Introduction to Carbon Compounds: Structures, Isomerism, and Reactions
Question 1
a-c b-d 3-b 4-a
Question 2: Electron Dot Structures
Draw an electron dot structure of the following molecules (without showing the circles):
a. Methane
Answer:
Molecular formula: CH4
b. Ethene
Answer:
Molecular formula: H2C = CH2
c. Methanol
Answer:
Molecular formula: H3C – OH
d. Water
Answer:
Molecular formula: H2O
Question 3: Structural Formulae
Draw all possible structural formulae of compounds from their molecular formula given below.
a. C3H8
b. C4H10
c. C3H4
Answer:
a. C3H8 Propane:
b. C4H10 Butane:
c. C3H4 Propyne:
Question 4: Explaining Key Terms
Explain the following terms with examples:
a. Structural Isomerism
Answer:
Structural isomerism is the phenomenon where compounds with the same molecular formula have different structural formulae. Butane, for example, can be represented by two different compounds with different structural formulae. The first compound is a straight chain, while the second is branched. Both have the same molecular formula: C4H10.
b. Covalent Bond
Answer:
A covalent bond is a chemical bond formed by the sharing of two valence electrons between two atoms.
Example 1: Hydrogen Molecule Formation
Hydrogen has an atomic number of 1, with one electron in its K shell. It needs one more electron to complete its K shell and achieve the stable configuration of helium (He). To achieve this, two hydrogen atoms share their electrons, forming an H2 molecule. A single covalent bond is formed between the two hydrogen atoms by sharing two electrons.
Example 2: Formation of Oxygen Molecule
- Oxygen has an atomic number of 8 and an electronic configuration of (2, 6), meaning it has 6 electrons in its outermost shell.
- It needs 2 more electrons to complete its L shell and achieve the stable configuration of neon (Ne).
- Each oxygen atom shares a valence electron with another oxygen atom, creating two shared pairs of electrons and forming an oxygen molecule.
- Two electron pairs are shared between the two oxygen atoms, forming a double covalent bond (=).
c. Heteroatom in a Carbon Compound
Answer:
Carbon compounds are formed by carbon bonding with other elements like halogens, oxygen, nitrogen, and sulfur. These elements replace one or more hydrogen atoms in the hydrocarbon chain, satisfying carbon’s tetravalency. The atom replacing hydrogen is called a heteroatom. Heteroatoms can exist individually or as part of a group of atoms.
d. Functional Group
Answer:
Functional groups are specific heteroatoms or groups of atoms containing heteroatoms that give a compound its particular chemical properties, regardless of the length or nature of the carbon chain.
e. Alkane
Answer:
Alkanes are hydrocarbons where carbon’s four valencies are satisfied only by single bonds. For example, methane has one carbon atom bonded to four hydrogen atoms by four single covalent bonds.
f. Unsaturated Hydrocarbons
Answer:
Unsaturated hydrocarbons are carbon compounds with a double or triple bond between two carbon atoms. Alkenes contain a carbon-carbon double bond, such as ethene (CH2 = CH2) and propene (CH3 – CH = CH2). Alkynes contain a carbon-carbon triple bond, such as ethyne (CH ≡ CH).
g. Homopolymer
Answer:
Homopolymers are polymers formed by the repetition of a single monomer, such as polyethylene (CH2 – CH2)n.
h. Monomer
Answer:
A monomer is a small unit that repeats regularly to form a polymer. For example, ethylene is a monomer.
i. Reduction
Answer:
Reduction is a chemical reaction involving the removal of oxygen from a compound or the addition of hydrogen to a compound.
j. Oxidant
Answer:
An oxidant, also known as an oxidizer or oxidizing agent, is a reactant that oxidizes or removes electrons from other reactants during a redox reaction. When the oxidant includes oxygen, it may be called an oxygenation reagent or oxygen-atom transfer (OT) agent.
Examples of oxidants:
- Hydrogen peroxide
- Ozone
- Nitric acid
- Sulfuric acid
Question 5: IUPAC Names
Write the IUPAC names of the following structural formulae:
a. CH3-CH2-CH2-CH3
= Butane
b. CH3-CH(OH)-CH3
= Propan-2-ol
c. CH3-CH2-COOH
= Propanoic acid
d. CH3-CH2-NH2
= Ethan-1-amine
e. CH3-CHO
= Ethanal
f. CH3-CO-CH2-CH3
= Butanone
Question 6: Reaction Types
Identify the type of the following reactions of carbon compounds:
a. CH3-CH2-CH2-OH → CH3-CH2-COOH
= Oxidation reaction (acidic KMnO4)
b. CH3-CH2-CH3 → 3CO2 + 4H2O
= Combustion reaction
c. CH3-CH=CH-CH3 + Br2 → CH3-CHBr-CHBr-CH3
= Addition reaction
d. CH3-CH3 + Cl2 → CH3-CH2-Cl + HCl
= Substitution reaction
e. CH3-CH2-CH2-CH2-OH → CH3-CH2-CH=CH2 + H2O
= Dehydration reaction
f. CH3-CH2-COOH + NaOH → CH3-CH2-COO– Na+ + H2O
= Neutralization reaction (reaction with base)
g. CH3-COOH + CH3-OH → CH3-COO-CH3 + H2O
= Esterification reaction
Question 7: Structural Formulae from IUPAC Names
Write structural formulae for the following IUPAC names:
a. Pent-2-one
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b. 2-chlorobutane
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c. Propan-2-ol
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d. Methanal
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f. 1-bromopropane
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h. Butanone
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Question 8: Carbon Compounds and Their Properties
a. What causes the existence of a very large number of carbon compounds?
Answer:
Carbon is unique in the periodic table due to its 4 valence electrons. Each carbon atom can form bonds with 4 other atoms of various types, and each of those atoms can further bond with 4 others. This leads to the formation of incredibly diverse and complex organic compounds, including short and long chains, ring structures, and branched structures. This self-linking property of carbon, called catenation, is responsible for the vast number of carbon compounds.
b. Saturated hydrocarbons are classified into three types. Write these names, giving one example each.
Answer:
Saturated hydrocarbons are compounds where carbon’s four valencies are satisfied only by single bonds. Methane, with one carbon atom bonded to four hydrogen atoms by single covalent bonds, is an example of a saturated hydrocarbon.
c. Give any four functional groups containing oxygen as the heteroatom. Write the name and structural formula of one example each.
Answer:
d. Give the names of three functional groups containing three different heteroatoms. Write the name and structural formula of one example each.
Answer:
e. Give the names of three natural polymers. Write the place of their occurrence and the names of the monomers from which they are formed.
Answer:
- Polysaccharide is a natural polymer found in starch/carbohydrates. It is formed from the monomer glucose.
- Protein is a natural polymer found in muscles, hair, enzymes, skin, and eggs. It is formed from alpha amino acids.
- Rubber is a natural polymer found in the latex of rubber trees. It is formed from the monomer isoprene.
f. What is meant by vinegar and gasohol? What are their uses?
Answer:
- Vinegar is a 5-8% aqueous solution of acetic acid. It is used as a preservative in pickles, for cooking meat, and as a salad dressing.
- Gasohol is a fuel blend of petrol with 10% anhydrous ethanol, used to increase petrol’s efficiency. It is used as a fuel in cars and other vehicles.
g. What is a catalyst? Write any one reaction which is brought about by the use of a catalyst?
Answer:
A catalyst is a substance that changes the rate of a reaction without being consumed in the process. For example, vegetable oil (unsaturated compound) undergoes an addition reaction with hydrogen in the presence of a nickel catalyst to form vanaspati ghee (saturated compound).