Organic Chemistry

1. Organic Chemistry Alkenes and Alkynes

2. Alkenes and Alkynes Triple carbon bond Double carbon bond

3. Alkenes and Alkynes • Saturated compounds (alkanes): • Have the maximum number of hydrogen • atoms attached to each carbon atom. • Unsaturated compounds: • Have fewer hydrogen atoms attached to • the carbon chain than alkanes. • Containing double bond are alkenes. • CnH2n • Containing triple bonds are alkynes. • CnH2n-2

4. Naming Alkenes & Alkynes Using the IUPACalkane names: Alkene names change the end to -ene. Alkyne names change the end to -yne

5. Alkenes • Alkenesare hydrocarbons with at least one double carbon to carbon bond. • To show the presence of the double bond, the –ane suffix from the alkane name is changed to –ene. • The alkenes are unsaturated with respect to hydrogen • This means it does not have the maximum number of hydrogen atoms as it would if it were an alkane (a saturated hydrocarbon).

6. The Alkenes An overview of the alkenes The alkenes: • Are members of the hydrocarbon family. • Are made of just HYDROGEN and CARBON. • Are made up of chains of carbon atoms with single and double covalent bonds between them. The double bonds make them far more reactive than alkanes. • Are UNSATURATED (contains double bonds) and  decolourise bromine water. • Are mostly used to make other chemicals and polymers, they burn with a sooty flame to produce carbon dioxide, soot (carbon) and water. • Have the general chemical formula  CnH2n • Another example of an homologous series

7. C2H4  The simplest alkene is ethene (notice that the word ends in'ene'), each molecule contains two carbon joined to 4 hydrogens C4H8  The next alkene is butene, each molecule contains four carbons joined to 8 hydrogens. The carbons are starting to form a chain. It's not important to know this for GCSE but notice that you can get different molecules of butene depending upon where the double bond is. C3H6  The next alkene is propene, each molecule contains three carbons joined to 6 hydrogens. Notice the double covalent bond between the two carbon atoms. Count the bonds around each carbon atom . . . . . . they all have 4.

8. Alkenes Reactions • Alkenes undergo combustion reactions with oxygen and, like alkanes, form carbon dioxide and water • Alkenes can undergo self-addition in which the alkene molecules join together to form long chains called polymers.

9. Review • Complete the revision questions page 177 (10, 11)

10. Alkynes • Analkyneis a hydrocarbon with at least one carbon to carbon triple bond. • Naming an alkyne is similar to the alkenes, except the base name ends in –yne. • The general formula for the alkynes is CnH2n-2 • Another example of an homologous series

11. Ethyne • Ethyne, C2H2Ethyne, which is also known as acetylene, is the smallest molecule in the Alkyne series and has two Carbon atoms which are triple bonded together. The diagram to the right shows the construction of this molecule from the electron dot diagrams of Carbon and Hydrogen. There is only one possible structure for this molecule so it does not require and numbering of the Carbon atoms.

12. Butyne • Butyne, C4H6 This is the first alkyne where there are two possible locations for the triple bond. Both are shown in the image. In but-1-yne, the triple bond is between the endmost carbon, C1 and its neighbour C2. The other possibility is but-2-yne where the triple bond is between the second and third Carbons in the skeleton of the molecule. • These two structural isomers have the same chemical formula C4H6, but have slightly different chemical properties. For example, But-1-yne boils at 8.1 degrees celsius whereas but-2-yne boils at 27 degrees celsius. But-1-yne is also far more flammable. This difference in properties allow these variations of Butyne to be identified and separated if required.

13. Propyne • Propyne, C3H4 By adding one more Carbon atom we have Propyne. The triple bond is between two of the Carbon atoms with the third singly bonded. This leaves four free electrons overall, meaning that four Hydrogens will be needed to complete the molecule. • It is possible to have the Carbon - Carbon triple bond on either the left or right of the Carbon chain. If one of these versions was rotated or flipped horizontally it would be identical to the other. This means that they are both the same structure, so there is only one isomer of Propyne. There is no need to put a "1" in the name (Prop-1-yne) so it is left out for simplcity's sake.

