Diels-Alder reactions Flashcards
what is the product of a Diels-alder reaction
a cyclic compound
describe the reactants of a Diels-Alder reaction
one has 4 electrons (2 pi bonds)=diene
the other has 2 electrons (1 pi bond)=dienophile
T or F: the reaction can proceed at room temperature
false, heat is required for the reaction to proceed
is the mechanism concerted?
yes
define concerted
all the steps happen at the same time
which reactant is electron rich? poor?
diene=electron rich
dienophile=electron poor
what is the driving force of the reaction
the driving force is the formation of new sigma bonds, which are more stable than the pi bonds
T or F: pi bonds are more stable than sigma bonds
false! sigma=more stable, which is why the reaction proceeds (a more stable product is formed)
why is this reaction type often called a [4+2] cycloaddition
4 and 2 refer to the electrons in the pi bonds of the reactants, and the product is a cyclic compound via addition of the reactants
T or F: there are no intermediates during the course of the reaction
true; the reaction is concerted
T or F: there are no intermediates during the course of the reaction
true; the reaction is concerted
describe how the electrons move to form the product
2 from the pi bond in the dienophile move to a pi bond in the diene, so 2 from that pi bond move over, and 2 from the other pi bond move to the dienophile = cycloadduct with one pi bond
T or F: the reaction may also be bicyclic
true
when is the reaction bicyclic
when the diene is cyclic
will increasing the temperature increase or decrease the yield
increase
to increase the yield, why can’t we only increase the temperature
sometimes there will be a max temp. that we cannot exceed
other than increasing the temperature, how may we increase the yield
there is a higher yield when the diene has electron donating substituents, and when the dienophile has electron withdrawing substituents
describe electron donating subs of the diene
called push groups, they donate electron density into the dienophile, and they’re typically alkyl groups
describe electron withdrawing subs of the dienophile
called pull groups, they are electronegative and will draw electron density towards them, and they’re typically halides, carbonyls, or nitriles
T or F: the stereochemistry of the reactants are retained in the product
true
does the reaction occur on the inside or outside of the reactants
inside
describe the product when we have subs on the outside of the dienophile
the subs will be wedges on the product
describe the product when we have subs on the inside of the dienophile
the subs will be dashes on the product
describe the product when we have subs on the outside of the diene
the subs will be dashes on the product
describe the product when we have subs on the inside of the diene
the subs will be wedges on the product
describe the ENDO rule
the dienophile subs will be in the ENDO position on the product rather than the EXO
this is due to sterics
will a reaction proceed faster when the dienophile is cis or trans? why?
faster when the dienophile is cis, because when it’s trans one of the subs interferes with the pi electrons approach (trans causes steric affects=slower)
