MIDTERM Flashcards Preview

CHEM 353 > MIDTERM > Flashcards

Flashcards in MIDTERM Deck (140):
1

What is the approximate pKa of an alkane (sp3 C-H)?

60+

2

What is the approximate pKa of an alkene (sp2 C-H)?

45

3

What is the approximate pKa of an alkyne (sp C-H)?

25

4

Why are alkynes more acidic than alkenes and alkenes are more acidic than alkanes?

The more s character in the orbital, the closer the electrons will be to the nucleus. The H will be slightly + and will be easier to pull away.

(alkanes are sp3 C-H → 25% s character)

(alkenes are sp2 C-H → 33% s character)

(alkynes are sp C-H → 50% s character)

5

What is the approximate pKa of ammonia (NH3) and amines (R-NH2)?

35

6

It is important to note that alkynes (sp C-H) have a pKa of 25 and are more acidic than _________________ which have a pKa of 35

ammonia (NH3) and amines (R-NH2)

7

What is the approximate pKa of H2O?

15

8

What is the approximate pKa of alcohols (R-OH)?

15

9

H2O has the same pKa as _____________

alcohols (R-OH)

10

What is the approximate pKa of phenols (Ar-OH)?

10

11

Which is more acidic: alcohols (R-OH) or phenols (Ar-OH)?

phenols (Ar-OH) are more acidic because their pKa value is 10, which is lower than the pKa value of 15 associated with alcohols (R-OH)

12

What is the approximate pKa of ammonium (NH4+/R-NH3+)?

10

13

Which is more acidic: ammonia (NH3) and amides (R-NH2) or ammonium (NH4+/R-NH3+)?

ammonium (NH4+/R-NH3+) is more acidic because its pKa value of 10 is lower than the pKa value of 35 associated with ammonia (NH3) and amides (R-NH2)

14

What is the approximate pKa of thiols (R-SH)?

10

15

Which is more acidic: alcohols (R-OH) or thiols (R-SH)?

thiols (R-SH) are more acidic because they have a pKa value of 10, which is lower than the pKa value of 15 associated with alcohols (R-OH)

16

What is the approximate pKa of carboxylic acids (R-CO2H)?

5

17

What is the approximate pKa of hydronium ions (H3O+)?

-2

18

What is the hydrogen halide (HX) that is a weaker acid than hydronium ions (H3O+)?

HF because its pKa of 2 is larger than the pKa of -2 associated with hydronium ions (H3O+)

 

19

What is the strongest acid listed on the pKa ladder with a pKa of -10?

sulfuric acid (H2SO4)

20

What are the hydrogen halides (HX) that are stronger acids than hydronium ions (H3O+)?

hydroiodic acid (HI), hydrobromic acid (HBr) and hydrochloric acid (HCl)

21

List the 3 hydrogen halides (HX) that are stronger acids than hydronium ions (H3O+) in order of increasing acidity

HCl < HBr < HI

22

What happens when an alkene reacts with H2SO4 in the presence of H2O?

the double bond becomes a single bond and OH is bonded to the more substituted carbon

A image thumb
23

What happens when an alkyne reacts with H2SO4 in the presence of H2O and a metal ion catalyst?

triple bond becomes single bond and O is double bonded to the more substituted carbon

A image thumb
24

Reacting an alkene with H2SO4 in the presence of H2O will yield a(n) ____________

alcohol

A image thumb
25

Reacting an alkyne with H2SO4 in the presence of H2O and a metal ion catalyst will yield a(n) ____________

ketone

A image thumb
26

_________ position: on the carbon in the double bond of an alkene

Q image thumb

vinylic

27

_________ position: on the atom next to a carbon in the double bond of an alkene

Q image thumb

allylic

28

This is called the _______ group

Q image thumb

allyl

29

The carbons in red are __________ whereas the carbon in green is __________

Q image thumb

red = vinylic carbons (on the double bond)

green = allylic carbon (next to the double bond)

A image thumb
30

The atoms shown in red are considered to be __________ substituents

Q image thumb

vinylic 

(vinylic substituents are attached to vinylic carbons)

A image thumb
31

The atoms shown in green are considered to be __________ substituents

Q image thumb

allylic 

(allylic substituents are attached to allylic carbons)

A image thumb
32

___________ reactions are characterized by the solvent acting as the electron-rich nucleophile

solvolytic

33

In solvolysis, the solvent acts as the ____________

nucleophile

34

What type of mechanism do solvolysis reactions undergo?

substitution - SN1

35

Which would undergo solvolysis faster: a 3º allylic halide or a simple 3º alkyl halide? Why?