14. Chemical Properties of Alkynes • The triple bond is unstable and so alkynes are generally quite reactive. They are also able to act as acids, are highly volatile and combust readily. As such Propyne is being considered as a rocket fuel.

15. Alkyne Reactions • Alkynes can undergo combustions (oxidation) and addition reactions.

16. Cyclic Hydrocarbons • The carbon backbone of some hydrocarbons can form rings (cyclo) • An important category of the hydrocarbons is the unsaturated cyclic compounds making up the aromatic series. • The simplest member of this series is benzene C6H6 • Benzene is found naturally in crude oil but is usually synthesized from other hydrocarbons when used in making pharmaceuticals.

17. Cyclic saturated hydrocarbons • Cyclic saturated hydrocarbons have a closed ring of carbon atoms in a polygon configuration having the same number of vertices as the number of carbon atoms, with each carbon atom being bonded to two hydrogen atoms and to two other carbon atoms. They are referred to as cycloalkanes, cycloparaffins or naphthenes. • Cycloalkanes with a single ring of carbon atoms have a general formula of CnH2n. The adjacent image depicts two such single ring cycloalkanes, namely cyclopentane (C5H10) and cyclohexane (C6H12). • Cycloalkanes may also have two fused (i.e., conjoined) rings. For example, two cyclohexane rings may be fused, so that two of the carbon atoms are shared by each of the two rings, to form decalin (C10H18) which is referred to as a bicycloalkane. • The general formula for cycloalkanes is CnH2(n+1-g) where g is the number of rings.

18. Cyclic unsaturated hydrocarbons • Cyclic unsaturated hydrocarbons have a closed ring of carbon atoms in a polygon configuration having the same number of vertices as the number of carbon atoms. If the hydrocarbons have a ring containing a single double bond between two of the carbons, the hydrocarbons are referred to as cycloalkenes or cycloolefins. The adjacent image depicts two such cycloalkenes with single double bonds, namely cyclopentene (C5H8) and cyclohexene (C6H10). • The general formula for single-ring cycloalkenes with a single double bond is CnH2n-2. • If single-ring alkenes have two double bonds, they are referred to as cyclodienes or cyclodiolefins. An example is cyclopentadiene (C5H6), and the general formula for single-ring cycloalkenes with two double bonds is CnH2n-4.

19. Aromatic Hydrocarbons • Aromatic hydrocarbons have a closed ring of 6 carbon atoms in the shape of a hexagon with 3 of the carbon atoms having a double bond with one connected carbon atom and a single bond with another connnected carbon. Such a ring is referred to as a benzene ring and all hydrocarbons containing one or more such rings are referred to as aromatics or aryl compounds. • The adjacent image depicts three of the most common aromatics, namely benzene (C6H6), toluene (C7H8 and o-xylene (C8H10). There are three possible xylenes referred to as ortho-xylene (o-xylene), meta-xylene (m-xylene) and para-xylene (p-xylene). • Aromatics may have two or more rings, either in fused or other configurations, and may have many different side groups or side chains (such as the methyl side group in toluene). There are quite literally hundreds (if not thousands) of various aromatic hydrocarbons.

20. Aromatic Hydrocarbons

21. Aromatic Compounds • Aromatic compounds contain benzene. • Benzene has: • 6 C atoms and 6 H atoms. • Two possible ring structures.

22. Aromatic Compounds Arene:A compound containing one or more benzene rings. • Aromatic compounds are named: • With benzene as the parentchain. • Name of substituent comes in front of the “benzene”. • methylbenzene chlorobenzene ethylbenzene CH2-CH3 Cl CH3

23. Review • Alkanes, Alkenes on line multiple choice • Complete the revision questions pages 178, 179 (12 – 23)