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CHEM 260 > Second Midterm (part 1) > Flashcards

Second Midterm (part 1) Flashcards

1
Q

Are resonance structures two different molecules?

A

No. A molecule with resonance structures is actually a hybrid between all the resonance structure where nothing is changing

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2
Q

Resonance structures are denoted by a _____ _____ arrow.

A

double headed

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3
Q

Do resonance structures have equal weightings?

A

Sometimes yes, but not always

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4
Q

What is the purpose of curved arrows on a resonance structure?

A

They are to show how we got from one resonance structure to another

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5
Q

Is a resonance structure with charge separation and an incomplete possible?

A

yes

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6
Q

A resonance structure with charge separation is _____ favourable than one without

A

less

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7
Q

A bronsted acid is a _____ _____.

A

proton donor

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8
Q

A bronsted base is a _____ _____.

A

proton acceptor

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9
Q

What is the scale of pKa in water?

A

0-14

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10
Q

The scale of pKa be extend in ____ ____ using extrapolation from ____ to ____

A

organic solvents

-10 to 50

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11
Q

Strong acids have ____ pKa’s

A

low

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12
Q

Weak acids have ____ pKa’s

A

high

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13
Q

The conjugate base of a strong acid is a ____ ____

A

weak base

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14
Q

the conjugate base of a weak acid is a ____ ____

A

strong base

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15
Q

HCl is a ____ acid

A

strong acid

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16
Q

why is HCl a strong acid?

A

because it completely dissociates in water and it conjugate base Cl- is very stable in water

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17
Q

Equilibria will always lie toward the ____ (more ____) acid and base

A

weaker

stable

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18
Q

basicity decreases as you go to the ____ (same row) on the Periodic Table

A

right

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19
Q

More electronegative atoms can hold a negative charge ____ and thus _____ anions or lone pairs

A

better

stabilize

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20
Q

Larger atoms can hold a negative charge ____ since the charge is spread out in a much larger orbital.

A

better

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21
Q

Resonance structures make a molecule ____ stable because the charge is _____.

A

more

delocalized

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22
Q

More electronegative atoms can ____ a negative charge through one or more bonds via “induction”

A

stabilize

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23
Q

A Lewis acid ____ a lone pair

A

accepts

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24
Q

A Lewis base ____ a lone pair

A

donates

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25
Q

___ ____ denote the “motion” of a pair of electrons

A

Curved arrows

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26
Q

Curved arrows denote the ____ or ___ of a covalent bond in a reaction

A

making

breaking

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27
Q

Curved hours always start at a pair of electrons either a ____ ____ or ____ ____

A

lone pair

bonded pair

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28
Q

______ means electron loving

A

electrophile

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29
Q

Electrophiles are ____ ____

A

Lewis Acids

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30
Q

nucleophiles ____ a pair of

electrons to an electrophile to form a new covalent bond

A

donate

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31
Q

Nucleophiles are ____ ____

A

Lewis bases

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32
Q

What do S, N, and 2 stand for in SN2?

A 
S = substitution
N = nucleophilic
2 = bimolecular
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33
Q

The SN2 reaction is bimolecular because the rate of the reaction depends on both the concentration of the ____ and the concentration of the _____: thus, the reaction is said to obey second- order kinetics.

A

nucleophile

electrophile

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34
Q

In SN2 reactions, the electrophilic carbon is said to undergo ____ ____

A

Walden Inversion

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35
Q

The transition state in ___ reactions has no definable lifetime

A

SN2

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36
Q

The SN2 reaction is said to be _____ because the attack by the nucleophile and the departure of the leaving group occur in concert (simultaneously)

A

concerted

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37
Q

Are there any intermediates in an SN2 reaction?

A

No because the reaction occurs in concert

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38
Q

The nucleophile attacks the electrophile from its “_____”

A

backside

39
Q

The substituted alkane is _____ if the electrophilic carbon has 1 R group and 2 H’s

A

1º, primary

40
Q

The substituted alkane is _____ if the electrophilic carbon has 2 R groups and 1 H

A

2º, secondary

41
Q

The substituted alkane is _____ if the electrophilic carbon has 3 R groups and 0 H’s

A

3º, tertiary

42
Q

The size of the R groups attached to a substituted alkane cause ___ ____ to attack by the nucleophile

A

steric hindrance

43
Q

______ electrophiles do not undergo SN2 reactions

A

tertiary

44
Q

____ electrophiles cannot undergo SN1

A

primary

45
Q

Good nucleophiles are compounds that can form good ____ with the backlobe of an electrophilic carbon and ____ a pair of electrons to this orbital.

A

overlap

donate

46
Q

______ refers to how easily the electron density in a orbital can be reshaped by a local charge or dipole

A

Polarizability

47
Q

Conjugate ____ are better nucleophiles than their conjugate ____

A

bases

acids

48
Q

The more polarizable a lone pair is on a molecule the more ____ that molecule will be

A

nucleophilic

49
Q

Nucleophilicity _____ as you go down the Periodic Table due to an increase in polarizability

A

increases

50
Q

Nucleophilicity ____ as you go to the left of the Periodic Table due to decreased nuclear charge

A

increases

51
Q

Electronegative elements produce an inductive effect, which can stabilize _____.

