Organic Chemistry

1. Organic Chemistry Chemistry A.S. 2.5 (91165) 4 External credits

2. Organic Chemistry The branch of chemistry that deals with carbon compounds. • fats, proteins, carbohydrates • fabrics • wood and paper products • plastics • medicinals

3. C Carbon has four valence electrons 1s2, 2s2, 2p2

4. H H H C H Carbon forms four single covalent bonds by sharing electrons with other atoms.

5. Carbon forms four single covalent bonds by sharing electrons with other atoms. H H H C H

6. The bonds between carbon and other atoms are often drawn at right angles. H H H C H

7. Actually the angle between the bonds is 109.5o

8. C C C Hydrocarbons • Hydrocarbons are compounds composed entirely of carbon and hydrogen atoms bonded to each other by covalent bonds. • Saturated hydrocarbons have only single bonds between carbon atoms. • Unsaturated hydrocarbons contain a double or triple bond between two carbon atoms. C C C

9. carbon to carbon double bonds carbon to carbon triple bonds Groups of Hydrocarbons carbon to carbon single bonds 19.3

10. Alkanes are saturated hydrocarbons. • They are straight or branched-chain hydrocarbons. • There are only single covalent bonds between the carbon atoms. • Each successive member of the alkane series differs from the next by a CH2 group. • Successive members are similar in structure but differ in formula. Alkanes The general formula of alkanes is CnH2n+2 If n = 7 formula = C7H16

11. Names of Straight-chain Alkanes

12. Formula • Molecular – gives the type and number of each atom • e.g. C2H6 • Structural – shows how each atom is balanced in molecule • e.g. • Condensed structural – abbreviated structural formula • e.g. CH3CH3 H H H C C H H H

13. nine carbon chain Carbon Bonding Long chains of carbon atoms form by linking one carbon atom to another through covalent bonds. C C

14. nine carbon branched chain Carbon Bonding Covalent network solids like diamond and graphite are formed like this Chains of carbon atoms may also form branches by linking one carbon atom to another through covalent bonds.

15. R C = C C Ξ C Halogens F, Cl, I, Br -OH -COOH -NH2 -COO Represents an alkyl Alkene Alkyne Form haloalkanes Form alcohols Form carboxylic acid Form amines Form esters Functional Groups Hydrocarbons often have the following functional groups O C O H O C O

16. Naming Alkanes • Identify the longest C chain and any groups • Write number for the functional group(s) keep the numbers as small as possible • Write name of group(s) alphabetically • Use di, tri, tetra to distinguish identical branches • Write prefix for long chain • Finish with –ane. 2-chloro pentane

17. line structure form of methane space filling form of methane CH4 There is 1 possible structure for CH4. 19.4 19.4

18. space filling form of ethane line structure form of ethane CH3CH3 There is 1 possible structure for C2H6. 19.4

19. space filling form of propane line structure form of propane CH3CH2CH3 There is 1 possible structure for C3H8. 19.4

20. space filling form of butane line structure form of butane CH3CH2CH2CH3 There are 2 possible structures for C4H10 unbranched chain 19.4

21. space filling form of methyl propane line structure form of methyl propane CH3 CH2CHCH3 branched chain branched chain There are 2 possible structures for C4H10. 19.4

22. normal butane (n-butane) C4H10 methyl propane C4H10 Structural (constitutional) Isomers b.p. 0.5oC m.p. -138.3oC m.p. -159.5oC b.p. -11.7oC • The properties of an organic substance are dependent on its molecular structure. Isomers are compounds with the same molecular formula but different structural formulas. Normal butane and 2-methyl propane are isomers.

