Chemistry 30 Unit C Organic Chemistry Chapter 9 and 10

Lab Safety Rap

Chapter 9 Hydrocarbons from Petroleum

Introduction Organic Chemistry is the study of carbon compounds, on which living (organic) matter is based.

The carbon cycle shows the interrelationship of all living things with the environment and with technologies that refine fossil fuels.

9.1 Fossil Fuels Organic Chemistry deals with compounds of carbon, excluding oxides (e.g., CO (g) ) & ionic compounds of carbon based ions such as carbonate.

9.1 Fossil Fuels The major source of carbon compounds is still living or previously living things, such as plants, animals and all types of fossil fuels. Fossil fuels are chemical potential energy. The original source of this energy is the sun.

Hydrocarbons These are molecules containing only carbon & hydrogen that are covalently bonded together.

Hydrocarbons Coal, oil and natural gas are all non-renewable sources of fossil fuels & the primary source of hydrocarbons. Hydrocarbons are the starting point in the synthesis of thousands of products, including fuels, plastics & synthetic fibers.

Refining Is the technology that includes chemical & physical processes for separating complex mixtures in simpler mixtures. Physical processes can separate coal & natural gas.

Refining Coal may be crushed, whereas components of natural gas are separated by solvent extraction or by condensation & distillation. Crude oil & oil sands refining is more complex, but yields a greater variety of products.

Table 1 Refining of Fossil Fuels

9.2 Alkanes from Natural Gas Geologists predict where oil &/or gas is to be found & then drill into the ground to recover it. The separation of oil & gas can be explained by solubility theory.  Oil (nonpolar) will not dissolve in water (polar), & limestone (ionic) are slightly soluble in water, but not soluble in oil.

Naming Alkanes Alkanes are hydrocarbons containing only single covalent bonds. They have the general formula C n H 2n + 2 The simplest example is methane, CH 4

Naming Alkanes A methane molecule consists of one carbon atom covalently bonded to four hydrogen atoms by the simultaneous sharing of their unpaired (bonding) valence electrons.

Structure of Methane Carbon always forms four covalent bonds, since it has four available bonding electrons. This is the basis of the structure of organic molecules. H I H - C - H I H

Carbon Chains Carbon can also make stable carbon to carbon bonds. This means that chains of carbon atoms can be produced of increasing size & complexity by adding more carbon atoms & allowing branching.

Carbon Chains Ethane (C 2 H 6 ) is the simplest hydrocarbon with a C - C bond:

Continuous Chain Alkanes Contain any number of C atoms in a straight chain. Alkanes are classified as saturated hydrocarbons - compounds of carbon & hydrogen containing only carbon-carbon single bonds with the maximum number of hydrogen atoms bound to each carbon.

Continuous Chain Alkanes The table on the next slide shows the first 10 continuous chain alkanes. Note the increasing boiling point of these alkanes, indicated by the state of the molecule, as the molecular weight increases.

These molecules form a homologous series, showing constant increment of change in the molecular structure. In alkanes this increment of change is - CH 2 -

Molecular Formula Molecular formula of organic molecules provide the number of each type of atom in the molecule. For example, propane: C 3 H 8(g)

Complete Structural Formula Structural formula of organic molecules show the arrangement of the atoms in the molecule. For example, propane: (C 3 H 8(g) ) H H H I I I H - C - C – C - H I I I H H H

Condensed Structural formula Condensed structural formula can be drawn for hydrocarbons by leaving out some bonds &/or atoms from the full structural formula, for example: C 3 H 8(g) H H H I I I H - C - C – C - H I I I H H H becomes CH 3 - CH 2 - CH 3

Condensed Structural formula The bond lines indicate the bond between carbon atoms, they can even be left out altogether, i.e. CH 3 CH 2 CH 3 Or can be reduced even further by placing brackets around the units forming an homologous series: CH 3 CH 2 CH 2 CH 2 CH 3 may become CH 3 (CH 2 ) 3 CH 3

Line Structural Formula Chemists further simplify structural formula by leaving out the symbols for atoms. This leaves only the bond lines to represent the structure of the molecule: e.g., octane, C 8 H 18(l) The “kinks” in the line are due to the bond angles between adjacent carbon atoms.

For example, a branched chain alkane: CH 3 - CH 2 - CH - CH 3 I CH 3 this is a branch

Branched Chain Alkanes Atoms or groups of atoms may take the place of a hydrogen atom on the parent hydrocarbon chain. These are called substituents. The substituents may be other hydrocarbons, halogens, oxygen, sulfur, phosphorus etc. For example, a branched chain alkane: CH 3 - CH 2 - CH - CH 3 I CH 3 this is a branch

This could also be drawn as a line structural formula as follows:

When the branch is another hydrocarbon, as above, the branch is called an alkyl group. The General formula for an alkyl group is C n H 2n + 1 The alkyl group is named for the parent alkane from which it is derived by changing the ending from -ane to –yl. The branch on the example before is called methyl (from methane, the name for a hydrocarbon with only one carbon in it).

