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Intro to Organic ChemistryPart 06: The Cycloalkanes

Chapter 10

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Remember this????

Hydrocarbons

Aliphatic

Alkanes

Aromatic

Cycloalkanes Alkenes Alkynes

UnsaturatedSaturated

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Part 06 Cycloalkanes

• Cycloalkanes– Saturated hydrocarbons– Have one or more rings– Also called alicyclic compounds

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Part 06 Cycloalkanes

• Structure of cycloalkanes– Rings form regular polygon structures

• Triangle, square, pentagon, etc.

– Each corner of polygon represents a carbon atom

– General formula: CnH2n

• Not CnH2n+2 because, when a ring forms, the alkane loses 2 H at its end.

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• Properties of cycloalkanes– Similar to alkanes

• Nonpolar• Relatively inert

– Different from alkanes• Alkanes have free rotation around C-C single

bonds– Lower member cycloalkanes (C3 to C7) do not & are

more rigid, planar structures– Attempts at bond rotation would cause the ring to break– Higher cycloalkanes less rigid

» Very large rings (C25 and up) behave like straight-chain alkanes.

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Part 06 Cycloalkanes

• Begin at three carbons– Smallest possible stable ring– Molecular formula:

– Structural formula:

– Name:

C3H6

CH2

CH2CH2

cyclopropane

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CHH

C CH

H

H

H

Cyclopropane

Complete structural formula

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Cyclopropane

Skeleton structure

Each corner represents a carbon atom (2 H attached to each one)

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• Cycloalkane with 4 carbon atoms– Molecular formula:

– Name:

– Structural formula:

– Skeleton structure:

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• Cycloalkane with 5 carbon atoms– Molecular formula:

– Name:

– Structural formula:

– Skeleton structure:

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• Cycloalkane with 6 carbon atoms– Molecular formula:

– Name:

– Structural formula:

– Skeleton structure:

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Cycloalkane Nomenclature

• Attach prefix cyclo- to the name of the corresponding open chain hydrocarbon having the same number of carbons as the ring

• If substituent(s) present, number the ring in such a way as to give the substituent groups the lowest possible numbers

• Cycloalkanes can also be substituent groups– Named like the alkyl groups, but with the cyclo- prefix– One less hydrogen than cycloalkane

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Name the following

Br

F

Cl

H – C – C – C – C – C – C – H

H H H NO2 H H

H H H H H

If there is only one substituentattached to the cycloalkane, it is not numbered.

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Draw the skeleton structure for the following:

1) iodocyclopropane

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Draw the skeleton structure for the following:

2) propylcyclopentane

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Draw the structural formula for the following:

3) 1 – amino – 2,3 – dicyclopropyl – 4 - methylheptane

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Cycloalkane isomers

• Cycloalkanes are “essentially” planar

• Location of substituents– Both on same side of ring: cis isomer

• cis (Latin): “on this side”

– One above & one below: trans isomer• trans (Latin): “across”

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Example: Draw the cis and transisomers of 1,2-

dichlorocyclopropane.

Cl Cl

Cl

Clcis trans

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Practice: Draw the cis and transisomers of 1,2-

diaminocyclobutane.

NH2 NH2

cis

NH2

NH2

trans

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Practice: Draw the cis and trans isomers of 1-ethyl-3-bromocyclopentane.

C2H5

Br

cis

C2H5

Br

trans

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Name the following:

C4H9

C4H9

cis-1,4-dibutylcyclohexane

C4H9

C4H9

trans-1,4-dibutylcyclohexane

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Name the following:

trans-1-hexyl-4-isopropylcyclohexane

C6H13

CH

CH3CH3

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Homework: Due Tomorrow 10/06/10

Page 21-22 (binder): 1-12

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Homework: Due Tuesday10/12/10

Page 356-357 (book)# 33, 34, 35, 37, 39c, 40c

(50 points)

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Quiz: Wednesday 10/13/10

Isomers & Cycloalkanes

50 points