Chapter 11: Basic Concepts of Organic Chemistry

Question 1

1. What is a hydrocarbon?
2. What is the difference between saturated and unsaturated hydrocarbons?

Answer 1

1. A hydrocarbon is a compound containing carbon and hydrogen atoms only.
2. A saturated hydrocarbon has single bonds only. An unsaturated hydrocarbon contains carbon-to-carbon multiple bonds.

Question 2

What is a homologous series?

Answer 2

A homologous series is a family of compounds with similar chemical properties whose successive members differ by the addition of a –CH₂– group.

Question 3

What is a functional group?

Answer 3

• A functional group is the part of the organic molecule that is largely responsible for the molecule’s chemical properties. In addition to hydrogen, carbon can bond to other elements, including oxygen, nitrogen, and halogens.
• This results in the formation of molecules containing different functional groups, such as alcohol (–OH) and amine (–NH₂) groups.

Question 4

Give the definitions of:

1. aliphatic hydrocarbons
2. alicyclic hydrocarbons
3. aromatic hydrocarbons.

Answer 4

1. aliphatic — carbon atoms are joined to each other in unbranched (straight) or branched chains, or non-aromatic rings
2. alicyclic — carbon atoms are joined to each other in ring structures (with or without branches) that are not aromatic
3. aromatic — containing one or more benzene rings

Question 5

There are three homologous series of aliphatics hydrocarbons that you should be aware of:

1. alkanes
2. alkenes
3. alkynes

Define these.

Answer 5

1. alkanes — containing single carbon-to-carbon bonds
2. alkenes — containing at least one double carbon-to-carbon bond
3. alkynes — containing at least one triple carbon-to-carbon bond.

Question 6

Give the definitions of the stem, prefix and suffix in a hydrocarbon name.

Answer 6

• The stem of the name indicates the number of carbon atoms in the longest continuous chain in the molecule.
• A prefix can be added before the stem, often to indicate the presence of side chains or functional groups.
• A suffix is added after the stem to indicate functional groups.

Question 7

What steps should be followed when naming alkanes?

Answer 7

Follow these steps when naming alkanes:

1. All alkanes have the the suffix -ane
2. Identify the longest continuous chain of carbon atoms (the parent chain) and use that to name the stem
3. Identify any side chains attached to the parent chain. These side chains are known as alkyl groups. An alkyl group has a hydrogen atom removed from an alkane parent chain. The name of the alkyl group is added as a prefix to the name of the parent chain.
4. Add number before any alkyl groups to show the position of the alkyl groups on the parent chain.

Question 8

Recall the names of the first ten alkanes and their alkyl groups.

Answer 8

Question 9

Which chain is identified as the longest chain when there are two possible chains of the same length in a molecule?

Answer 9

The chain with most branches is considered the longest chain when there are two or more possible chains of the same length in a molecule.

Question 10

How are cyclic alkanes named?

Answer 10

For cyclic alkanes, the same rules apply as when naming aliphatic alkanes. The prefix cyclo- in front of the stem is used to show that the carbon atoms are arranged in a ring structure.

Question 11

Describe how alkenes are named.

Answer 11

Alkenes are named using the same rules as for alkenes, except the suffix is -ene. The position of the C=C bond in the chain must be stated for alkenes that have four or more carbon atoms in the longest chain.

Question 12

Describe the method used to name compounds containing functional groups.

Answer 12

The same basic principles apply as for naming alkanes.

1. Identigy the longest unbranched chain of carbon atoms. The stem is now the name of the corresponding alkane.
2. Identify any functional groups and any alkyl side chains, and select the approporiate prefixes or suffixes for them.
3. Number any alkyl groups and functional groups to indicate their position on the longest unbranched chain.

Question 13

Recall the name, formulae, prefix and suffix for common functional groups.

Answer 13

Question 14

What is the molecular formula?

Answer 14

• The molecular formula shows the number and type of atoms of each element present in a molecule.
• The molecular formula does not show how the atoms are joined together and different molecules can have the same molecular formula.
• For example, the molecular formula of ethanol is C₂H₆O.

Question 15

What is the empirical formula?

Answer 15

• The empirical formula is the simplest whole-number ratio of the atoms of each element present in a compound.
• For example, glucose has the molecular formula C₆H₁₂O₆ and therefore the empirical formula CH₂O.

Question 16

1. What is the general formula?
2. Recall the general formula for alkanes, alkenes, alcohols, carboxylic acids, and ketones.

Answer 16

1. The general formula is the simplest algebraic formula for any member of a homologous series. You can use the general formula to generate the molecular formula for any member of that homologous series.

Question 17

What is the displayed formula?

Answer 17

A displayed formula shows the relative positioning of all the atoms in a molecule and the bonds between them.

Question 18

What is the structural formula?

Answer 18

The structural formula shows clearly the arrangement of atoms and which groups are bonded together in a molecule. For example, the structural formula of butane is CH₃CH₂CH₂CH₃ or CH₃(CH₂)₂CH₃.

Question 19

What is a skeletal formula?

Answer 19

A skeletal formula is a simplified organic formula. You remove:

• all of the carbon and hydrogen labels from carbon chains
• any bonds to hydrogen atoms.

This leaves just a carbon skeleton and any functional groups.

In skeletal formulae:

• a line represents a single bond
• an intersection of two lines represent a carbon atom
• the end of a line represents a –CH₃ group.

Question 20

One of the most common uses of skeletal formulae is in representing alicyclic and aromatic compounds, such as cyclohexane, cyclohexene and benxene.

Give the skeletal formula of cyclohexane, cyclohexene and benzene.

Answer 20

Question 21

1. What are structural isomers?
2. Identify two structural isomers that have the molecular formula C₄H₁₀.

Answer 21

1. Structural isomers are compounds with the same molecular formula but different structural formulae.
2. Image attached.

Question 22

Identify the two structural isomers of C₃H₇Cl.

Answer 22

Question 23

1. What functional groups can have molecules with the same molecular formulae?
2. Identify the structural isomers of C₃H₆O.

Answer 23

1. Aldehydes and ketones with the same number of carbon atoms have the same molecular formulae.
2. Image attached.

Question 24

What is homolytic fission? Explain.

Answer 24

When a covalent bond breaks by homolytic fission, each of the bonded atoms takes one of the shared pair of electrons from the bond.

• Each bond now has a single unpaired electron.
• An atom or groups of atoms with an unpaired electron is called a radical.

Question 25

What is heterolytic fission? Explain.

Answer 25

When a covalent bond breaks by homolytic fission, one of the bonded atoms takes both of the electrons from the bond.

• The atom that takes both electrons becomes a negative ion.
• The atom that does not take the electrons becomes a positive ion.

Question 26

1. What is the reaction mechanism?
2. In a reaction mechanism, what are curly arrows used for?

Answer 26

1. The reaction mechanism describes how the reaction takes place.
2. Curly arrows are used to show the movement of electron pairs when bonds are being broken or made. The arrow is drawn from the source of electrons (the bond). A pair of electrons is shown using an arrow with a full arrowhead. Arrows with half an arrowhead represent the movemnet of a single unpaired electron.

Question 27

What is an addition reaction? Give an example.

Answer 27

• In an addition reaction, two reactants join together to form one product.

Question 28

What is a substitution reaction? Give an example.

Answer 28

• In a substitution reaction, an atom or group of atoms is replaced by a different atom or group of atoms.

Question 29

What is an elimination reaction? Give an example.

Answer 29

An elimination reaction involves the removal of a small molecule from a larger one. In an elimination reaction, one reactant molecule forms two products.