1. Chapter 25/26: Simple Organic Chemistry
Basic Structure and Nomenclature
Graphic:

2. Chapter 25 Organic Chemistry Goals
25.1 Saturated Hydrocarbons
Describe bonding in hydrocarbons
Distinguish straight chain vs. branched chain alkanes
25.2 Unsaturated hydrocarbons
Explain saturated vs. unsaturated hydrocarbons
Differentiate alkenes, alkynes
25.3 Isomerism
Distinguish among structural, geometric, and stereoisomers.
Identify the asymmetric carbon or carbons in stereoisomers

3. Chapter 25 Organic Chemistry Goals
25.4 Hydrocarbon Rings
Identify common cyclic ring structures
Explain resonance in terms of the aromatic ring of benzene
25.5 Hydrocarbons from the Earth
Identify 3 important fossil fuels and their origins
Name some products obtained from natural gas, petroleum and coal.

4. 25.1 Hydrocarbons
Hydrocarbons are organic compounds composed of Carbon and Hydrogen only.
Alkanes – hydrocarbons with all single bonds (no double or triple bonds)
Methane
CH4 this is the main component in natural gas.
Rotting things and cows produce and emit methane.
Note that carbon always has four covalent bonds because it has four valence electrons.
Carbon bonds using a tetrahedral form to spread out H’s as much as possible due to repulsion.

5. 28.1 Alkanes
Ethane is the next one in the sequence, with two carbons and six hydrogens, where both carbons are tetrahedrons. It is also a gas at STP, like methane is.
Above are four different ways of representing methane.
1st: Lewis dot
2nd: 2D - Carbons at the junctions is implied
3rd: Ball and stick model
4th: Space fill model

6. Straight Chain Alkanes
C3H8 propane
C4H10 butane
Straight chain alkanes contain any number of carbon atoms, one after the other in a chain.
As you can see, they aren’t always straight though.

7. First Ten Alkanes Formula Name CH4 Methane C6H14 Hexane C2H6 Ethane
Heptane
C3H8
Propane
C8H18
Octane
C4H10
Butane
C9H20
Nonane
C5H12
Pentane
C10H22
Decane
Alkane = CnH2n+2
Note they all end in –ane
It’s a homologous series with increment –CH2

8. Alkanes What is the trend with boiling point? Why? Name
Molecule Formula
Structural Formula
Boiling point (oC)
Methane
CH4
-161.0
Ethane
C2H6
CH3CH3
-88.5
Propane
C3H8
CH3CH2CH3
-42.0
Butane
C4H10
CH3CH2CH2CH3
0.5
Pentane
C5H12
CH3CH2CH2CH2CH3
36.0
Hexane
C6H14
CH3CH2CH2CH2CH2CH3
68.7
Heptane
C7H16
CH3CH2CH2CH2CH2CH2CH3
98.5
Octane
C8H18
CH3CH2CH2CH2CH2CH2CH2CH3
125.6
Nonane
C9H20
CH3CH2CH2CH2CH2CH2CH2CH2CH3
150.7
Decane
C10H22
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
174.1
What is the trend with boiling point? Why?

9. Straight Chain Alkanes aren’t “Straight”
C – C bonds are sp3 hybridized (tetrahedral)
Butane, C4H10

10. Structural Shorthand
Explicit hydrogens (those required to complete carbon’s valence) are usually left off of drawings of hydrocarbons C1 C2 C3 C4 C1 C2 C3 C4
Line intersections represent carbon atoms

12. Branched Chain Alkanes
A hydrocarbon substituent is called an alkyl group.
On the drawing on the left, that is a methyl group on the top. You start by using the name methane, and removing the –ane and adding –yl instead.
When a substituent alkyl group is added to a straight-chain hydrocarbon, branches are formed. An alkane with one or more alkyl groups is called a branched chain alkane.
Let’s look at the rules for naming these (next page):

13. Rules for Naming Alkanes (Nomenclature)
For a branched hydrocarbon, the longest continuous chain
of carbon atoms gives the root name for the hydrocarbon 1 2 3 4
4 carbon chain = butane

14. Rules for Naming Alkanes (Nomenclature)
When alkane groups appear as substituents, they
are named by dropping the -ane and adding -yl.
—CH3 Methyl
—CH2CH3 Ethyl
—CH2CH2CH3 Propyl
—CH2CH2CH2CH3 Butyl
Methyl

15. Rules for Naming Alkanes (Nomenclature)
The positions of substituent groups are specified
by numbering the longest chain of carbon atoms
sequentially, starting at the end closest to the
branching. 1 2 3 4
Methyl

16. Rules for Naming Alkanes (Nomenclature)
The location and name of each substituent are followed by the root alkane name. The substituents are listed in alphabetical order (irrespective of any prefix – for example, ethyl comes before methyl), and the prefixes di-, tri-, etc. are used to indicate multiple identical substituents. 1 2 3 4
Name:
2-methylbutane
Methyl

17. Nomenclature Practice
Name this compound 1
9 carbons = nonane 2 4 3 5 6 7 8 9
Step #1: For a branched hydrocarbon, the longest continuous chain of carbon atoms gives the root name for the hydrocarbon

18. Nomenclature Practice
Name this compound
9 carbons = nonane 1 2 4 3 5 6
CH3 = methyl 7
chlorine = chloro 8 9
Step #2: When alkane groups appear as substituents, they are named by dropping the -ane and adding -yl.

