cycloalkanes and bicyclic alkanes
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Cycloalkanes and Bicyclic Alkanes
Cycloalkanes• alkanes in which the two ends of
the carbon chain are connected to one another.• are named like acyclic alkanes,
with the prefix cyclo- indicating the presence of a ring.• formula of a cycloalkane is CnH2n
Cycloalkanes• resemble the acyclic, open-chain
alkanes in their physical properties and in their chemistry.• nonpolar, relatively inert
compounds with boiling points and melting points that depend on their molecular weights
Cycloalkane Nomenclature
The name of the compound is based on the name of the parent alkane, with “cyclo” added to the front to show that the main chain
forms a ring.
Cycloalkane Nomenclature
Cyclobutane (C4H8)
Cyclohexane (C6H12)
Cycloalkane Nomenclature
Substituted cycloalkanes use the cycloalkane for the base name, with the alkyl groups named as substituents. If there is just one
substituent, no numbering is needed.
Cycloalkane Nomenclature
propylcyclohexane
tert-butylcycloheptane
Cycloalkane Nomenclature
• If there are two groups on the ring, rank them in alphabetical order.
• The carbon bearing the group first in the alphabet will be given the number “1,” and the rest of the carbons in the ring will be numbered in a way that results in the lowest possible number for the other substituent.
Cycloalkane Nomenclature
1,1,3-trimethylcyclopentane
Cycloalkane Nomenclature
When the numbering could begin with either of two substituted ring
carbons (as in a disubstituted cycloalkane), begin with the one that has more substituents, or
else the one that is alphabetically first.
Cycloalkane Nomenclature
1,1-diethyl-4-isopropylcyclohexane
Cycloalkane Nomenclature
When the acyclic portion of the molecule contains more carbon
atoms than the cyclic portion, the cyclic portion is sometimes
named as a cycloalkyl substituent.
Cycloalkane Nomenclature
4-cyclopropyl-3-methyloctane
Cycloalkane Nomenclature
cyclopentylcyclohexane
Identify!
(1,2-dimethylpropyl)cyclohexane
Identify!
3-cyclopropyl-1,1-dimethylcyclohexane
Bicyclic Alkanes• Two or more cycloalkanes joined
together• Can either be fused rings, bridged
rings, or spirocyclic compounds• found in many natural product
structures
Technically bicyclic, but needs no special nomenclature rules because the rings do
not share any carbon atom.
cyclopentylcyclohexane
Bicyclic Alkane Nomenclature• Fused rings are most common, sharing two
adjacent carbon atoms and the bond between them.
• Bridged rings are also common, sharing two nonadjacent carbon atoms (the bridgehead carbons) and one or more carbon atoms (the bridge) between them.
• Spirocyclic compounds, in which the two rings share only one carbon atom. (Rare)
Fused Bicyclic
Shared Carbon Atoms = Bridgehead Carbons
Bridged Bicyclic
Shared Carbon Atoms = Bridgehead CarbonsCarbon atom in between = Bridge Carbon
Spirocyclic Alkanes
Shared Carbon Atom = Spiro Carbon
Summary
Bicyclic Alkane Nomenclature• When the two rings of the bicyclic compound
have two carbons common there are three different paths between the two common carbons following C-C bonds.
Bicyclic Alkane Nomenclature• When the two rings of the bicyclic compound
have two carbons common there are three different paths between the two common carbons following C-C bonds.
Rules for numbering the rings in bicyclic alkanes
1. Start with one of the bridgehead carbons and number it 1.
Rules for numbering the rings in bicyclic alkanes
2. Proceed round the longest chain of carbons to the second bridgehead.
Rules for numbering the rings in bicyclic alkanes
3. Number the second bridgehead carbon and continue on round the next longest chain of carbons back towards the first bridgehead carbon.
Rules for numbering the rings in bicyclic alkanes
4. Pass over the first bridgehead carbon (it already has the number 1) and along the shortest chain of carbons to the second bridgehead carbon again.
Bicyclic Alkane Nomenclature• The generic name for bicyclic (fused and
bridges) alkanes is:
bicyclo[x.y.z]alkane• where x, y, and z are the numbers of intervening
carbons on the three paths between the two bridgehead carbons cited in decreasing numerical order
• alk refers to the total number of carbons in the ring systems
Bicyclic Alkane Nomenclature
Bicyclo[4.2.0]octane
Bicyclic Alkane Nomenclature
Bicyclo[5.3.0]decane
Bicyclic Alkane Nomenclature
Bicyclo[2.2.1]heptane
Bicyclic Alkane Nomenclature
Bicyclo[2.2.2]octane
Bicyclic Alkane Nomenclature
7,7-dimethylbicyclo[2.2.1]heptane
7
12
3 4
5
6
Spirocyclic Alkane Nomenclature
spiro[x.y]alkane• where x and y are the numbers of intervening
carbons on the two paths between the spiro carbon.• Shortest path named first!• Numbering begins at carbon in the shortest path
nearest to the spiro carbon.• alk refers to the total number of carbons in the ring
systems
Spirocyclic Alkane Nomenclature
spiro[3.4]octane
Spirocyclic Alkane Nomenclature
Spiro[4.5]decane
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