Transcript Branched-Chain Alkanes

ORGANIC CHEMISTRY
Any molecule that
contains the element
CARBON
“Natural”
Products:
Poison Ivy
Snake Venom
Tobacco
Poison Hemlock
"Organic" does not mean "natural."
Manmade Organic Substances
Organic
Chemistry
Hydrocarbons
ONLY
Carbon
and Hydrogen
Alkene
Alkyne
other
Substituded
Hydrocarbons
Alkane
Ring :Aromatic
(Benzene)
HYDROCARBONS:
“alk”-
Only contain Hydrogen and Carbon
Type of bond Between CARBONS
determines the family
Alkane = all single bond
Alkene = double bond
Alkyne = triple bond
Hydrocarbons
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Alkanes: general formula CnH2n+2
•CH4 = methane
•C2H6 = ethane
•C3H8 = propane
•C4H10 = butane
•C5H12 = pentane
HYDROCARBONS: Naming
ALKANES: name and formula
Structural Formulas
Alkanes are written with structural formulas that are
• expanded to show each bond
• condensed to show each carbon atom and the
attached hydrogen atoms
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Draw the condensed
structural formula for heptane.
Heptane, an alkane, has seven carbon atoms in its
carbon chain.
CH3─CH2─CH2─CH2─CH2─CH2─CH3
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Name each of the following:
A. CH3─CH2─CH2─CH3
four carbon atoms; butane
B. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3
eight carbon atoms; octane
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22.1 Hydrocarbons > Alkanes
Straight-Chain Alkanes
• For the straight-chain
alkanes with one to four
carbon atoms, the official
names and the common
names are the same.
• For the chains longer than
4, the prefixes are pent- for
5, hex- for 6, hept- for 7,
oct- for 8, non- for 9, and
dec- for 10.
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Straight-Chain Alkanes
Name
Formula
Methane
CH4
Ethane
C2H6
Propane
C4H8
Butane
C4H10
Pentane
C5H12
Hexane
C6H14
Heptane
C7H16
Octane
C8H18
Nonane
C9H20
Decane
C10H22
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Isomers of Butane
straight chain
Isomers
• have the same
molecular
formula
• have different
atomic
structure
branched
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
• The longest continuous carbon chain of a
branched-chain hydrocarbon is called the parent
alkane.
• All other carbon atoms or groups of carbon atoms
are regarded as substituents.
• Atoms such as halogens, oxygen, and nitrogen can also
be substituents.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
• A hydrocarbon substituent that is derived
from an alkane is called an alkyl group.
• You can think of any alkyl group as just
an alkane with one of the hydrogens
removed.
• Alkyl groups are named by removing the
-ane ending from the parent hydrocarbon
name and adding -yl.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
• The three smallest alkyl groups are
• the methyl group (–CH3)
• the ethyl group (–CH2CH3)
• the propyl group (–CH2CH2CH3)
• When a substituent alkyl group is attached to
a straight-chain hydrocarbon, branches are
formed.
• An alkane with one or more alkyl groups is
called a branched-chain alkane.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
Examples of primary, secondary, tertiary,
and quaternary carbons are labeled in the
structural formulas below.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
The compound with the following structural
formula can be used as an example.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
1. Find the longest continuous chain of carbons in
the molecule. This chain is considered the
parent hydrocarbon.
• The longest chain is highlighted in the
example. It contains seven carbon atoms.
So, the parent hydrocarbon is heptane.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
2. Number the carbons in the main chain in
sequence. To do this, start at the end that will
give the substituent groups attached to the chain
the smallest numbers.
• Numbering the chain from right to left gives
the substituents the lowest numbers (2, 3,
and 4).
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
3. Add numbers to the names of the substituent
groups to identify their positions on the chain.
These numbers become prefixes to the name of
the substituent group.
• The substituents and positions are 2-methyl,
3-methyl, and 4-ethyl.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
4. Use prefixes to indicate the appearance of the
same group more than once in the structural
formula. Common prefixes are di- (twice), tri(three times), and tetra- (four times).
• The two methyl groups are combined as 2,3dimethyl in the name.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
5. List the names of alkyl substituents in
alphabetical order. For purposes of
alphabetizing, ignore the prefixes di-, tri-, and so
on.
• The 4-ethyl group is listed first, followed by
the 2,3-dimethyl.
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22.1 Hydrocarbons > Alkanes
Branched-Chain Alkanes
6. Combine all the parts and use proper
punctuation. Write the entire name without any
spaces. Use commas to separate numbers, and
use hyphens to separate numbers and words.
• The correct name of the compound is 4ethyl-2,3-dimethylheptane.
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Naming Alkanes
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Give the IUPAC name of the
Alkane
CH3 CH3


