Pericycles

Question 1

what happens to bonds in cyclo additions

Answer 1

2 sigma bonds formed/broken

Question 2

what happens to bonds in sigmatropic rearrgangements

Answer 2

1 sigma bond is broken as another forms

Question 3

what happens to bonds in electrocyclic reactions

Answer 3

1 sigma bond is formed or broken

Question 4

what conformation must a diene have in diels alder

Answer 4

cis

Question 5

what characteristic does a dieneophile need to have

Answer 5

conjugation

Question 6

how can a diels alder product be easily identified

Answer 6

6 membered ring
double bond in the ring
conjugating ring outside the ring on opposite side to double bond

Question 7

what is important about the stereochemistry of dieneophiles

Answer 7

they react stereospecifically

Question 8

describe the stereospecificity of dienes

Answer 8

Z,Z - cis product
E,E - cis product
Z,E - trans product

Question 9

what causes endo stereoselectivity

Answer 9

bonding interaction between back of diene and carbonyls

Question 10

when is maximum stabilisation achieved in MOs

Answer 10

when humo and lumo have same energy

Question 11

what is the regioselectivity of diels alder

Answer 11

most reactive end of diene attacks most reactive end of dieneophile
otho/para directing aromatic transition state

Question 12

what is the woodward-hoffmann rule

Answer 12

total number of (4q+2)s + (4r)a must be odd

Question 13

what ‘facial’ is a C-H bond

Answer 13

suprafacial

Question 14

what happens when an alkene is excited

Answer 14

swaps homo for lumo

Question 15

what is the regiochemistry of [2+2] photochemistry

Answer 15

large lobes come together

Question 16

what orbitals are used with an electron poor dipolarophile

Answer 16

1,3 dipole = homo

alkene = lumo

Question 17

what orbitals are used with an electron rich dipolarophile

Answer 17

1,3 dipole = lumo

alkene = homo

Question 18

what is the stereochemistry of 1,3 dipolar cycloaddition of nitrile oxide

Answer 18

stereospecific

Question 19

what is formed from the cleavage of cis and trans nitrile oxide products

Answer 19

cis- syn aldol

trans - anti aldol

Question 20

what general product is made from aliphatic claisen

Answer 20

gamma delta unsaturated carbonyl

Question 21

what geometry is favoured by aliphatic claisen and why

Answer 21

chair transition state favours E

Question 22

what is the facialness of a sp3 orbital determine

Answer 22

if the bond reacts symmetrically

Question 23

why is oxycope better than cope

Answer 23

forms a stable enolate and then carbonyl

Question 24

what facialilty are 1.5 H shifts

Answer 24

suprafacial

Question 25

why cant 1,3 H shifts happen

Answer 25

must be anatarafacial - cant physically reach to orbital overlap