Year 12 Chemistry: Chapter 9 Compounds of Carbon
Unit 1: Area of Study (AOS) 2:~ Organic Chemical Pathways
Carbon compounds are the basis for a huge range of materials from fuels, plastics, fibres and paints through to the chemicals that make up living organisms.
The study of carbon compounds is sometimes called organic chemistry. Substances containing carbon, with the exception of carbon dioxide, carbon monoxide, cyanides and carbonates, are known as organic compounds.
The element hydrogen is usually present in organic molecules, atoms of carbon and hydrogen can be assembled to form many thousands of different hydrocarbon molecules.
9.1 Bonding in carbon compounds
To explain why there are so many carbon compounds you need to understand the structure of the carbon atom and the way carbon forms bonds.
J Carbon’s electronic configuration:
J Periodic table: Period ___ : Group ___
It is a small atom with four outer-shell electrons. The carbon atom forms covalent bonds by sharing these electrons with other atoms.
Carbon forms strong covalent bonds with hydrogen atoms, and nearly all organic molecules contain hydrogen bonded to carbon. Carbon also forms strong covalent bonds with other carbon atoms, forming long chains and rings. Single, double or triple bonds can form between carbon atoms.
Covalent bonds can also be formed between carbon and atoms of other elements such as oxygen, nitrogen, sulfur, phosphorus and the halogens (Group ___ ).
Tetrahedral: eg. Methane
Straight chain: Hexane
9.2 Homologous series (also see Unit 1 Ch:8)
In an homologous series the compounds have similar structures and chemical properties and the same general formula. Each member of a homologous series differs by a - - group from the previous member.
Alkanes – single carbon to carbon covalent bond
The simplest series of hydrocarbons.
The alkanes are called saturated hydrocarbons because they have the maximum number of hydrogens.
n / Name / Molecular Formula1
2
3
4
5
6
7
8
9
10
Example:
J Name: Butane
J Molecular formula:
J Semi-structural formula:
J Structural formula:
Cyclic molecules
Cyclic molecules are a chain of carbon atoms that can be bent round to form a ring.
Sometimes, as in the case of benzene, three of the four outershell electrons from each carbon atom form normal covalent bonds but the fourth electron is shared (delocalised) around the six-membered carbon ring. Compounds like this with rings of delocalised electrons are known as arenes.
The ring of delocalised electrons in benzene, C6H6
Shorthand
Isomers
Molecules of alkanes that contain less than four carbon atoms per molecule have only one possible structure. Molecules of butane or higher can have many different structural formulae.
Molecules having the same molecular formula but different structural formulae are known as structural isomers. Structural isomers have different ______and ______properties.
Example:
J Butane:
Straight chain Branched Chain: methyl propane
J Pentane:
Decane has 75 structural isomers and C20H42 has 350 000 possible isomers.
Naming Alkanes
Alkanes are named in a systematic way.
J First part indicates the number of carbon atoms
J Last part (-ane) indicates single carbon to carbon bonds.
No. of carbon atoms / Prefix1 / Meth
2 / Eth
3 / Prop
4 / But
5 / Pent
6 / Hept
7 / Hex
8 / Oct
9 / Non
10 / Dec
The side chain can be considered as an alkane molecule that has lost a hydrogen atom. The fragment of the alkane that forms the side chain is called an alkyl group, eg methane is CH4 its alkyl group is CH3 and known as methyl.
Alkane / Semi-structural Formula / Alkyl / Semi-structural formulaSystematic names for alkanes are made up of:
J The name of the longest straight chain
J The name and number of any alkyl side chains
J The position of the side chain on the main carbon chain.
Carbon atoms are numbered from the start to end of the longest continuous chain in the compound. The prefix is the alkyl group.
The systematic name usually contains a prefix, a stem and a suffix.
Example:
Step 1: Identify the longest straight chain of carbon atoms. If there is an alkyl group start from the end closest to the group. Stem: ______
Step 2: Identify the bonds between carbon atoms in the straight chain. Suffix: ____
Step 3: Identify the side chain and its position. Alkyl group: ______Position: ___. Therefore the prefix: ______
Name: ______
Now you try naming the following structure using the steps above:
Example: Write the structural formula for heptane and 2,2,4-trimethylpentane molecules.
Alkenes
Hydrocarbons with double covalent bonds between carbon atoms are called alkenes. Hydrocarbons that contain double or triple bonds between carbon atoms are known as unsaturated hydrocarbons.
The additional density of electrons held in bonds between the carbon atoms makes these substances much more reactive than the alkanes. The shape of alkenes in the region around the double bonds is planar. The angles between these bonds is 120°.
