Ketones and Aldehydes Flashcards
(26 cards)
Carbonyl Group
Sp2 hybridized carbon,120 degree sigma bonds, the p-p C-O double bond is higher in Energy than alkene.
Dipole moment in Carbonyl group
Large moment due to the charge difference between oxygen and carbon. Bonding electrons are not equally shared. We conclude the carbon is the Lewis acid (wants electrons) and the oxygen is the Lewis base (donates electrons).
Physical Properties
Higher boiling point than hydrocarbons due to the dipole moment. Lower than hydrogen bonds for alcohol however. These molecules may not be involved with hydrogen bonding, forming a hydrogen bond.
Oxidation of Alcohol synthesis
Used for secondary alcohols. Alcohols are oxidized to ketones by chromic acid (Na2Cr2O7), bleach (NaOCl), and KMnO4.
Oxidation of Primary Alcohols
Needs careful selection to avoid over-oxidation. PCC provides a good yield without overoxidation.
Ozonolysis
Cleaves alkenes to give ketones and aldehydes.
Acid and Salt Catalyzed
Note this process done in Markovnikov orientation.
Hydroboration of Alkynes
Done in anti-Markovnikov orientation.
1,3 Dithiane
It is the masked carbonyl group. Add this molecule to an alkyl group on the carbonyl group of target compound.
Note: Ketone uses BuLi with primary halide to add two groups to form the ketone. Both aldehyde and ketone use H+, HgCl2, and H2O to get the desired product.
Synthesis from Carboxylic Acid
Consult picture below:
Synthesis from Nitriles
View reaction below.
Note: ketone is formed after excess Gringnard reagent is destroyed so ketone isn’t attacked.
Synthesis of aldehyde from acid chloride
Produce acid chloride through addition of acid with thionyl chloride. After production of acid chloride, Need reducing agent to react faster with acid chloride than aldehyde.
Synthesis of ketone from acid chloride
Same production of acid chloride as in aldehyde. Need Grignard reagent to add to the acid chloride to give ketone. React too much so need Gilman’s reagent (a weak organometallic reagent) to react faster with acid than ketone.
Reactions of Aldehydes and Ketones
Undergo Nucleophilic addition (add nucleophile along with hydrogen across a C-O double bond)
Aldehydes are more reactive because only one electron donating alkyl group (better electrophile) and less steric hinderance.
Nucleophilic Addition to Carbonyl Groups
Basic conditions (strong nucleophile)
Nucleophile Addition to Carbonyl Group
Acidic conditions (weak nucleophile)
Wittig Reaction
Converts carbonyl group into C-C double bond
Ylide
Molecule used in WIttig Reaction (no net charge).
Negative Carbon, Positive heteroatom. Note the two resonance structures, the double bond is unfavored because phosphorus uses d orbital.
Also, want unhindered alkyl group as ylide is a SN2 reaction.
Hydration of Ketones and Aldehyde
Ketones are favored in keto form (unhydrated) due to the 2 alkyl substituents that stabilize the charge.
Aldehydes more likely to be seen as hydrate due to the not so stable positive charge (strong electrophile)
Cyanohydirn
Strong conjujate base nucleophile, attacks ketone and aldehyde to give cyanohydrin.
Note: Greatest reactivity?
Formaldehyde>Other aldehydes>ketones
Imines
Other Condensation Reactions (Table)
Acetals
Tollens Test
Involves adding silver-ammonia complex to an unknown compound. If aldehyde is present, black or silver deposit forms.
