Conjugated Dienes

Question 1

preparation

Answer 1

NBS, hv, CCl4

t-butO

Question 2

2 theories of stability

Answer 2

orbital hybridization

resonance/molecular orbital theory

Question 3

hybridization

Answer 3

all sp2, more s-char

holds e- closer to nucleus, therefore more stable

Question 4

molecular orbital theory

Answer 4

different visualization of delocalization (resonance)

add nodes one at a time, symmetrically

Question 5

colorful compounds

Answer 5

more conjugated absorbs lower E/longer wavelengths (less E)

when light is absorbed, HOMO –> LUMO

delta E (homo-lumo) is smaller so higher E state (pi*) is more stable due to resonance

Question 6

pi to pi*

Answer 6

in UV range; can’t see

Question 7

bathochromic shift

Answer 7

conjugation shifts to longer wavelength (less E) is red

Question 8

electrophilic addition

Answer 8

mixture of 1,2-addn and 1,4-addn

1,2-addn: more stable carbocat, less stable product, higher yield at low T, kinetic control (faster forming)

1,4-addn: more stable product, higher yield at higher T, thermodynamic control

Question 9

temps for 1,2 & 1,4

Answer 9

-80ºC for 1,2

40ºC for 1,4

Question 10

kinetics vs. thermodynamics

Answer 10

Ea of 1,2 is lower, kinetics

enthalpy (deltaH) of 1,4 is greater, thermodynamics