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Unformatted text preview: ules). Determine the equilibrium geometries of each of the conformers using
the MMFF94 Molecular Mechanics force field (see Appendix 3 for instructions on performing molecular mechanics
calculations). Record the total energy of each one in kcal/mol. Discuss whether or not the results agree with your
qualitative predictions. PART B ( 7 p oints) - E quilibrium G eometry o f B iphenyl a nd S ubstituted B iphenyl
What is the equilibrium torsional angle of biphenyl? To find out, first build the biphenyl molecule using Avogadro. biphenyl 2
The torsional angle in question is for rotation about the central C-C bond. In order to build biphenyl, it is helpful to
start with pre-built benzene rings available in the Avogadro library. To locate the fragment library, select "Build →
Insert → Fragment". Open the aromatics folder, select benzene, and then click "Insert Fragment". At this point a
benzene molecule should appear in the display window highlighted in blue. Use the mouse buttons to translate and
rotate the molecule into a suitable position to form biphenyl; then insert a second benzene fragment and orient it
The last step is to use the Drawing Tool to connect the two benzene rings to form biphenyl. To do this, select the
Drawing Tool, make sure that the element selected is Carbon, and make sure to click ON the button to "Adjust
Hydrogens". Then use the mouse to draw a bond from one benzene ring to the other as shown above in the sketch of
Once you have built the biphenyl molecule, perform a calculation to determine its equilibrium geometry using the
MMFF94 force field. Measure the torsional (dihedral) angle (use the Measure Tool,
; see Appendix 4 for
additional information on measurement). With the torsional angle displayed, repeat the selection of "Extensions →
Optimize Geometry" until the torsional angle stops varying – this is the final result. Report the calculated value of
the torsional angle of biphenyl. Does the result of your molecular mechanics calcul...
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This document was uploaded on 03/04/2014 for the course CHEM 380.37 at Illinois State.
- Fall '13