What is Re and Si face?
A face is labeled re if, when looking at that face, the substituents at the trigonal atom are arranged in decreasing Cahn-Ingold-Prelog priority order (1 to 2 to 3) in a clockwise order, and si if the priorities decrease in anti-clockwise order; note that the designation of the resulting chiral center as S or R depends …
What is Re and Si in chemistry?
These faces are designated by the terms re and si. To determine which is the re and which is the si face of a planar organic group, we simply use the same priority rankings that we are familiar with from the R/S system, and trace a circle: re is clockwise and si is counterclockwise.
What is R and S configuration in organic chemistry?
R and S Notation Follow the direction of the remaining 3 priorities from highest to lowest priority (lowest to highest number, 1<2<3). A counterclockwise direction is an S (sinister, Latin for left) configuration. A clockwise direction is an R (rectus, Latin for right) configuration.
How can you tell if hydrogen is pro or pro-r?
When appropriate, label prochiral hydrogens as HR or HS. Groups other than hydrogens can be considered prochiral. The alcohol below has two prochiral methyl groups – the red one is pro-R, the blue is pro-S.
Is D and L the same as R and S?
(D-L system labels the whole molecule, while R/S system labels the absolute configuration of each chirality center.) In short, the D-L system doesn’t have direct connection to (+)/(-) notation. It only relates the stereochemistry of the compound with that of glyceraldehyde, but says nothing about its optical activity.
How do you configure S & R?
Draw an arrow starting from priority one and going to priority two and then to priority 3: If the arrow goes clockwise, like in this case, the absolute configuration is R. As opposed to this, if the arrow goes counterclockwise then the absolute configuration is S.
What does pro-R mean?
Prochirality. In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step. If two identical substituents are attached to a sp³-hybridized atom, the descriptors pro-R and pro-S are used to distinguish between the two.
What is a prochiral molecule?
A prochiral molecule is an achiral molecule containing at least one pair of enantiotopic ligands. eg: 1 is achiral, and Ha and Hb in 1 are enantiotopic. If a prochirality center is a carbon atom, it can also be called a prochiral carbon.
Is a clock face chiral or achiral?
A clock face is chiral. This is because the different numbers and potential positions of the differently sized clock hands result in no plane of symmetry on the clock face.
How do you find the re and Si face of planar organic groups?
To determine which is the re and which is the si face of a planar organic group, we simply use the same priority rankings that we are familiar with from the R/S system, and trace a circle: re is clockwise and si is counterclockwise. Below, for example, we are looking down on the re face of the ketone group in pyruvate:
What is the difference between Si face and re face?
When the priorities of three substituents of the carbonyl group are oriented in a clockwise fashion (highest –> lowest), front face is called the Re face and the back face is referred to as the Si face.
What is the stereochemistry of re face and Si face nucleophiles?
“Re face” “Si face”. Nucleophiles may attack carbonyl groups from the Re face or the Si face. The stereochemistry of the product depends on the priorities of the substituents and the priority of the nucleophile.
Why does carboxylate not have re and SI Faces?
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). As we will see in chapter 10, enzymes which catalyze reactions at carbonyl carbons act specifically from one side or the other.
