State which of the following hydrogen atoms are pro-R or pro-S. Note that the carboxylate group does not have re and si faces, because two of the three substituents on that carbon are identical when the two resonance forms of carboxylate are taken into account. Hint : there are two pairs of prochiral groups! If either H R or H S is replaced by a deuterium, the two resulting molecules will be diastereomers - thus, in this molecule, H R and H S are referred to as diastereotopic hydrogens. When appropriate, label prochiral hydrogens as H R or H S. Notice that the 'hydrogenation' reaction above is specific not only in terms of which face of the carbonyl group is affected, but also in terms of which of the two diastereotopic hydrogens on NADH is transferred we will study this type of reaction in more detail in section In a reaction of the citric acid cycle Krebs cyclea water molecule is specifically lost on the pro-R arm we will study this reaction in section The pro-R hydrogen along with the two electrons in the C-H bond is transferred to the si face of the ketone in greenforming, in this particular example, an alcohol with the R configuration. Trigonal planar, sp 2 -hybridized carbons are not, as we well know, chiral centers— but they can be prochiral centers if they are bonded to three different substitutuents. The importance of the distinction between enantiotopic and diastereotopic groups will become apparent when we learn about the analytical technique called nuclear magnetic resonance.
For this reason, we can refer to the red H as the pro-R hydrogen of leave red H as a hydrogen, the configuration of the molecule would be S. For this reason, we can refer to HB as the pro-S hydrogen of ethanol, and label it the configuration of the molecule becomes R, so we can refer to HA as the pro- R hydrogen of ethanol, and label it HR. Notice also that it is specifically the pro- R hydrogen on the pro-R arm Have questions or comments?.
R-configuration. Ha is referred to as "pro-R".
Hb is referred to as "pro-S". PROCHIRALITY IN NUCLEOPHILIC ACYL ADDITIONS. Prochiral carbonyl carbons are.
The alcohol below has two prochiral methyl groups - the red one is pro-Rthe blue is pro-S.
Identify which side is Re or Si. Thus, in this molecule, H R and H S are referred to as diastereotopic hydrogens.
Looking back at our isoprenoid biosynthesis example, we see that it is specifically the pro-R hydrogen that the isopentenyl diphosphate substrate loses in the reaction. To name the two prochiral hydrogens on ethanol, we again need to engage in a thought experiment. These faces are designated by the terms re and si.
In stereochemistry, prochiral molecules are those that can be converted from achiral to Promoting the pro-R substituent to higher priority than the other identical myocardial infarction, lung problems in those who smoke it, blood infections.  The advantages of the MPV reduction lie in its high chemoselectivity, and its. dopamine) used for treatment of Parkinson's disease is effective only as the. molecule the configuration is R, and the complete name of this enantiomer is R-3 -chloro-.
the chiral compound is S, then the H atom is called pro-S. It is a simple .
Simple - just arbitrarily make methyl A higher priority than methyl B, and the compound now has the R configuration.
The central carbon is a prochiral center with two 'arms' that are identical except that one can be designated pro-R and the other pro-S.
Prochiral hydrogens can be designated either enantiotopic or diastereotopic. The alcohol below has two prochiral methyl groups - the red one is pro-Rthe blue is pro-S. Are these prochiral groups diastereotopic or enantiotopic?
Citrate is another example. Conversely, if we change the blue H to D and leave red H as a hydrogen, the configuration of the molecule would be Sso we can refer to blue H as the pro-S hydrogen of ethanol, and label it H S.
Video: Pros and pro r stereochemistry problems Tutorial: Prochirality 2
Pros and pro r stereochemistry problems
|When appropriate, label prochiral hydrogens as H R or H S.
The three hydrogen atoms on the methyl CH 3 group of ethanol and on any methyl group are homotopic. Citrate is another example. H a and H b on the alkene below, for example, are diastereotopic: if we change one, and then the other, of these hydrogens to deuterium, the resulting compounds are E and Z diastereomers.
Although an alkene carbon bonded to two identical groups is not considered a prochiral center, these two groups can be diastereotopic. For example in the following reaction, which is a key step in the oxidation of fatty acids, it is specifically H A and H D that are lost, while H B and H C remain in the resulting conjugated alkene.
For each of the carbonyl groups in uracil, state whether we are looking at the re or the si face in the structural drawing below.