Chapter 19: The Chemistry of Aldehydes and Ketones

Aldehydes and ketones are _____ compounds.

carbonyl

What is the carbonyl group?

C=O

What is the suffix for this terminal functional group?

al

What is the suffix for this terminal functional group?

oic acid

What is the suffix for this terminal functional group?

amide

What is the common name for when R attached to a terminal functional group is H?

form

What is the common name for when R attached to a terminal functional group is CH₃?

acet

What is the common name for when R attached to a terminal functional group is CH₃CH₂?

propion

What is the common name for when R attached to a terminal functional group is CH₃CH₂CH₂?

butyr

What is the common name for when R attached to a terminal functional group is Ph?

benz

Give the common name and IUPAC name for this structure.

Common: formaldehyde

IUPAC: methanal

Give the common name and IUPAC name for this structure.

Common: acetaldehyde

IUPAC: ethanal

Give the common name and IUPAC name for this structure.

Common: propionaldehyde

IUPAC: propanal

Give the common name and IUPAC name for this structure.

Common: butyraldehyde

IUPAC: butanal

Give the common name and IUPAC name for this structure.

Common: β-chloropropionaldehyde

IUPAC: 3-chloropropanal

Give the common name and IUPAC name for this structure.

Common: phenylacetaldehyde

IUPAC: 2-phenylethanal

Give the common name and IUPAC name for this structure.

Common: acrolein

IUPAC: prop-2-enal

Aldehydes bonded to a ring are named using the suffix _____.

carbaldehyde

Give the IUPAC name for this structure.

cyclohexanecarbaldehyde

The final e (is/isn’t) dropped when the carbon chain has more than one aldehyde group.

isn’t

How are common names constructed for ketones?

cite the two groups in alphabetical order and add “ketone” at the end

How are IUPAC names constructed for ketones?

IUPAC name then add “-one” at the end

Give the common name and IUPAC name for this structure.

Common: acetone

IUPAC: propanone

Give the common name and IUPAC name for this structure.

Common: ethyl methyl ketone

IUPAC: butan-2-one or 2-butanone

Give the common name and IUPAC name for this structure.

Common: methyl propyl ketone

IUPAC: pentan-2-one or 2-pentanone

Give the common name and IUPAC name for this structure.

Common: allyl methyl ketone

IUPAC: pent-4-en-2-one

Give the IUPAC name for this structure.

acetophenone

Give the IUPAC name for this structure.

benzophenone

Give the IUPAC name for this structure.

cyclohexanone

Give the IUPAC name for this structure.

3,3-dimethylcyclohexanone

If there is more than one functional group present in the compound, how do you name the compound?

one of the functional groups is given priority as principle functional group and the others are considered substituents and given prefix names

How is priority assigned to the principle functional group when there is more than one present in a compound?

aldehyde > ketone > —OH > NH₂ > —SH

What is the prefix name for this functional group?

formyl-

What is the prefix name for this functional group?

oxo-

What is the prefix name for this functional group?

hydroxy-

What is the prefix name for this functional group?

amino-

What is the prefix name for this functional group?

mercapto-

Give the IUPAC name for this structure.

4-hydroxy-6-methyl-5-propyl-6-hepten-2-one

Are aldehydes and ketones polar?

yes

Why are aldehydes and ketones polar?

because of their C=O bond dipoles

Most simple aldehydes and ketones are (solids/liquids/gases).

liquids

Aldehydes and ketones have considerably (higher/lower) boiling points than their corresponding alcohols. Why?

lower;

they are not H-bond donors

What is the solubility of small aldehydes and ketones (≤ 4 carbons) in water? Why?

fairly soluble;

they are H-bond acceptors

What is the IR spectroscopy for the strong C=O stretch of both aldehydes and ketones?

1700 cm^-1

How do you differentiate between aldehydes and ketones on an IR spectrum?

aldehydes have a C—H stretch around 2700 - 2800 cm^-1

Conjugation with a π bond (increases/decreases) absorption frequency/

decreases

The C=O stretching frequency (increases/decreases) with increasing ring size.

decreases

The C=O stretching frequency (increases/decreases) with decreasing ring size.

increases

Why do aldehydic protons have a large chemical shift?

magnetic field of π electrons and inductive effect of O

What is the chemical shift range of aldehydic protons (¹H NMR)?

9 - 10 ppm

What is the chemical shift range of ketonic protons (¹H NMR)?

2 - 3 ppm

What is the chemical shift range of aldehyde and ketone C=O carbons (¹³C NMR)?

190 - 220 ppm

What is the UV-vis spectroscopy for π → π^* of aldehydes and ketones?

150 nm (below operating range)

What is the UV-vis spectroscopy range for n → π^* of aldehydes and ketones?

