Organic Functional groups

You will explore carbon compounds, with a focus on understanding the differences between organic and inorganic compounds. You will also learn about different types of organic compounds and the patterns they follow. Through various

activities, you will demonstrate your knowledge and practice classifying organic compounds.

At the end of this section, you will be able to:

• Distinguish between organic and inorganic compounds and classify organic compounds.

• Explain homologous series and state their properties.

Key Ideas

• Alkanes are saturated hydrocarbons with only single bonds (e.g., methane, ethane).

• Alkenes are unsaturated hydrocarbons with at least one double bond (e.g., ethene).

• Alkynes are unsaturated hydrocarbons with at least one triple bond (e.g., ethyne).

• Aromatic compounds: are compounds that contain a benzene ring (e.g., benzene, toluene).

Organic chemistry is a branch of chemistry which studies the structure and properties of carbon compounds, except oxides of carbon, carbonates, carbides and cyanides.

An organic compound is a compound containing carbon atoms covalently bonded to other atoms.

Properties Of Carbon That Make It Possible To

Form Many Stable Compounds

1. Carbon has a valency of four (tetravalent) and can form four covalent bonds.

C Valence electrons

2. Carbon atoms can join to form straight chains, branched chains and ring structures.

straight chain branched chain ring butane (C₄H₁₀) isobutane ((C₄H₁₀) cyclobutane (C₄H₈)

3. Carbon can form single, double or triple bonds with itself and other elements

4. Carbon can form isomers (compounds with the same chemical formula but a different structure).

Differences Between Organic And Inorganic

Compounds

Table 10.1

Inorganic compounds Organic compounds Contain any element except organic carbon.

Must contain a carbon atom.

Are usually ionic compounds and some covalent compounds.

Are usually covalent compounds.

Usually have relatively high melting and boiling points.

Usually have relatively low melting and boiling points.

Often soluble in polar solvents. Usually soluble in nonpolar solvents.

Usually occurs as solids at room temperature.

Often exist as liquids and gases.

Classes of Organic Compounds

Organic compounds can be classified into:

1. Aliphatic hydrocarbons

2. Alicyclic hydrocarbons

3. Aromatic hydrocarbons

4. Heterocyclic compounds Hydrocarbons Hydrocarbons are organic compounds containing only carbon and hydrogen atoms. Hydrocarbons can be saturated or unsaturated. Hydrocarbon names are derived from the number of carbon atoms they contain. A few of the common prefixes are listed below:

Prefix Number of Carbon atoms Formula meth- 1 C eth- 2 C2 prop- 3 C3 but- 4 C4 pent- 5 C5 hex- 6 C6 hept- 7 C7 oct- 8 C8 non- 9 C9 dec- 10 C10 undec- 11 C11 dodec- 12 C12 tridec- 13 C13 tetradec- 14 C14 pentadec- 15 C15 hexadec- 16 C16 heptadec- 17 C17 octadec- 18 C18 nonadec- 19 C19 eicosan- 20 C20 Saturated hydrocarbons Have single bonds between two carbon atoms (C – C). An example is the alkane family. Specific examples are:

Fig. 10.1: Alkane (butane)

Unsaturated hydrocarbons Have double or triple bonds between two carbon atoms. Examples are alkenes and alkynes.

Specific examples of alkenes are:

Fig 10.2: Examples of alkenes Specific examples of alkynes are:

Fig 10.3: Examples of alkynes Aliphatic hydrocarbons These are organic compounds containing carbon and hydrogen atoms that are usually linked together in chains via single, double or triple bonds. They can be open straight chains or branched chains. Aliphatic hydrocarbons may be saturated or unsaturated.

Examples are alkanes (which have C − C bonds), alkenes (which have C = C bonds) and alkynes (which have C ≡ C bonds).

Many of the aliphatic compounds are flammable and so they are used as fuels such as butane in LPG and ethylene in welding.

