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