260 - 290 nm

Conjugated systems have (strong/weak) absorptions in the UV spectrum.

strong

What is the order of orbitals from lowest to highest energy level?

σ < π < n < π^* < σ^*

Lower ∆E = (higher/lower) λ_max

higher

Increased number of conjugated double bonds and substitution on double bonds → (higher/lower) λ_max

higher

In aldehydes and ketones, peaks arise in mass spectrometry due to…

inductive cleavage and α-cleavage

What is the McLafferty rearrangement? Show the mechanism.

a H transfer via a transient 6-membered ring

What does the McLafferty rearrangement require?

an available gamma-H

What is the reagent used in oxidation of 1º alcohols to synthesize aldehydes? Draw the simplified reaction.

PCC and CH₂Cl₂
or
CrO₃, Py and CH₂Cl₂

What is the reagent used in oxidation of 2º alcohols to synthesize ketones? Draw the simplified reaction.

Na₂Cr₂O₇, H₂SO₄
or
CrO₃, H₂SO₄, H₂O and acetone

What is the reagent used in the synthesis of aldehydes from alkynes? Draw the simplified reaction.

1. (Sia)₂BH, THF

2. H₂O₂, NaOH, H₂O

What is the reagent used in the synthesis of ketones from alkynes? Draw the simplified reaction.

H₂O, H₂SO₄ and HgSO₄

What is the reagent used in the synthesis of aldehydes through the Friedel-Crafts acylation? Draw the simplified reaction.

no reaction

What is the reagent used in the synthesis of ketones through the Friedel-Crafts acylation? Draw the simplified reaction.

AlCl₃

What is the reagent used in the synthesis of aldehydes and ketones through the ozonolysis of alkenes? Draw the simplified reaction.

1. O₃

2. (CH₃)₂S

What is the reagent used in the synthesis of aldehydes and ketones through the periodate cleavage of glycols? Draw the simplified reaction.

HIO₄

α-hydroxy and α-alkoxy carbocations → (more/less) stable than ordinary carbocations.

more

Conjugate acids of aldehydes and ketones can be viewed as…

α-hydroxy carbocations

Less stable carbocations rearrange to more stable by…

1,2 shift

draw the pinacol rearrangement mechanism

The carbonyl oxygen is (strongly/weakly) basic.

weakly

Protonated alcohols are (more/less) acidic.

less

Which are more basic, alcohols or ketones?

alcohols

Why are alcohols more basic than ketones?

alcohols deprotonate at a faster rate than ketones;

hybridization is sp²;

solvent effect

Order these by increasing electrophilicity of C.
alkyl group, electronegative group, H, steric factor, resonance

resonance < steric factor < alkyl group < H < electronegative group

What are the two strong basic nucleophiles?

1. R’MgX or R’Li

2. LiAlH₄ (H^- source)

What are the moderate/weak basic nucleophiles?

moderate = CN^- and RNH₂

weak = H₂O and ROH

Which are the irreversible nucleophiles?

1. R’MgX or R’Li

2. LiAlH₄ (H^- source)

Which are the reversible nucleophiles?

CN^-, RNH₂, H₂O, and ROH

What are the reversible additions to aldehydes and ketones?

1. addition of HCN (NaCN, pH 9-10 H₂O)

2. addition of H₂O

draw the forward mechanism for addition of HCN to a carbonyl group

What is HO—C—CN?

cyanohydrin

Is cyanohydrin formation reversible?

yes, under basic conditions and carbonyl formation is thermodynamically favored

draw the reverse mechanism for addition of HCN to a carbonyl group

draw the forward mechanism for addition of water to a carbonyl group in acidic conditions

draw the reverse mechanism for addition of water to a carbonyl group in acidic conditions

draw the forward mechanism for addition of water to a carbonyl group in basic conditions

draw the reverse mechanism for addition of water to a carbonyl group in basic conditions

What does the addition of water to a carbonyl group in the presence of an acid or base catalyst result in?

formation of hydrates

What is a hydrate?

compound with two OH groups attached to the same carbon

Compounds with the (most/least) favorable addition equilibria tends to react most rapidly.

most

What does the equilibrium for a reversible addition depend strongly on?

the structure of the carbonyl compound

Electron donating groups (increase/decrease) reactivity of a carbonyl compound.

decrease

Electron withdrawing groups (increase/decrease) reactivity of the carbonyl carbon.

increase

Partial positive charge (increases/decreases) reactivity of the carbonyl carbon.

increases

More hyper-conjugation structures for ketones (increase/decrease) reactivity of the carbonyl carbon.

decrease

Why do more hyper-conjugation structures for ketones decrease reactivity of the carbonyl carbon?

it stabilizes the structure, which lowers reactivity