23. This is the carbon skeleton with the longest continuous carbon chain. It is the first isomer of pentane. Hydrogen is added to each carbon to form four bonds. Draw the structural isomers of Pentane (C5H12). pentane

24. Add the fifth carbon atom to either of the middle carbon atoms. Hydrogen is added to each carbon to form four bonds. To form the next isomer write a four carbon chain. Pentane (C5H12) has 3 isomers. 2-methylbutane

25. Hydrogen is added to each carbon to form four bonds. To form the third isomer write a 3 carbon chain. Add the remaining two carbon atoms to the central carbon atom. Pentane (C5H12) has 3 isomers. 2,2-dimethylpropane

26. Cycloalkanes • Draw and name the structural isomers of C4H8 • Did you get all 3? • But -1-ene • But -2- ene • Cyclobutane • Cycloalkanes have the same general formula as alkenes CnH2n • Chains longer than 4C’s can form cyclic molecules • Alkyl side chains maybe attached • Name the side chain first then the cyclic group • Ethyl-cyclopentane

27. Physical Properties of Alkanes • Colourless • Soluble in water? Why? • Non-polar • Like dissolves like – solvents • Less dense than water so they float • Conductors? Why? • No free charged particles

28. Physical Properties of Alkanes • What is the trend in boiling and melting points? • Both increase with chain length because of greater wif between molecules • Not much energy is needed to break wif between small chains so they are more volatile.

29. Chemical Properties of Alkanes • Combustion (used as fuels) • C3H8 + 5O2 3CO2 + 4H2O • Burns completely hot blue flame • C3H8 + 3.5O2 3CO + 4H2O • Burns incompletely yellow flame C3H8 + 2O2 3C + 4H2O Soot

30. Halogenation of alkanes uv light CH3CH3 + Cl2→ CH3CH2Cl + HCl uv RH + X2 → RX + HX light A substitution reaction When a specific halogen is used the name reflects this: Chlorination, Bromination Damp blue litmus test? Name of Haloalkane? 1, chloroethane Reaction can continue so further Hydrogens can be replaced forming di, tri, tetra etc. (only monosubstitution in the exam) Classification Primary haloalkane (X attached to C that is attached to one other carbon Secondary RX (X attached to C that is attached to two other carbons Tertiary RX ....

31. Chemical Properties of Haloalkanes • Substitution reactions with KOH(aq) form alcohols • CH3F + KOH(aq) CH3OH + KF • Name the products and the type of bonding in each • Substitution reactions with conc. NH3form amines • CH3F + 2NH3 CH3NH2 + NH4F • Name the products, what is the bond angle between N – H in the amine • Name and classify these Haloalkanes high pressure

32. Chemical Properties of Haloalkanes • Elimination reactions involve the removal of a hydrogen and halogen atom to form a hydrogen halide and an alkene. • CH3CH2CH2I CH3CHCH2 + HI • Consider the elimination reaction of 2-Bromobutane, what products are formed? • But-2-ene and HBr and … • Markovnikoff’s rule “The rich get richer, poor get poorer” • Hydrogen is eliminated from the C with least H’s already • But-2-ene is the major product and But-1-ene the minor Heat and conc. KOH (alc) But-1-ene

33. They contain fewer than the maximum number of hydrogens. Name as for alkanes, the longest chain containing the multiple bond is the parent. Alkenes and Alkynes • Alkenes and alkynes are unsaturated hydrocarbons. Alkyne Alkene

34. Alkenes contain a carbon-carbon double bond. General formula for alkenes: CnH2n Alkynes contain a carbon-carbon triple bond. General formula for alkynes: CnH2n-2

35. When naming you must state the position of the multiple bond • What about cycloalkenes?

36. Geometric Isomers • If the Carbon chain is on different sides of the multiple bond it is trans otherwise cis • Double bonds cannot rotate about the C atoms • Each carbon in the double bond must have 2 different groups attached • Draw the formula for But-2-ene H CH3 = C H CH3 C CH3 CH3 = Trans but-2-ene C C H H Cis but-2-ene

37. Reactions of Alkenes • Combustion reactions are not as “clean” as the corresponding alkanes • Alkenes are more reactive than their corresponding alkanes. • This greater reactivity is due to the carbon-carbon double bonds. • Addition reactions at the carbon-carbon double bond are the most common.

