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CHEM 1570: Intro to Organic and Biological Chemistry > Prelim 3 > Flashcards

Prelim 3 Flashcards

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1
Q

If you have two thermodynamic graphs, which would be the one showcasing the faster/fastest reaction?

A

The graph where the highest hill is the lowest in comparison to the other graphs.

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2
Q

What is the activation energy barrier?

A

The activation energy barrier is the energy threshold that must be crossed in order to start a reaction.

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3
Q

What does the activation energy barrier do?

A

The activation energy barrier determines the rate of reaction.

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4
Q

Where is the activation energy barrier on a thermodynamics graph?

A

The activation energy barrier refers to the area on the graph from the start of the graph to the peak of the highest hill.

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5
Q

What does it mean for a reaction to be fast?

A

It has a lower activation energy barrier. (lower hump).

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6
Q

What does it mean for a reaction to be slow?

A

It has a higher activation energy barrier. (taller hump)

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7
Q

What is equilibrium?

A

The point at which the reaction has come to a stop.

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8
Q

At equilibrium, Keq=

A

products/reactants

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9
Q

At equilibrium, Keq=

A

products/reactants

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10
Q

At equilibrium, when Keq > 1

A

Products are favored/ More products than reactants

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11
Q

At equilibrium, when Keq < 1

A

Reactants are favored/ More reactants than products

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12
Q

How to determine the position of equilibrium in a thermodynamics graph?

A

By looking at relative heights of the reactants to products.

  • When the activation energy is higher going from
    reactants to products, Keq < 1: reactants are favored
  • When the activation energy is higher going from
    products to reactants, Keq > 1: products are favored
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13
Q

What does Markovnikov’s Rule state?

A

The reaction will always form the most stable carbonation b/c that is faster than forming a less stable carbocation and requires less energy.

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14
Q

In a multi-step reaction, where is the 1st transition state?

A

Peak of the first hill

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15
Q

In a multi-step reaction, where is the subsequent transition states?

A

From the reaction intermediate (there can be more than one), to the peak of the hill immediately following it.

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16
Q

In a multi-step reaction, where are the reaction intermediates?

A

Reaction intermediates are located in the divets of the graph

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17
Q

What does Ea1 stand for?

A

Activation energy barrier 1.

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18
Q

Can a reaction have more than 1 activation energy barrier?

A

Yes, in multi-step equations there can be more than one activation energy barrier
Ex:
Ea1, Ea2, Ea3…

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19
Q

What do the different activation energy barriers for a multi-step reaction determine?

A

The different activation energy barriers of a multi-step reaction determine the rate of reaction for each step.

Ex:
Ea1 determines the rate of reaction for step 1

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20
Q

What is needed in order to go over the intermediate in multi-step reactions?

A

The first step must be slow

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21
Q

If Ea1 > Ea2, what does that mean

A

Step 1 is slower than step 2

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22
Q

What is a step?

A

Going over one hill

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23
Q

What is the name of the slow step?

A

Rate determining/rate-limiting step

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24
Q

What is true about the speed of reactions in multi-step reactions?

A

The reaction cannot go faster than its slowest step.

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25
Q

What do catalysts do?

A

Accelerate reactions/ make reactions go faster.

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26
Q

How do catalysts make accelerate reactions?

A
  1. Stabilizing transition states
  2. Provides an alternate reaction pathway
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27
Q

How do you stabilize transition states?

A

First, you lower the energy of the transition state and that will lower the activation energy barrier.

28
Q

What don’t catalysts do?

A

Catalysts do not alter the position of equilibrium.

29
Q

What is a base?

A

Anything w/ a lone pair that can steal a proton/ H+. Basically, an H+ acceptor.

30
Q

What is the transition state?

A

The place in a reaction where bonds are breaking and forming.

31
Q

During the transition state, where does the atom/molecule being transferred lie?

A

It will lie wherever it is closet to in energy. If the transition state is closet to reactants, to will lie next to the reactants. If the transition state is closer to products, it will lie next to products.
Ex:
[H3C(O)OH….H+…………NH3]

32
Q

What does the Hammond Postulate state?

A

The Hammond Postulate states that the transition state looks more like whichever compound it is closet to in energy.

33
Q

What is the difference between an intermediate and a transition state?

A

An intermediate is a physical step in a reaction. If you were to stop a reaction at the intermediate, it will exist. However, at the transition state, the breaking and forming of bonds occur simultaneously, so there is no set molecule present.

34
Q

What is an acid?

A

An H+ donor. Acids have a free H+ to donate.

35
Q

What are conjugate acid-base pairs?

A

If a reaction is at equilibrium, it can go both forwards and backward. A conjugate acid-base pair refers to a molecule that acts as a base in one direction and as an acid in the other.

