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Chem 202 > Exam 3 > Flashcards

Exam 3 Flashcards

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
Electrophile
species that can accept an electron pair | acids
26
Nucleophile
species that can donate an electron pair | bases
27
Why does a pi-bond make carbonyl groups electrophilic?
pi-bond has a low energy barrier to breaking if the species accepts more electrons
28
Dunitz-Burgi angle
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
29
Where do electrons go when a collision between a carbonyl group and a nucleophile happen?
the pi-bond is broken electrons are placed in the LUMO which is the π* orbital
30
Why is amide less of an electrophile than acid chloride?
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
31
What makes a better leaving group?
want the group to be a weaker base weaker base = lower pKa
32
Do catalysts affect the equilibrium of a reaction?
No they affect the kinetics
33
How does an acid catalyst speed up a reaction?
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
What does a lower pKa indicate?
more acidic greater electrophile (in terms of leaving groups, weaker base and better)
35
What does a higher pKa indicate?
more basic greater nucleophile (in terms of leaving groups, stronger base and worse)
36
What is the first step of using an acid catalyst?
protonate the ester
37
How do you determine where to protonate the ester?
look for the site that is the most basic (nucleophilic) by comparing pKas
38
Steps of acid catalysts
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
If a catalyst increases the forward reaction does it also increase the reverse reaction?
yes
40
What is another term for "addition"?
Nucleophilic attack
41
What will acid catalysts never make?
negatively charged products/intermediates a negative charge would be immediately neutralized by the acid catalyst
42
What will basic catalysts never make?
positively charged products/intermediates a positive charge would be immediately neutralized by the basic catalyst
43
Fisher esterification reaction
the reverse of the acid-catalyzed ester hydrolysis
44
What is the reverse of protonation?
Deprotonation
45
What is the reverse of a nucleophilic attack (addition)?
Departure of the leaving group
46
Fisher esterificiation steps
1. Protonation 2. Addition 3. Deprotonate 4. Protonate 5. Departure of leaving group 6. Deprotonate (form the catalyst)
47
Uphill reaction
a reaction where the products are higher in energy than the reactants
48
Acid-promoted reaction
requires an acid to occur, but the acid is not catalytic nature the acid is not regenerated
49
Example of an acid-promoted reaction
hydrolysis of an amide in acid
50
How many steps do acid-promoted reactions have
6
51
What are acid-promoted reactions similar to?
acid-catalyzed reactions
52
What is specifically different about the final deprotonation step of acid-promoted reactions?
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
What step drives the reaction uphill in the hydrolysis of amide by an acid?
the final deprotonation step this forms an acid that is more stable than the starting acid HCl vs. NH4+
54
Carboxylate anion
carboxylic acid with a deprotonated -OH group
55
In a base promoted reaction what becomes the base?
the carbonyl group
56
In a base promoted reaction is the base conserved?
No It is a promoter, not a catalyst
57
Can a buffer be a strong acid?
No Buffers occur with weak acids and conjugate bases
58
Who discovered aspirin?
German scientist named Hoffman
59
What is the chemical name of aspirin?
acetylsalicylic acid
60
In anhydrides what is the leaving group?
carboxylic acid leaving group of anhydrides will have a pKa~5
61
How to determine which carbonyl group will act as the electrophile and which will act as the nucleophile if there are multiple present?
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
Why are amides hydrolyzed at higher temperatures than esters?
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
What does carboxylic acid and thionyl chloride react to form?
acid chloride SO2 HCl
64
What are some of the steps of acid chloride synthesis?
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
What would be the pH of KCl?
Neutral (7) Because they derive from a strong acid HCl and a strong base KOH this is the same for NaCl
66
What would be the pH of NaOH?
basic
67
What do you do if there is more OH- or H3O+ than weak acid/base in the buffer?
Use the concentration of OH- or H3O+ to calculate pH pH=14-pOH
68
What is the leaving group ability of ROH?
high corresponds to a pKa of <0 because ROH2 is a protonated oxygen which is highly acidic
69
Why do you need to deprotonate at the end of a base promoted reaction?
this is will stabilize the strong base that you used this will also make the carbonyl group more stable
70
Big picture of acid and base-promoted reactions?
makes the products have a lower pKa to drive the reaction
71
Acid-catalyzed reactions
the pKa could still be the same on both sides and K=1, just happens faster catalysts do not change equilibrium constants
72
Greenhouse gases
``` H2O CH4 (methane) Dinitrogen monoxide Sulfure hexaflouride O3 CHF3 (and other hydrofluorocarbons) ```
73
Photochemical smog
NO NO2 O3
74
What is the rate of a chemical reaction?
change in concentration (M) over time (s)
75
Why is fluoride the most acidic of the halogens?
it is the most electronegative pulls the electrons the most and creates largest partial positive on the carbon
76
Acetate
CH3COO-
77
Acetic acid
CH3COOH

Chem 202 (7 decks)

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