19. Nomenclature Practice
Name this compound
9 carbons = nonane 1 2 4 3 5 6
CH3 = methyl 7
chlorine = chloro 8 9 1 9
NOT 9 1
Step #3: The positions of substituent groups are specified by numbering the longest chain of carbon atoms sequentially, starting at the end closest to the branching.

20. Nomenclature Practice
Name this compound
9 carbons = nonane 1 2 4 3 5 6
CH3 = methyl 7
chlorine = chloro 8 9
2-chloro-3,6-dimethylnonane
Step #4: The location and name of each substituent are followed by the root alkane name. The substituents are listed in alphabetical order (irrespective of any prefix, meaning chloro comes before methyl), and the prefixes di-, tri-, etc. are used to indicate multiple identical substituents.

21. Branched Chain Alkanes Rules Summary
Find the longest chain of carbons in the molecule (doesn’t have to be straight or linear). Here it’s 7, so the parent hydrocarbon is heptane.
Number the carbons in the main chain in sequence as shown. To do this, you must start at the end that will end up giving the alkyl groups the smallest number for the carbon they are attached to. Here they are on carbon # 2,3,4. If you numbered it the other way they would have been on 4,5,6.

22. Branched Chain Naming (contin.)
Add numbers to the names of the substituent groups to identify their positions on the chain. These numbers become prefixes that come before the name of the parent alkane. Here we have : methyl, 3-methyl, 4-ethyl.
Use prefixes to indicate the appearance of a group more than once. Use di- (twice), tri- (three times), tetra- (four times) and penta- (five times). In the structure above, we’ll be using dimethyl

23. Branched Chain Naming (contin.)
List the names of the alkyl substituents in alphabetical order, ignoring the di-, tri- part. For example, ethyl groups will come before methyl groups.
Commas are used to separate numbers, hyphens are used to separate numbers and words. There are no spaces anywhere in the name!
So the compound above is:
4-ethyl-2,3-dimethylheptane

24. Sample Problem 25-2
Name the above compounds using the rules given on the last slides.
a. The chain is six carbons long (longest configuration).
There are two methyl groups on the 3rd carbon.
The name is 3,3-dimethylhexane
The chain is five carbons long.
There are two methyl groups on 2nd and 4th carbon.
The name is 2,2,4,4-tetramethylpentane

25. Sample problem 25-3 Draw structural formulas for the following:
3-ethylhexane
2,2,4-trimethylpentane

26. Properties of Alkanes
The electron pairs in hydrogen-carbon bonds are shared nearly equally between the nuclei of the C and H. Therefore hydrocarbon compounds such as alkanes are nonpolar.
Therefore the alkanes of low molar mass tend to be gases or low boiling point liquids (refer to slide #8 for boiling points).
Since water is a polar molecule, nonpolar organic materials such as alkanes are not attracted to water. You already know that oil and water do not mix because they don’t meet the rule that “like dissolves like” because one is polar (water) and the other is nonpolar (alkanes/oil/hydrocarbons).

27. Structural Isomers n-Pentane, C5H12 Isopentane, C5H12
Isomers are molecules with the same chemical formula, but different organization of atoms (different bonding). Here are some examples using branched and unbranched alkanes. They are all examples of C5H12.
n-Pentane, C5H12
Isopentane, C5H12
Neopentane, C5H12

28. Cyclic Alkanes Cyclopropane, C3H6 Cyclobutane, C4H8
Cyclopentane, C5H10
Cyclohexane, C6H12
Cycloheptane, C7H14
Remember, explicit hydrogens are left out

29. 25.2 Unsaturated hydrocarbons
An unsaturated hydrocarbon compound is similar to an alkane but it has double or triple bonds.
For every double bond, there is one less H atom on the carbon. Molecules with double bonds are alkenes.
For every triple bond, there are two less H atoms on the carbon. Molecules with triple bonds are alkynes.
The word “saturated” means there are the maximum number of H atoms possible, meaning there are only single bonds on the molecule.
The word “unsaturated” means there are less than the maximum number of H atoms possible, which means there are double or triple bonds somewhere.

