Also, what can we conclude from D and L about R or S or enantiomers, etc.
Regiospecific - given a reaction that could potentially form multiple structural isomers (structural isomers = regioisomers) a regiospecific reaction only forms one regioisomer. Example, as above - hydroboration is regiospecific for adding boron to the least substituted carbon.***
Stereospecific - Starting with one steroisomer, the reaction produces one (and only one) stereoisomer. The classic example is the SN2. Given a chiral alkyl halide, SN2 will lead to inversion of configuration at the carbon, 100% of the time.
Regioselective and stereoselective - refer to above, except produce mixtures where one regioisomer/stereoisomer is dominant.
D/L and R/S. Caution: it's coincidental that D tends to be R and L tends to be S. All 20 natural amino acids are L, but cysteine is R because of the SH. If you remember that exception, you should be OK.
Hope this helps - James
PS - not on the exam: D/L refers to the absolute configuration assigned to sugars/amino acids by Fischer back in the early 1900s. R/S was developed in the 1950s, much more broadly applicable than D/L.] ***this is a white lie - hydroboration is actually highly regioselective (~99:1 in some cases) not regiospecific, but pretend I didn't tell you this.]