1 2.6 cycloalkanes cycloalkanes are alkanes that have carbon atoms that form a ring (called...
TRANSCRIPT
![Page 1: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/1.jpg)
1
2.6 Cycloalkanes
• Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds)
• Simple cycloalkanes are rings of CH2 units, (CH2)n, or CnH2n
• Structure is shown as a regular polygon with the number of vertices equal to the number of C’s (a projection of the actual structure)
![Page 2: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/2.jpg)
Nomenclature of Cycloalkanes
IUPAC naming rules are followed with the addition of the prefix cyclo-
With multiple substituents, use lowest numbering sequence
cyclopropane cyclobutane cyclohexane
1-ethyl-3-methylcyclohexane
not 1-ethyl-5-methylcyclohexane
![Page 3: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/3.jpg)
3
2.6 Cycloalkanes
![Page 4: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/4.jpg)
4
Complex Cycloalkanes
• Naturally occurring materials contain cycloalkane structures
• Examples:
– chrysanthemic acid (cyclopropane),
– prostaglandins (cyclopentane),
– steroids (cyclohexanes and cyclopentane)
![Page 5: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/5.jpg)
5
Complex Cycloalkanes
![Page 6: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/6.jpg)
6
Properties of Cycloalkanes
Melting points are affected by the shapes and the way that crystals pack so they do not change uniformly
![Page 7: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/7.jpg)
7
2.7 Naming Cycloalkanes• Count the number of carbon atoms in the ring and the number
in the largest substituent chain. If the number of carbon atoms in the ring is equal to or greater than the number in the substituent, the compound is named as an alkyl-substituted cycloalkane.
• For an alkyl- or halo-substituted cycloalkane, start at a point of attachment as C1 and number the substituents on the ring so that the second substituent has as low a number as possible. When two substituents are present, we number the ring beginning with the substituent first in the alphabet.
• Wenn three or more substituents are present, we begin at the substituent that leads to the lowest set of locants
• Number the substituents and write the name
![Page 8: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/8.jpg)
8
1. Find the parent:
or butylcyclopropane
![Page 9: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/9.jpg)
9
Number the substituents & write the name:
![Page 10: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/10.jpg)
10
Examples:
![Page 11: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/11.jpg)
11
Problem 2.15: IUPAC names?
![Page 12: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/12.jpg)
1
2
3
4 5
1-ethyl-2,3-dimethylcyclopentane
![Page 13: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/13.jpg)
3-ethyl-4-methyl-1-cyclopropylcyclohexane
![Page 14: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/14.jpg)
5-ethyl-3-cyclohexyl-4-methyloctane
![Page 15: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/15.jpg)
15
2.8 Cis-Trans Isomerism in Cycloalkanes
• Rotation about C-C bonds in cycloalkanes is limited by the ring structure
• Rings have two “faces” and substituents are labeled as to their relative facial positions
• There are two different 1,2-dimethyl-cyclopropane isomers, one with the two methyls on the same side
(cis) of the ring and one with the methyls on opposite sides (trans)
![Page 16: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/16.jpg)
Isomerization with Cycloalkanes
Isomers - molecules that are the same but yet different
C4H10Constitutional (structural) isomers - same formula but different connectivity
CH3CH3
CH3
CH3
Stereoisomers- same formula and connectivity but different spatial arrangement
cis -isomersame side
trans - isomeropposite sides
![Page 17: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/17.jpg)
Cis/Trans Isomers
CH3
CH3
CH3
CH3
Cis-1,2-dimethylcyclohexane Trans-1,2-dimethylcyclohexane
![Page 18: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/18.jpg)
Cis/Trans Isomers
Also written as:
Cis-1,2-dimethylcyclohexane Trans-1,2-dimethylcyclohexane
CH3
CH3
CH3
CH3
![Page 19: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/19.jpg)
19
2.8 Cis-Trans Isomerism in Cycloalkanes
![Page 20: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/20.jpg)
20
Stereoisomers
• Compounds with atoms connected in the same order but which differ in three-dimensional orientation, are stereoisomers
• The terms “cis” and “trans” should be used to specify stereoisomeric ring structures
• Recall that constitutional isomers have atoms connected in different order
![Page 21: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/21.jpg)
21
Stereoisomers
![Page 22: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/22.jpg)
22
Practice Prob. 2.4: Name?
![Page 23: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/23.jpg)
23
Problem 2.18: IUPAC Name?
