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Chem 204 > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

Ka of acetic acid

A

1.8 * 10^-5

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2
Q

Acetic acid formula

A

CH3COOH

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3
Q

Ka of phosphoric acid

A

7.1 * 10^-3

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4
Q

Recycling Codes

A 
1 - polyethylene tetraphtalate (PET)
2 - polyethylene high density
3 - polyvinyl chloride
4 - polyethylene low density
5 - polypropylene
6 - polystyrene
7 - other
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5
Q

How many recycling codes are there?

A

7

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6
Q

Structure of PET

A

has benzene ring with ester groups opposite to eachother

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7
Q

Alternating copolymer

A

ABABA

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8
Q

Statistical copolymer

A

ABBBABBBA

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9
Q

Random copolymer

A

ABBAAABAABBB

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10
Q

Block copolymer

A

AAAABBBB

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11
Q

Graft copolymer

A

Has main chain of AAAA

Then has branches of BBBB

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12
Q

Crystalline regions

A

ordered regions of the polymer that lie in close proximity and are held together by intermolecular interactions such as Van Der Waals forces or hydrogen bonding

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13
Q

Amorphous regions

A

segments of the polymer structure where the polymer chains are randomly arranged, resulting in weaker intermolecular interactions

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14
Q

Glass transition temperature (Tg)

A

temperature at which a hard-amorphous polymer becomes soft

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15
Q

Melt transition temperature (Tm)

A

temperature at which crystalline regions of the polymer melt to become amorphous

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16
Q

What type of polymers have higher Tm?

A

More ordered polymers / less branching

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17
Q

Ceiling Temperature (Tc)

A

measure of the tendency of a polymer to revert to its constituent monomers

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18
Q

What is true when a polymer is at its ceiling temp?

A

The rate of polymerization and depolymerization are equal

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19
Q

How can you calculate ceiling temperature?

A

Set Gibbs Free Energy equal to 0

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20
Q

Step growth polymerization

A

polymerizations in which the polymer chain grows stepwise by reactions that can occur between any two monomers

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21
Q

Chain growth polymerization

A

a polymer chain grows only by reaction of a monomer with a reactive end-group on the growing chain

requires an initiator

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22
Q

Heterolysis versus homolysis

A

Homolysis (homolytic cleavage) produces 2 free radical species

Versus heterolysis which produces a full negative charge and a full positive charge on the two species

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23
Q

What are two methods to initiate radical formation?

A

Thermolysis (delta)

Photolysis (E = hv)

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24
Q

What can you use to measure resulting radical stability?

A

Bond Dissociation Energy

Lower BDE indicates a more stable radical

Easier to break a bond because the resulting radical is more stable

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25
Q

What is the rate determining step of radical polymerization?

A

during propagation when a radical is formed

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26
Q

What leads to regioselectivity within alkane halogenation?

A

Want radical formed during propagation to be placed on a more stable carbon

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27
Q

What is unique about alkyl radical stabilization?

A

C2p (with radical) and C-H bond come together in alkane halogenation (total of 3 electrons)

Makes pi-stabilization, but also promotes one electron to the pi*

This raises energy of the SOMO

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28
Q

Is alkane halogenation regioselective?

A

Yes. Want to have more stable radical intermediate on alkane

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29
Q

SOMO

A

singly occupied molecular orbital

the orbital that the radical is normally in

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30
Q

BDE of alkyl peroxide

A

151 kJ/mol

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31
Q

Why is the BDE of alkyl peroxide so low?

A

There is lots of repulsion from the two OO atoms

This is similar to Cl2 and Br2

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32
Q

Why should the rates of propagation I and II be similar in alkane halogenation?

A

After propagation I there would be a buildup of radicals on carbons

This would increase the likelihood of 2 carbons terminating eachother and no halogenation occurring

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33
Q

Why is the rearrangement of the cyclopropyl methyl radical exothermic?

A

Cyclopropane has significant steric strain

By breaking open the ring, you reduce strain and release energy

(this is not a radical stability argument)

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34
Q

How is bisphenol generated?

Starting products are phenol and carbonyl group

A

Electrophilic aromatic substitution

The alkene grabs the activated carbonyl group

Then the phenol can stabilize the positive charge

And goes from there

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35
Q

Does an alkyl group better stabilize a radical or a carbocation?

A

Better stabilizes a carbocation

Hyperconjugation of completely empty 2p orbital versus a radical that gets promoted to antibonding orbital

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36
Q

Is LDPE more or less branched than HDPE?

A

More branched

This prevents chains from getting close together and being high in density

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37
Q

Types of termination for radical polymerization

A

1) Combination

2) Disproportionation

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38
Q

What hydrogen is transferred in disproportion?

A

A beta hydrogen from neighboring carbon

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39
Q

Which termination method of free radical is favored at high temperatures?

