Name the following cycloalkanes.
1) taking the cycle as the main chain.
2) taking the chain as the main one.

problem3-01.gif

 

SOLUTION:

1) Taking the cycle as main chain

problem3-02.gif
1. Main chain: six-membered cycle (cyclohexane).
2. Numbering: The main chain ( red ) is numbered starting with the carbon that has the substituent, the direction in which the numbering continues is indifferent.
The substituent ( blue ) is numbered by giving the locant 1 to the carbon attached directly to the main chain (cycle).
3 Substituents: complex substituent, with a 5-carbon chain and a methyl in position 3 . ( 3 -methylpentyl).
4. Construction of the name: The substituent is named (no locator is necessary and it ends with the word cyclohexane.



1. Main chain: four-membered cycle (cyclobutane)
2. Numbering: the same as in section a)
3. Substituents: Complex substituent in position 1 of the main chain. The longest chain of the substituent is 3 carbons (propyl) with methyl in position 1 . Thus, 1 -methylpropyl .
4. Construction of the name: substituent without localizer, ending the name in cyclobutane.



1. Main chain: five-membered cycle (cyclopentane)
2. Numbering: the same as in section a)
3. Substituents: complex substituent in position 1 of the cycle. The longest chain of the substituent is 2 carbons ( ethyl ) with methyl in position 1 . Therefore, 1 -methylethyl .
4. Construction of the name: 1 -methylethyl cyclopentane.


{info}When a cycloalkyl is attached to a chain and the cycle is taken as the main chain, the numbering of the cycle begins at the carbon that has the chain and the numbering of the chain begins at the carbon that joins the cycle.{/ info}

b) Taking the string as principal.

problem3-03.gifMain chain: chain of 5 carbons (pentane)
Numbering: it is numbered so that the substituents take the lowest locants ( 1,3 ).
Substituents: cyclohexyl in position 1 and methyl in 3 .
Construction of the name: substituents in alphabetical order, preceded by their locants, ending with the name of the main chain .





Main chain: 4-carbon chain (butane)
Numbering: number so that the substituent takes the lowest locant ( 2 ).
Substituents: 2 -position cyclobutyl .
Name construction: substituent preceded by its locant ( 2 - cyclobutyl ) followed by the name of the main chain (butane)




Main chain: 3-carbon chain (propane)
Numbering: number so that the substituent takes the lowest locant ( 2).
Substituents: 2 -position cyclopentyl .
Name construction: substituent preceded by its locant ( 2 -c cyclopentyl ) followed by the main chain name (propane)


{notice}Both forms of nomenclature are correct. Both the cycle and the chain can be taken as the main group. However, it should be noted that as the string becomes more complex, it is easier to construct the name by choosing the string as the main one. {/warning}