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OCHEM 335 > Quiz 8 > Flashcards

Quiz 8 Flashcards

1
Q

what is the main thing that carboxylic acids and derivatives have in common

A

they all have a group that can be substituted by another group

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2
Q

why is the carbonyl carbon an electrophile

A

the polarity of the carbonyl group causes the carbonyl carbon to be an electrophile (partial negative oxygen vs. partial positive carbon).

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3
Q

what is the structure of a carbonyl

A

C double bonded to R and a Y group

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4
Q

what happens when a nucleophile attacks an alkyl halide

A

when a nucleophile attacks an alkyl halide, the sigma bond breaks

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5
Q

what happens when a nucleophile attacks a carbonyl compound

A

the pi bond breaks to form a tetrahedral intermediate and a group is eliminated. the nucleophile is added to the carbonyl carbon.

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6
Q

what is the difference between nucleophilic addition vs. nucleophilic substitution

A

(carbonyl with two R groups (an aldehyde) vs. a carbonyl with an R and a Y group (carboxylic acid derivative))

both reactions begin with the addition of a nucleophile to a polar C=O bond to give a tetrahedral alkoxide intermediate.

the intermediate formed from an aldehyde or ketone is protonated to give an alcohol

the intermediate formed from a carboxylic acid derivative expels a leaving group to give a new carbonyl compound (same structure, different leaving group)

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7
Q

what is an alkoxide intermediate

A

C bonded to Nu, Y, O-, and R

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8
Q

what is the key reaction of carboxylic acid derivatives (steps)

A
  1. nucleophile adds to carbonyl
  2. tetrahedral intermediate is formed
  3. other reactions happen via the tetrahedral intermediate (which is unstable due to the presence of oxygen and another electronegative atom)
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9
Q

what happens if the nucleophile (Z) is stronger than the base (Y) in a reaction

A

a new product will be formed, so Y- is eliminated. the weakest base (i.e. the better leaving group) is eliminated from the tetrahedral intermediate

(carbonyl with Y attached –> tetrahedral intermediate –> carbonyl with Z attached)

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10
Q

what happens if the nucleophile (Z) is weaker than the base (Y) in a reaction

A

than the reactants are reformed and there is no reaction

(carbonyl with Y attached –> tetrahedral intermediate)

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11
Q

what happens if the nucleophile (Z) and the base (Y) have similar basicities in a reaction

A

a mixture of reactants and products is obtained if the two potential leaving groups have similar basicities

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12
Q

how to determine the basicity of the leaving group

A
  • weak base = good leaving group

(weakest base)
Cl
C double bonded to O and single bonded to R and O-
-OR
-OH
-NH2
(strongest base)

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13
Q

what are the reactive rates of carboxylic acid derivatives

A

(most reactive)
C double bonded to O and single bonded to R and Cl
acid anhydride
ester
carboxylic acid
amide
(least reactive)

the stronger the base attached, the less reactive the compound is

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14
Q

why does a weak base make the formation of a tetrahedral intermediate faster

A
  • since a weak base leaves the compound in the tetrahedral formation, the weaker base us easier to be eliminated (vs. if the carbonyl structure was retained which would make it difficult to remove due to resonance).
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15
Q

what strength of carboxylic acid derivative can be derived

A

a carboxylic acid derivative can be converted ONLY to a less reactive carboxylic acid derivative

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16
Q

acyl chloride

A

CH3-C=O
|
Cl

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17
Q

what is a feature of acyl chloride reactivity

A

have good leaving groups (Cl is a weak base) - so they are very reactive with anionic nucleophiles

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18
Q

describe the reaction of acyl chloride with anionic nucleophiles

A

forms a tetrahedral intermediate and the weaker base is eliminated (the Cl) - see slide 24

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19
Q

describe the reaction of acyl chloride with neutral nucleophiles

A

acyl chloride + H2O (for example) –> the Cl is replaced with the substituent (water) with one less proton - see slide 25

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20
Q

how many equivalents of amine are needed for amide formation and what are they used for

A

two equivalents of AMINE are needed for AMIDE formation
- the first equivalent acts as a nucleophile
- the second equivalent acts as a base and reacts with HCl that us formed
see slide 28

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21
Q

what is an amine group

A

functional group where nitrogen has a lone pair

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22
Q

how to activate carboxylic acids (and what reagents should you use / what is the purpose of these reagents)

A

convert them into acyl chlorides

SOCl3 and heat
PCl3 and heat
PBr3 and heat

see slide 29

these reagents turn the carboxylic acid (-OH) into a Cl, which can then become a better leaving group

