1. Organic Chemistry Chapter 24
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2. Common Elements in Organic Compounds

3. Classification of Hydrocarbons
Hydrocarbons are made up of only hydrogen and carbon.

4. Alkanes Alkanes have the general formula CnH2n+2 where n = 1,2,3,…
only single covalent bonds
saturated hydrocarbons because they contain the maximum number of hydrogen atoms that can bond with the number of carbon atoms in the molecule
CH4
C2H6
C3H8
methane
ethane
propane

5. Structural isomers are molecules that have the same molecular formula but different structures.

6. 24.1
How many structural isomers can be identified for pentane, C5H12?

7. 24.1
Strategy
For small hydrocarbon molecules (eight or fewer C atoms), it is relatively easy to determine the number of structural isomers by trial and error.

8. 24.1 Solution The first step is to write the straight-chain structure:
The second structure, by necessity, must be a branched chain:

9. 24.1 Yet another branched-chain structure is possible:
We can draw no other structure for an alkane having the molecular formula C5H12. Thus, pentane has three structural isomers, in which the numbers of carbon and hydrogen atoms remain unchanged despite the differences in structure.

10. Physical Properties of Some Alkanes

11. Alkane Nomenclature
The parent name of the hydrocarbon is that given to the longest continuous chain of carbon atoms in the molecule.
CH3
CH2 CH
4-methylheptane
heptane 1 2 3 4 5 6 7
An alkane less one hydrogen atom is an alkyl group.
CH4
methane
CH3
methyl

12. Alkane Nomenclature
When one or more hydrogen atoms are replaced by other groups, the name of the compound must indicate the locations of carbon atoms where replacements are made. Number in the direction that gives the smaller numbers for the locations of the branches.
CH3 CH
CH2 1 2 3 4 5
2-methylpentane
CH3
CH2 CH 1 2 3 4 5
4-methylpentane

13. Alkane Nomenclature
Use prefixes di-, tri-, tetra-, when there is more than one alkyl branch of the same kind.
CH3 CH
CH2 1 2 3 4 5 6
2,3-dimethylhexane
CH3
CH2 C 1 2 3 4 5 6
3,3-dimethylhexane

14. Alkane Nomenclature
Use previous rules for other types of substituents.
CH3 CH Br 1 2 3 4
NO2
2-bromo-3-nitrobutane
CH2 CH
CH3 Cl 1 2 3 4 F
1-chloro-3-fluorobutane

15. 24.2
Give the IUPAC name of the following compound:

16. 24.2
Strategy
We follow the IUPAC rules and use the information in Table 24.2 to name the compound.
How many C atoms are there in the longest chain?

17. 24.2
Solution The longest chain has six C atoms so the parent compound is called hexane. Note that there are two methyl groups attached to carbon number 2 and one methyl group attached to carbon number 4.
Therefore, we call the compound 2,2,4-trimethylhexane.

18. 24.3
Write the structural formula of 3-ethyl-2,2-dimethylpentane.

19. 24.3
Strategy We follow the preceding procedure and the information in Table 24.2 to write the structural formula of the compound. How many C atoms are there in the longest chain?
Solution The parent compound is pentane, so the longest chain has five C atoms. There are two methyl groups attached to carbon number 2 and one ethyl group attached to carbon number 3. Therefore, the structure of the compound is

20. Alkane Reactions Combustion
CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) DH0 = kJ/mol
Halogenation
CH4 (g) + Cl2 (g) CH3Cl (g) + HCl (g)
light
Cl2 + energy Cl• + Cl•
Cl• + C H C H •
+ HCl C H • C Cl H
+ Cl Cl
+ Cl•

21. Optical Isomerism
achiral
chiral

22. 24.4
Is the following molecule chiral?

23. 24.4 Strategy Recall the condition for chirality.
Is the central C atom asymmetric; that is, does it have four different atoms or different groups attached to it?
Solution
We note that the central carbon atom is bonded to a hydrogen atom, a chlorine atom, a –CH3 group, and a
–CH2 – CH3 group. Therefore, the central carbon atom is asymmetric and the molecule is chiral.