![Page 24: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/24.jpg)
Cis and trans isomerization of cycloalkanes is only for
disubstitued rings.Multi-substituted requires additional nomenclature
Examples of disubstituted:
cis-1-ethyl-3-methylcyclohexane trans-1,2-dimethylcyclopentane
![Page 25: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/25.jpg)
Structure of Cycloalkanes
Ring strain accounts for the unstability in certain cycloalkanes
Remember - sp3 has 109.5° bond angle
60°90° 105°
Ring Strain is combination of eclipsing strain and bond-angle strain
![Page 26: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/26.jpg)
QuickTime™ and a Animation decompressor are needed to see this picture.
Each cycloalkane adopts a conformation that tries to
alleviate ring strain as much as possible
cylcopropane
“banana” bonds that do not have end-to-end overlap of typical σ-bonds
Highly unstable ring-system that will “open” or react readily
![Page 27: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/27.jpg)
Cyclobutane
Instead of flat conformation, a “puckered” conformation reduces eclipsing strain
QuickTime™ and a Animation decompressor are needed to see this picture.
![Page 28: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/28.jpg)
Cyclopentane
An “envelope” conformation reduces eclipsing strain
![Page 29: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/29.jpg)
Ring Conformation
• Cyclopentane puckers
![Page 30: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/30.jpg)
Cyclohexane
The “chair” conformation eliminates all eclipsing strain and nearly all bond-angle strain
![Page 31: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/31.jpg)
Ring Strain vs. Cycloalkane Size
Cycloalkane Ring Size
kcal/mol
Cyclohexane the most stable
![Page 32: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/32.jpg)
Axial and Equatorial positions are not energetically equivalent
H3C
H
H
H
HCH
H
H
equatorial
axial
1,3-diaxial interaction (steric hinderance)
More Stable
The larger the group, the greater the 1,3-diaxial interaction
Cyclohexane prefers larger groups at equatorial positions
![Page 33: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/33.jpg)
A ball-and-stick model of cyclopropane shows the ring strain when the bond angles are deformed from their normal 109.5° to 60°.
Ball-and-stick Model of Cyclopropane
Cyclopropane
![Page 34: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/34.jpg)
Cyclobutane A ball-and-stick model of cyclobutane shows the ring strain when the bond angles are deformed from their normal 109.5° to approximately 90°.
![Page 35: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/35.jpg)
Cyclopentane
The ball-and-stick model of cyclopentane reveals a nearly planar molecule with bond angles of 108°.
![Page 36: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/36.jpg)
Cyclohexane: Chair and Boat Conformations
The chair conformation of cyclohexane can be twisted into the boat conformation.
![Page 37: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/37.jpg)
Cyclohexane: Chair and Boat Conformations
The chair conformation of cyclohexane can be twisted into the boat conformation. Further twisting results in a second chair conformation. By labeling one axial substituent with a white sphere you can see how the axial position of one chair becomes equatorial by twisting into the second chair conformation.
![Page 38: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/38.jpg)
38
Chapter 11 Organic Compounds: Alkanes
11.9
The Shape of Cycloalkanes
![Page 39: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/39.jpg)
39
Bond Angles
Ideal bond angle is 109º
• Cyclopropane - 60º
• Cyclobutane - 90º
• Strained bonds, unstable
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cumming
![Page 40: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/40.jpg)
40
Free Rotation
Free rotation is not possible in cycloalkanes.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
![Page 41: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/41.jpg)
41
Chair and Boat
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
![Page 42: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/42.jpg)
42
Geometric Isomers
Geometric isomers have restricted rotation around C-C
bonds and differ in 3-dimensional arrangement of atoms.
Named “cis-” and “trans– “
![Page 43: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/43.jpg)
43
Learning Check
Identify each of the following as cis- or trans-
![Page 44: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/44.jpg)
44
Learning Check
Draw and name all the isomers of dichlorolcyclobutane.
(There are 5.)
![Page 45: 1 2.6 Cycloalkanes Cycloalkanes are alkanes that have carbon atoms that form a ring (called alicyclic compounds) Simple cycloalkanes are rings of CH](https://reader035.vdocuments.mx/reader035/viewer/2022062518/56649e765503460f94b77339/html5/thumbnails/45.jpg)
45
Stereoisomers
Stereoisomers are compounds with the same structural
formula but different spatial arrangements of atoms
• Cannot superimpose.