Ochem Ch16 Conjugated Dienes

Front 1

What is the hybridization at the O- in CH3COO-?

Back 1

Sp2

Front 2

What is unusual about the C-C sigma bond joining two double bonds in conjugated dienes?

Back 2

it is short because it is actually partially a double bond

Front 3

what do you need for conjugation?

Back 3

3 adjacent p orbitals

Front 4

CH2=CHCH2+

Back 4

allyl arbocation

Front 5

why is an allyl carbocation more stable than a one degree carbocation?

Back 5

because of p orbital overlap

Front 6

In any system X=Y-Z, Z is ___ hybridized to allow the lone pair to ___ __ __ ___, making the system ___

Back 6

occupy a p orbital, making the system conjugated

Front 7

Four things to watch for with resonance:

Back 7

1.three atom 'allyl system (x=y-Z*<-->X*---Y=Z
2.conjugated double bonds
3.cations having positive charge adjacent to a lone pair
4.double bands having one atom more electronegative than the other

Front 8

Structures with ___ bonds and ___ charges are more stable.

Back 8

more, fewer

Front 9

structures in which every atom has an ___ are more stable.

Back 9

octet

Front 10

Structure that place a ___ charge on a more ____ element are more stable.

Back 10

negative, electronegative

Front 11

products of electrophilic addition to conjugated dienes. which one is more stable? which one is faster?

Back 11

1,2 and 1,4 addition products. 1-4 is more stable. 1,2 is faster.

Front 12

1,2 product, 1,4 product (other names). why? under whatconditions do each happen?

Back 12

kinetic product and thermodynamic product. kinetic happens in cold temps, thermodynamic warmer. Thermodynamic is preferred because it is exothermic.

Front 13

CH2=CH-CH-CH2---HX-->>

Back 13

CH2-CH-CH=CH2,
| |
H X
CH2=CH-CH-CH2,
| |
x H

Front 14

electrophilic addiction of HX
1.steps
2.markovnikov rule followed? what kind of intermediate?
3.Products? Nature?
4.More stable product?

Back 14

1.two steps
2.mark rule is followed, allylic carbocation formed.
3.1,2 product is kinetic because when H+ adds to double bond X- just adds to the closest one. Kinetic is formed faster at low temp.
4.Thermodynamic product has more substituted, more stable double bond, and predominates at equillibrium

Front 15

Diels alder-reaction forms 2 ___ bonds and one___ bond in a six-membered ring.

Back 15

sigma, pi

Front 16

what initiates diels-alder rxn?

Back 16

heat

Front 17

concerted mechanism

Back 17

all bonds broken, formed in single step

Front 18

what condition must the diene meet to react in D-A reaction

Back 18

it must be s-cis

Front 19

what increases the reaction rate in a diels-alder reaction?

Back 19

electron-withdrawing groups on dienophile

Front 20

s. chemistry of diels-alder

Back 20

retained

Front 21

endo product

Back 21

product closer to the two-carbon bridge

Front 22

draw:
1.(2E,4E)-2,4-octadiene
2.(3E,5Z)-3,5-nonadiene in s-cis

Back 22

see ssm 16-5

Front 23

draw
(3Z,5Z-4,5-dimethyl-3,5-decadiene in a)cis and b)trans conformation

Back 23

see 16-5

Front 24

does a more stable reaction have higher or lower heat of hydrogenation?

Back 24

lower

Front 25

if two conjugated dienes are equal, what do you look for for a tiebreaker regarding reactivity and stability?

Back 25

look for the most substituted double bond.

Front 26

sum up the addition reaciton with conjugated diene

Back 26

1.pi bond steals the hydrogen
2.2+ carbocations form
3.1,2 and 1,4 products form (nucleophilic attack on the carbocation_

Front 27

Addition of H+ forms a ____ __ ___
Nucleophilic attack of X- forms _,_ and _,_ products

Back 27

resonance-stabilized carbocation, 1,2 and 1,4

Front 28

what is an endo product?