38. double bond breaks saturated Halogenation C=C bond is broken to make 2 new C- bonds Addition reaction of bromine to pent-2-ene e.g. Bromine adds across the double bond. Geometric isomer? 2,3-dibromopentane Alkene gases will need to be bubbled through bromine water Distinguishing test for alkene Vs alkane Orange/Brown liquid decolourises

39. double bond breaks saturated Reaction with HCl Hydrogen chloride adds across the double bond. Addition of hydrogen chloride to But-1-ene In an unsymmetrical alkene there are 2 possible products 2-chlorobutane (major product) Hydrogen usually attaches to the Carbon with most Hydrogen atoms already CH2ClCH2CH2CH3 1- chlorobutane (minor product)

40. double bond breaks saturated Hydrogenation Hydrogen adds across the double bond to form an alkane. Addition of hydrogen to But-1-ene Pt at room temp CH2=CH-CH2-CH3 + H-H CH3-CH2-CH2-CH3 butane Name? But-1-ene

41. double bond breaks saturated Hydration Addition of water to But-1-ene Water (as steam at 3000C) adds across the double bond to form an alcohol. Classification of the alcohols? heat/H+ CH2=CH-CH2-CH3 + H-OH CH2OH-CH2-CH2-CH3 Butan- 1- ol Name? Is this the major or minor product? Catalyst

42. double bond breaks saturated Oxidation Addition of oxygen to but-1-ene Alkene is oxidised under acidified conditions to form an alcohol (diol). H+ CH2=CH-CH2-CH3 + MnO4- CH2OH-CHOH-CH2-CH3 Butan-1,2- diol Distinguishing test for alkene Vs alkane purple solution turns colourless

43. Polymers from Alkenes • A polymer (macromolecule) is a natural or synthetic giant molecule formed from smaller molecules (monomers). • Monomers are the small units that undergo addition polymerisation to form a polymer ( very large molecule of high molar mass) Addition polymers

44. H H H H C C C C H H H H Ethene Ethene Poly(e)thene H H H H C C C C H H H H n C C n C C C C e.g. Polypropylene CH3 CH3 H H 15000 C C 15000 H H H H Formation of Polymers High temp and pressure General formula for addition polymerisation: • n = the number of monomer units. • n ranges from 2,500 to 25,000

45. Polymers • Chain lengths are 500 - 25000 monomers in length • Longer chains get tangled • Weak intermolecular forces increase with chain length so… • Melting point increases and … • Polymer becomes stronger

47. Reactions of Alkynes • Addition reactions occur with halogens and hydrogen to produce alkenes and then alkanes. Hydrogenation • H-C=C-H + H2 CH2=CH2 • CH2=CH2 +H2 CH3-CH3 Halogenation • H-C=C-H + Br2CHBr=CHBr • CHBr=CHBr +Br2CHBr2-CHBr2 • Name the products • 1,2 – dibromoethene and 1,1,2,2 - tetrabromoethane Ni/1500C Ni/1500C Br2 Br2

48. Alcohols • Alcohols are organic molecules whose molecules contain the –OH (hydroxyl) functional group. • The general formula for alcohols is ROH. • Alcohol molecules with 4 or less C are soluble in water because EN difference between OH makes the molecule polar • Longer chain alcohols are non-polar and insoluble in water. • Alcohols burn in air to produce water and carbon dioxide.

49. Naming Alcohols • Find the longest C chain containing –OH • Identify any branches • Number C atoms so –OH has the lowest number 2 - methyl but OH 2 - CH3 C CH2 CH3 Name: CH3 an - ol

50. Polyhydroxy Alcohols • Alcohols that contain more than one OH group attached to different carbons are called polyhydroxy alcohols. • Monohydroxy: one OH group per molecule. • Dihydroxy: two OH groups per molecule. • Trihydroxy: three OH groups per molecule. Name? Ethan-1,2 -diol