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23
Q

describe an acid anhydride

A
  • two carbonyl (C=O) groups
  • same oxidation state as other carboxylic acid derivatives
  • interchangeable with other carboxylic acid derivatives
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24
Q

how to make an acid anydride

A

formed when water is lost from two molecules of a carboxylic acid (so you need to dehydrate - take away - an equivalent of water)

two carboxylic acids – heat –> an acid anhydride + water

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25
Q

reactivity for an acid anhydride vs. acid chloride vs. ester

A

the acid anhydride is less reactive than an acid chloride
the acid anhydride is more reactive than an ester
the acid chloride is more reactive than an ester

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26
Q

how many equivalents are needed to form an acid anydride

A

2 equivalents of AMINE

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27
Q

what will happen if a dicarboxylic acid can form a ring and why does it do this

A

the dicarboxylic acid will lose water when heated if they can form a five or six membered ring. this is because the intramolecular reactions (bonds that hold the molecule together) are usually easier to do than the intermolecular reactions (exterior interactions / bonds made). intermolecular reactions usually have very extreme heating points - slide 38

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28
Q

what is needed to activate a carboxylic acid to convert them to an acid anhydride

A

2 equivalents of a carboxylic acid and P2O5

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29
Q

how to prepare a mixed acid anhydride

A

formed by reacting an acyl chloride of one acid with the carboxylate salt (carboxylic acid with a sodium ion attached to an oxygen - not the one with the double bond) - slide 40

30
Q

what is acetic acid

A

CH3-C=O
|
OH

31
Q

what are the reactivities of carboxylic acid derivatives toward nucleophilic acyl substitutions

A

a carboxylic acid must be in its acidic form (can’t have a negative charge) in order to undergo a nucleophilic acyl substitution (so the nucleophile can attack)

(most reactive)
carboxylic acid
amide
carboxylate ion
(least reactive)

32
Q

can carboxylate ions react with nucleophiles?

A

no, because of the negatively charged anion

33
Q

what is the fischer esterification reaction

A

reaction of a carboxylic acid with an alcohol

34
Q

describe the fischer esterification reaction

A
  • requires an acid catalyst (HCl)
  • excess alcohol drives the reaction to the right (Le Chat. Principle)

carboxylic acid + alcohol –HCl–> new carbonyl + water
** R group on alcohol replaces the -OH on carboxylic acid

35
Q

what occurs during the reaction of a carboxylic acid with an amine and what happens when the reaction is heated

A

carboxylid acid is an ACID and amine is a BASE, so an acid-base reaction occurs - slide 46

when heated, the product forms an amide
- in general, yields are poor

36
Q

amine vs. amide

A

Amines and amides contain one or more nitrogen atoms. Amines have an amino group. Amides are the product of reaction between an amine and a carboxylic acid derivative.

37
Q

describe an ether

A

R-O-R

38
Q

describe the reaction of an ester with water

A

an ester reacts with water to form a carboxylic acid and an alcohol via a hydrolysis reaction

requires an acid catalyst (HCl) because the ester is not very reactive and water is a poor nucleophile - see slide 51

39
Q

what are the carboxylic acid derivatives major resonance contributors

A

carboxylic acid derivatives have three major resonance contributors (ex. esters, carboxylic acids, and amides all have this third resonance contributor).
- the third major resonance form means that most carboxylic acid derivatives are not as electrophilic as aldehydes and ketones - see slide 52

40
Q

how to drive the reaction of an ester with water to the right

A

add an excess of water (Le Chat. Principle)

41
Q

for the reaction of ester and water, which oxygen is protonated and why

A

the carbonyl oxygen is protonated (instead of the OCH3). This is because more partial negative charge in the carbonyl oxygen gives greater the electron density. This helps with resonance stabilization - see slide 55

42
Q

in a carbonyl compound, what has the greatest electron density

A

carbonyl oxygen has the greatest electron density

43
Q

what does protonation of the carbonyl group make the compound more susceptible to

A

nucleophilic addition - see slide 57 / 58

44
Q

what is hydroxide-ion-promoted hydrolysis of an ester

A

saponification

45
Q

describe the hydroxide-ion-promoted hydrolysis of an ester (what reagents are used, what bonds are broken, how many equivalents are required)

A

(aka saponification)

reagents: 1. NaOH, H2O and 2. H3O+
the oxygen bond is broken and replaced with OH.
one equivalent of base is used, thus, it is not a catalyzed reaction

slide 59

46
Q

are acid-catalyzed ester hydrolysis or hydroxide-ion-promoted ester hydrolysis reversible?

