1. Alkanes and Aromatic Hydrocarbons

2. biology…is that everything that animals do,
“The most important hypothesis in all of
biology…is that everything that animals do,
atoms do. In other words, there is nothing
that living things do that cannot be
understood from the point of view that
they are made of atoms acting according
to the laws of physics.”
Richard Feynman ( )

3. What You Will Learn
Defintions, organic compound, hydrocarbon, fossil fuels, saturated and unsaturated compounds, homologous series, structural isomers.
How to name and draw alkanes.
Difference between structural and molecular formulas.
Physical and chemical properties of alkanes.
Aromatic vs aliphatic compounds and the structure of Benzene.

4. Organic Compounds Contain carbon Have covalent bonds
Have low melting points
Have low boiling points
Burn in air (oxygen)
Are soluble in nonpolar solvents
Form large molecules

5. Organic Compounds
Fossil fuels are fuel that were formed from remains of plants and animals that died millions of years ago.
A saturated compound is one in which there are only single bonds between the atoms in the molecule.

6. Alkanes Contain C and H only Contain single bonds C-C
Have 4 bonds to every carbon (C) atom
Are nonpolar

7. Homologous Series
A homologous series is a family of organic compounds with the same general formula , similar chemical properties, and successive members differing by CH2
A hydrocarbon is that contains carbon and hydrogen only.

8. Complete Structural Formulas
Show the bonds between each of the atoms
H H
 
H  C  H H C H
CH4 , methane
In methane, CH4 the four valence electrons of carbon are shared with the single electrons of four hydrogen (H) atoms. Each pair of electrons is a single bond, which can be drawn as a line. When a structure is drawn to show each bond, it is called a complete structural formula.

9. More Alkanes Structural Formulas Condensed H H H C C H CH3 CH3
H H Ethane
H H H
H C C C H CH3 CH2 CH3
H H H Propane
The complete structural formula for ethane shows the single bonds between two carbon atoms and six H atoms. The complete structural formula of propane shows the 3-carbon chain with single bonds to the attached H atoms. To write a condensed structural formula, the H atoms are written as a group next to their respective C atoms.

10. IUPAC Names Methane 1 CH4 Ethane 2 CH3CH3 Propane 3 CH3CH2CH3
Name # carbons Structural Formula
Methane 1 CH4
Ethane 2 CH3CH3
Propane 3 CH3CH2CH3
Butane 4 CH3CH2CH2CH3
Pentane 5 CH3CH2CH2CH2CH3
The names of organic compounds are determined by the IUPAC rules (International Union of Pure and Applied Chemistry). The stem of the name states the number of carbon atoms in the carbon chain of the compounds. The suffix, in this case –ane, indicates the alkane family.

11. IUPAC NAMES Hexane 6 CH3CH2CH2CH2CH2CH3
Name # carbons Structural Formula
Hexane CH3CH2CH2CH2CH2CH3
Heptane CH3CH2CH2CH2CH2CH2CH3
Octane CH3CH2CH2CH2CH2CH2CH2CH3
Nonane CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

12. Learning Check Alk1 A. What is the condensed formula for H H H H
H C C C C H
B. What is its molecular formula?
C. What is its name?

13. Solution Alk1
A. CH3CH2CH2CH3
B. C4H10
C. butane

14. Reactions of Alkanes Always to form carbon dioxide and water.
Combustion
Always to form carbon dioxide
and water.
alkane + O CO2 + H2O + heat

15. Combustion In the Cell Metabolic oxidation is combustion
C6H12 O6 + 6O CO2 + 6H2O + heat
glucose

16. Learning Check Alk2 Complete the combustion reaction for C3H8 + O2 +
Balance your equation

17. Solution Alk2 Step 1 C3H8 + O2 CO2 + H2O Step 2
To balance the atoms in the formula C3H8, we place a coefficient of 3 in front of CO2 and a coefficient of 4 in front of H2O. The total O in the products is 10 O (6 O in 3CO2 and 4 O in 4 H2O). To balance the 10 O, a coefficient of 5 is placed in front of the O2.

18. Learning Check Alk3
Complete and balance the reaction for the complete combustion of C7H16

19. Solution Alk3 Step 1 C7H16 + O2 CO2 + H2O Step 2
The carbon has a subscript 7, which means we need to place a coefficient of 7 in front of CO2. The H subscript 16 is balanced by placing a coefficient of 8 in front of H2O. Finally, the total O of 22 ( ) indicates that a coefficient of 11 in front of O2 will balance the O atoms.