A

Disproportion

Since there is no change in entropy, you want high temperatures to lower Gibbs free energy

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40
Q

Chain transfer

A

Reactions in which the active center is transferred from the active chain end to another species in the polymerization system

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41
Q

What type of branching does 1,5 Hydrogen Atom Abstraction create?

A

Results in n-butyl branching

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42
Q

Why does polystyrene have less chain transfer and correspondingly less branching than polyethylene?

A

Polystyrene’s active center is 2º whereas polyethylene’s active center is 1º

Since polystyrene has a more stable radical it is less likely to undergo chain transfer

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43
Q

Are radicals stabilized by EWGs or EDGs?

A

Both!

An EWG will lower SOMOs and make more electrophilic

An EDG will raise SOMOs (since promote radical to antibonding) and make nucleophilic

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44
Q

How does the type of group stabilizing the radical result in alternating copolymers?

A

If an EWG is stabilizing the copolymer this makes the SOMO more electrophilic by lowering it

This means that the radical will be attracted to the more nucleophilic monomer with the EDG

This creates an alternating pattern

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45
Q

Combination and steric hinderance

A

With a sterically hindered molecule combination is less favored and disproportionation is more favored

Also more steric hinderance a lot of times means more beta hydrogens that can be used in disproportionation

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46
Q

Polydisperse

A

a characteristic of polymers

most are mixtures of individual polymers with variable molecular weights

molecular weights make bell shaped distribution

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47
Q

Mn

A

number average molecular weight

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48
Q

Mw

A

weight average molecular weight

biased towards heavier weights and will be overall heavier than Mn

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49
Q

Polydispersity Index

A

ratio of Mw to Mn

Should always be a positive number since Mw > Mn, unless there is no polydispersity

Greater ratio shows that there is more variation between Mw and Mn and thus a greater polydispersity

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50
Q

How are molecular weights determined for polydispersity indexes?

A

Gel permeation chromatography

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51
Q

How does gel permeation chromatography work?

A

small molecules take longer to elute since they can have more chemical interactions with the highly polar silica gel

large molecules elute faster because they cannot enter the gel and form as many chemical reactions with gel

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52
Q

What kind of groups do you want on the monomers for cationic polymerization?

A

Want EDGs

Will be able to stabilize the positive charge

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53
Q

Three types of initiators of cationic polymerization

A
  1. Strong protic acid with non-nucleophilic conjugate base
  2. Weak protic acid (initiator) and Strong lewis acid (co-initiator)
  3. Akyl halide and a strong lewis acid
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54
Q

Examples of strong protic acids with non-nucleophilic conjugate bases

A

H2SO4, HClO4, H3PO4

NOT anything that will produce a halide like HCl

55
Q

Examples of weak protic acids with strong lewis acids

A

BF3 and H2O

56
Q

Examples of alkyl halides and a strong lewis acid

A

RCl + AlCl3

RCl + SnCl4

57
Q

Termination definition

A

a reaction in which the active center is destroyed irreversible and propagation ceases

58
Q

How do cationic polymerizations often get terminated?

A

Deprotonate a neighboring hydrogen and form an alkene on the end

59
Q

Why are polar solvents favored in cationic polymerization?

A

Polar solvents favor the solvent separated ion pair

the solvent separated ion pair allows a molecule to get past the counter ion (shielding) and react

60
Q

Counter ions, size, and shielding

A

Larger counter ions do not mean more shielding of carbonic active end

Rather larger counter ions have more diffusion of charge and correspondingly less shielding

61
Q

What kind of groups do you want on the monomers for anionic polymerization?

A

Want EWGs

Will be able to stabilize the negative charge

62
Q

Is anionic polymerization living?

A

Yes

There is no termination

63
Q

What can lead to the synthesis of coblock polymers?

A

living polymerizations

64
Q

Ways to deactivate carbanionic living polymerizations

A

1) H2O
2) Epoxide and acid
3) CO2 and H2O

65
Q

What actually happens in solvent separated ion pairs?

A

The solvent’s polar section surrounds the counter ion and prevents it from shielding

66
Q

Why is living polymerizations does the rate of termination need to be faster than the rate of propagation?

A

If initiation is much faster than propagation, polymer chains start growing uniformly and simultaneously

This achieves low polydispersity since no termination/chain transfer

67
Q

Living polymerization

A

chain transfer polymerization from which chain transfer and chain termination are absent

68
Q

Characteristics of a living polymerization

A
  1. Low polydispersity
  2. Predictable molecular weights
    3) Provide access to complex copolymers architecture
69
Q

Benefits of anionic chain growth versus free-radical polymerizations

A

Anionic: living but limited to a monomers with EDGs

Free-radical: have large set of suitable monomers but are not naturally living

70
Q

Why does lowering the concentration of growing free radical chains affect the rate of termination more than the rate of propagation?