30. Alkenes An alkene, ethene left and below left
Other alkenes below right
Note the “2-pentene” and “2-butene”: you also have to specify where the double bonds are!

31. Alkenes
When working with an alkene, you will find the longest chain in the molecule that contains the double bond, and that will be the parent alkene.
It has the same root name as the alkane with the same number of carbons, but the ending changes to –ene.
The smallest alkenes are ethene and propene, which are often called by the common names ethylene and propylene.
Did you notice on that last page that ethene is planar?
The CH2 groups on the ends of the double bond can’t be rotated about the double bond, so no rotation occurs about a C=C double bond.

32. Alkynes Alkynes have triple CΞC bonds. This is ethyne.
Note that the triple bond is rigid, so no rotation about this bond can occur.

33. Boiling Points
What do you notice about the trend in boiling points as a function of single, double and triple bonds?
Anything?

34. Reactions of Alkenes and Alkynes
Hydrogenation
Propene
Propane
Halogenation
1-Pentene
1-2-dibromopentene
Polymerization
Small molecules are joined together to form a large molecule
Polyethylene

35. 25.3 Isomers
Some structures of hydrocarbons are similar, differing only in the way the groups are assembled.
Here’s an example, two ways to build C4H10 :
Structural isomers like these two differ in physical properties such as boiling point, melting point, and chemical reactivity.
Generally the more branched, the lower boiling point.

36. Geometric Isomers trans cis
Because a double C=C bond cannot rotate, that has some important structural implications.
There are two possible arrangements for the methyl groups on 2-butene, the cis and the trans configuration.
The cis configuration has both groups on the same side of the double bond.
The trans has the groups on opposite sides of C=C.
trans
cis

37. Cis and Trans Geometric Isomers
Identical chemical formula and bonding, just different geometric position.
cis trans

38. Geometric Isomers (continued)
Cis-1,2-dichloroethene Trans-1,2-dichloroethene
The cis and trans isomers can have physical properties that are different, especially if there is a polar atom like Cl on there.

39. Stereoisomers
Molecules that we draw on paper in two dimensions can look the same on paper but different in three dimensions if they are nonsuperimposable mirror images of each other.
Your two hands are an example of what a steroisomer is like. They are nonsuperimposable mirror images of each other, and they cannot be placed on top of each other to obtain a match.
Do you see how these
two appear to be mirror
images of each other?
With four different atoms
attached like this, it is an
assymmetric carbon.

40. Sample Problem 25-4
Here you are asked to evaluate if the compounds have an asymmetric carbon

41. 25.4 Hydrocarbon Rings Cyclic hydrocarbons
Compounds that contain a hydrocarbon ring exist when the two ends of the carbon chain are attached to each other.
Hydrocarbon compounds that do NOT contain rings (Sections ) are called aliphatic compounds.
Five- and six-carbon rings are the most abundant.
Shapes like these are used to
represent the ring, with a
carbon at each junction.

42. 25.4 Hydrocarbon Rings, saturated

43. Hydrocarbon Rings, Aromatic
A special group of unsaturated cyclic hydrocarbons are known as arenes.
These can be rings or groups of rings.
They were originally called aromatic compounds, meaning that they had sweet, pleasant odors.
The simplest aromatic hydrocarbon is benzene, C6H6
This is one of four (or more) ways to show benzene. The single and double bonds alternate positions, so they show dotted lines to represent that. See next slide for more…

44. Benzene ring – aromatic hydrocarbon
Benzene is a six-carbon ring (C6H6) with one H attached to each C. That leaves one electron free from each Carbon to participate in a double bond.
Benzene is a cyclic unsaturated hydrocarbon with delocalized electrons, which results in resonance structures.
OR…
See how the drawing on the left and center are resonance structures that are represented by the drawing on the right?

45. More ways to show benzene…

46. This shows a benzene ring group (called a phenyl group) attached to hexane on the 3 carbon. When a benzene is a substituent on an alkane, it is called a phenyl group.
This one is an ethyl group attached to a benzene ring as a substituent. This compound is called ethylbenzene.

47. Geometric Isomerism in Aromatics
ortho (o-) = two adjacent
substituents
o-dichlorobenzene
meta (m-) = one carbon between
substituents
m-dichlorobenzene
para (p-) = two carbons between
substituents
p-dichlorobenzene

48. 25.5 Hydrocarbons from the Earth
Natural gas
Natural gas is an important source of alkanes of low molar mass.
Natural gas is typically about 80% methane, 10% ethane, 4% propane and 2% butane.
Natural gas is good for combustion (your gas stove, your water heater) because it burns with a nice hot clean flame to form CO2 and water.
Propane and butane, which are separated from the other gases by liquifaction, are also good heating fuels. They are sold in liquid forms.
I have a 500 gallon propane tank in my front yard because there is no natural gas where I live.

