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Medicinal Chemistry > Functional Groups 5&6 - carbonyls > Flashcards

Functional Groups 5&6 - carbonyls Flashcards

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1
Q

Describe the structure of carbonyls.

A
  • Trigonal planar sp2 carbon and oxygen
  • All sigma bonds lie in same plane - 120 degrees apart
  • C-O pi bond between parallel p orbitals on carbon and oxygen
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2
Q

What is the driving force behind carbonyl activity?

A

The difference in electronegativity between carbon and oxygen - oxygen is more electronegative

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3
Q

Why are carbonyls higher in energy than alkenes?

A

The dipole in C=O means the bond is shorter, stronger and more polar

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4
Q

Why is hydrogen bonding important for carbonyl groups when taking drugs?

A
  • Can bond with water so the drug can dissolve and travel around the body
  • Will then interact with different physiochemical conditions e.g. pH or temp and change its bonding
  • Can then find enzyme or receptor (binding site)
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5
Q

State the interaction of hydrogen bonding with carbonyl groups.

A

Short range, directional
Intramolecular or non-bonded interaction

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6
Q

Which two factors play an initial role in the binding of a carbonyl?

A
  • It is a planar molecule
  • It has a dipole moment
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7
Q

How do carbonyls interact with the binding site?

A
  • Hydrogen bonding: carbonyl group is a hydrogen bond acceptor and two interactions are possible as there are two lone pairs on oxygen
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8
Q

Describe the reactions at the carbonyl carbon.

A
  • Nucleophile attacks delta positive carbon from above or below planar
  • Electron pair moves from C=O bond to electronegative oxygen atom producing tetrahedral alkoxide ion intermediate
  • Lone pair on oxygen moved to proton (formation of O-H bond)
  • Formation of new bonds increases steric crowding
  • Possible introduction of chiral centre as carbonyl carbon changes from sp2 to sp3
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9
Q

Give three examples of good nucleophiles.

A
  • Hydride
  • Alkyl anions
  • Alkoxides
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10
Q

Why are aldehydes more reactive than ketones?

A
  • Proton in aldehyde is much smaller so approach of nucleophile at desired angle of 100-115 degrees is easier by comparison to ketone where there is more electrostatic charge to pass through
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11
Q

How can the reactivity of carbonyls be enhanced?

A
  • By protonation of the carbonyl oxygen
  • The carbonyl carbon becomes more electrophilic
  • The carbonyl carbon is more susceptible to nucleophilic attack
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12
Q

Name the mechanism that carbonyls undergo

A

Nucleophilic Addition

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13
Q

What are carboxylic acids?

A

Weak acids (proton donors) - they transfer a proton to water to give H3O+ and carboxylate anions RCO2-

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14
Q

What is the acidity constant (Ka) for a typical carboxylic acid?

A

10^-3 - 10^-5

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15
Q

What is the pKa range for most aliphatic and aromatic carboxylic acids?

A

3-5

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16
Q

What is the greater acidity of carboxylic acids relative to alcohols due to?

A
  • resonance stabilisation of the carboxylate anion
17
Q

How can we identify stronger acids from pKa?

A
  • The lower the pKa the stronger the acid
18
Q

Describe the role of electron withdrawing groups in the stabilisation of carboxylic acids.

A
  • stabilises the carbon making it more reactive
19
Q

Describe the role of electron-donating groups in the stabilisation of carboxylic acids.

A
  • destabilises the carbon as it becomes less positively charged and so less able to accept electrons
20
Q

State the mechanism that carboxylic acid derivatives undergo.

A

addition-elimination

21
Q

Name the condition for acyl substitutions.

A
  • acid chlorides OR acid anhydrides (react more slowly)
22
Q

What are aldehydes oxidised to?

A

Carboxylic acids - CHO hydrogen abstracted during oxidation or chemically with an oxidising agent: CrO3, KMnO4, HNO3

23
Q

What is the second site of reactivity on carbonyls?

A

the alpha-hydrogen is acidic enough to be removed by a strong base
- The anion is stabilised by resonance

24
Q

How else can we drive the process of interconversion?

A

Can be acid or base catalysed

25
Q

Why do many drug compounds contain carbonyl groups?

A

As they can make hydrogen bonding interactions with receptor binding sites in the body helping drug molecules to bind strongly.

26
Q

Explain why carboxylic acids are stronger acids than alcohols.

A

Due to resonance stabilisation of the carboxylate ion.

27
Q

Why is trifluroacetic acid more acidic than acetic acid?

A

The CF3 group is electron withdrawing which stabilises the carboxylate ion and increases acidity.

28
Q

Why do nucleophiles add to carbonyl compounds?

A

The carbon of the carbonyl group has a partial positive charge, which attracts nucleophiles.

29
Q

Name a reagent used for the reduction of aldehydes and ketones.

A

NaBH4

Medicinal Chemistry (21 decks)

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