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Remember this????
Hydrocarbons
Aliphatic
Alkanes
Aromatic
Cycloalkanes Alkenes Alkynes
UnsaturatedSaturated
3
Part 06 Cycloalkanes
• Cycloalkanes– Saturated hydrocarbons– Have one or more rings– Also called alicyclic compounds
4
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.
6
Part 06 Cycloalkanes
• Begin at three carbons– Smallest possible stable ring– Molecular formula:
– Structural formula:
– Name:
C3H6
CH2
CH2CH2
cyclopropane
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• Cycloalkane with 4 carbon atoms– Molecular formula:
– Name:
– Structural formula:
– Skeleton structure:
10
• Cycloalkane with 5 carbon atoms– Molecular formula:
– Name:
– Structural formula:
– Skeleton structure:
11
• Cycloalkane with 6 carbon atoms– Molecular formula:
– Name:
– Structural formula:
– Skeleton structure:
12
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.
16
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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Practice: Draw the cis and trans isomers of 1-ethyl-3-bromocyclopentane.
C2H5
Br
cis
C2H5
Br
trans