Carbonyl Groups Flashcards
what causes an oxygen lobe in π bonding to be bigger than a carbon lobe?
O is more electronegative.
pullse e- more closely towards itself.
lower energy value.
tell me about the synthesis of primary and secondary alcohols to form aldehydes/carboxylic acids and ketones.
1⁰ = aldehyde.
2⁰ = ketone.
Chromium
what is the relative reactivity of aldehydes and ketones?
aldehydes more reactive than ketones, due to having an electronegative H on carbonyl group.
H is more acidic, easily abstracted by Nu, carbonyl is more electrophilic and susceptible to nucleophilic attack.
ketones have two alkyl groups which reduce the electrophilicity, and increase stability.
can you link the reactivity of aldehydes and ketones to hyperconjugation and conjugation?
In aldehydes, carbonyl is attached to H, becomes electron-rich due to hyperconjugation.
More susceptible to nucleophilic attack, hence more reactive.
carbonyl group has a weaker π bond due to lack of electron donation from neighbouring C atom.
in ketones, carbonyl group has greater steric bulk.
This provides more electron density to the carbonyl C through conjugation.
stronger π bond and less reactive carbonyl group.
what are some steric effects on the position of equilibrium in carbonyl chemistry?
Steric hindrance can hinder the appraoch of Nu to Carbon, making the reaction slower and shifting eq. towards the reactants.
(steric effect).
electron-donating groups can increase the electron density on Carbon. More susceptible to Nu attack.
(conjugation effect).
electron-withdrawing groups decrease the electron density on the carbonyl, less susceptible to Nu attack.
(conjugate effect).
tell me about the relative rates of stability in the nucleophilic addition of water to form hydrates.
carbonyl stability decreases due to hyperconjugation as it becomes more bulky.
inductive effects also further destabilises the C=O bond.
hydrate stability increases as steric crowding around sp³ increases.
tell me about the rates of carboxylic acid derivatives.
the higher the wavelength for C=0, the less LP donation.
can see inductive and resonance effects in max C=O wavelength.
inductive>resonance because LP on Cl is in 3p orbital.
3p> π* LUMO = less e- donation.
as the wavelength decreases, there is decreasing e- withdrawal through σ bonds.
increasing e- donation from LP into C=O through π* bonds.
in the Nu addition to carboxylic acid derivatives, what determines whether the intermediate reacts further or stops?
LG ability of X ion.
bond strength of C-X.
solvent effects.
describe the structure and bonding in aldehydes:
C=O bond is sp2 hybridised.
O has two LP, can accept electron density.
carbonyl group has a polarised db.
describe the structure and bonding in ketone:
C = sp2 hybridised, bond angle is 120⁰.
C has trigonal planar geometry.
carbonyl group has a π bond between C and O = planar structure.
