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Copyright © Houghton Mifflin Company. All rights reserved. 14 | 1
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
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