24. Cycloalkanes
Alkanes whose carbon atoms are joined in rings are called cycloalkanes. They have the general formula CnH2n where n = 3,4,…

25. Geometry of Cycloalkanes
more stable

26. Alkenes Alkenes have the general formula CnH2n where n = 2,3,…
contain at least one carbon-carbon double bond
also called olefins
CH2 CH
CH3
CH3 CH
2-butene
1-butene C Cl H C Cl H
cis-dichloroethylene
trans-dichloroethylene

27. Alkene Reactions Cracking C2H6 (g) CH2 CH2 (g) + H2 (g)Pt
catalyst
Addition Reactions
CH2 CH2 (g) + HBr (g)
CH3 CH2Br (g)
CH2 CH2 (g) + Br2 (g)
CH2Br CH2Br (g)

28. and/or
Markovnikov’s rule: in the addition of unsymmetrical (that is, polar) reagents to alkenes, the positive portion of the reagent (usually hydrogen) adds to the carbon atom that already has the most hydrogen atoms.

29. Cis-Trans Isomerization in the Vision Process
electron micrograph
of retinal rods

30. Alkynes Alkynes have the general formula CnH2n-2 where n = 2,3,4,…
contain at least one carbon-carbon triple bond CH C
CH2
CH3
CH3 C
1-butyne
2-butyne
Production of acetylene
CaC2 (s) + 2H2O (l) C2H2 (g) + Ca(OH)2 (aq)

31. Alkyne Reactions Hydrogenation CH CH (g) + H2 (g) CH2 CH2 (g)
Addition Reactions
CH CH (g) + HBr (g)
CH2 CHBr (g)
CH CH (g) + Br2 (g)
CHBr CHBr (g)
CH CH (g) + 2Br2 (g)
CHBr2 CHBr2 (g)

32. Chemistry In Action: Ice That Burns
methane hydrate

33. Aromatic Hydrocarbons
Electron micrograph
of benzene

34. Other Representations of Benzene

35. Aromatic Compound Nomenclature
CH2CH3
ethylbenzene
NH2
aminobenzene Cl
chlorobenzene
NO2
nitrobenzene Br Br 1 2 3 4 5 6
1,2-dibromobenzene
1,3-dibromobenzene

36. Aromatic Compound Reactions
Substitution reaction H Br
+ HBr
+ Br2
FeBr3
catalyst H
CH2CH3
+ HCl
+ CH3CH2Cl
AlCl3
catalyst

37. Polycyclic Aromatic Hydrocarbons

38. Functional Group Chemistry
Alcohols contain the hydroxyl functional group and have the general formula R−OH.

39. Biological production of ethanol
C6H12O6 (aq) CH3CH2OH (aq) + 2CO2 (g)
enzyme
Commercial production of ethanol
CH2 CH2 (g) + H2O (g) CH3CH2OH (g)
H2SO4
Metabolic oxidation of ethanol
CH3CH2OH CH3CHO + H2
alcohol dehydrogenase

40. Functional Group Chemistry
Ethers have the general formula R−O−R′.
Condensation Reaction
CH3OH + HOCH CH3OCH3 + H2O
H2SO4
catalyst

41. Functional Group Chemistry
Aldehydes and Ketones contain the carbonyl ( ) functional group. O C
R C H O
aldehydes have the general formula
R C R′ O
ketones have the general formula
H C H O
H C O
CH3 C O
CH3
H3C
formaldehyde
acetaldehyde
acetone

42. Functional Group Chemistry
Carboxylic acids contain the carboxyl ( −COOH ) functional group.

43. Properties and Reactions of Carboxylic Acids
Generally weak acids
React with alcohols to form esters
Neutralization
Production of acid halides (intermediates in syntheses)

44. Functional Group Chemistry
Esters have the general formula R′COOR, where R is a hydrocarbon group.
Characteristic odors and flavors
Hydrolysis
Alkaline hydrolysis (saponification)

45. Functional Group Chemistry
Amines are organic bases with the general formula R3N.
CH3NH2 + H2O RNH3+ + OH-
Neutralization
CH3CH2NH2 + HCl CH3CH2NH3+Cl-

46. Some Aromatic Amines

48. 24.5
Cholesterol is a major component of gallstones, and it is believed that the cholesterol level in the blood is a contributing factor in certain types of heart disease. From the following structure of the compound, predict its reaction with (a) Br2, (b) H2 (in the presence of a Pt catalyst), (c) CH3COOH.

49. 24.5 Strategy To predict the type of reactions a molecule may
undergo, we must first identify the functional groups present
(see Table 24.4).
Solution There are two functional groups in cholesterol: the
hydroxyl group and the carbon-carbon double bond.
The reaction with bromine results in the addition of bromine
to the double-bonded carbons, which become single-bonded.
(b) This is a hydrogenation reaction. Again, the carbon-carbon
double bond is converted to a carbon-carbon single bond.

50. 24.5 (c) The acid reacts with the hydroxyl group to form an ester and
water. Figure shows the products of these reactions.

51. Chemistry In Action: The Petroleum Industry
Crude Oil