Cycloadditions

Question 1

Diels-Alder characteristics

Answer 1

Concerted [4π+2π], one step and stereospecific

Question 2

Diels-Alder HOMO LUMO interactions

Answer 2

Interaction with smallest ΔE determines favoured transition state

Question 3

Endo-rule

Answer 3

Endo product preferred if dienophile substituent has conjugated π-bonds due to secondary orbital overlap

Question 4

X substituent

Answer 4

EDG, +M, raises HOMO and raises LUMO

Question 5

Z substituent

Answer 5

EWG, -M, -I, lowers HOMO and lowers LUMO

Question 6

C substituent

Answer 6

Extended conjugation eg Ph, raises HOMO and lowers LUMO

Question 7

Diels-Alder regioselectivity

Answer 7

Match up terminal atoms with largest coefficients

Question 8

Retro-Diels-Alder

Answer 8

Reverse Diels-Alder, needs a driving force

Question 9

LA catalysis of DA

Answer 9

LA can form complex with CO groups and make it more withdrawing, lowers LUMO of dienophile, makes ΔE smaller, makes orbital coefficient on carbon α to ester group smaller which improves selectivity