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Cycloalkanes• Members of the cycloalkane group

possess rings of carbon atoms in a ring or circular structure.

• They have the general formula CnH2n.

• The smallest possible ring consists of cyclopropane, C3H6.

Section 14.3

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The First Four Cycloalkanes

Section 14.3

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Is it the Parent or the Branch?• When naming Cycloalkanes, you must

determine if the ring is the “Parent” (main chain) or is it an attachment group.

• If the Cyclo ring has more carbons than any of the other alkyl groups attached, it is the parent.

• If the Cycloring has less carbons, then name it as a side group.(Cyclopropyl, Cyclobutyl…)

Section 14.3

Cyclic Compounds – Parent?• In this example, the ring has four

carbons and the chain has eight.

• The chain is longer than the cyclo group, so the ring is a prefix.

• The ring is a cyclobutyl group on Carbon #1

• 1-cyclobutyloctane.

Parent vs Side Group• In this example, the ring has five carbons

and the alkyl group has three.

• The five-carbon ring is longer than the three carbon chain, so the ring is the parent and is called cyclopentane.

• The is an alkyl group will be on #1 (of course – that #1 isn’t even needed!)

Cyclic Compounds• Word of caution: don’t double dip… its

really easy to double count the carbon (*)

• Alkyl groups consist of only those Carbons BEYOND the ring carbons. Thus, this is a propyl group not a butyl group.

• Propylcyclopentane

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Draw: 1-chloro-2-ethylcyclopentane

Section 14.3

When Multiple Groups are Attached

• When a ring has multiple groups, the rule for numbering is: “Number around the ring so as to arrive at the lowest possible sum of the position numbers”.

• The sum in this molecule is 1 + 3 = 4.

Cyclic Compounds – Multiple Groups

• How about this one?

• 1,2,4-trimethylhexane

Cyclic Compounds – Multiple Groups

• If you have two possibilities for lowest possible sum, THEN (and only then) you should alphabetize to prioritize your groups.

• What about this one?

1-etyl-3-methylcyclopentane

Practice Problem

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1) Draw the line structure for: 1-ethyl-3-iodocyclopentane

2) Draw the line structure for: 2-ethyl-1,1,3-trimethyl-cyclobutane

Name these molecule

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3) Draw the line structure for: 4-cyclobutyl-3,5-difluoro-3-methyloctane