The top and bottom carbons are both enantiomeric and the
molecule does not contain an internal plane of symmetry,
making the two products enantiomers.
The top and bottom carbons are both enantiomeric but the
molecule contains an internal plane of symmetry, making the
two products identical and meso.
The top and bottom carbons are both enantiomeric and the
molecule does not contain an internal plane of symmetry,
making the two products enantiomers.
The top and bottom carbons are both enantiomeric and the
molecule does not contain an internal plane of symmetry,
making the two products enantiomers.
The addition of bromine to an alkene involves an
intermediate bromonium cation. The addition of
bromide anion to this intermediate is from the opposite
face, making the net addition trans. In this
example, the alkene is symmetrical, hence there is no
regioselectivity.
The oxidation of an alkene with alkaline permanganate
produces an intermediate manganate diester, which
rapidly breaks down to give the cis 1,2-diol (a
glycol).
The addition of HOBr to an alkene involves the formation of
an intermediate bromonium cation, identical to that
observed in the addition of bromine. This bromonium ion
reacts rapidly with hydroxide anion from the opposite
face to give the trans adduct. In this example,
the alkene is symmetrical, hence there is no
regiochemistry, otherwise, the hydroxide will typically
be bound to the carbon of the alkene which would form the
most stable carbocation center (Markovnikov addition).
The reaction of al alkene with BH3 in THF
solvent proceeds by a concerted mechanism to add the
boron and the hydrogen cis relative to each
other. The regiochemistry is anti-Markovnikov
(the hydrogen bonds to the carbon which would form the most
stable carbocation center). Work-up with alkaline peroxide
oxidizes the intermediate borane to the alcohol, with
retention of stereochemistry at the borane carbon.
Set #1
Reactions Generating Stereocenters
For each of the reactions on the left, predict the major
organic product(s) and determine the stereochemical
relationship between any products which are formed (i.e.,
enantiomers, diastereomers or identical).
Click the mouse on the molecule to view the answer;
click on the reagents to
view information about the stereochemistry of the
reaction.