Q image thumb

the 3º allylic halide would undergo solvolysis faster because there's resonance stabilization of the carbocation intermediate (the reaction is SN1)

A image thumb
36

Which is more stable: a 3º allylic carbocation or a simple 3º carbocation? Why?

Q image thumb

the 3º allylic carbocation is more stable due to resonance

A image thumb
37

A pi bond is the result of sideways overlap of 2 ____________ p orbitals

unhybridized

38

The _____________ of a reaction dictates where it will react

regioselectivity

39

The _____________ of a reaction dictates how it will react in terms of 3D space

stereoselectivity

40

A conjugated alkene has ___________ double bonds

adjacent

41

Explain why these molecules are conjugated

Q image thumb

they have resonance forms that are conjugated

42

The Diels-Alder reaction is a conjugate addition reaction of a ______________ to an _________ to produce a cyclohexene

Q image thumb

conjugated diene

alkene

A image thumb
43

In a Diels-Alder reaction, the alkene is called the __________

dienophile

44

What is the product in a Diels-Alder reaction?

a cyclohexene

45

This molecule is an example of a(n) __________ diene

Q image thumb

isolated

46

This molecule is an example of a(n) ___________ diene

Q image thumb

cumulated

47

Since the Diels-Alder reaction forms a cyclic product, via a cyclic transition state, it can also be described as a _____________

cycloaddition

48

TRUE OR FALSE - the Diels-Alder reaction is a concerted process

TRUE

A image thumb
49

Why is the Diels-Alder reaction thermodynamically favourable?

it converts 2 pi bonds into 2 new, stronger sigma bonds

50

In the Diels-Alder reaction, the dienophile is _____________ and the diene is ______________

electrophilic

nucleophilic

 

51

Due to the Diels-Alder reaction having a converted mechanism, the addition is ______ on both components

syn

52

What favours the Diels-Alder reaction?

electron withdrawing groups on the electrophilic dienophile and electron donating groups on the nucleophilic diene

53

In the stereospecific Diels-Alder reaction, what happens with a cis-dienophile?

Q image thumb

cis-substituents in the product

A image thumb
54

In the stereospecific Diels-Alder reaction, what happens with a trans-dienophile?

Q image thumb

trans-substituents in the product

A image thumb
55

In the stereospecific Diels-Alder reaction, what happens with a diene whose substituents have the same stereochemistry (both E or both Z)?

Q image thumb

both diene substituents end up on the same face of the product

A image thumb
56

In the stereospecific Diels-Alder reaction, what happens with a diene whose substituents have the opposite stereochemistry (one E and one Z)?

Q image thumb

the diene substituents end up on opposite faces of the product

A image thumb
57

In the Diels-Alder reaction, ___________ can give stereoisomeric products 

cyclic dienes

58

In the Diels-Alder reaction, if the cyclic diene and dienophile are aligned directly over each other, it gives the ______ product  

Q image thumb

endo

59

In the Diels-Alder reaction, if the cyclic diene and dienophile are staggered, it gives the ______ product  

Q image thumb

exo

60

In a Diels-Alder reaction with a cyclic diene, when the dienophile is "under" in the product, it is called the _______ product

Q image thumb

endo

61

In a Diels-Alder reaction with a cyclic diene, when the dienophile is "out" in the product, it is called the _______ product

Q image thumb

exo

62

A carbonyl group (such as in an ester) is electron __________

withdrawing

63

An alkoxy group (such as in an ether) is electron ___________

donating

64

Can methyl shifts happen when reacting an alkene with aq. H2SO4? Why?

yes

reaction proceeds via a carbocation intermediate

65

In the reaction of an alkene with a hydrogen halide (HX), the rate is controlled by the rate of carbocation formation. Therefore, the stronger the _______, the faster the reaction

acid

66

What was the most reactive with sodium borohydride: esters, ketones or aldehydes?

aldehydes

67

What didn't react with sodium borohydride: esters, ketones or aldehydes?

esters

68

Which had an intermediate reaction speed when reacted with sodium borohydride: esters, ketones or aldehydes?

ketones

69

What are tautomers?

constitutional isomers that exist together in equilibrium and readily interconvert

70

This molecule is an example of a(n) _________

Q image thumb

enol

71

Hydroboration-oxidation is a two-step reaction sequence. Name the steps.