Alicyclic hydrocarbons These are organic compounds that have closed rings of carbon atoms.

H₂C CH₂ CH₂

cyclopropane cyclopropane or Fig. 10.4: Examples of alicyclic hydrocarbons Aromatic hydrocarbons These are organic compounds that have one or more benzene rings in their structure. The different ways of representing the structure of benzene are shown below:

CH CH

CH CH

HC HC

1 2 3 benzene benzene benzene Fig. 10.5: Aromatic hydrocarbon Heterocyclic compounds These are organic compounds which are not hydrocarbons. They contain rings of atoms and carbon and hydrogen atoms, including other atoms such as oxygen, nitrogen and sulphur.

Examples are S thiophene NO furan pyridine Fig. 10.6: Heterocyclic compounds

Activity 10.1: Understanding Organic Chemistry

Objective: To introduce you to the meaning of organic chemistry.

Form a small group of three or four with your classmates and discuss the following points:

1. The meaning of organic chemistry.

2. Examples of organic compounds (such as methane, ethene, or glucose).

3. The significance of carbon in organic chemistry.

4. The role of organic chemistry in everyday life (e.g., in medicines, plastics, food).

5. Summarise the key points about the meaning of organic chemistry, emphasising the importance of carbon compounds.

Questions

a. What element is most commonly found in organic compounds?

b. Why is carbon so important in organic chemistry?

c. Give two examples of organic compounds and explain why they are considered organic.

d. What types of bonds are most common in organic compounds?

e. What is the difference between a hydrocarbon and an organic compound?

Activity 10.2: Differentiating Between Organic and Inorganic

Compounds Objective: To understand the differences between organic and inorganic compounds.

In your small groups from Activity 10.1, discuss the key differences between organic and inorganic compounds under the following points:

Some key points to focus on:

1. Presence of carbon in organic compounds.

2. Organic compounds are often found in living things, while inorganic compounds are typically minerals or non-living substances.

3. Differences in types of bonds (covalent bonds in organic compounds vs.

ionic or metallic bonds in inorganic compounds).

Questions

a. Can inorganic compounds contain carbon? If so, give an example.

b. Do organic compounds tend to have higher or lower melting and boiling points than inorganic compounds?

Activity 10.3: Why Carbon Forms Many Compounds

Materials needed: Periodic table, molecular models, access to textbooks or online resources for reference.

1. Brainstorm and list examples of carbon-containing compounds you are familiar with (e.g., sugar, plastics, gasoline, diamonds).

2. What is special about carbon’s position in the periodic table?

3. Identify carbon’s group and its number of valence electrons.

4. How does carbon bond with other atoms?

5. Use molecular models to build simple molecules (e.g., CH₄, CO₂, and C₂H₆). Visualise carbon’s ability to form four covalent bonds.

6. Why do you think carbon can form different types of structures, like chains, rings, and networks?

7. Build different carbon-based structures using the models or diagrams (e.g., a ring structure like benzene, and a network structure like diamond or graphite).

Compare and discuss your findings with a classmate.

Extended Activity Questions

1. What are organic compounds?

2. State four reasons why carbon forms many stable compounds.

3. Distinguish between alicyclic hydrocarbons and aromatic hydrocarbons.

4. What is meant by the term aromatic hydrocarbon?

5. In a tabular form, state the differences between organic compounds and inorganic compounds.

6. Describe the general differences in chemical bonding between organic and inorganic compounds.

7. Compare and contrast the physical and chemical properties of organic and inorganic compounds.

Homologous series is a group of compounds having the same general molecular formula and similar chemical properties. The tables below show examples of the homologous series for alkanes and alkenes.

