Ch 9 - Carboxylic Acid Derivatives

Question 1

What are amides and their nomenclature?

Answer 1

• the condensation products of carboxylic acids and ammonia or amines
• given the suffix -amide
• the alkyl groups on a substituted amide are written at the beginning of the name with the prefix N-

Question 2

What are lactams and their nomenclature?

Answer 2

• cyclic amides

- named by the greek letter of the carbon forming the bond with nitrogen (beta-lactam, gamma-lactam, and so on)

Question 3

What are esters and their nomenclature?

Answer 3

• the condensation products of carboxylic acids with alcohols (Fischer esterification)
• given the suffix -oate
• the esterifying group is written as a substituent, without a number

Question 4

What are lactones and their nomenclature?

Answer 4

• cyclic esters
• named by the number of carbons in the ring and the Greek letter of the carbon forming the bond with the oxygen (alpha-acetolactone, beta-propiolactone, and so on)

Question 5

What are triacylglycerols and how are they formed?

Answer 5

a form of fat storage

- include 3 ester bonds between glycerol and fatty acids

Question 6

What is saponification?

Answer 6

the breakdown of fat using a strong base to form soap (salts of long-chain carboxylic acids)

Question 7

What are anhydrides?

Answer 7

the condensation dimers of carboxylic acids

Question 8

How are symmetric/asymmetric anhydrides named?

Answer 8

• symmetric: named for the parent carboxylic acid, followed by anhydride
• asymmetric: named by listing the parent carboxylic acids alphabetically, followed by anhydride

Question 9

How can some cyclic anhydrides be synthesized and what form is most stable?

Answer 9

• by heating dioic acids

- 5- or 6-membered rings are generally stable

Question 10

How does the reactivity of amides, anhydrides, and esters compare in nucleophilic substitution reactions?

Answer 10

anhydrides are more reactive than esters, which are more reactive than amides (need a strong acid/base to react)

Question 11

What does steric hindrance describe?

Answer 11

when a reaction cannot proceed (or significantly slows) because of substituents crowding the reactive site

Question 12

What are protecting groups?

Answer 12

• like acetals

- can be used to increase steric hindrance or otherwise decrease the reactivity of a particular portion of a molecule

Question 13

What is induction?

Answer 13

• refers to uneven distribution of charge across a sigma bond because of differences in electronegativity

Question 14

What is conjugation?

Answer 14

• refers to the presence of alternating single and multiple bonds, which creates delocalized pi electron clouds above and below the plane of the molecule

Question 15

How does resonance affect stability?

Answer 15

electrons experience resonance through unhybridized p-orbitals, increasing stability

Question 16

How does electronegativity of carbonyl-containing compounds affect reactivity?

Answer 16

• the more electronegative groups in a carbonyl-containing compound, the greater its reactivity

Question 17

Why are conjugated carbonyl-containing compounds more reactive?

Answer 17

because they can stabilize their transition states

Question 18

How does strain affect reactivity?

Answer 18

• increased strain in a molecule can make it more reactive

- beta-lactams are prone to hydrolysis because they have significant ring strain

Question 19

What causes ring strain?

Answer 19

due to torsional strain from eclipsing interactions and angle strain from compressing bond angles below 109.5 degrees.

Question 20

Which carboxylic derivatives undergo nucleophilic substitution reactions?

Answer 20

all can undergo these reactions, the rates at which they do are determined by their relative reactivities

Question 21

How can anhydrides be cleaved?

Answer 21

by the addition of a nucleophile

• addition of ammonia/amine results in an amide and a carboxylic acid
• addition of an alcohol results in an ester and a carboxylic acid
• addition of water results in 2 carboxylic acids

Question 22

What is transesterification?

Answer 22

the exchange of one esterifying groups for another on an ester
- the attacking nucleophile is an alcohol

Question 23

How can amide be hydrolyzed to carboxylic acids?

Answer 23

under strong acidic or basic conditions

- the attacking nucleophile is water or the hydroxide anion

Question 24

What happens in a condensation reaction?

Answer 24

• 2 molecules combine to form 1, with the loss of a small molecule (water)
• how carboxylic acid derivatives are formed

Question 25

What properties account for the difference in reactivity seen between anhydrides, esters, and amides with nucleophiles?

Answer 25

• electronic effects like induction have some effect on the reactivity of the carbonyl in these 3 functional groups
• differences in resonance also explains increased reactivity of anhydrides in particular
• steric effects could also be significant, depending on the specific leaving group present

Question 26

How do strongly acidic/basic conditions catalyze the hydrolysis of an amide?

Answer 26

• strongly acidic conditions catalyze amide hydrolysis by protonation of the oxygen in the carbonyl, increasing the electrophilicity of the carbon, making it more susceptible to nucleophilic attack
• strong basic conditions greatly increase the concentration of OH-, which can act as a nucleophile on amide carbonyls

Question 27

What is formed when an anhydride and ammonia combine?

Answer 27

amide and carboxylic acid

Question 28

What happens in a Fischer esterification?

Answer 28

reacting a carboxylic acid and an alcohol with an acid catalyst

Question 29

How do dicarboxylic acids react to heat?

Answer 29

anhydrides, specifically cyclic anhydrides, will form spontaneously from dicarboxylic acids when heated

Question 30

How do substituents affect reactivity?

Answer 30

the less substituted the nucleophile, the easier it will be for the nucleophile to attack the carbonyl carbon and form the amide

Question 31

What are beta lactams?

Answer 31

• amides in the form of 4-membered rings; amides are generally the least reactive type of carboxylic acid derivative
• experience significant ring strain from both eclipsing interactions (torsional strain) and angle strain, and are therefore more susceptible to hydrolysis than the linear form of the same molecule

Question 32

Why would a positive charge on a molecule have greater stability when cyclic than when straight-chain alkane of the same molcule?

Answer 32

conjugation which permits delocalization of the charge through resonance