CHM 266 Spring 2007 Organic Chemistry Lab

Experiment 8 Mutarotation of Glucose

Please fill out the report in the following order

A. Your Name (-0.5 pt. if missing)

B. Date (-0.5 pt. if missing)

C. Experiment Title and Number (-0.5 pt. if missing)

D. Write the equation of mutarotation (1 pt)

E. Calculations: (14 pt.)

Follow the exact order for your calculations and show them clearly.

1- Calculate what the observed rotation should be at zero time (a_o) assuming a specific rotation of +112° (corresponding to the a-anomer). The equation for the relationship of specific rotation to observed rotation of solution is

[a]_D^25° = a_obs / l c

a_obs = observed rotation

l = length of tube in decimeters (2 dm)

c = concentration of g per ml.

2- Calculate what the observed rotation should be at infinite time (a_¥) assuming a specific rotation of +53° (corresponding to the equilibrium mixture). Compare this value with your observed rotation at after 30 minutes.

3. Using a spreadsheet program like Excel or Quattro Pro, prepare a table including the time (s), observed rotations at time t (a_t), a_t - a_¥ , ln(a_t - a_¥), and k (first order rate constant calculated from step 9) and find the average value of k.

4. Plot a_obs vs. time (s). (Use a plotting program)

5. Plot ln(a_t - a_¥) vs. time (s). Which one of these two plots shows a linear relationship?

6. Fit the best line to the data. (Use a plotting program)

7. From extrapolation of the line find the y-intercept (a_o) and compare it with the calculated value at step 1.

8. Find the slope of the line at step 6. The early points should be in a line. This is the k (first order rate constant)

9. Assume a first order reaction and calculate the rate constant k for each reading by the following equation and include it in the table at step 3:

k = (1/t) ln [(a_o-a_¥)/(a_t - a_¥)]

a_o = observed polarimeter reading at zero time

a_¥ = reading after equilibrium is reached

a_t = reading at time t

10. Repeat steps 3-10 for the second run.

11. Calculate the average value of k from step 8 (or step 3 table) for the two runs.

12. Calculate the average value of k from step 9 for the two runs.

F. Write your name on all polarimeter print out and staple them to your report (1 pt.)