Table 10.2: Molecular formula of Alkanes Number of carbon atoms (n) Molecular formula, (Cn H 2n+2 ) 1 CH₄ 2 C₂H₆ 3 C₃H₈ 4 C₄H₁₀ 5 C₅H₁₂

Table 10.3: Molecular formula of Alkenes Number of carbon atoms (n) Molecular formula, (Cn H 2n+2 ) 2 C₂H₄ 3 C₃H₆ 4 C₄H₈ 5 C₅H₁₀

Note that the alkenes cannot have a compound with a single atom of carbon, this is because the alkenes are defined as having a single carbon-to-carbon double bond.

Properties of a Homologous Series

1. They have a general molecular formula.

2. They have a general method of preparation.

3. They exhibit similar chemical properties.

4. They have the same functional group.

5. They exhibit a gradual change in physical properties along the series.

How to Represent Organic Compounds

Organic compounds are represented by using their molecular formula, condensed formula or structural formula.

The tables below show examples of alkanes and alkenes

Table 10.4: Structural formula of Alkanes Number of carbon atoms (n) Molecular formula, (CₙH₂ₙ₊₂) Structural formula 1 CH₄ CH₄ 2 C₂H₆ CH₃CH₃ 3 C₃H₈ CH₃CH₂CH₃ 4 C₄H₁₀ CH₃CH₂CH₂CH₃ 5 C₅H₁₂ CH₃CH₂CH₂CH₂CH₃

Table 10.5: Structural formula of Alkenes Number of carbon atoms (n) Molecular formula, (CₙH₂ₙ) Structural formula 2 C₂H₄ CH₂=CH₂ 3 C₃H₆ CH₃CH=CH₂ 4* C₄H₈ CH₃CH₂CH=CH₂ 5* C₅H₁₀ CH₃CH₂CH₂CH=CH₂ 6* C₆H₁₂ CH₃CH₂CH₂CH₂CH=CH₂ *Note here that the double bond could in fact be in different positions along the chain, this will give a subtle difference in properties and change the reactions it will undergo.

Activity 10.4: Writing the Homologous Series for Alkanes and Alkenes Materials needed: Periodic table, molecular model kits, access to textbooks or online resources (for reference).

1. What are the general formulae for alkanes and alkenes?

2. Give a few examples of alkanes (e.g., methane, ethane, propane) and alkenes (e.g., ethene, propene, but-1-ene, but-2-ene).

3. Using molecular model kits, build molecular structures of the first three or four alkanes and alkenes (methane, ethane, ethene, etc.).

4. Write down the first five members of the homologous series for alkanes and alkenes. For each compound, they should write molecular formula and Structural formula.

Activity 10.5: Discussing the Properties of Homologous Series

1. With a classmate, discuss how physical properties such as states of matter, boiling points, and solubility change as you go up the homologous series.

2. Predict the trend in boiling points and physical states as they move up the series.

3. Discuss how chemical properties change as you move up the series?

Do compounds become more or less reactive?

Activity 10.6

1. What are organic compounds?

2. State four reasons why carbon forms many stable compounds.

3. Distinguish between alicyclic hydrocarbons and aromatic hydrocarbons.

4. Explain the term homologous series.

5. State three properties of a homologous series.

6. The following compound is a member of the alkane homologous series:

CH₃CH₃ Draw the structures of the next three members of the series that follow the compound.

Review Questions 10.1

1. Which of the following is an example of an organic compound?

A. Water (H₂O) B. Carbon dioxide (CO₂) C. Glucose (C₆H₁₂O₆) D. Ammonia (NH₃)

2. How are organic compounds classified based on their structure?

3. What are the main types of hydrocarbons, and how are they classified?

4. Why is it important to classify organic compounds?

5. Why are homologous series important in organic chemistry?

6. Why do boiling and melting points increase along a homologous series?

7. What is the difference between alkanes, alkenes, and alkynes?

8. Why are hydrocarbons important?

9. What is the primary difference between organic and inorganic compounds?

10. What types of bonds are typically found in organic compounds compared to inorganic compounds?

11. Can organic compounds only be found in living organisms?