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Chem 202 > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

What are the two possible ways to create a buffer?

A
  1. Add conjugate acids and bases

2. Add strong acid/base as limiting reagent. Will leave leftover acid or base reactant and will generate conjugate

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2
Q

What should you do when you see a dilution?

A

Consider using M1V1 = M2V2

*look at the context

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3
Q

Buffer

A

mixture of weak acid and weak conjugate base

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4
Q

What must the ratio weak acid : weak base for it to be a buffer?

A

10:1 or lower

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5
Q

Major species

A

species present in high enough concentration to affect the pH

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6
Q

Order from most to least reactive carbonyl groups (general)

A
  1. Acid chloride
  2. Anhydride
  3. acid sulfide ?
  4. carboxylic acid (or Oxygen binded to anything besides H as well)
  5. amide
  6. deprotonated carboxylic acid (O-)
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7
Q

Anhydride

A

symmetric looking carbonyl group with two double bonded oxygens and an oxygen connecting them

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8
Q

Amide

A

carbonyl group with nitrogen

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9
Q

Why can a carbonyl compound be electrophilic?

A

the double bonded oxygen is highly electrophilic and pulls electrons towards it, creating a dipole

this leaves the carbon slightly positive and therefore, electrophilic

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10
Q

Mechanism

A

step by step sequence of elementary reactions that lead to an overall chemical change

a sequence of events where electrons are transferred

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11
Q

Reaction pathway

A

reaction coordinate diagram that plots change in free energy over the progress of the reaction

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12
Q

Transition state

A

the state just before the formation of new molecules

high in energy

making and breaking of bonds is occurring simultaneously

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13
Q

Intermediate

A

a reactive species formed during the reaction

lower in energy than the transition state

often we make tetrahedral intermediates on the central carbon in the carbonyl group

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14
Q

Formaldehyde

A

simplest neutral carbonyl compound

carbon double bonded to oxygen and 2 hydrogens

reactive because their LUMO is a pi-bond

a pi-bond is easier to break than a sigma-bond, so they are more reactive

??

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15
Q

LUMO

A

lowest energy unoccupied molecular orbital

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16
Q

Molecular orbital diagram difference with valence bond theory

A

valence bond theory just works with atoms, while the molecular orbital diagram works with ~molecules~

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17
Q

Constructive interference

A

when two orbitals are in the same phase and their waves overlap to form a bond

(two positive humps on graph)

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18
Q

Destructive interference

A

when two orbitals are in different phases and their waves do not form a bond

phases cancel eachother out

(negative and positive humps on graph)

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19
Q

Aufbau’s principle and the molecular orbital diagram

A

Aufabu tells us that the lowest level energy orbital will be filled first, so that is why we fill bonding orbitals and not antibonding orbitals

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20
Q

What is higher in energy antibonding or nonbonding orbital?

A

Antibonding

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21
Q

What is nonbonding orbital?

A

There is no interaction between the two orbitals of separate atoms

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22
Q

Steric hinderance

A

the stopping of a chemical reaction due to size or structure

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23
Q

Why are aldehydes more reactive than ketones?

A

Aldehydes have a relatively small hydrogen group and a R-group, while as ketones have two large R-groups

This makes steric hindrance less in ketones

Overall, aldehydes are more reactive than ketones

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24
Q

Two reasons why a carbonyl group is electrophilic

A

1) pi-bonds

2) polarity

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25
Q

Electrophile

A

species that can accept an electron pair

acids

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26
Q

Nucleophile

A

species that can donate an electron pair

bases

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27
Q

Why does a pi-bond make carbonyl groups electrophilic?

A

pi-bond has a low energy barrier to breaking if the species accepts more electrons

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28
Q

Dunitz-Burgi angle

A

the orientation that the nucleophile must have in order to collide with the carbonyl group

about 105º to 110º

it is very close to a tetrahedral angle

makes sense since a tetrahedral intermediate is formed

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29
Q

Where do electrons go when a collision between a carbonyl group and a nucleophile happen?

A

the pi-bond is broken

electrons are placed in the LUMO which is the π* orbital

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30
Q

Why is amide less of an electrophile than acid chloride?

A

both amide and acid chloride have a second resonance structure in the carbonyl group

however, chloride is located in the 3rd period of the periodic table and nitrogen is located in the 2nd

when 2p carbon overlaps with 3p chloride, it is not as direct as nitrogen 2p and carbon 2p

this stabilizes nitrogen through resonance more and makes less reactive, and less of an electrophile

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31
Q

What makes a better leaving group?

A

want the group to be a weaker base

weaker base = lower pKa

32
Q

Do catalysts affect the equilibrium of a reaction?

A

No

they affect the kinetics

33
Q

How does an acid catalyst speed up a reaction?

A

Makes the carbonyl group a better electrophile

Protonates the oxygen

Oxygen pulls electron density even more, creating a larger dipole

The carbon becomes even more slightly positive

34
Q

What does a lower pKa indicate?

A

more acidic

greater electrophile

(in terms of leaving groups, weaker base and better)

35
Q

What does a higher pKa indicate?

A

more basic

greater nucleophile

(in terms of leaving groups, stronger base and worse)

36
Q

What is the first step of using an acid catalyst?

A

protonate the ester

37
Q

How do you determine where to protonate the ester?

