cycloalkanes and bicyclic alkanes

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.


Cyclobutane (C4H8)

Cyclohexane (C6H12)


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.


propylcyclohexane

tert-butylcycloheptane


• 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.


1,1,3-trimethylcyclopentane


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.


1,1-diethyl-4-isopropylcyclohexane


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.


4-cyclopropyl-3-methyloctane


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.

Rules for numbering the rings in bicyclic alkanes

1. Start with one of the bridgehead carbons and number it 1.


2. Proceed round the longest chain of carbons to the second bridgehead.


3. Number the second bridgehead carbon and continue on round the next longest chain of carbons back towards the first bridgehead carbon.


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


Bicyclo[5.3.0]decane


Bicyclo[2.2.1]heptane


Bicyclo[2.2.2]octane


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


spiro[3.4]octane


Spiro[4.5]decane

cycloalkanes and bicyclic alkanes

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