A

Termination requires two free radical polymers

Propagation requires a free radical polymer and a monomer

*look at their rate laws

71
Q

How does nitrogen mediated radical polymerization result in “living” polymerizations?

A

Nitroxide radical binds to free radical polymer and terminates but this is a reversible process

Some of the polymers reverse and keep propagating to a polymer with low polydiversity

72
Q

Properties of nitroxides

A

persistent radical that doesn’t couple with itself

has resonance net stabilization of the radical

the O-O bond that forms through coupling is less stable than the 2x resonance stabilization in the nitroxide radical

73
Q

Where does the lone pair “exist” in a nitroxide molecule?

A

Resonates between the N2p and O2p orbital

Has pi-like net stabilization

74
Q

Resonance stabilization of nitoxide BDE

A

125.5 kJ/mol (2x when comparing)

75
Q

O-O bond of nitroxide BDE

A

146 kJ/mol

76
Q

Why do we want nitroxides to be sterically hindered in NMP?

A

steric hinderance makes it more likely for the reverse process to take place and more propagation

77
Q

What is the relationship between the rate of initiation and the polydispersity?

A

Faster rate of initiation means less polydisperse

Lower rate of initiation means more polydisperse

78
Q

When designing an ATRP system the C-X bond of the initiator should be weaker than the C-X bond of the deactivated polymer chain. Why is this true?

A

Want the rate of initiation to be fast to achieve similar polydispersity

Therefore the initiator bond should be able to break easily into a radical

79
Q

What are the two types of “living” free radical polymerizations?

A

ATRP

NMP

80
Q

What is unique about styrene?

A

It is able to self-generate free radicals

Through diels alder like reaction

81
Q

How can you form graft copolymers?

A

Through the use of controlled radical polymerization

82
Q

What types of polymers does step growth polymerization result in?

A

polyesters

polyamides

polycarbonates

polyurethanes

83
Q

Polycarbonates

A

a polymer that contains a carbonate group

carbonate group has a carbonyl group with two oxygens attached

84
Q

What monomers come together to make the polyester, PET?

A

diethanol and benzene with two carboxlyic acids attached

85
Q

What is an example of a polyamide?

A

Kevlar

Benzene rings with amide groups attached

86
Q

Polyurethane

A

a polymer containing NHCO2 groups

87
Q

How do polyurethanes differ from polyamides?

A

Polyurethanes have carbonyl group attaches to NH and an O

Polyamides have carbonyl group attached to NH and an R group (not an O)

88
Q

What monomers come together to make polyamides?

A

Something with NH2

89
Q

What monomers come together to make polyurethanes?

A

Something with N=C=O group

90
Q

Where do you protonate in N=C=O?

A

Can protonate the N and then break the double bond between the C and the N

This keeps the C=O intact in the resulting polymer

91
Q

Chain growth versus step growth timing

A

Chain growth shows polymers with high MW almost immediately

Step growth shows polymers with high MW near the end of the reaction

***True “living” is a linear line between the two of high MW

92
Q

Differences between chain versus step growth

A

Chain has a single active site

Chain has a single growing polymer, whereas step growth has many active ogliomers

Concentration of monomers decreases steadily overtime in chain, whereas step growth the monomers decrease almost immediately and make ogliomers

93
Q

What is Tm determined by?

A

The number of intermolecular interactions (hydrogen bonding) and the flexibility of the structure

94
Q

What will have a higher Tm Nylon 6,6 or Nylon 6,10?

A

Nylon 6,6 since there is a greater number of hydrogen bonding per unit

95
Q

Do benzene rings increase or decrease Tm and Tg? Why?

A

Since they are rigid they make the polymer more ordered and harder to break

This leads to a lower Tm and Tg

96
Q

How does kevlar compare to nylon 6,6?

A

Kevlar has benzene rings in addition to hydrogen bonding, so it raises the Tm

97
Q

What is Kw?

A

1*10^-14

98
Q

What is the relationship between ka and Kb?

A

Kw = Ka * Kb

99
Q

What is the formula for Ka?

A

H+*A- / HA

100
Q

Henderson Hasselbach Equation

A

pH = pKa + log (A-/HA)

101
Q

When a base is dissolved in water what is the lowest possible pH?

A

7.0

102
Q

Is it true that a strong acid will always have a lower pH than a weak acid?