A

look for the site that is the most basic (nucleophilic) by comparing pKas

38
Q

Steps of acid catalysts

A
  1. Protonate
  2. Addition
  3. Deprontonate (also remakes catalyst)
  4. Protonate (normally the leaving group)
  5. Departure of leaving group
  6. Deprotonate (remakes catalyst)
39
Q

If a catalyst increases the forward reaction does it also increase the reverse reaction?

A

yes

40
Q

What is another term for “addition”?

A

Nucleophilic attack

41
Q

What will acid catalysts never make?

A

negatively charged products/intermediates

a negative charge would be immediately neutralized by the acid catalyst

42
Q

What will basic catalysts never make?

A

positively charged products/intermediates

a positive charge would be immediately neutralized by the basic catalyst

43
Q

Fisher esterification reaction

A

the reverse of the acid-catalyzed ester hydrolysis

44
Q

What is the reverse of protonation?

A

Deprotonation

45
Q

What is the reverse of a nucleophilic attack (addition)?

A

Departure of the leaving group

46
Q

Fisher esterificiation steps

A
  1. Protonation
  2. Addition
  3. Deprotonate
  4. Protonate
  5. Departure of leaving group
  6. Deprotonate (form the catalyst)
47
Q

Uphill reaction

A

a reaction where the products are higher in energy than the reactants

48
Q

Acid-promoted reaction

A

requires an acid to occur, but the acid is not catalytic nature

the acid is not regenerated

49
Q

Example of an acid-promoted reaction

A

hydrolysis of an amide in acid

50
Q

How many steps do acid-promoted reactions have

A

6

51
Q

What are acid-promoted reactions similar to?

A

acid-catalyzed reactions

52
Q

What is specifically different about the final deprotonation step of acid-promoted reactions?

A

the leaving group acts as the base to deprotonate the carbonyl group

the conjugate base of the acid does not since it is not reformed

53
Q

What step drives the reaction uphill in the hydrolysis of amide by an acid?

A

the final deprotonation step

this forms an acid that is more stable than the starting acid

HCl vs. NH4+

54
Q

Carboxylate anion

A

carboxylic acid with a deprotonated -OH group

55
Q

In a base promoted reaction what becomes the base?

A

the carbonyl group

56
Q

In a base promoted reaction is the base conserved?

A

No

It is a promoter, not a catalyst

57
Q

Can a buffer be a strong acid?

A

No

Buffers occur with weak acids and conjugate bases

58
Q

Who discovered aspirin?

A

German scientist named Hoffman

59
Q

What is the chemical name of aspirin?

A

acetylsalicylic acid

60
Q

In anhydrides what is the leaving group?

A

carboxylic acid

leaving group of anhydrides will have a pKa~5

61
Q

How to determine which carbonyl group will act as the electrophile and which will act as the nucleophile if there are multiple present?

A
  1. Determine the strongest electrophile by looking for the leaving group with the lowest pKa (strongest base)
  2. Then, determine the nucleophile by looking for the oxygen with the highest Pka (strongest base =strongest nucleophile)
62
Q

Why are amides hydrolyzed at higher temperatures than esters?

A

There is greater delocalization between the C-N than the C-O

This stabilizes the amide

Need more energy to overcome the activation barrier

63
Q

What does carboxylic acid and thionyl chloride react to form?

A

acid chloride

SO2

HCl

64
Q

What are some of the steps of acid chloride synthesis?

A
  1. Follow dipoles (double bonded Oxygen pulls S)
  2. Neutralize the Sulfur
  3. Use Cl- to attack carbonyl
  4. Resonant through Oxygen to kick off Cl- and SO2
  5. Use Cl- to deprotonate oxygen
65
Q

What would be the pH of KCl?

A

Neutral (7)

Because they derive from a strong acid HCl and a strong base KOH

this is the same for NaCl

66
Q

What would be the pH of NaOH?

A

basic

67
Q

What do you do if there is more OH- or H3O+ than weak acid/base in the buffer?

A

Use the concentration of OH- or H3O+ to calculate pH

pH=14-pOH

68
Q

What is the leaving group ability of ROH?

A

high

corresponds to a pKa of <0 because ROH2 is a protonated oxygen which is highly acidic

69
Q

Why do you need to deprotonate at the end of a base promoted reaction?

A

this is will stabilize the strong base that you used

this will also make the carbonyl group more stable

70
Q

Big picture of acid and base-promoted reactions?

A

makes the products have a lower pKa to drive the reaction

71
Q

Acid-catalyzed reactions

A

the pKa could still be the same on both sides and K=1, just happens faster

catalysts do not change equilibrium constants

72
Q

Greenhouse gases

A 
H2O
CH4 (methane)
Dinitrogen monoxide
Sulfure hexaflouride
O3
CHF3 (and other hydrofluorocarbons)
73
Q

Photochemical smog

A

NO
NO2
O3

74
Q

What is the rate of a chemical reaction?

A

change in concentration (M) over time (s)

75
Q

Why is fluoride the most acidic of the halogens?

A

it is the most electronegative

pulls the electrons the most and creates largest partial positive on the carbon

76
Q

Acetate

A

CH3COO-

77
Q

Acetic acid

A

CH3COOH

Chem 202 (7 decks)

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