20. Alkanes
Branched Alkanes
Structural Formulas

21. Alkyl Groups Branches on carbon chains H H C CH3 methyl H H
H C C CH3CH2 ethyl or C H
An alkyl group is composed of one or more carbon atoms attached to a carbon chain. An alkyl group is derived from an alkane by removing one hydrogen. The ending –ane of the alkane is changed to –yl. The carbon branch from methane is the methyl group. The carbon branch from ethane is the ethyl group. 2 5

22. Branched Alkanes CH3 CH3CHCH3 methyl groups CH3 CH3 CH3CHCH2CHCH3
In the structural formula of an alkane, the alkyl group is typically attached vertically above or below the carbon chain.

23. Naming Branched Alkanes
CH methyl branch
CH3CH2CH2CHCH2CH3
Count
A branched-chain alkane is named by indicating the attached groups on the longest carbon chain. In this example, the longest carbon chain has 6 carbon atoms.

24. Naming Branched Alkanes
CH methyl branch
CH3CH2CH2CHCH2CH3
Count
3-Methylhexane
on third C CH six carbon chain
group
The chain is numbered to give the side group or methyl group a location on carbon 3 in the chain.

25. Naming Summary 1. Count the C’s in the longest chain
2. Name each attached group
3 Count the longest carbon chain to give the first attached group the smallest number
4. Name and locate each group

26. Learning Check Alk4 A. CH3 CH3 CH3CHCH2CHCH3 B. CH3 CH3
CH3CH2CHCH2CCH2CH3
CH3

27. Solution Alk4 A. CH3 CH3 CH3CHCH2CHCH3 2,4-dimethylpentane B. CH3 CH3
CH3CH2CHCH2CCH2CH3
CH ,3,5-trimethylheptane

28. Learning Check Alk5 Write a condensed structure for
A. 3,4-dimethylheptane
B. 2,2-dimethyloctane

29. Solution Alk5 3,4-dimethylheptane CH3 CH3CH2CHCHCH2CH2CH3
2,2-dimethyloctane
CH3CCH2CH2CH2CH2CH2CH3

30. Isomers Same molecular formula Same number and types of atoms
Different structural formula arrangement of atoms
Structural isomers are compounds that have the same molecular formula with different arrangements of the atoms.

31. Examples of Isomers CH3 The formula C4H10 has two different structures
CH3CH2CH2CH3 CH3CHCH3
Butane methylpropane
When a CH3 is is used to form a branch, it makes a new isomer of C4H10.

32. Learning Check Alk6
Write 3 isomers of C5H12 and name each.

33. Solution Alk6 CH3 CH3CH2CH2CH2CH3 pentane CH3CHCH2CH3 2-methylbutane
CH3CCH3 2,2-dimethylpropane

34. Learning Check Alk7
Write the structural formulas of 3 isomers that have the formula C5H12. Name each.

35. Solution Alk7
Write the structural formulas of 3 isomers that have the formula C5H12. Name each.
CH3CH2CH2CH2CH3 pentane
CH CH3
CH3CHCH2CH CH3CCH3
CH3
2-methylbutane 2,2-dimethylpropane

36. Alkanes and Aromatic Hydrocarbons
Cycloalkanes
Aromatic Hydrocarbons

37. Cycloalkanes Cyclopropane CH2 CH2 CH2 Cyclobutane CH2 CH2 CH2 CH2
The is a group of alkanes that have a cyclic structure. These cycloalkanes contain a carbon chain that is in a ring. Each cycloalkane has a formula that is 2C less than the corresponding alkane. For example, propane is C3H8 whereas cyclopropane ic C3H6. Butane is C4H10 and cyclobutane is C4H10. The names of the cyclic structures use the prefix cyclo in from of the alkane name for the carbon chain.

38. More Cycloalkanes
Cyclopentane CH2
CH CH2
CH CH2
Cyclohexane
CH2

39. Aromatic Hydrocarbons39

40. Unsaturated Hydrocarbons
Unsaturated hydrocarbons have a double or triple bond e.g. propene and ethyne.
Aromatic hydrocarbons are very unsaturated but their properties are very different. The most important of these is benzene,C6H6.

