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Conformational Analysis
Conformations of Alkanes
CH3
C C
H
ClClF
F
CH3
C C
Cl
FClF
H= =
CH3
C C
F
HClF
Cl
• 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
C C
H
ClClF
F=
CH3
C C
F
Cl
ClF
H
Eclipsed Staggered
CH3
Cl F
H
F
Cl
H
FCl
CH3
Cl F
Hash-Wedge
NewmanProjection
Conformations of Alkanes
CH3
Cl F
H
F
Cl
H
FCl
CH3
Cl F
Cl
HF
CH3
Cl F
CH3
Cl F
Cl
H
F
F
ClH
CH3
Cl F
CH3
Cl F
F
Cl
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
H
C C
H
H
HH
H
ECLIPSED CONFORMER OF ETHANE
H
HH
H
H H
ECLIPSED CONFORMER OF ETHANESPACE-FILLING REPRESENTATION
Staggered Ethane
http://lightning.chem.wwu.edu/dept/vmolckit/ethanstg.pdb
H
C C
H
HH
HH
STAGGERED CONFORMER OF ETHANE
H
H H
H
H
H
STAGGERED CONFORMER OF ETHANESPACE-FILLING REPRESENTATION
ENERGY DIAGRAM FOR ETHANE CONFORMATIONS
Eclipsed Butane—0 dihedral
http://lightning.chem.wwu.edu/dept/vmolckit/butecl0.pdb
CH3
C C
CH3
H
HH
H
ECLIPSED CONFORMER OF BUTANE
CH3
HH
CH3
H H
ECLIPSED CONFORMER OF BUTANESPACE-FILLING MODEL
Staggered Butane—Gauche
http://lightning.chem.wwu.edu/dept/vmolckit/butgauch.pdb
STAGGERED CONFORMER OF BUTANE—GAUCHE
CH3
C C
H
HCH3
HH
CH3
H H
H
H
CH3
STAGGERED CONFORMER OF BUTANE—GAUCHESPACE-FILLING MODEL
Eclipsed Butane—120 dihedral
http://lightning.chem.wwu.edu/dept/vmolckit/butec120.pdb
ECLIPSED CONFORMER OF BUTANE
CH3
C C
H
H
CH3
HH
H
HCH3
CH3
H H
ECLIPSED CONFORMER OF BUTANESPACE-FILLING MODEL
Staggered Butane—Anti
http://lightning.chem.wwu.edu/dept/vmolckit/butanti.pdb
STAGGERED CONFORMER OF BUTANE—ANTI
CH3
C C
CH3
HH
HH
CH3
H H
H
CH3
H
STAGGERED CONFORMER OF BUTANE—ANTISPACE-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
AXIAL
AXIAL
EQUATORIAL EQUATORIAL
SIDE VIEW OF CYCLOHEXANE
AXIAL
EQUATORIAL
TOP VIEW OF CYCLOHEXANE
Conformations of Cyclohexane
http://lightning.chem.wwu.edu/dept/vmolckit/cheqcode.pdb
d (eq)
up (ax)
up (ax)
up (ax)
d (ax)d (ax)
d (ax)d (eq)
up (eq)
up (eq)d (eq)
up (eq)
CHAIR CONFORMER REPRESENTATION
d (eq)
up (ax)
up (ax)
up (ax)
d (ax) d (ax)
d (ax)d (eq)
up (eq)
up (eq)d (eq)
up (eq)
CHAIR CONFORMER REPRESENTATION
Chemscape Chime
http://www.bluffton.edu/~bergerd/Models/homez.html#index
http://lightning.chem.wwu.edu/dept/vmolckit/molecule.html
The below websites will require that you download Chemscape Chime: http://www.mdlchime.com
http://www.bluffton.edu/courses/TLC/BergerD/Stutzman/Morphine/model.html
http://www.wellesley.edu/Chemistry/Flick/molecules/newlist.html