49. Petroleum
Petroleum typically has the higher molar mass hydrocarbons that compose it. Cracking is the process where large molecules are broken into smaller ones.
Most are straight chain and branched alkanes.
Petroleum does have a small amount of aromatic compounds and sulfur, oxygen and nitrogen containing compounds.
Crude oil gets distilled to divide it into fractions according to its boiling point (fractionation into individual chemicals).
The crude oil is heated so that it vaporizes and rises through a column. Compounds with the highest boiling points condense first near the bottom and compounds with the lowest boiling points at the top.

50. Fractionation column to separate crude oil into usable components.

51. Fractions obtained from Crude Oil
Composition of carbon chains
Boiling range in oC
Percent of crude oil
Natural Gas
C1 to C4
Below 20
Below 10%
Petroleum ether (solvent)
C5 to C6
30 to 60
Naphtha (solvent)
C7 to C8
60 to 90
Gasoline
C6 to C12
40 to 175
40%
Kerosene
C12 to C15
150 to 275
10%
Fuel oils, mineral oil
225 to 400
30%
Lubricating jelly, petroleum jelly, greases, paraffin wax, asphalt
C16 to C24
Over 400

52. Coal
Coal has its origin about 300 million years ago when forests and swamps were buried under layers of vegetation and decayed under intense pressure.
The pressure, coupled with the heat from the Earth’s interior, turned the plant remains into coal.
In some places, such as Eastern Pennsylvania, the hardest and most carbon rich coal, anthracite, was produced. Anthracite has a carbon content exceeding 80% which makes it an excellent fuel source.
Coal is usually found underground in seams 1-3 meters thick. In America, most coal is less than 100 meters underground. In Europe, it may be as much as 1500 meters underground.

53. Coal
Coal is mostly condensed ring compounds with extremely high molar mass.
If you recall benzene, it’s ratio of C to H was 1 to 1, unlike hexane which is 6 carbons to Because of this, coal leaves more soot upon burning than do the more aliphatic (non-ring) compounds.
Another issue with coal is that it can have as much as 7% sulfur, which creates SO2 and SO3 air pollution.
Coal can be used to produce (through distillation) products such as coal gas (H2 + CH4 + CO), coal tar, coke (fuel for industrial processes) and ammonia (to make fertilizer).
Coal tar can be used to produce benzene, toluene, naphthalene, phenol and pitch.

54. 26.1 Introduction to Functional Groups
A functional group is a specific arrangement of atoms in an organic compound that is capable of characteristic chemical reactions.
Organic compounds can be classified according to their functional groups.
The double and triple bonds of alkene and alkyne groups are chemically reactive so they are considered functional groups as well.

55. Hydrocarbon Functional Groups
Class
Functional Group
General Formula
Alcohol
hydroxyl group O — H
R – OH
Alkyl halide or halocarbon
halogen — X
R — X
Ether
— O —
R — O — R’
Aldehyde
carbonyl group O
with H ||
— C — H O ||
R — C — H
Ketone
— C —
R — C — R’
Carboxylic acid
carboxyl group O
— C — OH
R — C — OH
Ester
— C — O—
R — C — O — R’
Amine (also see amide in table 26.1)
amine group |
—N— R’
R — N — R’’

57. Halogen Substituents
Halocarbons are organic compounds with a halogen bonded onto them (F, Cl, Br, I).
Halocarbons in which a halogen attached to a carbon of an aliphatic chain (non-ring) are called alkyl halides.
Halocarbons in which a halogen attaches to an aromatic hydrocarbon (or arene) are called aryl halides.
Space filling models of the three above >>

58. Why do you think the boiling point changes so much as a function of how many chlorines are on a methane?
Recall that hydrocarbons are nonpolar typically. The addition of Cl makes them polar. The more polar they are, the more the attraction they have to overcome to boil off and escape in the gas phase.

59. Halocarbons Halocarbons are easily prepared from hydrocarbons.
Hydrofluorocarbons (freons) are used as refrigerants.
A common way to prepare halocarbons is using a substitution reaction. A halogen can replace a hydrogen on an alkane. The symbol X stands for the halogen in this reaction below:
R-H X → R-X HX
Alkane Halogen Halocarbon Hydrogen halide
Here’s an example:
CH Cl2 → CH3Cl + HCl

60. Halocarbons (continued)
Halogens on carbon chains can readily be displaced to produce an alcohol and a salt. (Purpose is to make an alcohol).
The general reaction is as follows:
R-X OH → R-OH X-
Hydrocarbon hydroxide ion alcohol halide ion (salt)
Here’s an example:
H2O, 100oC
CH3I(l) KOH (aq) → CH3OH (l) + KI (aq)