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GAMSAT March 2016 > Org 7 - Aldehydes & Ketones > Flashcards

Org 7 - Aldehydes & Ketones Flashcards

1
Q

What is the general structure of an aldehyde ?

A

suffix: -al

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2
Q

What is the general structure of a ketone ?

A

Suffix: -one

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3
Q

What is the functional group of aldehydes and ketones ?

A

The carbonyl group C=O

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4
Q

Describe the Carbonyl functional group, including bond angles

A

Planar, with bond angles of 120º

The Carbonyl Carbon atom has 3 σ bonds.

The C=O bond is shorter and stronger than the C-O.

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5
Q

What is an Aryl group ?

A

Benzene minus 1 hydrogen e.g. C6H5 Phenyl

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6
Q

Name five important features of the Carbonyl group

A
  1. Resonance
  2. Polarity
  3. Acidity of the alpha hydrogen
  4. Keto-enol tautomerisation
  5. Hydrogen bonding
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7
Q

Sketch the two resonance structures of a ketone

A
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8
Q

Why is polarity important in the Carbonyl group ?

A

It may participate in nucelophilic or electrophilic reactions. Nucleophiles attack the partially positive carbon, and electrophiles attack the partially negative oxygen.

In both of these reactions, the character of the double bond is altered.

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9
Q

Where is the alpha carbon located in a Carbonyl compound ?

A

The alpha carbon is always adjacent to the functional group.

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10
Q

What is the relationship between resonance structures and stability ?

A

If you can draw resonance structures for a compound, then it displays increased stability.

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11
Q

Explain why acidity of the alpha hydrgen occurs in a carbonyl compound ?

A

The acidity is a result of the resonance stabilisation of the alpha carbanion formed.

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12
Q

Are the beta and gamma hydrogens also acidic in a carbonyl compound ?

A

No, only the alpha hydrogen is acidic

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13
Q

What happens to acidity if the alpha hydrogen is situated between 2 Carbonyl groups ?

A

It will display increased acidity

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14
Q

What are tautomers ?

A

Constitutional isomers that readily interconvert (= tautomerization).

This happens so quickly that they are usually considered to be the same compound.

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15
Q

What is an enol ?

A

Alkene & Alcohol

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16
Q

What are conjugated double bonds ?

A

Double bonds separated by a single bond

17
Q

Sketch the equilibrium present in tautomerization

A
18
Q

Describe tautomerization ?

A

Fast interconnection between constitutional isomers

e.g. Carbonyl and Enol

19
Q

How do Carbonyl groups participate in hydrogen bonding ?

A
20
Q

Why don’t aldehydes and ketones form hydrogen bonds with themselves ?

A

There is no hydrogen on the carbonly oxygen

21
Q

What influences reactivity of the Carbonyl compounds ?

A

The carbonyl group is the functional group, but adjacent groups can influence reactivity, e.g. an e- withdrawing group adjacent to the carbonyl carbon will increase the partially positive charge on the carbon making the carbonyl group more attractive to a nucleophile.

An e- donating ligand would decrease the reactivity of the carbonyl group.

22
Q

How does steric hindrance influence the reactivity of the carbonyl compounds ?

A

Generally, aldehydes oxidise and more easily undergo nucleophilic addition than ketones.

23
Q

Explain oxidation of Carbonyl compounds ?

A

Aldehydes oxidise to Carboxylic acids (using agents such as KMnO4, CrO3 (Jones reagent), HNO3, Ag2O (Tollens)

24
Q

Describe a diagnostic tool for the presence of an aldehyde group ?

A

Using Tollen’s reagent (Ag2O) metallic silver Ag is produced if an aldehyde is present.

Ketones cannot be oxidised to Carboxylic acids.

25
Q

Describe 7 reactions that result in the formation of aldehydes or ketones ?

A
  • Ozonlysis
  • REDOX
  • Hydroformylation
  • 1º alcohols → Aldehydes (Oxidation)
  • 2º alcohols → Ketones (Oxidation)
  • Friedel-Crafts Acylation
  • Hydration of terminal alkynes
26
Q

Explain the difference in boiling points between alcohols and ketones ?

A

Alcohols exhibit hydrogen bonding, ketones exhibit dipole-dipole bonding (weaker intermolecular forces) therefore ketones have a lower boiling point.

27
Q

Why do alkanes have a lower boiling point than ketones or alcohols ?

A
  • Alkanes - Intermolecular (london) forces
  • Ketones - Dipole dipole forces
  • Alcohols - hydrogen bonding

London forces < dipole dipole < hydrogen bonding

(In terms of relative bond strength)

28
Q

What is the impact of increasing alkyl groups on reactivity of the carbonyl group ?

A

The more alkyl groups present (and therefore, the longer the carbon chain), the more stable the carbonyl group.

There is more polarisation in an aldehyde than a ketone, therefore a ketone is more stable.

29
Q

What are the two classes of reactions that carbonyl compounds undergo ?

A
  • Nucleophilic addition reactions at the C=O bond
  • Reactions at adjacent positions
30
Q

Describe nucleophilic addition reactions in Carbonyl compounds ?

A
31
Q

Describe reduction of aldehydes and ketones ?

A

Reduction with Grignards reagent yields alcohols:

  • Formaldehyde → 1º Alcohol
  • Other aldehydes → 2º Alcohol
  • Ketones → 3º Alcohol

N.B. Other reducing agents include NaBH4, and LiAlH4

32
Q

What is the general formula of a Primary amine ?

A

R-NH2

33
Q

What is the product when a Carbonyl compound reacts with a primary amine ?

A

An Imine (Schiff base) is formed.

The Carbonyl group is replaced with a C=N-R group.

34
Q

What is the product when a Carbonyl compound reacts with a secondary amine ?

A

An enamine is formed

35
Q

What is a secondary amine ?

A
36
Q

What is the product when a tertiary amine reacts with a Carbonyl compound ?

A

There is no reaction

37
Q

What is an Aldol ?

A

An aldol is both an aldehyde and an alcohol, e.g. the intermediate product in aldol condensation reactions

38
Q

What is Aldol condensation ?

A

The Aldol undergoes a dehydration reaction, producing a C-C bond in the condensation product (an enal - alkene and aldehyde)

39
Q
A

GAMSAT March 2016 (26 decks)

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