[Big-Daddy]

The specific rotation [α] for pure (R)-2-bromooctane is [α]²⁵_D = +36.0, while the specific rotation [α] for pure (S)-2-octanol is[α]²⁵_D = -10.3.

A sample of 2-bromooctane gives [α]²⁵_D = +30.0; it is then reacted with NaOH to form 2-octanol. This 2-octanol then gives [α]²⁵_D = -6.0.

a.   Calculate the fraction of stereocenters which have inverted during the course of the reaction.
b.   Consider the symmetry of the expression obtained, by calculating the fraction of stereocenters which would have been inverted if we had observed instead [α]²⁵_D = +6.0 for the 2-octanol.

[Big-Daddy]

No correct answers yet so I'll post a hint which hopefully will not make things too obvious:

We must suppose that inversion of centres is symmetrical and random in this process - i.e. whatever fraction of (R)-2-bromooctane was inverted to make (S)-2-octanol is the same as the fraction of (S)-2-bromooctane inverted to make (R)-2-octanol.

[momoho]

87.46 percent for a?

[Big-Daddy]

87.46 percent for a?

Close (within a few percent) but no dice unfortunately 

In a couple of days I will post another hint.

[momoho]

I didn't use the hint in my first attempt.
Now i use it and i think it's 69.91 percent for a.
Correct?

[momoho]

I'm sorry...i made a ridiculous mistake...my answer is 84.953 %

[Big-Daddy]

I'm sorry...i made a ridiculous mistake...my answer is 84.953 %

Correct! The exact value is 175/206 = 84.9515%. Do you want to explain how you got there?

Any ideas for the second part? It's basically a repeat of the calculation, but using the second value, and note down what strikes you about the situation.

[momoho]

Why didn't anyone ask another question?
I mean practice problem 7!!!

[Rutherford]

That should be you, because you gave the answer. Also the problem isn't solved completely.

[momoho]

The second part is almost same with the first and i don't want to give a problem because i don't have any problems!!!

[Borek]

i don't want to give a problem because i don't have any problems!!!

That's your problem.

[Big-Daddy]

The second part is almost same with the first and i don't want to give a problem because i don't have any problems!!!

why don't you explain your working for the first part, then I'm sure someone else will step up and solve the second and then maybe that person can offer Problem 7.