41. Benzene Molecule
Six carbon atoms joined to form a hexagonal planar ring.
Each carbon has four valence electrons
One of these is used to form a bond with a hydrogen atom.
Two other electrons are used to form sigma bonds with the carbon atoms on the either side.

42. Benzene Molecule
X-ray analysis showed that all carbon-carbon bonds in benzene are of equal length intermediate between a single and a double bond.

43. Delocalised Pi bonds
The 6 valence electrons not involved in sigma bonding are shared between the six carbon atoms in the molecule
not localised into 3 double bonds
For convenience the C and H atoms are not shown
Ring in centre essential

44. Aromatic Compounds
Aromatic compounds are compounds which contain a benzene ring in their molecules.

45. Aromatic hydrocarbons
Benzene C6H6
Methylbenzene C7H8
Ethylbenzene C8H10

46. Benzene

47. Benzene Formula C6H6 unsaturated

48. Benzene
Its molecular formula, C6H6 , was established in 1834, after the compound's discovery by Faraday.
The formula of benzene (C6H6) caused a mystery for many years after its discovery, as no explanation had been found that could account for all the bonds — carbon usually forms four single bonds and hydrogen one.
The chemist Friedrich August Kekulé was the
first to deduce the ring structure of benzene (1865).
The cyclic nature of benzene was confirmed by the crystallographer Kathleen Lonsdale.

49. Benzene
Using X-ray diffraction, researchers discovered that all of the carbon-carbon bonds in benzene are of the same length, and it is known that a single bond is longer than a double bond.
In addition, the bond length, the distance between the two bonded atoms in benzene is greater than a double bond, but shorter than a single bond.
There seemed to be in effect, a bond and a half between each carbon.

50. Benzene
Benzene is also a planar molecule (all the atoms lie in one plane). Each carbon atom is bonded to its neighbor with one electron from each atom. Since each atom has two neighbors, this uses two electrons from each atom.
Another electron from each carbon is used to bond the hydrogen attached to it.
The remaining six electrons orbit the atomic nuclei at right angles to the plane of the ring and also overlap each other, consequently blurring their orbits both above and below the ring ( 3 electrons in upper ring and 3 electrons in down ring).

51. Benzene
As a result, the electrons are shared equally between the carbon atoms and exist as two clouds, one above and one below the plane of the carbon ring.
Since these latter six electrons are not confined to specific carbon atoms, they are said to be delocalised.
This is usually represented in structural formula as a hexagon with a circle in the centre to represent the shared nature of the electrons

52. Bonding in benzene 6 electrons in a delocalised  bond CH
6 electrons in a delocalised  bond
above and below the plane of the atoms

53. Benzene
References
Steve Lewis for the Royal Society of Chemistry

54. Methylbenzene

55. Ethylbenzene

56. Physical properties
Physical state: Benzene. methylbenzene and ethylbenzene are liquids
Insoluble in water
Soluble in non-polar solvents such as cyclohexane

57. Aromatic Compounds in Nature and Health
Many aromatic compounds are common in nature and in medicine.

58. Naming Aromatic Compounds
Aromatic compounds are named with benzene as the parent chain. One side group is named in front of the name benzene.
methylbenzene chlorobenzene
(toluene)

59. Naming Aromatic Compounds
When two groups are attached to benzene, the ring is numbered to give the lower numbers to the side groups. The prefixes ortho (1,2), meta (1,3-) and para (1,4-) are also used.

60. Some Common Names
Some substituted benzene rings also use a common name. Then naming with additional more side groups uses the ortho-, meta-, para- system.

61. Learning Check Alk9 Select the names for each structure:
1. Chlorocyclohexane
2. Chlorobenzene
3. 1-chlorobenzene
1. Meta-methyltoluene
2. Meta-dimethylbenzene
3. 1,3-dimethylbenzene

62. Solution Alk9 Select the names for each structure: 2. Chlorobenzene
1. Meta-methyltoluene
2. Meta-dimethylbenzene
3. 1,3-dimethylbenzene

63. Learning Check Alk10
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
B. Ortho-chlorotoluene

64. Solution Alk10
Write the structural formulas for each of the following:
A. 1,3-dichlorobenzene
B. Ortho-chlorotoluene