hydrocarbons — all carbon–carbon (C–C) bonds are single bonds.
  • General formula: \(\mathrm{C_nH_{2n+2}}\)
  • Example: Methane (\(\mathrm{CH_4}\)), Ethane (\(\mathrm{C_2H_6}\)), Propane (\(\mathrm{C_3H_8}\))

2. Compounds Ending in –ene

  • Names ending in –ene indicate an alkene.
  • Alkenes are unsaturated hydrocarbons — they contain at least one carbon–carbon double bond (C=C).
  • General formula: \(\mathrm{C_nH_{2n}}\)
  • Example: Ethene (\(\mathrm{C_2H_4}\)), Propene (\(\mathrm{C_3H_6}\))

3. Compounds Ending in –ol

  • Names ending in –ol indicate an alcohol.
  • Alcohols contain the –OH (hydroxyl) functional group attached to a carbon atom.
  • General formula: \(\mathrm{C_nH_{2n+2}O}\)
  • Example: Methanol (\(\mathrm{CH_3OH}\)), Ethanol (\(\mathrm{C_2H_5OH}\))

How to Identify from a Formula:

  • If the formula fits \(\mathrm{C_nH_{2n+2}}\) → Alkane.
  • If the formula fits \(\mathrm{C_nH_{2n}}\) → Alkene.
  • If the formula contains an O–H group → Alcohol.
  • If the displayed formula shows a C=C bond → Alkene.

Example 

A compound has the formula \(\mathrm{C_3H_8}\). What type of compound is it?

▶️ Answer/Explanation

Step 1: The formula fits the pattern \(\mathrm{C_nH_{2n+2}}\).

Step 2: This is the general formula for an alkane.

Final Answer: The compound is an alkane (propane).

Example

The displayed formula shows a carbon–carbon double bond. What type of compound is it?

▶️ Answer/Explanation

Step 1: A C=C double bond indicates unsaturation.

Step 2: Compounds with C=C bonds are alkenes.

Final Answer: The compound is an alkene.

Unbranched Alkanes and Alkenes (up to Four Carbon Atoms)

Unbranched compounds have carbon atoms connected in a single straight chain without side branches.

(a) Alkanes – Saturated Hydrocarbons

General formula: \(\mathrm{C_nH_{2n+2}}\)  
All carbon–carbon bonds are single (C–C).

NameMolecular FormulaStructural FormulaDisplayed Formula
MethaneCH₄CH₄
EthaneC₂H₆CH₃–CH₃
PropaneC₃H₈CH₃–CH₂–CH₃
ButaneC₄H₁₀CH₃–CH₂–CH₂–CH₃

All alkanes are saturated hydrocarbons — only single bonds between carbon atoms.

(b) Alkenes  Unsaturated Hydrocarbons   

General formula: \(\mathrm{C_nH_{2n}}\)
Contain at least one carbon–carbon double bond (C=C).

NameMolecular FormulaStructural FormulaDisplayed Formula
EtheneC₂H₄CH₂=CH₂
PropeneC₃H₆CH₂=CH–CH₃
But-1-eneC₄H₈CH₂=CH–CH₂–CH₃
But-2-eneC₄H₈CH₃–CH=CH–CH₃

All alkenes are unsaturated hydrocarbons — they contain a C=C double bond.

Example :

What is the structural difference between ethane and ethene?

▶️ Answer/Explanation

Step 1: Ethane (C₂H₆) is an alkane — all single C–C bonds.

Step 2: Ethene (C₂H₄) is an alkene — contains a C=C double bond.

Final Answer: Ethane is saturated; Ethene is unsaturated.

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