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Organic Chemistry > Ch. 6 – Organic Reactions > Flashcards

Ch. 6 – Organic Reactions Flashcards

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1
Q

T/F: When two ions with unlike charge bond, an ionic bond is always formed.

A

False. Many organic reactions involve the combination of two ions that form a covalent bond. For example, if a carbocation is attracted to an ion with a negatively charged oxygen atom, the oxygen will contribute two bonding electrons to the carbon, and a covalent bond will be formed.

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2
Q

Why are reagents often drawn on top of arrow?

A

to focus on organic starting materials

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3
Q

Where is the solvent or temp of a reaction added in an equation?

A

above or below arrow

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4
Q

What is the symbol for light?

A

hv

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5
Q

What is the symbol for heat?

A

∆

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6
Q

What do numbers above or below the arrow signal?

A

sequential steps of a reaction

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7
Q

T/F: Organic byproducts are often omitted.

A

True

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8
Q

What occurs during a substitution reaction?

A

atom/group is replaced by another atom/group

one sigma bond breaks, another one forms

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9
Q

When do substitution reactions most likely occur?

A

most commonly occur when a heteroatom more EN than carbon replaces a hydrogen

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10
Q

What occurs during an elimination reaction?

A

elements of starting materials are lost

2 sigma bonds are broken, one pi bond is formed

(two groups removed)

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11
Q

When does elimination reaction most commonly occur?

A

when one group is hydrogen and another group on adjacent carbon is a heteroatom more EN than carbon

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12
Q

What occurs during an addition reaction?

A

elements are added to starting materials

a pi bond is broken and two sigma bonds form

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13
Q

What is a reaction mechanism?

A

detailed description of how bonds are broken and formed as starting materials are converted to products

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14
Q

What is a concerted reaction?

A

a one-step reaction

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15
Q

What is a stepwise reaction?

A

A multiple-step reaction where starting materials are converted to unstable intermediates (reactive) and then form product

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16
Q

What is bond cleavage?

A

breaking of a bond, electrons can either be divided equally or unequally between two atoms of the bond

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17
Q

What is homolytic cleavage?

A

equal dividing of electrons (each atom gets one electron)

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18
Q

What does homolysis generate?

A

uncharged reactive intermediates with unpaired electrons

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19
Q

What is heterolytic cleavage?

A

unequal dividing of electrons (each atom gets both or none electrons)

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20
Q

Where do electrons go in heterolysis?

A

usually to more EN atom

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21
Q

What does heterolysis generate?

A

charged intermediates that are reactive

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22
Q

What are fishhook arrows?

A

used to show movement of one electron

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23
Q

What are radicals?

A

reactive intermediates with a single unpaired electron

generated by homolysis, highly unstable, no charge

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24
Q

What is a carbocation?

A

electrophile carbon with plus charge (electron deficient)

result of heterolysis where electrons go to more EN heteroatom

+ intermediate, unstable, reactive

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25
Q

What is a carbanion?

A

nucleophile carbon with negative charge (electron rich)

has lone pair of e- (- intermediate, reactive, unstable)

generated by heterolysis where two electrons are given to C and none are given to heteroatom

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26
Q

Are radicals, carbocations and carbanions electrophilic or nucleophilic?

A

electrophilic: radials and carbocations
nucleophilic: carbanions

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27
Q

Does forming bonds absorb or release energy?

A

bond formation ALWAYS RELEASES energy

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28
Q

What is bond dissociation energy? What is symbol?

A

energy needed to homolytically cleave a covalent bond

∆Hº

BDE is always positive!

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29
Q

What is enthalpy? What is symbol?

A

∆Hº

energy absorbed or released in a reaction

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30
Q

What is a positive/negative ∆Hº indicate?

A 
positive = endothermic
negative = exothermic
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31
Q

How does BDE change with bond strength?

A

as bond strength increases, BDE increases

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32
Q

How does BDE change with ptable?

A

going down ptable, atom size increases and BDE decreases

33
Q

How does BDE change with % s character?

A

as % s character increases, so does BDE

34
Q

How is BDE determined for a reaction?

