Chem 380.37 Assignment 1

# The slope of the line is related to the o h

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Unformatted text preview: quare of the bond displacement is placed on the x-axis. The slope of the line is related to the O-H stretching force constant (refer to Section 4.3 of your text for an equation). Calculate the stretching force constant and report its value in units of kcal mol–1 Å–2. Include a table of your data and both graphs when you turn in your assignment. 3 4. Using the relationship between the harmonic frequency ν o and the force constant k, 1 ȹ k ȹ νo = ȹ ȹ 2π ȹ µ Ⱥ € 1/ 2 , determine the harmonic frequency in s–1 corresponding to the stretching force constant that you calculated in step 3. The quantity µ is referred to as the reduced mass and is defined in terms of the masses of the atoms in the € bond. For an A-B bond, the reduced mass is µ= mA mB . mA + mB Note that the masses in this equation refer to the mass of a single atom of A or B, not the molar mass. Finally, convert the result to units€ f cm–1 and discuss whether or not this value is what you would expect for o the typical IR stretching frequency of an O-H group. Determination o f B ending F orce C onstant 1. Starting from scratch, build and determine the equilibrium geometry of a new copy of the water molecule using the MMFF94 force field. Measure and record the total energy in kcal/mol and the equilibrium bond angle in degrees. 2. The next step is to vary the H-O-H bond angle from 90 to 120 degrees in 7 steps (5 degree increments). To do this, follow the instructions in Appendix 4 to use the Bond Manipulation tool, , to adjust the bond angle to each of the suggested values (the O-H bond distances should not be changed). Compute single point energies for each bond angle and record these values in kJ/mol (see Appendix 3 for instructions on computing single point energies). 3. Follow a similar procedure to that described above for the stretching force constant to make graphs of your results and calculate the H-O-H bending force constant. Report the value that you obtained for the bending force constant in kcal m...
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## This document was uploaded on 03/04/2014 for the course CHEM 380.37 at Illinois State.

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