 
  1. BH3
  2. aq. NaOH, H2O2

 

 

72

What happens when a terminal alkyne undergoes acid catalyzed hydration (react with H3O+, HgSO4)?

Q image thumb

methyl ketone is the major product (follows Markovnikov's rule)

A image thumb
73

What happens when an unsymmetrical, internal alkyne undergoes acid catalyzed hydration (react with H3O+, HgSO4)?

Q image thumb

mixture of ketone products

A image thumb
74

TRUE OR FALSE - in hydroboration - oxidation (1. BH3 2. aq. NaOH, H2O2), the regioselectivity is anti-Markovnikov

TRUE

75

What happens when a terminal alkyne undergoes hydroboration - oxidation (1. BH3 2. NaOH, H2O2)?

Q image thumb

product is aldehyde

A image thumb
76

What happens when an alkene undergoes hydroboration - oxidation (1. BH3 2. NaOH, H2O2)?

Q image thumb

alcohol with anti-Markovnikov regiochemistry

A image thumb
77

Why is the allylic carbocation more stable than the carbocation adjacent to the bromine atom?

Q image thumb

They can both stabilize the positive charge, but the bromine atom is very large, so the C-Br bond is longer. This means there's less orbital overlap, which means less stabilization.

78

When looking at C-C bond strengths, such as the example shown, what is it that determines the order of strength?

Q image thumb

% s character in the bond

i. sp2-sp2 → most s character → strongest bond

ii. sp3-sp3 → least s character → weakest bond

iii. sp2-sp3 → intermediate s character → intermediate strength

79

What kind of isomers are these 2 molecules?

Q image thumb

not isomers (different molecular formulas)

80

What kind of isomers are these 2 molecules?

Q image thumb

constitutional isomers (different connectivities)

81

What kind of isomers are these 2 molecules?

Q image thumb

constitutional isomers (different connectivities)

82

What kind of isomers are these 2 molecules?

Q image thumb

conformational isomers (can be interconverted via single bond rotation)

83

What kind of isomers are these 2 molecules?

Q image thumb

diastereomers (no mirror image relationship)

84

What kind of isomers are these 2 molecules?

Q image thumb

conformational isomers (can be interconverted via single bond rotation (ring flip))

85

Which one of these molecules is more stable? Why?

Q image thumb

the left molecule - equatorial position is lower energy than axial position

A image thumb
86

What kind of isomers are these 2 molecules?

Q image thumb

diastereomers (no mirror image relationship)

87

What kind of isomers are these 2 molecules?

Q image thumb

enantiomers (non-superimposable mirror images)

88

What kind of isomers are these 2 molecules?

Q image thumb

enantiomers (non-superimposable mirror images)

89

What kind of isomers are these 2 molecules?

Q image thumb

diastereomers (no mirror image relationship)

90

What kind of isomers are these 2 molecules?

Q image thumb

enantiomers (non-superimposable mirror images)

91

What kind of isomers are these 2 molecules?

Q image thumb

meso (at least 2 chiral centers and superimposable on mirror image)

92

For optical isomers, most physical and chemical properties are the same, but they have a different effect on a _____________________________

beam of plane polarized light

93

A chiral substance is said to be _________________

optically active

94

How is optical activity measured?

polarimeter

95

All achiral substances are said to be _____________ - they don't rotate plane-polarized light

optically inactive

96

A molecule is ________ if its 2 mirror image forms are superimposable

achiral

97

Enantiomers have the same physical properties. Do enantiomers interact in the same way with plane-polarized light?

no - they're shaped differently

98

An enantiomer is said to be ______________ if it contains 100% of one configuration

optically pure

99

A __________ mixture contains a mixture of both enantiomers

racemic

100

If a reaction occurs at a chiral center, _____________ may occur, which is the conversion of an optically pure mixture into a racemic mixture

racemization

101

_____________ configuration compares the arrangement of atoms in space of one compound with those of another

relative

102

_____________ configuration is the precise arrangement of atoms in space

absolute

103

A pair of ___________ have the opposite configurations (R vs S) at all chirality centers

enantiomers

104

Are meso form structures chiral or achiral?

achiral (superimposable on mirror image) but they do have chirality centers (at least 2)

105

In this optical rotation equation, what does represent?