Back 28

it's on a six-membered result of the diels-alder reaction, in the axial position, closest to the two member bridge with the double bond

Front 29

3 steps to finding diene and dienophile needed to make products

Back 29

1.find six-membered ring with c-c double bond
2.draw three arrows to work back
3.follow arrows to show diene and dienophile

Front 30

16.38
just do

Back 30

see ssm 16-13

Front 31

steroid

Back 31

tetracyclic lipid

Front 32

200-400 nm is what type of light?

Back 32

uv

Front 33

400-750 nm is what type light?

Back 33

visible

Front 34

750+ nm is what type light?

Back 34

infrared

Front 35

what wavelength of light do electrons in unconjugated systems need to reach an excited state?

Back 35

greater than 200 nm

Front 36

the more conjugated a diene is, the ____ wavelength of light it needs to reach an excited state

Back 36

shorter, least, less

Front 37

chemical that makes tomatoes red. why?

Back 37

lycopene makes tomatoes red. it has 11 conjugated pie bonds and so absorbs all clors except red.

Front 38

different s and trans on the same bonds are different (stereoisomers/conformations)

Back 38

conformations

Front 39

different E and Z are different (s.isomers/conformations)

Back 39

conformations

Front 40

How many pi electrons in this? Why?

Back 40

There's 8, the O lone pairs make it sp hybridized

Front 41

Will this or a diene like this with a phenyl at the end absorb longer wavelengths?

Back 41

this one, because it's trans and more stable and reactive.

Front 42

Which of the following compounds absorbs at the longest wavelength?
a1,3,5-Hexatriene
b1,3,5,7-Octatetraene
c1,7-Diphenyl-1,3,5-heptatriene
d1,6-Diphenyl-1,3,5-heptatriene

Back 42

d

Front 43

In comparing kinetic control to thermodynamic control for the reaction of butadiene and HCl, which of the following statements respresents kinetic control?
1.The intermediate is more stable and the product is more stable.
2.The intermediate is less stable and the product is more stable.
3.The intermediate is more stable and the product is less stable.
4.The intermediate is less stable and the product is less stable.

Back 43

intermediate is more stable, product is less stable

Front 44

When 1,3-butadiene reacts with HCl, two products form: 3-chloro-1-butene and 1-chloro-2-butene. At low temperatures (–78˚C), which of the following statements is correct?
1.Thermodynamic control favors formation of 3-chloro-1-butene.
2.Kinetic control favors formation of 3-chloro-1-butene.
4.Thermodynamic control favors formation of 1-chloro-2-butene.
Kinetic control favors formation of 1-chloro-2-butene.

Back 44

Kinetic control favors formation of 3-chloro-1-butene.

Front 45

In the addition of HBr to 1,3-butadiene, one product is called the kinetic product and the other is called the thermodynamic product. Which of the following descriptors applies to the kinetic product?
a) 1,2 product
b) 1,4 product
c) most stable
d) least stable
e) formed slowest
f) formed fastest
g) formed at low temperature
h) formed at high temperature
i) most substituted alkene
j) least substituted alkene
k) bromide attack at more substituted site
l) bromide attack at least substituted site
a, c, e, g, j, l
b, c, f, g, i, l,
a, d, f, g, j, k
b, d, f, h, i, k

Back 45

a, d, f, g, j, k

Front 46

How many products are expected from 1,2- or 1,4-addition of HBr to 1,3-pentadiene? Disregard stereoisomers.

Back 46

3

Front 47

Which of the following conjugated dienes gives a single product upon 1,2- or 1,4-addition of HCl?
1.Butadiene
2-Methylbutadiene
1,3-Cyclohexadiene
2,3-Dimethylbutadiene

Back 47

1,3-Cyclohexadiene

Front 48

Find the product.

Back 48

f

Front 49

What's the final product

Back 49

Front 50

product

Back 50

Front 51

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Front 52

do the retro

Back 52

Front 53

What do you need to make a cyclohexadiene?

Back 53

an alkyne having an electron withdrawing group attached directly to it

Front 54

What to use to make alkyl cyanides by direct substition?Why?

Back 54

1o and 2o alkyl bromides. They are reactive enough.

Front 55

Under special conditions, conjugated dienes will undergo 1,4-addition to add H and Br to the ends of the diene, forming a
C-C double bond with the middle two carbons.

Back 55

make fc tom

Front 56

Use conc. H2SO4 to make an alkene by dehydration of an alcohol.

