1. Hydrogenation hell. Hydrogenation is one of the simplest of the addition reactions to an alkene, yet understanding the stereochemical outcome can be challenging. Hydrogenation is considered a syn-addition reaction (both atoms are added to the carbons on one side of the \(\pi\)-bond). As H$_2$ or D$_2$ are symmetric, no regioselectivity (i.e. which carbon of the alkene to add to) is in play. The stereochemical patterns developed below for both symmetric and non-symmetric alkenes are applicable to any syn-addition reactions. For the following deuteration reactions, provide the information requested in the boxes. The first two examples are completed.
structure and absolute
stereochemistry of products
number of stereo-
isomeric products
stereoisomer
relationship
D
D
+ D$_2$ \(\longrightarrow\) H H
H H
H H
D
1
achiral
D
D
Et
H
+ D$_2$ \(\longrightarrow\) H
Et
H
Et
2
enantiomers
Et
H
D
D
3R, 4R
3S, 4S
+ D$_2$
+ D$_2$
+ D$_2$
+ D$_2$