CH3─CH─CH─CH2─CH2─CH3
1
2
3
4
5
6
STEP 1 Write the alkane name of the longest
continuous chain of carbon atoms.
hexane
STEP 2 Number the carbon atoms starting from the
end nearer a substituent.
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Example of Naming an Alkane
(continued)
STEP 3 Give the location and name of each
substituent as a prefix to the alkane name.
CH3 CH3
methyl groups on carbons 2 and 3


CH3─CH─CH─CH2─CH2─CH3
1
2
3
4
5
6
2,3-dimethylhexane
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Give the IUPAC name of
CH3

CH3─CH2─CH─CH─CH3
5
4
3
2
1
STEP 1 Write the alkane name of the longest
continuous chain of carbon atoms.
pentane
STEP 2 Number the carbon atoms starting from the end
nearer a substituent.
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Solution (continued)
STEP 3 Give the location and name of each
substituent as a prefix to the alkane name.
methyl on
carbon 3
CH3

CH3─CH2─CH─CH─CH3
5
4
3
2
1
3-methylpentane
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Give the IUPAC name for the
methyl on
CH
following
carbon 3
3
|
CH3─CH2─CH─CH2─C─CH2─CH3
7
6
5
4
3
2
1
STEP 1 Write the alkane name of the longest continuous
chain of carbon atoms.
heptane
STEP 2 Number the carbon atoms starting from the end
nearer a substituent.
STEP 3 Give the location and name of each substituent as a
prefix to the alkane name.
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3-methylheptane
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Drawing Alkane Formulas
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Draw the condensed structural formula for
2-methylbutane
STEP 1 Draw the main chain of carbon atoms. For butane, there are four
carbon atoms in the chain.
C─C─C─C
STEP 2 Number the chain and place the substituents on the carbons indicated
by the numbers.
CH3

C─C─C─C
1
2
3
4
STEP 3 Add the correct number of hydrogen atoms to give four bonds
to each C atom.
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CH3

CH3─CH─CH2─CH3
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Cyclic Hydrocarbons
 Just
as straight-chain and branchedchain alkanes can be either saturated
or unsaturated, so can cyclic
hydrocarbons.
A
cyclic hydrocarbon that contains
only single bonds, and is therefore
saturated is called a cycloalkane.
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A compound that contains a hydrocarbon ring is
called a cyclic hydrocarbon.
• Many
molecules
found in nature
contain cyclic
hydrocarbons.
• Rings with five
and six carbons
are the most
abundant.
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Cyclic Hydrocarbons

To determine the IUPAC
name of a cycloalkane, first
count the number of carbons
in the ring and assign the
corresponding alkane name.