A

acid-catalyzed ester hydrolysis is reversible

hydroxide-ion-promoted ester hydrolysis is irriversible because it produces a negative oxygen which cannot react with nucleophiles

47
Q

describe the reaction of an transesterification with an alcohol (what are the reactants, what kind of compounds are needed, what is produced, does it need a catalyst, how do you drive it to the right)

A

(trans esterification) - looks similar to the hydrolysis reaction

alcohol + an ester –HCl–> new ester and new alcohol
- ex. methoxy becomes an ethoxy
- reaction needs an acid catalyst
- excess alcohol drives rxn right (Le Chat. Principle)

slide 63

48
Q

why is transesterification catalyzed by acid

A
  • an ester is not very reactive and is a poor nucleophile, so an acid catalyst is required
49
Q

what is an alternative to the transesterification rxn and what are the reagents

A

the reaction of an ester with an alcohol can be catalyzed by an alkoxide ion

same reactants as the transesterification, but instead of HCl catalyst, this reaction uses CH3CH2O- (alkoxide ion)

50
Q

describe the reaction of an ester with an amine

A

(aminolysis rxn)
ester + amine –heat–> amide and an alcohol

slide 67

51
Q

what is acetamide

A

CH3-C=O
|
NH2

52
Q

do amides undergo nucleophilic acyl substitution reactions under typical conditions

A

no, amides do not undergo nucleophilic acyl substitution reactions unless the acid is catalyzed

53
Q

what reagents are needed for the reaction of amides with water and alcohols

A

HCl and heat

54
Q

why does hydrolysis and alcoholysis of an amide require a catalyst

A

NH2 must be portonated by an acid catalyst, otherwise the OH will act as the leaving group. This is because the weakest base is the best leaving group.

slide 72 / 74

55
Q

what reactants are necessary for amide hydrolysis

A

amide + H2O –HO- and heat–> carboxylate ion + NH3 (similar to supnification

slide 73

56
Q

explain the reaction of amides with hydride ions (what are the reactants and what is formed)

A

amide –> amine

reactants:
1. LiAlH4
2. H2O

slide 79

57
Q

how does the structure of the amide when reacted with a hydride ion effect the amine prodiced

A

if the NH group is primary, then a primary amine is formed and thus for sec and tert.

slide 80

58
Q

what is the purpose of activating a carboxylic acid by converting it to thioester

A

a thioester is more susceptible than an oxygen ester to nucleophilic addition because it has a better leaving group. This is because sulfur is so big that its electrons are far out and can’t form a third resonance structure, so the carbonyl is not stabilized as well (making the reaction quicker).

RS- is a better leaving group than RO-

59
Q

what is the pKa of SH

A

10.5

60
Q

what is the pKa of OH

A

15.9

61
Q

what is polymerization

A

a polymer is a large molecule that is made by linking together repeating units of small molecules (monomers). The process of linking monomers is polymerization.

62
Q

what is a chain-growth polymer

A

(ex. polystyrene) chain growth polymers are also known as addition polymers. They are made by chain reactions where monomers add to the growing end of the chain. They are formed by one of three mechanisms:
- radical polymerization
- cationic polymerization
- anionic polymerization

63
Q

what is a step growth polymer

A

(ex. dacron) step-growth polymers are also known as condensation polymers. They are made by combining two molecules while removing a small molecule (such as water or methanol)

they are formed by addition-elimination mechanisms used to make carboxylic acid derivatives

64
Q

compare step growth polymers of the same vs. different functional groups

A

different functional groups:
A-B and B-A –> A-X-B

bifunctional compounds:
A-A and B-B –> A-X-B

65
Q

what kind of yields are required by step growth polymerization

A

very high yields (~99.9%). Even 75% is not a polymer because ligaments are still being connected.

66
Q

what is a plasticizer

A

an organic compound added to a polymer to make it more flexible. it dissolves the polymer

67
Q

how long is this polymer chain and what is the repeating unit: R-[(CH2)5C]n-R

A

6 carbon atoms long; X is the repeating unit

68
Q

what is the easiest way to identify a step-wise polymer

A

presence of carbonyls

69
Q

how long is this polymer chain: nylon 7

A

7 carbons long

70
Q

ease of recycling chain growth vs. step growth polymers

A

chain growth:
- extremely difficulty because it would require the cleavage of strong carbon-carbon bonds

step growth:
- easy because the amide or ester groups can undergo reactions typical of a carboxylic derivative

OCHEM 335 (7 decks)

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