CH7: Aldehydes + Ketones

Question 1

Aldehyde, Ketone, Alcohol B.P. + Solubility

Answer 1

Aldehydes and Ketones can’t H bond to each other so their B.P. is much lower than the corresponding alcohol

They can, however, H bond with water making them soluble

Question 2

Aldehydes from primary alcohols

Answer 2

Oxidize with PCC to stop early

Question 3

How can aldehydes be made from esters, acyl chlorides, C.A. and nitriles?

Answer 3

C.A. can’t do-Convert to acyl chloride with SOCl2

Acyl chloride- 1) LiAH(O-t-Bu)3, Et2O, -78 2) H2O

Ester-DIBAL-H

Question 4

LiAH(O-t-Bu)3

Answer 4

Used with Et2O, -78 2) H2O to form aldehydes from acyl chlorides…prior to this, we can convert a C.A. to an acyl chloride

Question 5

DIABL-H

Answer 5

Converts ester to aldehyde

Question 6

How can ketones be made?

Answer 6

1) Ozonolysis of alkenes
2) Oxidation of secondary alcohols
3) Friedel-Crafts acylation
4) From alkynes through Markovnikov hydration
5) Nitriles + Organolithium/metallic

Question 7

Ozonolysis of alkenes

Answer 7

1) O3
2) Zn, HOAc

Both are used to split an alkene and form a ketone

Question 8

Aromatic ketones

Answer 8

Made by Friedel-Crafts acylation

Question 9

Oxidation of secondary alcohols

Answer 9

With Jones reagent, we form ketones

Question 10

Vinyl vs allyl

Answer 10

Vinyl is on the carbon of the D.B.

Allyl is one over

Question 11

Vinylic alcohol

Answer 11

Called an enol, they are relatively unstable, will change to a ketone

Question 12

Alkyne hydration

Answer 12

When an alkyne reacts with H2O and acid (H2SO4/HgSO4) a vinylic alcohol (enol) forms. This then converts to a ketone

Question 13

Enol

Answer 13

Vinylic alcohol that interconverts between this form and keto form

Question 14

Keto-Enol tautomerization

Answer 14

The changing from an enol (vinylic alcohol) to a keto form

Once the vinylic alcohol forms strong acid converts it in an equilibrium

Question 15

What is needed for keto-enol tautomerization

Answer 15

Strong acid, which has often already been used during alkyne hydration. The D.B. grabs the H

Question 16

Ketones from nitriles + organometallic/lithium

Answer 16

1) React organometallic with Nitrile (C t.b. N)

2) H3O+ hydrolysis

Question 17

Hydrolysis of H=N

Answer 17

Turns to H=O every time

Question 18

Weak vs strong nucleophiles and carbonyl compounds

Answer 18

Weak need a catalys ex Lewis acid H-A to protonate the carbon

Strong ex. R: or H: can attack right away and shift the D.B. up

Question 19

Aldehyde vs ketone reactivity

Answer 19

Aldehydes are more reactive

1) Less electron pushing “R” groups
2) Less steric-hinderance

Question 20

Hemiacetal

Answer 20

A ketone or aldehyde in alcohol will form an eq mix with the corresponding hemiacetal. This has -OR and -OH on the same carbon

Question 21

Ketone and aldehyde in alcohol forms

Answer 21

Hemiacetal

Question 22

Noncyclic vs cyclic hemiacetals

Answer 22

Non-cyclic aren’t stable 5/6 membered rings are

Question 23

Hemiacetal formation can be catalyzed by:

Answer 23

Acid or base (alcohol) RO(-) or ROH
Acid is 3 steps
Base is 2 steps

Question 24

Aldehyde or Ketone + Water

Answer 24

Forms a hydrate (gem diol)…proton transfer occurs

Question 25

Acetal

Answer 25

Two -OR groups on the same carbon

Question 26

Acetal formation

Answer 26

An aldehyde or ketone can be reacted with ACID ONLY and excess alcohol to form it. Formation goes through the hemiacetal

Question 27

How to go away from an acetal

Answer 27

Dilute acid catalyst

Question 28

What is the key step in hemiacetal --> acetal formation

Answer 28

OR shifts db down to expell H2O+

Question 29

Acetal formation from ketones vs aldehydes

Answer 29

Aldehydes formation is favored, however ketones can cyclicly form rings with acid catalyst. These cyclic acetals (formed by OH-CH2-CH2-OH are good protecting groups for ketones and aldehydes. Cyclic favors ketones.

Question 30

Addition of primary and secondary amines + ketones/aldehydes

Answer 30

They form Immines with primary amines | They form Enamines with secondary amines

Question 31

Immine

Answer 31

Primary amine and ketone/aldehyde. C=N:-R | Have a D.B. and a lone pair

Question 32

Enamine

Answer 32

Secondary amine and ketone/aldehyde C-N:-R + R' | No D.B. or lone pair. STRONG ACID USED

Question 33

Immine formation

Answer 33

Primary amine + carbonyl system with H3O+...there is also a proton transfer. The acid makes the OH a good L.G.

Question 34

Enamine formation

Answer 34

Secondary amine + carbonyl system with HA...key step is removal of an H on the alpha carbon shifting everything back (final step)

Question 35

Cyanohydrin formation

Answer 35

Carbonyl system + :C t.b.N: | The CN group can be reduced with LAH to a amine group or hydrolyzed to a carboxylic acid

Question 36

Hydrolysis of a cyanohydrin yields

Answer 36

alpha-hydroxycarboxylic acid

Question 37

Reduction of a cyanohydrin yields

Answer 37

beta-aminoalcohol

Question 38

Wittig reaction

Answer 38

Aldehydes and ketones react with a phosphorous ylide to form an alkene with both isomers

Question 39

Ylide

Answer 39

A neutral molecule with adjacent positive and negative charges

Question 40

Phosphorus ylide formation

Answer 40

1) (C6H5)3P: attacks a primary or secondary alkyl halide via SN2 forming a salt 2) Base deptotonates this salt

Question 41

Oxophosphatane

Answer 41

The 4 membered ring formed during the Wittig reaction

Question 42

Tollen's test Ag(NH3)2+/H20

Answer 42

Distinguishes aldehydes from ketones Aldehydes react-Silver Ketones don't react-Nothing Alpha hydroxy ketone-Reacts (Silver)

Question 43

Alpha hydroxy ketone

Answer 43

OH on alpha carbon