Compounds of Carbon Chapter 9

Carbon Over seven million compounds containing carbon are known. Think of all the things you know that contain carbon, what are they?? Carbons electronic structure is 1s22s22p2 It is found in period 2, group 14 of the periodic table It has four outer shell electrons and it can form covalent bonds with these electrons.

Bonding in carbon compounds 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. It can form single, double or triple bonds. It can also form covalent bonds with other atoms.

Bonding in carbon compounds When four single bonds are formed around a carbon atom, the pairs of electrons in each bond act as a charge cloud. These charge clouds repel each other so that they spread out as far as possible. This arrangement is called a tetrahedral distribution.

Homologous series Homologous series just means a family of certain molecules. Alkanes and alkenes are both forms of these homologous series.

Alkanes Saturated hydrocarbons as every carbon has a hydrogen attached. Molecular formula CnH2n+2 The molecules can be written by a structural formula, as shown right or a semi-structural formula. CH3CH2CH2CH3 or CH3(CH2)2CH3

Cyclic Molecules A chain or carbon atoms can also be bent round to form a ring. Benzene is a bit different, three of the four outer shell electrons form normal covalent bonds but the fourth electron is shared (delocalised) around the six-membered ring. Compounds like this are called arenes. OR

Isomers Isomers are the same molecular formula but different structural formula. Structural isomers can have different chemical and physical properties. Butane and bigger all have structural isomers. There are 75 structural isomers for decane. What are the three for pentane, what are they??

Naming alkanes Remember from last year. Alkanes are named in a certain way. The first part of the name indicates the number of carbon atoms and the last part ends in ane. The fragment of alkane that forms a side chain is called an alkyl group.

Naming Alkanes Systematic names for alkanes are made up of: The name of the longest alkane hydrocarbon chain The name and number of any alkyl side chain The position of the side chain on the main carbon chain. The longest unbranched carbon chain is chosen as the stem for naming the molecule

Time to test you Name these

Alkenes Hydrocarbons with double covalent bonds are called alkenes. Their names end in ene. Alkenes are unsaturated hydrocarbons as the double bonds prevent the carbons from bonding with the maximum number of hydrogens. The formula is CnH2n. For butene and higher the double bond can be located in various positions in the carbon chain

Naming alkenes Look at the longest carbon chain that contains the double bond. The position of the double bond is indicated by the number of the first carbon atom involved in the double bond. The numbering should start at the end nearest to the double bond. The rules for naming any side chains are the same for alkanes.

Naming Alkenes

Over to you Page 137 Question 2, 3 and 6

Functional Groups So far we have looked only at compounds containing hydrogen and carbon. Carbon can also form 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.

Functional groups Many compounds can be produced by substituting a hydrogen atom in an alkane with different functional groups. -C-C- and –C-H bonds are strong and relatively unreactive, but when a functional group is added it can completely change the properties of the carbon chain.

Chloroalkanes It is possible to replace a hydrogen atom in an alkane with chlorine atoms to form a chloroalkane. The systematic name for a chloroalkane starts with chloro followed by the name of the alkane from which it is derived. For compounds with more than 3 carbons it is possible to place a chlorine atom at the end or in the middle of the chain so we use numbers to indicate the position of the chlorine. Lets look at page 138.

Alkanols Alkanols are more commonly called alcohols. They have the functional group R-OH The hydroxy group has been substituted for one hydrogen in an alkane. Hydrogen bonds involving the polar head of the –OH group influence the properties of alcohols. Compared to alkanes, alcohols are more soluble in water and have higher boiling points.

Alcohols Alcohols are named by dopping the ‘e’ at the end of the alkane and replacing it with an ‘ol.’ Ethane becomes ethanol. For propanol and higher it is important to number the carbon chain and give the number where the alcohol group is located. Draw Propan-1-ol and propan-2-ol. Can you name this structure?

Carboxylic acids Contain the carboxy functional group R-COOH Bonds with the COOH functional group are polarised, resulting in the formation of hydrogen bonds between molecules. Low molecular carboxylic acids are soluble in water.

Naming Carboxylic acids The stem of the systematic name of carboxylic acids is determined from the number of carbon atoms in the longest chain that contains the COOH functional group. Add “oic acid” at the end of the name. Ethane becomes ethanoic acid

Amines Organic compounds that contain the –NH2 functional group are called amines Around the nitrogen atom there are three pairs on electrons involved in bond formation and one lone pair of electrons. The bonds around the nitrogen atom are polar due to the high electronegativity of nitrogen. The smaller amines are very soluble in water but solubility decreases as the size of the alkyl group gets larger.

Amines The amines are named by adding amino to the name of the alkane Amino acids are basic building blocks for proteins. They contain the amine and the carboxylic acid functional groups.

Name these structures???

Your Turn Page 142 Question 8, 9, 11 and 12 Page 143 Question 15, 16 Questions 18 - 21