A

anions

52
Q

The more “s-character,” the more the electrons are held close to the nucleus, the tighter they are held, the less available they are for a ____-

A

proton

53
Q

Charges are usually _____

A

unstable

54
Q

SN2 (and SN1) reactions require ____ groups

A

leaving

55
Q

Good leaving groups are those that are ____ ____ ____ with the pair of electrons they have secured from the C–leaving group covalent bond

A

stable in solution

56
Q

Good nucleophiles must also have ____ C–leaving group bonds

A

weak

57
Q

Name 4 good leaving groups

A

I-
Br-
H20
ROH

58
Q

H- (hydride) and R- (carbanions) are ____ leaving groups

A

awful

they are highly unstable

59
Q

for water to leave, one must first create a ____ ____

A

protonated alcohol

60
Q

For an alcohol to leave, one must first create a ____ ____

A

protonated ether

61
Q

Good solvents for SN2 reactions are ___ ____

A

moderately polar

62
Q

If the solvent is too polar in an SN2 reaction, it will _____ the nucleophile too well and tie it up, hindering it from reaction

A

solvate

63
Q

____ ____ solvents enhance SN1 reactions

A

Highly polar

64
Q

____ ____ solvents (e.g., THF, DMSO, DMF) are good for SN2 reactions.

A

Polar aprotic

65
Q

____ solvents are good for SN1 reactions.

A

Protic

66
Q

____ solvents contain a (weakly) acidic hydrogen

A

protic

67
Q

protic solvents can ___ bond

A

hydrogen

68
Q

An ____ solvent does not have an acidic hydrogen

A

aprotic

69
Q

Although most polar solvents can solvate cations (and tie them up) readily, protic solvents are far ___ than aprotic solvents at solvating anions.

A

better

70
Q

Protic solvents ____ SN2 reactions by solvating (tieing-up) nucleophiles which ___ SN2 reactions because the nucleophilicity is a big factor in the
rate-determining (i.e., slowest) step.

A

retard

slows

71
Q

an SN2 mechanism ___ ___ occur at a tertiary center

A

will not

72
Q

SN2 reactions will occur in protic solvents if the electrophilic center is ____, and may to a small extent if the center is ____

A

primary

secondary

73
Q

if a molecule has no stereogenic centers and undergoes an SN2 reaction the products will be ____

A

achiral

74
Q

if a molecule has stereogenic centers but not at the electrophilic carbon and undergoes an SN2 reaction the products will be ____ _____ if the reactants were _____ _____

A

optically pure

optically pure

75
Q

If the electrophilic carbon is the only stereogenic center in a optically pure molecule and the molecule undergoes an SN2 reaction the products will be ____

A

optically pure

76
Q

If a molecule has many stereogenic centers including the electrophilic carbon and the molecule undergoes a SN2 reaction the products will be ____ ____ if the reactants were _____ _____

A

optically pure

optically pure

77
Q

SN1 reactions are _____ meaning the rate is only dependent on the concentration of the electrophile

A

unimolecular

78
Q

the rate of an SN1 reaction is only dependent on the concentration of the ____

A

electrophile

79
Q

How many steps does a SN1 reaction take?

A

two

80
Q

How many steos does a SN2 reaction take?

A

one. It is concert

81
Q

What are the two steps of an SN1 reactions

A
  1. the leaving group leaves, yielding an intermediate called a carbocation
  2. The nucleophile then attacks then carbocation
82
Q

Carbocations are ____ and ____ hybridized

A

planar

sp2

83
Q

the product of an SN1 reaction is a _____ _____

A

racemic mixture

84
Q

What are the best solvents for an SN1 reaction?

A

highly polar protic solvents

85
Q

SN1 reactions do not occur at ____ centers

A

primary

86
Q

SN1 reactions occur at ____ and ____ centers

A

tertiary and secondary

87
Q

The likelyhood of an SN1 reaction occuring is dependent on the stability of the ___ ____ ____

A

carbocation reaction intermediate

88
Q

If you are told that an optically pure reactant with a secondary electrophilic carbon center results in a racemic mixture of racemic mixture of products, what is the reaction mechanism?

A

SN1

89
Q

If you are told that an optically pure reactant with a secondary electrophilic carbon center results in a optically pure product, what is the reaction mechanism?

A

SN2

90
Q

give to examples of a highly polar protic solvent

A

water or alcohol

91
Q

_______ reactions are reactions within a molecule

A

Intramolecular

92
Q

____- reactions are reactions between two molecules.

A

Intermolecular

93
Q

Intramolecular reactions to form 3-6 membered rings are much _____ than intermolecular reactions.

A

faster

CHEM 260 (3 decks)

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