Number / Name / Molecular formula1 / ------/ ------
2 / Ethene
3 / Propene
4 / Butene
5 / Pentene
6 / Hexene
7 / Heptene
8 / Octene
9 / Nonene
10 / Decene
For butene and alkenes higher in the homologous series the double bond can be located in various positions in the carbon chain.
The suffix is =ene. Use the same steps as alkanes except that double/triple bonds take precedence over the starting point for number the longest chain.
Example:
J CH2=CHCH2CH3 = ______
J CH3CH=CHCH3 = ______
Draw the structural formula of but-1-ene, but-2-ene and 2-methylpropene
Questions: 1, 2, 3, 4, 5 & 26 (it just says prepare notes).
9.3 Functional Groups
Carbon can also form covalent bonds with other atoms or groups of atoms. These are called functional groups. A functional group is an atom or a group of atoms that gives a characteristic set of chemical properties to a molecule containing that group.
Many compounds can be produced by substituting a hydrogen atom in an alkane molecule with different functional groups. The fragment of the alkane, which has one hydrogen removed, is called an alkyl group and represented by R. The bonds formed between carbon atoms and between carbon and hydrogen atoms, -C-C- and C-H bonds – are strong and relatively unreactive.
Knowing the characteristics properties of particular functional groups allows us to classify the vast number of organic chemicals systematically and to understand and predict their properties.
Functional groups located in different positions in a molecule result in structural isomers. Example: There are two isomers of C3H7OH:
Propan–1-ol (1-propanol) Propan-2-ol (2-propanol)
Name / Structural formulaChloro
Hydroxy
Carboxy
Amino
Ester
Amide
Ether
Chloroalkanes
It is possible to replace a hydrogen atom in an alkane with chlorine atom to form a chloroalkane. The systematic name for chloroalkane starts with chloro followed by the name of the alkane from which it is derived.
Name: Chloromethane Chloroethane
Molecular formula:
Structural formula:
Name: 1-chloropropane 2-chloropropane
Molecular formula:
Structural formula:
NOTE: Functional groups are numbered before a branch.
More than one hydrogen atom in an alkane can be replaced with a chlorine atom.
Example: Name the below compound
The other halogens fluorine, bromine, iodine, form similar homologous series to the chloroalkanes.
Structural formula:
Molecular formula:
Name:
Alkanols
Ethanol is a member of the alkanol homologous series. Alkanols is the systematic name for the group of chemicals commonly called alcohols.
Hydrogen bonds involving the polar bond of the –OH group influence the properties of alcohols.
J Higher boiling points
J More soluble
Alkanols are named by dropping the ‘e’ and replacing with ‘ol’, eg methane = methanol.
Name / Semi-Structural formula / Structural formulaPropan-1-ol
(1-propanol)
Propan-2-ol
(2-propanol)
2-methylpropan-1-ol
FACT: Antifeeze solutions are made with ethan-1,2-diol, HOCH2CH2OH, more commonly known as ethylene glycol. Pure ethylene glycol is a viscous, colourless liquid. It is soluble in water as a result of the two polar hydroxy groups in the molecule.
*Draw the structure
Glycerol (propan-1,2,3-triol) HOCH2CHOHCH2OH is used as a sweetener in confectionary and as a moisturising agent in hand lotions.
Carboxylic acid
Carboxylic acids contain the carboxy functional group.
The acid properties of this group of organic compound is due to the ionisation of the COOH functional group.
Bonds within the COOH functional group are polarised resulting in the formation of bonds between molecules or between carboxylic acid molecules and water.
Carboxylic acids are named by dropping the ‘e’ and replacing with ‘oic acid’, eg methane = methanoic acid.
Number of carbons / Semi-structural formula / Name1 / Methanoic acid
2 / Ethanoic acid
3 / Propanoic acid
4 / Butanoic acid
5 / Pentanoic acid
Branched carboxylic acids are named in a similar way to the other branched organic compounds.
*Draw the structure of 3-methylbutanoic acid
Amines
Organic compounds that contain the –NH2 functional group are called amines.
The smaller amines are very soluble in water due to the formation of hydrogen bonds. This solubility decreases as the size of the alkyl group becomes larger.
The amines are named by adding amino to the name of the alkane.
Structural formula:
Molecular formula:
Name:
Amino acids are the basic building block for proteins. They contain the amine and carboxylic acid functional groups.
*Draw the structural formula of 2-aminopropanoic acid (alanine)
FACT: Like ammonia, the smaller amines have a strong odour. The characteristic odour of decaying flesh is caused by the diamines putrescine, H2N(CH2)4NH2 and cadaverine H2N(CH2)5NH2.
Questions: 8, 9, 11, 12, 13, 15, 16, 18, 19, 22, 24 & 25.
Summary notes using key terms and Outcomes