Y2 Carbonyls (O) Flashcards
(58 cards)
Nucleophile definition
An electron pair donor
Electrophile definition
An electron pair acceptor. Attracted to areas of high electron density
Why do acyl chlorides undergo nucleophilic addition reactions?
- The oxygen and chlorine atoms attached to the carbonyl carbon are electronegative. - - They pull the electrons in the covalent bonds toward them, leaving the carbonyl carbon positive
- This makes it available for attack by nucleophiles.
What type of reactions do acyl chlorides undergo?
Nucleophilic addition elimination
What acyl chloride reactions do you need to know?
Reactions with:
- water,
- alcohol (ethanol),
- ammonia,
- a primary amine
What is the product of acyl chloride and each reactant?
with water —> carboxylic acid
with alcohol —> ester
with ammonia —> primary amide
with primary amine —> secondary amide (N-subsituted amide)
What is the mechanism for the reduction of a ketone or aldehyde?
Nucleophilic addition with NaBH4 (with methanol and water) or LiAlH4 (with dry ether)
ketones and aldehydes can also undergo nucleophilic addition with…?
- A cyanide ion
- chain length +1
- hydroxy nitrile formed
What is the nucleophile of nucleophilic addition reactions
H(-) /hydride /hydrogen anion
Solubility of carbonyls
- as the length of the chain increases
- carbonyls become less soluble in water
- the significance of the polar C=O bond decreases
- aren’t then dissolved in a polar solvent
Why does ‘like’ dissolve ‘like’?
-polar compounds are dissolved by polar solvents as small intermolecular forces between the molecules will be created e.g dipole-dipole bonding and hydrogen bonding.
- non polar compounds will be disolved in non polar solvents depending on chain length creating v.d.w imf.
Why won’t a non-polar compound dissolve in a polar solvent? e.g hexane in a water solvent
as water is polar it is far more likely to undergo hydrogen bonding with other water molecules than bond to hexane.
How many H does one reduction require?
2 [H+]
Reactant for oxidation
Potassium dichromate (K2Cr2O7) and dilute H2SO4
colour change of potassium dichromate
orange Cr(6+) to green Cr(3+) colour change
Reactant for reduction
NaBH4 (sodium borohydride) or LiAlH4 (lithium aluminium hydride)
What to Tollen’s and Fehlings solution indicate?
aldehyde is present ( as can be partially oxidised further but ketones can’t)
Fehling’s solution colour change
Blue Cu(2+) ions –> brick red ppt Cu2O
Tollen’s reagent colour change
colourless –> silver mirror
[Ag(NH3)2]+ complex ions form metallic Ag+ (silver)
What two Nucleophilic addition reactions happen with ketones and aldehydes?
Reduction with cyanide or hydride ion
If undergoing Nucleophilic addition of a carbonyl with cyanide ion
Hydroxy nitrile produced will be an optically active isomer. And form two enantiomers with a chiral carbon.
- Watch out for it! Think
Why are racemates formed in equimolar ratios (50:50)?
- Attacks onto a planar molecule at the carbon
- There is equal opportunity of the cyanide ion attacking above or below the plane
- Therefore, enantiomers and racemates are formed
- Results in a trigonal planar molecule
What are all reducing sugars?
Aldehydes
What are all non-reducing sugars?
Ketones