A

No

Quantity matters. Could have a little strong and a lot of weak

103
Q

pi backbonding

A

when the alkene acts as the LUMO and used empty pi*cc

and the metal donates through the filled dxy orbital

104
Q

Dewar Chatt Model

A

the alkene acts as the HOMO

alkene is donating electrons to the electron deficient (+) transition metal

in doing so, the alkene becomes more electrophilic since giving up electrons

105
Q

Metalacyclopropane (MCP) model

A

the alkene acts as the LUMO

alkene is recieving electrons from the electron rich (no positive charge) transition metal

in doing so, the alkene becomes more nucleophilic since receiving electrons

pi-backbiting model

106
Q

Steps of the Zeigler-Natta Polymerization

A

pi complexation where the alkene attaches

migratory insertion (windhshield wiper)

flips where the alkene attaches and then repeats

107
Q

How many arrows drawn in migratory insertion?

A

2

One from polymer to alkene

then from alkene to transition metal

108
Q

How does Zeigler Natta polymerization compare to radical polymerizations of ethylene?

A

Radical polymerizations can lead to lots of branching due to chain transfer (low density)

Zeigler Natta does not have chain transfer which leads to high density poly ethylene

109
Q

Isotactic polymer

A

Indentical configurations

110
Q

Syndiotactic polymers

A

Alternating configurations

111
Q

Atatic polymers

A

random configurations

112
Q

What are the 3 types of configurations for polymers?

A

Isotactic, syndiotactic, and atactic

113
Q

How can Zr catalysts control stereochem of polymer?

A

C2 symmetric Zr produces isotactic polymers

CS symmetric Zr produces syndiotactic polymers

114
Q

Why does C2 produce isotactice polymers?

A

When it rotates during migratory insertion, there is no change in face configuration

Re face configuration often seen

Has 2 fold rotation axis

115
Q

Why does CS produce syndiotactic polymers?

A

When it rotates during migratory insertion, there is a change in face configuration

Will rotate between re and si

116
Q

Re configuration

A

Is technically clockwise

But is reverse our view, so is actually counterclockwise

117
Q

Si configuration

A

Is technically counterclowise

But is reverse our view, so it actually counterclockwise

118
Q

What is the Homo/Lumo of carbon monoxide?

A

HOMO: Csp3 lone pair

LUMO: pi*CO

119
Q

Why does C2 have no change in face configuration?

A

Two active sites are structurally identical so coordination of the same face is always favored

Methyl is forced down and polymer is forced up

Has 2-fold rotation axis

120
Q

Why is the planar cyclopentadienyl ligand of the zirconium catalyst oriented at a 90° angle to its bond to the metal?

A

Zirconium’s empty d-orbital alligns with cyclopentadienyl’s psi orbitals

the psi orbitals are at a 90º angle from Zr’s d-orbitals

121
Q

Do strained alkenes bind more tightly or less tightly than unstrained alkenes to ligands?

A

Strained alkenes bind more tightly to ligands

122
Q

How can you determine if pH is just going to remain 7.0?

A

when the concentration of the added acid/base is less than 1*10^-7

Water contributes this on its own

123
Q

What are the signs of enthalpy and entropy when water freezes?

A

both negative

bonds are going from more weak in water to stronger in ice so enthalpy is negative

entropy decreases because liquid water is able to move around more than ice

124
Q

What drives the hydrophobic effect?

A

Water molecules are less structured when only around nonpolar molecule than 2

This leads to an increase in entropy in the system

There is no inherent attraction of two nonpolar molecules

125
Q

Hydrophobic effect

A

Refers to the aggregation of nonpolar molecules in water

126
Q

How does pH affect the surface charge of biomolecules?

A

Large biomolecules have regions of weakly acidic and weakly basic groups on their surface

When pH is lower than pKa, more groups will have H+ and have a greater positive charge

When pH is higher than pKa, more groups will not have H+ and will have a greater negative charge

This makes sense that in more acidic environments there is more of a positive charge as electrophiles are normally weakly acidic and positively charged

127
Q

Do strong acids have higher or lower Kas?

A

higher

128
Q

What do you do when you have a weak acid or weak base in a water solution?

A

Subtract “x” and add two “xs” to the otherside to see how many protons dissociated

129
Q

Types of chain transfers

A

Transfer to monomer (active site moves to a new monomer)

Transfer to polymer (intramolecular)

Transfer to solvent

130
Q

What is something to watch for when Ph is involved in polymerizations?

A

May be able to do a hydride shift in order to transfer a charge/radical to be stabilized by resonance

131
Q

Why not use F2 or I2 for alkane halogenation?

A

F2 is too exothermic

I2 forms weak bonds

132
Q

What initiates anionic polymerization?

A

Grinard and organometallics

133
Q

When using Ziegler Natta to synthesize polyethylene what is used as transition metal? What is the initial step?

A

TiCl5

There is a ligand exchange, where a ligand fills empty space and Cl departs which opens up a new empty space

134
Q

Back migration

A

seen when using TiCl5 for Ziegler Natta of polyethylene

after migratory insertion, the growing polymer will go back to its same place

this opens up the same spot on the metal every time for pi complexation to occur at

Chem 204 (1 decks)

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