Chem 112 Class Guide: BASIC ORGANIC NAMING
Chapter 24, Sections 1, 2 and 3 Learning Goals:
Upon completion of Chapter 24, Sections 1-3, you should be able to determine the following:
Identify alkanes, alkenes and alkynes
Name simple and branched alkanes
Name simple alkenes
Name simple alkynes
Chapter reading Guide: Chapter 24, Sections 1, 2 and 3
Section 1: General Characteristics of Organic Molecules
Read Chapter 24.1
The study of compounds whose molecules contain a high amount of carbon is called organic
chemistry.
Because carbon has four valence electrons, carbon will generally form four bonds in some
combination (4 single, 1 double & 2 single, 1 triple & 1 single).
Section 2: Introduction to Hydrocarbons
Read Chapter 24.1
The simplest class of organic compounds is called hydrocarbons – hydrocarbons contain only
carbon and hydrogen.
Hydrocarbons can be broken down into 4 different types:
1.)
2.)
3.)
4.)
Alkanes – contain only C-C
Alkenes – contain at least one C=C
Alkynes – contain at least one C≡C
Aromatic – contain a ring structure (not discussed in this class)
How to name hydrocarbons:
All organic compounds follow a certain naming structure:
Prefix-Base-Suffix
BASE NAME: The base name for a hydrocarbon is based upon the longest continuous chain
of carbons within a molecule. Table 24.2 contains the base name of the most common
hydrocarbons (NOTE: drop the –ane ending from the names in the table to get the base
name)
# C in chain
1
2
3
4
5
6
7
8
9
10
Base name
MethEthPropButPentHexHeptOctNonDec-
Formula Example
CH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Example Named
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
SUFFIX: The suffix for a hydrocarbon is based on the type of hydrocarbon.
1.) Alkanes end in –ANE
2.) Alkenes end in #–ENE
3.) Alkynes end in #-YNE
Where the # sign is the position of the multiple bond (ie, the number of the carbon
preceding the double bond)
PREFIX: This is only needed if there are substituent groups coming off of the base chain of a
hydrocarbon. The name of a substituent group is based on the number of carbons in the
substituent group
1 carbon – methyl
2 carbons – ethyl
3 carbons – propyl
You must also put number of the carbon that the substituent group is bonded to.
Example:
In this example, each carbon has four bonds but the bonds to hydrogen atoms are assumed.
Add imaginary hydrogen atoms to each carbon atom so that the total number of bonds the
carbon has is 4.
The red carbon chain is the longest continuous chain. It is 8 carbons long, so the base name
is HEX. Since this is an alkane (there are no double or triple bonds), the base name and
suffix is HEXANE.
The green substituent group is off of the 2nd carbon in the chain (NOTE: we start counting
from the end closest to the first substituent group) and has one carbon, so it is called 2methyl (the 2 is for the carbon the methyl group is attached to).
The blue substituent group has 2 carbons and is off the 3rd carbons. It is named 3-ethyl
(again, the 3 is for the carbon the ethyl group is attached to).
The yellow substituent group is off of the 5th carbon and has one carbon, so it is called 5methyl.
To fully name this hydrocarbon, you must:
1.) Combine the two methyl groups into one name. Since you have 2 methyl groups off of
carbons 2 and 5, call it 2,5-dimethyl
2.) List the substituent group alphabetically BY TYPE (ethyl comes before methyl; ethyl
comes BEFORE dimethyl)
So the name of this hydrocarbon is then:
5-ethyl-2,5-dimethylhexane
To see why we’re ignoring the hydrogen atoms, the above compound is shown below with
all the hydrogen atoms shown.
Try practice exercises 24.1 and 24.2
Section 3: Alkenes, Alkynes and Aromatic Hydrocarbons
Read Chapter 24.3
When we name alkenes (compounds with at least one carbon-carbon double bond), the
suffix changes to ene.
When we name alkynes (compounds with at least one carbon-carbon triple bond), the suffix
changes to yne.
Example:
Name this:
The red carbon chain is the longest continuous chain. It is 8 carbons long, so the base name
is OCT. Since this is an alkene with the double bond after the first carbon, the base name
and suffix is OCT-1-ENE. For alkenes and alkynes, we start numbering at the end closest to
the double or triple bond.
The green substituent group is off of the 2nd carbon in the chain and has one carbon, so it is
called 2-methyl.
The blue substituent group has 2 carbons and is off the 3rd carbon. It is named 3-ethyl.
The yellow subsitituent group is off of the 5th carbon and has one carbon, so it is called 5methyl.
To fully name this hydrocarbon, you must:
1.) Combine the two methyl groups into one name. Since you have 2 methyl groups off of
carbons 2 and 5, call it 2,5-dimethyl
2.) List the substituent group alphabetically BY TYPE (ethyl comes before methyl; ethyl
comes BEFORE dimethyl)
So the name of this hydrocarbon is then:
5-ethyl-2,5-dimethyloct-1-ene
Try Practice exercise 24.5
Learning Resources
Chapter Learning Goals
Chapter 24, Sections 1-3 Learning Goals
Pre Class Assignment: This assignment must be completed prior to the next class. Check your syllabus
for the exact due date and time.
Complete to the pre class assignment
(http://berks.psu.edu/clt/chem112/BasicOrganicNaming_HW.docx)
Submit a copy to the dropbox located in ANGEL called “Pre Class Assignment Submission: Basic
Organic Naming”
End of Chapter Problems:
Practice with these problems if you are having difficulty with any of the concepts covered in this
class guide AFTER we have met in class. If you cannot easily complete these problems, seek
help from your instructor, your mentor or the learning center
Chapter 24: 15, 17, 29 c only, 29 e only