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Naming Hydrocarbons Tutorial
(nomenclature)
Drawing structures: it’s all good
2-butene
H
H
H
C
C
C
C
H
This is called the
“skeletal structure”
H
H
H
H
H3C CH CH CH3
CH3
H3C
This is called the
“condensed structure”
CH3CH=CHCH3
Using brackets can also shorten some formulas:
CH3(CH2)4CH3 vs. CH3CH2CH2CH2CH2CH3
Background: formulas for HCs
• Alkanes= CnH2n+2, enes= CnH2n, ynes= CnH2n-2
• Remember enes, then think of what would
happen if bond was single or triple instead.
• Provides some useful information (e.g. for
compositional analysis, or to check work)
• Cannot always tell hydrocarbon type based on
numbers (e.g. propyne vs. propadiene)
Q - how many hydrogens in each of these:
6 carbon alkane
Alkene: C22H?
H3C
CH3
Background: formulas for HCs
Q - how many hydrogens in each of these:
Answer:
14
6 carbon alkane
44
Alkene: C22H
H3C
CH3
8 (2x5 - 2 = 10 - 2)
Naming: common vs. IUPAC
• Common names used in the 1800’s are still
used for some compounds today:
O
O
H
C
H
OH
Formic acid
C
C
Acetylene
H
C
H 3C
CH3
Acetone
• The International Union of Pure and Applied
Chemistry (IUPAC) was established in 1900s
• Frequent revisions to nomenclature
• Systematic method allows an infinite number
of compounds to be named given a few rules
Basic names of hydrocarbons
• Hydrocarbon names are based on: 1) class 2)
# of C, 3) side chain type and 4) position
• 1) name will end in -ane, -ene, or -yne
• 2) the number of carbons is given by a “Prefix”
1 meth- 2 eth- 3 prop- 4 but- 5 pent6 hex- 7 hept- 8 oct- 9 non- 10 dec• Actually, all end in a, but a is dropped when
next to a vowel. E.g. a 6 C alkene is hexene
Q - What names would be given to these:
7C, 9C alkane
2C, 4C alkyne
1C, 3C alkene
Basic names of hydrocarbons
Q - What names would be given to these:
Answers:
7C, 9C alkane
2C, 4C alkyne
1C, 3C alkene
-heptane, nonane
-ethyne, butyne
-does not exist, propene
Mnemonic for first four prefixes
First four prefixes
•
•
•
•
MethEthPropBut-
Monkeys
Eat
Peeled
Bananas
Other prefixes
• Pent• Oct• Dec• Hex-, Hept-, Non-
Numbering carbons in alkenes and
H H
alkynes
H 3C
Draw pentene
C
C
C
C
H
H
H
H
H
Q- How do we know where the double bond is?
A-We number C atoms (number carbons so that
the multiple bond has the lowest number)
H3C
1
H
H
C
C
C
C
H
H
H
H
2
3
4
4-pentene
5
H
H3C
5
H
H
C
C
C
C
H
H
H
H
4
3
2
1-pentene
1
H
Numbering carbons
Name these:
H 3C
H3C
C
H
H
C
CH3
CH3
Numbering carbons
Answers:
H 3C
H3C
C
H
H
C
2-butene
CH3
CH3 3-nonyne
Cyclic structures
• Cyclic structures are circular
• Have “cyclo” in name
H
H
H
H
C
C
H
H
C
C
C
H
H
H
H
• cyclopentane
Q- Draw these:
cyclobutene
cyclopropane
Cyclic structures
Q- Draw these:
cyclobutene
H 2C
CH2
HC
CH
cyclopropane
CH2
H2C
CH2
Naming side chains
CH3
│
CH3CHCHCH2CH3
│
CH3
• Names are made up
of: side chains, root
• 2,3-dimethylpentane
• Root is the longest possible HC chain
• Must contain multiple bonds if present
• Add -yl to get name of side chain H C
CH3
3
• Common side chains include:
CH
CH3- methyl
CH3CH2- ethyl
CH3CH2CH2- propyl
(CH3)2CH-
*
isopropyl
• “iso” (branched) is not an IUPAC convention
• Br- (bromo), Cl- (chloro), F- (fluoro), I- (iodo)
Naming side chains
Example: use the rules on the bottom of
the slide to name the following structure
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
Rule 1: choose the correct ending
ene
Naming side chains
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
Rule 2: Find the longest carbon chain
(note: since this is an alkene, we choose the
longest carbon chain that includes the double
bond)
ene
Naming side chains
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
Rule 3: attach prefix (according to # of C)
1-hexene
ene
Naming side chains
CH2
CH3 CH2 C
CH2 CH3
CH2 C
CH3
CH3
Rule 4: Assign numbers to each carbon
You try numbering the carbons now.
Naming side chains
CH2
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
6
CH3
CH3
Rule 4: Assign numbers to each carbon
(note: chain is number to give double
bond the lowest number)
1-hexene
Naming side chains
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
Rule 5: Determine name for side chains
1-hexene
Naming side chains
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
Rule 6: When more than one of the same
side chains are present, use carbon
numbers and the di, tri, tetra prefixes
before the side chain name:
4,4-dimethyl
Naming side chains
CH2
ethyl
CH2 CH3
1
CH3 CH2 C
2
5
CH2 C
3
4
CH3
6
CH3
methyl
methyl
Rule 6: Attach name of branches in
alphabetical order:
2-ethyl-4,4-dimethyl-1-hexene
Note: we alphabetize the side chain names, do not
alphabetize based on the di, tri, etc. prefixes
Practice: Naming side chains
Name the following compounds:
H3C
H3C
CH2
CH CH3
H2C
CH2
CH2 CH2 CH3
CH CH CH2 CH3
H3C
CH3
CH
CH3
CH3
CH3
CH3
CH3 CH2 CH CH CH CH2 CH CH3
CH2 CH3
Answers:
H3C
H3C
CH2
CH CH3
H2C
CH2
CH CH CH2 CH3
H3C
CH3
3-methylhexane
CH2 CH2 CH3
CH
CH3
4-ethyl-2,3-dimethylheptane
CH3
CH3
CH3
CH3 CH2 CH CH CH CH2 CH CH3
CH2 CH3
5-ethyl-2,4,6-trimethyloctane
Naming side chains
Name the structure below:
CH3
CH
H3 C
CH2
CH
CH3
H2 C
CH3
Naming side chains
Answer:
CH3
CH
H3 C
CH2
CH
CH3
H2 C
CH3
3-ethyl-2-methylpentane
Aromatic Nomenclature H C
3
There are 2 naming methods
H3C
1) Numbering carbons
2) ortho, meta, para (stOMP) 1,2-dimethylbenzene
orthodimethylbenzene
CH3
ST Ortho
Meta
H3C
H3C
Para
Benzene is very stable
(does not generally
undergo addition)
1,3-dimethylbenzene
metadimethylbenzene
H3C
CH3
1,4-dimethylbenzene
paradimethylbenzene