A

∆Hº = (sum of bonds broken) + (sum of bonds formed (-))

35
Q

What are the limitations of BDE?

A

only give overall energy change
don’t give info about reaction mechanism
only for gas phase

36
Q

What is thermodynamics?

A

relation of energy and equilibrium

37
Q

What is kinetics?

A

reaction rates

38
Q

How is Keq calculated?

A

[products]/[reactants]

39
Q

What does Keq>1 mean?

A

products are favored

40
Q

What does Keq<1 mean?

A

reactants favored

41
Q

What determines the positive of equilibrium?

A

relative energies of reactants and products

42
Q

What is Gibbs Free Energy?

A

free energy in a molecule (Gº)

43
Q

What does ∆Gº represent?

A

overall E difference between R and P

44
Q

How is ∆Gº calculated?

A

Gº products – Gº reactants

or

-2.303RT log Keq

45
Q

What does it mean if ∆Gº is positive or negative?

A

positive: Keq < 1, endothermic, reactants favored
negative: Keq > 1, exothermic, products favored

46
Q

When does equilibrium favor products?

A

when Keq > 1 and when products are more stable (have less E) than reactants

47
Q

What is entropy?

A

measure of a system’s disorder

48
Q

What causes higher entropy? (five factors)

A

1) more freedom of motion
2) more disorder
3) gas > liquid > solid
4) acyclic > cyclic
5) more than one product

49
Q

What is ∆Sº?

A

change in disorder/entropy between R and P

50
Q

What does positive/negative ∆Sº mean?

A

positive: products more disordered
negative: reactants more disordered

51
Q

Is positive or negative ∆Sº reaction favored?

A

positive, nature favors disorder

52
Q

How is ∆Gº calculated including entropy?

A

∆Gº = ∆Hº – T∆Sº

53
Q

What contributes to total energy change for reaction?

A

change in bonding E, change in disorder

54
Q

How does temperature affect ∆Sº?

A

at high T, entropy is small compared to ∆Hº and can be neglected

55
Q

What does negative/positive ∆Hº signal?

A

positive: starting materials favored (endothermic)
negative: products favored (exothermic)

56
Q

What is an energy diagram?

A

represents E change when R becomes P

57
Q

What is a transition state?

A

unstable energy max where bonds are partially broken and formed; can never be isolated, caused by e-e repulsion in cloud when atoms get too close (high energy)

58
Q

What is activation energy?

A

E difference between starting materials and transition state (minimum amount of energy needed to break R bonds)

59
Q

How are transition states drawn?

A

in brackets, partial bonds and charges, add double dagger to outside bracket

60
Q

How many humps are in a multistep reaction?

A

humps = number of steps

61
Q

In energy diagram, what is rate-determining step?

A

step with highest Ea

62
Q

What is the reaction rate?

A

how fast a reaction proceeds

63
Q

What does a larger Ea mean for reaction rate?

A

larger Ea = slower reaction

64
Q

How does concentration affect reaction rate?

A

higher concentration = faster rate

65
Q

How does temp affect reaction rate?

A

higher temp = faster rate

66
Q

How many degrees increase (in ºC) are needed to double reaction rate?

A

10 ºC

67
Q

What is a rate law?

A

shows relationship between reactant concentration and reaction progress

68
Q

What is rate law equation?

A

rate = k[reactants]

69
Q

How does size of k affect rate?

A

large k = fast

small k = slow

70
Q

For multistep reaction, which reactants should be put in rate law?

A

those included in rate-determining step

71
Q

What is a bimolecular reaction?

A

reaction with 2 reactants

72
Q

What is the order of a reaction (kinetics)?

A

sum of exponents of concentration terms

73
Q

How are exponents determined for rate law?

A

experimentally

74
Q

What is a unimolecular reaction?

A

reaction involving only one reactant

75
Q

What is a catalyst?

A

a substance that speeds up a reaction rate and does not change during a reaction, not a product

76
Q

Where are catalysts written in rxn equation?

A

above or below arrow

77
Q

Does a catalyst affect Keq?

A

nope

78
Q

What are enzymes?

A

biochemical catalysts composed of amino acids held together in very specific 3D shape, have active site

Organic Chemistry (26 decks)

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