Back 56

make fc

Front 57

Use HBr with modest heating to accomplish 1,4-addition to a conjugated diene.

Back 57

make fc tom

Front 58

KCN provides CN- for nucleophilic substitution to convert 1o and 2o alkyl halides into alkyl cyanides.

Back 58

make fc tom

Front 59

Thiols are best made by direct substitution using a precursor that has a good leaving group. In this case, the alkyl bromide precursor is the best choice, considering the starting material available.

Back 59

make fc tom

Front 60

Use KSH to replace bromide to make a thiol.

Back 60

make fc tom

Front 61

Use an alkene having an electron withdrawing group attached directly to it as one of the partners in a Diels-Alder reaction to make a substituted cyclohexene.

Back 61

make fc tom

Front 62

You can make disubstituted alkenes preferentially having the Z stereochemistry by reducing an alkyne.

Back 62

make fc tom

Front 63

Use H2 together with a special catalyst, Lindlar Pd, to reduce a disubstituted alkyne to an alkene preferentially having the Z stereochemistry.

Back 63

TOM

Front 64

H2 together with Ni, Pd, Pt, or Rh as a catalyst reduces alkenes.TOM

Back 64

TOM

Front 65

Use this bulky base to eliminate HX from an alkyl halide to make an alkene.

Back 65

TOM

Front 66

Use an alkyne having an electron withdrawing group attached directly to it as one of the partners in a Diels-Alder reaction to make a substituted cyclohexadiene.

Back 66

TOM

Front 67

Removal of HBr from an alkyl bromide is an effective way to make alkenes. Use a precursor having the Br at an allylic position, because it is readily made and will result in forming a conjugated diene.

Back 67

TOMM

Front 68

Use NBS together with a radical source, such as a peroxide, to replace an allylic H by Br.

Back 68

TOM

Front 69

H2 together with Ni, Pd, Pt, or Rh do what?

Back 69

alkenes.

Front 70

What to use to remove HX from an alkyl halide? Makes what?

Back 70

bulky base to eliminate HX from an alkyl halide to make an alkene.

Front 71

alkyne with electron withdrawing group attached to it in DL reaction makes whta?

Back 71

Use an alkyne having an electron withdrawing group attached directly to it as one of the partners in a Diels-Alder reaction to make a substituted cyclohexadiene.

Front 72

How to make alkene with a br

Back 72

Removal of HBr from an alkyl bromide is an effective way to make alkenes. Use a precursor having the Br at an allylic position, because it is readily made and will result in forming a conjugated diene.

Front 73

What should you use to replace allylic H by Br?

Back 73

Use NBS together with a radical source, such as a peroxide, to replace an allylic H by Br.

Front 74

use what to make alkene by dehydration?

Back 74

Use conc. H2SO4 to make an alkene by dehydration of an alcohol.

Front 75

use what to get 1,4 addition conjugated diene

Back 75

Use HBr with modest heating to accomplish 1,4-addition to a conjugated diene.

Front 76

How to make thiols

Back 76

Thiols are best made by direct substitution using a precursor that has a good leaving group. In this case, the alkyl bromide precursor is the best choice, considering the starting material available.

Front 77

How to make a thiol out of a bromide

Back 77

Use KSH to replace bromide to make a thiol.

Front 78

how to make disubstituted alkenes with z stereochemistry

Back 78

You can make disubstituted alkenes preferentially having the Z stereochemistry by reducing an alkyne.

Front 79

H2 + Lindar Pd. does what?

Back 79

Use H2 together with a special catalyst, Lindlar Pd, to reduce a disubstituted alkyne to an alkene preferentially having the Z stereochemistry.

Front 80

how to discern heat of hydrogenation

Back 80

the most conjugated and most substituted diene will have the lowest heat of hydrogenation.

Front 81

16.43
a cis or trans dienophile will form a ____ or ____ thinger

Back 81

cis or trans product of diels-alder

Front 82

steps for doing retro diels-alder

Back 82

1.identify ring
2.draw lines
3.disconnect

Front 83

what happens when you mix an alkyne in a diels-alder rxn?

Back 83

you get kind of a box-looking thing with double bonds on both ends of the bottom folds and a two-carbon bridge across the top.

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