[treadlightly]

How can you tell if a structure will keep its R/S configuration after a reaction?

So, I have (R)-2-bromobutane  reacting with H3CCO2- Na+. I drew out the mechanism and got an ester (sec-butyl acetate).

That ester then reacts with OH- and water. The product I got from that was carboxylic acid and 2-butanol.

Now here's my question: Was there ever a point in these reactions in which I lost that R/S configuration from the bromobutane? The first time I drew out (R)-2-bromobutane, I had the bromide as a wedge sticking out, so when the carboxylate anion attacks the alkyl halide, the bromide went out. I guess I lost the configuration then. But is that right? How could you tell if the configuration is lost, generally?

[discodermolide]

If you have pure (R) it will have a value for the optical rotation. Do a reaction, in your case an S_n2 you should get inversion of configuration.
Usually you can tell from the optical rotation and even the MPt. if the compound is pure (R) or (S).
Note the (R) and (S) do not tell you about the optical activity. They are determined by a sequence of rules in your case you end up with the (S)-acetate.

[orgopete]

Whether the configuration of a chiral center changes will depend on whether it can or will change in any given reaction. This is determined by the reaction mechanism.

In the instance of starting with the R-bromide, the SN2 reaction inverted the chirality to the S-ester. Hydrolysis of the ester involved reaction of the carbonyl group without affecting the originating chirality center. Therefore the alcohol should be an S-alcohol.

You can have a reaction in which the chirality center is removed from the reacting carbon and thus it does not change. If the chirality center becomes a carbocation in an SN1 reaction, then the product will lose the chirality at that center.