Q image thumb

observed optical rotation (experimentally measured)

106

In this optical rotation equation, a represents the observed optical rotation. The magnitude depends on the ___________ and the _____________ of the sample.

Q image thumb

path length

concentration

107

In this optical rotation equation, what does c represent?

Q image thumb

concentration (g/cmor g/mL)

108

In this optical rotation equation, what does l represent?

Q image thumb

path length (dm)

109

In this optical rotation equation, what does [a] represent?

Q image thumb

specific optical rotation

110

The specific optical rotation [a] of a sample takes into account _____________ and _____________

concentration

path length

111

The value of the _____________________ of an enantiomeric pair is equal and opposite

specific optical rotation [a]

112

An enantiomer that rotates the plane polarized light to the ________ is known as the (+)-enantiomer

right

113

An enantiomer that rotates the plane polarized light to the ________ is known as the (-)-enantiomer

left

114

What would be the observed optical rotation (a) of a sample containing an exactly 50:50 mixture of R- and S- enantiomers?

0

115

Light has _______ properties

wave

116

Optical activity is usually measured using light with a wavelength of ________

589 nm

117

589 nm is the wavelength of the ________ light from a sodium lamp and is called the __________ of sodium

yellow

'D-line'

118

Plane-polarized light consists of beams that _________ in the same plane

vibrate

119

If the specific optical rotation ([a]) of (R)-mandelic acid is -155.4, what would be the specific optical rotation ([a]) of (S)-mandelic acid?

+155.4

120

Enantiomers can be described as (+) or (-) as well as (d) or (l). A (d) enantiomer rotates the plane of polarized light to the _________

right

121

Enantiomers can be described as (+) or (-) as well as (d) or (l). An (l) enantiomer rotates the plane of polarized light to the _________

left

122

The direction in which plane-polarized light is rotated has no relationship to the _________________ of the chiral center

absolute configuration (R vs S)

123

What is important to note about these 2 equations?

Q image thumb

% optical purity = enantiomeric excess (ee)

124

D- and L- are terms used to refer to absolute stereochemistry. What is D- associated with?

sugar

125

D- and L- are terms used to refer to absolute stereochemistry. What is L- associated with?

amino acid

126

Which bond length is longer: C-C or C-H? Why?

C-C is longer because H is very small so it can get really close to C in a C-H bond

127

Do pi bonds react with electrophiles or nucleophiles?

electrophiles - they have high electron density

128

The IUPAC name for the compound is ethyne. What is the common name?

Q image thumb

acetylene

129

Does the electrophilic addition of hydrogen halides to alkenes proceed via a carbocation intermediate?

yes

130

How does a polar solvent help the electrophilic addition of a hydrogen halide to an alkene?

polar solvent helps to stabilize the carbocation intermediate

131

Does the regioselectivity of electrophilic addition of hydrogen halides to alkenes follow Markovnikov's rule?

Q image thumb

yes

132

Comment on the stereoselectivity of electrophilic addition of hydrogen halides to alkenes

Q image thumb

not stereoselective - proceed via a planar carbocation

133

Generally, alkynes are less reactive towards _____________ than alkenes

electrophiles

134

What does geminal mean?

on the same atom

135

When treated with 1 equivalent of HX, alkynes form _________________

trans-vinyl halides

A image thumb
136

When treated with excess HX, alkynes form ___________________

geminal dihalides

A image thumb
137

What does vicinal mean?

on adjacent atoms

138

What is the rate law of the electrophilic addition of hydrogen halides to alkynes?

rate = k [alkyne] [HX]2 - termolecular step

139

For dehydrohalogenation, when the alkyl halide is 1°, KOt-Bu in _____________ is the base/solvent system that is normally used

dimethyl sulfoxide

140