Ex: NH3/ N+H4
It is a base, as it has a free lone pair to accept an H+. However, once it accepts the H+ and becomes N+H4, it becomes an acid, as it has a free H+ to donate.

36
Q

What is pKa?

A

pKa is the measure of acid strength. Basically, you are looking at how easy/hard it is for a acid to give up its proton (H+).

37
Q

What makes an acid a weak acid?

A

Weak acids are not good at giving up their protons.

38
Q

What makes an acid a strong acid?

A

Strong acids are good at giving up their protons.

39
Q

What is the position of equilibrium?

A

The position of equilibrium is a measure used to determine if there are mostly products or reactants at equilibrium.

40
Q

How do you determine the position of equilibrium>

A

You determine the position of equilbirum using pKa.

41
Q

What does a lower pKa mean?

A

A lower pKa is a stronger acid

42
Q

What does a lower pKa mean for equilibrium?

A

For equilibrium, if you have a lower pKa, that means equilibrium lies towards the side where the acid gives up its proton.

43
Q

What does a lower pKa mean for protonation/deprotonation?

A

A lower pKa means that there is a larger % of the molecule deprotonated at equilibrium

44
Q

What does protonation mean?

A

Gaining a proton/protons

45
Q

What does deprotonation mean?

A

Losing a proton/protons

46
Q

What happens to the protonation of a molecule if the pH of a solution is greater than the pKa of a molecule?

A

The molecule is predominantly deprotonated

47
Q

What happens to the protonation of a molecule if the pH of a solution is < the pKa of a molecule?

A

The molecule is predominately protonated

48
Q

What happens to the protonation of a molecule if the pH of a solution is equal to the pKa of the molecule?

A

The molecule is 50% protonated and 50% deprotonated.

49
Q

What is the charge of protonated amine bases?

A

Positive

50
Q

What is the charge of deprotonated amine bases?

A

Neutral

51
Q

What is the charge of protonated acids?

A

Neutral

52
Q

What is the charge of deprotonated acids?

A

Negative

53
Q

What does the Rule of 9s state?

A

The Rule of 9s states that for every unit you move away from the pKa, you add a 9 to the percentage of protonation/deprotonation.

Ex: The pKa of a molecule is 6.4
- The pH one unit away is 7.4, so the molecule will be 90% protonated or deprotonated

54
Q

In general, what types of molecules can cross membranes?

A

Neutral/uncharged molecules, charged molecules cannot, so specific pHs are required

55
Q

What is the pKa cutoff of acids?

A

~5 or less

56
Q

What is the protonation of acids at a pH of 7.4 (healthy human blood)?

A

Nearly 100% deprotonated and negatively charged.

57
Q

What is the pKa cutoff of bases?

A

~8 or more

58
Q

What is the protonation of bases at a pH of 7.4 (healthy human blood)?

A

Predominantly protonated and positively charged, but there is a smaller percentage that is neutrally charged

59
Q

If a molecule requires the input of energy to deprotonate, what does that say about its acid strength?

A

It is a weak acid.

60
Q

If a molecule results in the release of energy upon deprotonation, what does that say about its acid strength?

A

It is a strong acid.
It will result in the largest concentration of H+

61
Q

How are kinetic products identified?

A

Kinetic products are identified due to a change in activation energy.

62
Q

How are thermodynamic products identified?

A

Thermodynamic products are identified due to a change in its final energy.

63
Q

In CAIRO, what is the purpose of A?

A

A - Atom
Basically, whenever the charges are balanced between two conjugate bases, identify the atom that has the most sensible charge.

Ex: Between O and N, it would be more stabilized and have less energy for the negative charge to be on O instead of N

64
Q

In CAIRO, what is the purpose of C?

A

C- Charge
Basically, when you are looking at conjugate bases, examine the difference in charges.

Ex: Neutral charges are more stable than negative charges. Negative charges are more stable than positive charges hen trying to act as a base (H+ acceptor).

65
Q

In CAIRO, what is the purpose of R?

A

R- Resonance
Basically, when you are looking at conjugate bases, you want to examine two things:
1. Whether resonance structures are possible to be
drawn for all conjugate bases. If resonance is possible, that means that the conjugate base is resonance stabilized and lower energy.

  1. If all conjugate bases are able to participate in resonance, then you will examine how resonance stabilization occurs. If the conjugate base is resonance stabilized across multiple atoms, especially if their different, then that is higher energy and less stable, than if it was resonance stabilized across one atom or the same type of atom.
66
Q

What is the isoelectric point?

A

pI

67
Q

What does pI mean?

A

The point at which the average net charge is = to 0.

CHEM 1570: Intro to Organic and Biological Chemistry (4 decks)

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