Then simply add the prefix
cyclo- to the alkane name.
Name: cyclopropane
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Alkenes: Compounds with
C=C Double Bonds
37
Alkenes: general formula CnH2n
3 4
CH2CH3 H
H
1
C
1
C
2
C
H
H
1-butene
3
CH3
H
1
H3C
2
C
4
CH3
2
C
CH3
2-methylpropene
(isobutene)
H
4
CH3
H
3
C
2
C
H
cis-2-butene
1
H3 C
3
C
H
trans-2-butene
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Alkynes
• Alkynes have
carbon-carbon
triple bonds.
C2H2:
name = ethyne
FAMILIES OF HYDROCARBONS:
ALKANE, ALKENE, ALKYNE
FAMILIES OF HYDROCARBONS:
ALKANE, ALKENE, ALKYNE
Unsaturated Compounds:
Alkenes and Alkynes
• have fewer hydrogen
atoms attached to the
carbon chain than
alkanes
• are alkenes with C=C
double bonds
• are alkynes with
triple C≡C bonds
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Saturated vs Unsaturated
Saturated: all SINGLE BONDS
Alkanes
Unsaturated: double and/or triple
bond(s) present.
Alkenes
Alkynes
Naming Alkenes and Alkynes
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22.2 Unsaturated Hydrocarbons > Alkenes
• The chain is
numbered so that
the carbon atoms of
the double bond
have the lowest
possible numbers.
• Substituents on the
chain are named
and numbered in the
same way they are
for alkanes.
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Naming Alkenes and Alkynes
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Write the IUPAC name for
the following
CH
3
|
CH3─CH=C─CH3
4
3
2
1
STEP 1 Name the longest carbon chain that contains a
double or triple bond.
butene
STEP 2 Number the carbon chain starting from the end
nearer the double or triple bond.
STEP 3 Give the location and name of each substituent as a
prefix
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2-methyl-2-butene
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Write the IUPAC name for the
following
CH3─CH─CC─CH3
5
4
3
2
1
STEP 1 Name the longest carbon chain that contains a
double or triple bond.
pentyne
STEP 2 Number the carbon chain starting from the end
nearer the double or triple bond.
STEP 3 Give the location and name of each substituent as a
prefix
2-pentyne
47
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Draw the condensed
structural formula for
2-methyl-3-hexyne.
STEP 1 Draw the main chain of carbon atoms. For
3-hexyne, there are six carbon atoms in the chain, with a
triple bond between carbons 3 and 4,
C─C─C≡C─C─C
STEP 2 Number the chain and place the substituents on
the carbons indicated by the numbers.
CH3

C─C─C≡C─C─C
1
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2
3
4
5
6
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Solution (continued)
STEP 3 Add the correct number of hydrogen
atoms to give four bonds to each C atom.
CH3

CH3─CH─C≡C─CH2─CH3
1
2
3
4
5
6
2-methyl-3-hexyne
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Special
HYDROCARBONS
bond Between CARBONS = family
Alkane = all single bond
Alkene = double bond
Alkyne = triple bond
AROMATIC
Hydrocarbons: contain
benzene molecule
22.4 Hydrocarbon Rings> Aromatic Hydrocarbons
Any compound not classified as an
aromatic compound is an aliphatic
compound.
Alkanes, alkenes, alkynes, and
cycloalkanes are aliphatic
compounds.
The properties of aromatic
compounds are quite different from
those of aliphatic compounds.
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22.4 Hydrocarbon Rings>
Aromatic Hydrocarbons
• An aromatic
compound, or arene, is
now defined as an
organic compound that
contains a benzene ring
or other ring in which the
bonding is like that of
benzene.
52
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Aromatic Hydrocarbons
Benzene is
the
simplest
aromatic
compound
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22.4
Hydrocarbon
The
StructureRings>
of Benzene
•
•
The benzene molecule is a six-membered carbon
ring with one hydrogen atom attached to each
carbon.
This arrangement leaves one electron from each
carbon free to participate in a double bond.
– Two different structures with alternating double
bonds can be written for benzene.
54
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Benzene
•
is also represented as a hexagon with a circle
drawn inside
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The
of Benzene
22.4Structure
Hydrocarbon
Rings>
Drawing a solid or
dashed circle inside
a hexagon
represents how the
electrons are
distributed.
• However, the traditional structure, shown
to the right in the series above, is used in
this textbook.
• Remember, though, that each bond in the
ring is identical.
56
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Organic
Chemistry
Hydrocarbons
ONLY
Carbon
and Hydrogen
Alkene
Alkyne
other
Substituded
Hydrocarbons
Alkane
Ring :Aromatic
(Benzene)
Lab: building organic compounds