Download 8. What are saturated hydrocarbons?

Chapter 15 Organic Compounds and the Atomic Properties of Carbon
The basis of this chapter is to understand how organic molecules are named and
structured. Although organic chemistry is a vital part of chemistry, it is not a strong
focus in the AP curriculum. There will only be a small number of questions addressing
organic chemistry. This chapter goes into great detail about organic reactions and
biological applications of organic chemistry.
Major Concepts to Know:
 Students need to be able to determine a formula of an organic compound undergoing
combustion—an organic acid like ethanoic in an acid-base reaction. Students should
also be able to draw structures and explain properties based on the structure.
Recognition of ethanoic acid as acetic acid (vinegar) and methanoic acid as formic
acid is helpful, so basic naming should be understood.

Students should know how to write out structures that are correct, and may find it
helpful to recognize that a large fraction of organic molecules follow the “HONC”
rule (bonds are H=1, O=2, N=3, C=4). However, they also need to learn how this is
modified in simple molecules with multiple bonds between atoms.

Students should know basic functional groups and their properties. For example, a
common mistake students make on the exam is to say alcohols are basic because they
end in an –OH group.
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
Students should know how to classify basic organic compounds. On the exam,
common names are frequently given, as well as, or instead of, formal IUPAC names
(e.g., acetic acid, instead of ethanoic acid).

Basic alkanes have the base formula CnH2n+2. Cycloalkanes lose 2 H atoms, so the
formula is CnH2n, the same as for alkenes, which have 1 pair of doubly bonded carbon
atoms for each two atoms of hydrogen lost. In the alkenes, students need to recognize
the difference between a cis and trans structure. Alkynes lose 2 more hydrogen atoms
for a triple bond between a pair of C atoms, so the formula is CnH2n2.

Students also need to recognize the basic prefixes used in organic nomenclature:
o Meth- is used for a 1-carbon molecule.
o Eth- is used for a 2-carbon chain.
o Prop- is used for a 3-carbon chain.
o But- is used for a 4-carbon chain.
o The rest of the prefixes are similar to what students have learned in math
and the prefixes in covalent naming.
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Structures of the First Four Alkanes

Another concept students need to know is isomers. Isomers have the same formula
but a different structure. Students should know butane is the first alkane molecule
with an isomer as shown in the diagram above. However, in molecules with
functional groups, propyl has isomers (e.g: n-propanol and iso-propanol). In past
multiple-choice exams, students have been asked which of the following are isomers,
or have been asked to draw an isomer in the free response section.

Of the aromatic compounds, students need to recognize benzene, draw its structure
given C6H6, and explain its properties.

The basic types of functional groups should be recognized by students.
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
Some of the more common alcohols and acids are in the following diagrams.
Students should be able to draw simple alcohols such as methanol and simple
carboxylic acids such as methanoic (formic) acid.
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Common Alcohols
Common Carboxylic Acids

A list of many of the organic compounds recently on the exam include ethanoic acid,
ethanol, methanoic acid, propanone, butanol, propane, 1-propanol, ethanol, propanol,
ethane, methane, propene, benzene, propanoic acid, dimethyl ether, and ethyne
(acetylene).

Students need to be able to look at structures like those above and count the number
of sigma and pi bonds and/or identify the hybridization of any carbon. A common
mistake often seen by those grading exams is the student stating that double bonds
ARE pi bonds, instead of one sigma and one pi.
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
Students need to be able to explain whether or not a compound is soluble in water,
and be able to determine the intermolecular forces involved. This may need to be
done from looking at a Lewis structure.
Vocabulary to Know:
 Alkane, alkene, and alkyne
 Hydrocarbon
 Alcohol
 Carboxylic acids
 Ethers
 Ketones
 Aldehydes
 Isomer
 Cis and trans isomers
 Saturated and unsaturated hydrocarbons
Math Skills Students Must Know:
 Counting and balancing numbers of electrons and bonds in determining
Lewis structures.
Suggested Problems:
 Structures and Classes of Hydrocarbons: 8, 20, 21, 22, 23, 28, 30, 31
 Properties and Reactivities of Common Functional Groups: 50, 55, 58, 59, 60, 61, 62,
63, 65
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Suggested Demonstrations or Labs:
Synthesis of an organic compound is on the AP recommended list.
 Paradis, Jeffrey A. “Chemical Nomenclature, Part II: Naming Organic Compounds,”
Hands On Chemistry Laboratory Manual (McGraw-Hill, 2006).
Synthesis of an organic: The actual compound doesn’t matter although many teachers do
the synthesis of aspirin.
 Ehrenkranz, David and John Mauch. “Synthesis of Esters,” Chemistry in Microscale
(Kendall/Hunt Publishing Company, 1995).
 Paradis, Jeffrey A. “Introduction to Organic Analysis: Infrared Spectroscopy,” Hands
On Chemistry Laboratory Manual (McGraw-Hill, 2006).
Questions
1. What do organic compounds contain?
a. How has the definition of organic chemistry changed?
2. How many bonds does carbon form in most compounds?
a. Why is the Si–Si bond weaker then a C–C bond?
b. What is a functional group?
3. What elements do hydrocarbons contain?
a. What are common heteroatoms that carbon bonds to?
4. Explain the difference in polarity and strength between the C–C, C–H, and the
C–O bond.
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5. How many arrangements can be made with a 5-carbon single-bonded chain?
6. What are the prefixes used for carbon chain with 1,2,3,4 …10 carbons?
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7. What are alkanes?
8. What are saturated hydrocarbons?
a. What is the general formula for alkanes?
b. What type of bond and hybridization is present in alkanes?
c. Why are alkanes saturated?
d. What is the hybridization of the carbon in alkanes?
e. Give three rules for naming alkanes.
(1)
(2)
(3)
9. What are cycloalkanes?
a. What is the general formula for a cycloalkane?
10. What are isomers?
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11. What property of alkanes determines boiling points?
a. Are alkanes generally soluble in water? Explain.
12. What is an alkene?
a. What are unsaturated hydrocarbons?
b. What is the general formula of alkenes?
c. What type of hybridization is present to be called an alkene?
d. How do you indicate the position of the double bond in the name?
e. What do cis and trans refer to?
13. What are alkynes?
a. What is the general formula of an alkyne?
14. What are aromatic hydrocarbons?
15. What is a benzene ring and how is it drawn?
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16. What is the functional group in organic alcohols?
a. How are alcohols named?
17. What is the functional group in carboxylic acids?
a. What is the formula of ethanoic acid?
18. What is the functional group of an aldehyde?
19. What is the functional group of a ketone?
a. What is the formula of propanone?
20. Why are oxoacids acidic in water?
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