Diels-Alder reactions

Question 1

what is the product of a Diels-alder reaction

Answer 1

a cyclic compound

Question 2

describe the reactants of a Diels-Alder reaction

Answer 2

one has 4 electrons (2 pi bonds)=diene

the other has 2 electrons (1 pi bond)=dienophile

Question 3

T or F: the reaction can proceed at room temperature

Answer 3

false, heat is required for the reaction to proceed

Question 4

is the mechanism concerted?

Answer 4

yes

Question 5

define concerted

Answer 5

all the steps happen at the same time

Question 6

which reactant is electron rich? poor?

Answer 6

diene=electron rich

dienophile=electron poor

Question 7

what is the driving force of the reaction

Answer 7

the driving force is the formation of new sigma bonds, which are more stable than the pi bonds

Question 8

T or F: pi bonds are more stable than sigma bonds

Answer 8

false! sigma=more stable, which is why the reaction proceeds (a more stable product is formed)

Question 9

why is this reaction type often called a [4+2] cycloaddition

Answer 9

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

Question 10

T or F: there are no intermediates during the course of the reaction

Answer 10

true; the reaction is concerted

Question 10

T or F: there are no intermediates during the course of the reaction

Answer 10

true; the reaction is concerted

Question 11

describe how the electrons move to form the product

Answer 11

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

Question 12

T or F: the reaction may also be bicyclic

Answer 12

true

Question 13

when is the reaction bicyclic

Answer 13

when the diene is cyclic

Question 14

will increasing the temperature increase or decrease the yield

Answer 14

increase

Question 15

to increase the yield, why can’t we only increase the temperature

Answer 15

sometimes there will be a max temp. that we cannot exceed

Question 16

other than increasing the temperature, how may we increase the yield

Answer 16

there is a higher yield when the diene has electron donating substituents, and when the dienophile has electron withdrawing substituents

Question 17

describe electron donating subs of the diene

Answer 17

called push groups, they donate electron density into the dienophile, and they’re typically alkyl groups

Question 18

describe electron withdrawing subs of the dienophile

Answer 18

called pull groups, they are electronegative and will draw electron density towards them, and they’re typically halides, carbonyls, or nitriles

Question 19

T or F: the stereochemistry of the reactants are retained in the product

Answer 19

true

Question 20

does the reaction occur on the inside or outside of the reactants

Answer 20

inside

Question 21

describe the product when we have subs on the outside of the dienophile

Answer 21

the subs will be wedges on the product

Question 22

describe the product when we have subs on the inside of the dienophile

Answer 22

the subs will be dashes on the product

Question 23

describe the product when we have subs on the outside of the diene

Answer 23

the subs will be dashes on the product

Question 24

describe the product when we have subs on the inside of the diene

Answer 24

the subs will be wedges on the product

Question 25

describe the ENDO rule

Answer 25

the dienophile subs will be in the ENDO position on the product rather than the EXO this is due to sterics

Question 26

will a reaction proceed faster when the dienophile is cis or trans? why?

Answer 26

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)