Chapter 16 Flashcards
carbonyl group
consists of 1 sigma bond formed by overlap of sp2 hybrid orbitals and 1 pi bond
functional group of aldehyde
carbonyl + H atom + C atom
functional group of ketone
carbonyl group + 2 carbons
IUPAC of aldehyde
- parent chain is longest chain that contains carbonyl
- suffix from -e to -al
- unsaturated aldehyde infix from -an- to -en-
- cyclic: carbaldehyde
IUPAC ketone
- suffix -e to -one
- # chain o give c=o lowest #
physical properties of aldehydes and ketones
- C=O is polar
- both are polar
- have higher boilingpoints
protonation
makes carbonyl a better electrophile (more partially +)
reaction of aldehyde/ketone with a proton or Lewis acid
- forms a resonance stabilized cation
- protonation increases the electron deficiency of the carbonyl carbon and make sit more reactive toward nucleophilic
- neutral nucleophiles are “wimpy”
cyanide ion
HCN adds to C=O group of aldehyde or ketone to give cyanohydrin
cyanohydrin
molecule containing -OH group and CN group bonded to same carbon
addition of water to carbonyl group
give geminal diol (hydrate)
addition of alcohol to C=O group
gives hemiacetal
hemiacetal
molecule containing -OH & -OR or -OA at same C
hemiactel + alcohol
form acetals
-w/ ethylene glycol and other glycols they produce a 5 membered cyclic acetal
acetals
a molecule containing 2 -OR or -OAr
- act like ethers - stable to organometallics
- can be protecting group
addition of nitrogen nucleophiles to aldehydes/ketones
-ammonia, primary aliphatic amines, and primary aromatic amines react w/ carbonyl group of aldehydes and ketones to give imines (Schiff bases)
imines
-value: carbon-nitrogen double bond can be reduced to a carbon-nitrogen single bond
wittig reaction
very versatile synthetic method for synthesis of alkenes from aldehydes and ketones
ylid
molecule, which when written as a Lewis acid, has positive and negative charges
- normally cis (Z) product
- if negative carbon is stabilized, mostly trans (E)
phosphonium ylids formed in two steps
- nucleophilic displacement of I by (Ph)3P
2. treatment of phosphonium salt w/ a very strong base (BuLi, NaH, NaNH2)
Horner-Emmons-Wadsworth modification
- use a phosphonester
- use trimethylphosphate, rather than triphenylphosphine
- 2nd SN2 to get intermediate
acidity of alpha hydrogens
- hydrogens alpha to a carbonyl group are more acidic than hydrogens of alkanes, alkenes, & alkynes
- less acidic than hydroxyl hydrogen of alcohols
enol
protonated enolate
keto-enol tautomerism
- proton transfer to carbonyl oxygen
2. proton transfer to Base
racemization at alpha carbon
may be catalyzed by acid or base
alpha halogenation
two types:
- in dilute acid - typically one halogen added
- in base - all alpha H’s replaced
after 3x halogenation
loss of leaving group
-methyl ketones may be converted to carboxylic acids w/ loss of carbon atom via haloform reaction
oxidation of aldehydes
- aldehydes are oxidized to carboxylic acids by variety of agents (H2CrO4)
- also oxidized by Ag+ in aqueous ethanol or THF
- oxidized by O2 in radical chain reaction
- sensitive to air, must be stored in N2
oxidation of ketones
- very hard
- not oxidized by H2CrO4
- oxidized by powerful oxidants at high temp and high conc of acid or base
reductions
H- sources metal hydride reactions NaBH4 & LiAIH4
NaBH4 reduction
- carried out in aqueous or pure methanol or ethanol
- 1 mol reduces 4 mol aldehyde or ketone
catalytic hydrogenation
- not as easy as C=C reduction
- selectively possible