Other examples: CH 3 – CH 2 –is ethyl CH 3 – CH 2 – CH 2 –is propyl Alkyl groups are also sometimes referred to as radicals. The physical & chemical properties of a branched chain alkane will be different than those of a continuous chain alkane. So it is important to be able to recognize & name these different compounds.

Rules for Naming Branched Chain Alkanes Naming of organic compounds follows IUPAC rules.IUPAC This is a precise, internationally recognized system allowing for the systematic naming of all organic compounds.

The Rules 1.Find the longest continuous chain of C atoms and name it. 2.Locate the branches on the chain. 3.Number the C atoms in the continuous chain starting at the end closest to the branching which will give the carbon atoms to which the branches are attached the lowest possible numbers. 4.Name the branches.

The Rules (Continued) 5.Show the location of the branches by the number of the C atom to which it is attached on the continuous chain. 6.Use the prefixes di-, tri-, etc. to indicate the appearance of the same alkyl group more than once. 7.List the names of the alkyl groups alphabetically (ignore di-, tri-, etc.). 8.Use commas to separate numbers & hyphens to separate numbers & words. There are to be no spaces within the name of the alkane.

CH 3 – CH 2 - CH 2 - CH - CH 3 I CH 3 Example 1:

CH 3 – CH 2 - CH 2 – CH 2 – CH I CH 3 Example 2:

Example 3: CH3 CH2 CH3 | | CH 3 – CH 2 - CH - CH – CH 2 – CH 2 - CH – CH 2 - CH 3 I CH 3

Alkanes Worksheet

Alkanes worksheet

Alkanes Worksheet

Structural Isomers Consider the following two molecules: CH 3 - CH 2 - CH 2 - CH 3 and CH 3 - CH - CH 3 I CH 3 This is butane This is methylpropane

Both have the molecular formula, C 4 H 10, but different structural formula. One is a straight chain alkane, the other is a branched alkane. They are different compounds & have different properties. These two molecules demonstrate a phenomenon that occurs constantly in organic chemistry called isomerization. CH 3 - CH 2 - CH 2 - CH 3 CH 3 - CH - CH 3 I CH 3

Since there are many possible combinations of the atoms that go to make up organic molecules, especially as the molecules increase in size, there are often two or more possible structures for the same combination of atoms. The type of isomerization seen above is structural isomerization. These two molecules are structural isomers. CH 3 - CH 2 - CH 2 - CH 3 CH 3 - CH - CH 3 I CH 3

They differ in chemical and physical properties, for example boiling point. These two isomers have very similar chemical properties. They both burn in the presence of oxygen to form carbon dioxide and water vapour. They are used as precursors for the manufacture of other organic compounds and as additives in gasoline. Both are colourless gases. The boiling point of butane is –0.5ºC while that of methylpropane is –11.7ºC.

The number of structural isomers increases with the number of carbon atoms, ie. 5 for C 6 H 14, 75 for C 10 H 22 and over 4 million for C 30 H 62 !!!

Isomers of C 6 H 14

Properties of Alkanes Alkanes are non-polar, since electrons are equally shared by the nuclei of the carbon atoms in the chain. Alkanes are gases or low boiling point liquids, since only very weak forces hold the molecules together. Larger molecular weight alkanes (>16 C) form waxy solids.

Due to the fact that they are non-polar, alkanes are not misable with water. Remember the rule that “like dissolves like”, so alkanes do not dissolve in water, but liquid alkanes are very good solvents for other hydrocarbons.

Cyclic Hydrocarbons So far we have been concerned with straight chain hydrocarbons. However, it is possible for the two ends of a carbon chain to become attached to form a ring structure called a cyclic compound (hydrocarbon). These ring structures contain between 3 and 30 carbons when found in nature. The most common are 5 and 6 membered rings.

Cycloalkanes Saturated cyclic hydrocarbons are called cycloalkanes. They have the general formula C n H 2n This is the same general formula as for alkenes. In fact they are structural isomers of alkenes.

An example of a cycloalkane is cyclopentane: If a branch is present treat the cycloalkane as the parent chain and identify the branches (Use the lowest numbers possible).

Example What is the name of the following branched cycloalkane? 1,2-dimethylcyclopentane

Properties of cycloalkanes They have higher boiling points than the corresponding alkane. The smaller compounds are more reactive than the corresponding alkane, since they have a strained structure.