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Conformational Analysis
Conformations of Alkanes
CH3
C
F
CH3
H
C
F
Cl
Cl
=
Cl
C
F
CH3
C
H
Cl
F
=
F
C
F
C
Cl
Cl
H
• Relatively low energy barrier to rotation
about C-C bonds (4 – 40 kJ/mole)
• Different shapes resulting from single
bond rotations are called conformations
Conformations of Alkanes
CH3
H
C
F
C
F
Cl
Cl
=
F
F
Eclipsed
H
C
F
Hash-Wedge
C
F
Cl
CH3
H
Cl
Cl
Cl
CH3
CH3
Cl
H
Cl
F
F
Staggered
Newman
Projection
Conformations of Alkanes
CH3
H
Cl
Cl
CH3
F
F
Cl
H
Cl
F
F
F
Cl
CH3
F
CH3
H
F
Cl
F
Cl
CH3
Cl
H
F
CH3
F
H
Cl
Cl
F
Cl
Cl
F
H
Energy and Conformations
Contributions to energies of conformations
• Steric Strain: an increase in energy due to
electrons on atoms occupying the same
region of space
• Torsional Strain: an increase in energy
due to electrons in bonds overlapping in an
eclipsed conformation
• Angle Strain: an increase in energy due to
distortion of a bond angle from its optimum
value
Eclipsed Ethane
http://lightning.chem.wwu.edu/dept/vmolckit/molecule.html
http://lightning.chem.wwu.edu/dept/vmolckit/ethanecl.pdb
ECLIPSED CONFORMER OF ETHANE
H
H
C
C
H
H
H
H
H
H
H
H
H
H
ECLIPSED CONFORMER OF ETHANE
SPACE-FILLING REPRESENTATION
Staggered Ethane
http://lightning.chem.wwu.edu/dept/vmolckit/ethanstg.pdb
STAGGERED CONFORMER OF ETHANE
H
H
C
H
C
H
H
H
H
H
H
H
H
H
STAGGERED CONFORMER OF ETHANE
SPACE-FILLING REPRESENTATION
ENERGY DIAGRAM FOR ETHANE
CONFORMATIONS
Eclipsed

Butane—0
dihedral
http://lightning.chem.wwu.edu/dept/vmolckit/butecl0.pdb
ECLIPSED CONFORMER OF BUTANE
CH3
CH3
C
C
H
H
H
CH3
CH3
H
H
H
H
H
ECLIPSED CONFORMER OF BUTANE
SPACE-FILLING MODEL
Staggered Butane—Gauche
http://lightning.chem.wwu.edu/dept/vmolckit/butgauch.pdb
STAGGERED CONFORMER OF BUTANE—GAUCHE
H
CH3
C
CH3
C
H
H
CH3
CH3
H
H
H
H
H
STAGGERED CONFORMER OF BUTANE—GAUCHE
SPACE-FILLING MODEL
Eclipsed

Butane—120
dihedral
http://lightning.chem.wwu.edu/dept/vmolckit/butec120.pdb
ECLIPSED CONFORMER OF BUTANE
CH3
H
C
H
H
H
CH3
H
CH3
H
H
H
C
CH3
ECLIPSED CONFORMER OF BUTANE
SPACE-FILLING MODEL
Staggered Butane—Anti
http://lightning.chem.wwu.edu/dept/vmolckit/butanti.pdb
STAGGERED CONFORMER OF BUTANE—ANTI
CH3
H
C
H
C
H
H
CH3
H
H
H
H
CH3
CH3
STAGGERED CONFORMER OF BUTANE—ANTI
SPACE-FILLING MODEL
TUBE BOND REPRESENTATION OF THE ANTI
CONFORMATION OF BUTANE
ENERGY DIAGRAM FOR BUTANE
CONFORMATIONS
Conformations of Cyclohexane
http://lightning.chem.wwu.edu/dept/vmolckit/cheqcode.pdb
SIDE VIEW OF CYCLOHEXANE
AXIAL
EQUATORIAL
EQUATORIAL
AXIAL
TOP VIEW OF CYCLOHEXANE
AXIAL
EQUATORIAL
Conformations of Cyclohexane
http://lightning.chem.wwu.edu/dept/vmolckit/cheqcode.pdb
CHAIR CONFORMER REPRESENTATION
up (ax)
up (ax)
up (eq)
up (ax)
d (eq)
up (eq)
up (eq)
d (ax)
d (ax)
d (eq)
d (eq)
d (ax)
CHAIR CONFORMER REPRESENTATION
up (ax)
d (eq)
up (ax)
up (eq)
up (ax)
up (eq)
d (eq)
d (ax)
d (eq)
d (ax)
up (eq)
d (ax)
Chemscape Chime
The below websites will require that you download
Chemscape Chime: http://www.mdlchime.com
http://www.bluffton.edu/~bergerd/Models/homez.html#index
http://lightning.chem.wwu.edu/dept/vmolckit/molecule.html
http://www.wellesley.edu/Chemistry/Flick/molecules/newlist.html
http://www.bluffton.edu/courses/TLC/BergerD/Stutzman/Morphine/model.html