Ch. 6: Aldehydes and Ketones I Flashcards
basic components: ketone vs. aldehyde
ketone: two alkyl groups bonded to the carbonyl
aldehyde: one alkyl group and one hydrogen
what do the components of ketone vs. aldehyde imply about where the group lies in a compound?
the carbonyl in a ketone is never a terminal group, whereas it always is in an aldehyde
aldehydes and ketones are often strong-smelling compounds, give 5 examples of compounds containing volatile carbonyls
- cinnamon
- vanilla
- cumin
- dill
- ginger
how are aldehydes named and what are the common names of the first 5 aldehydes?
how are aldehydes named when they are substituents?
named: replacing the -e at the end of the alkane name with the suffix -al
first 5 aldehydes: common (real)
formaldehyde (methanal)
acetaldehyde (ethanal)
propionaldehyde (propanal)
butryaldehyde (butanal)
valeraldehyde (pentanal)
when substituent: named with the prefix oxo-
how is an aldehyde named if it is attached to a ring?
the suffix -carbaldehyde is used instead
how are ketones named? when about when they are substituents?
replacing the -e with -one
when naming by their common names: the two alkyl groups are named alphabetically, followed by -ketone
when they are named as substituents: use the prefix oxo- or keto-
how are the physical properties of aldehydes and ketones governed by the presence of the carbonyl group in comparison to the forces and physical properties of alcohols? (3)
- the dipole of the carbonyl is stronger than the dipole of an alcohol because the double-bonded oxygen is more electron-withdrawing than the single bond to oxygen in the hydroxyl group
- in solution, the dipole moments associated with these polar carbonyl groups increase intermolecular attractions, causing an elevation in boiling point relative to their parent alkanes
- however, even though aldehydes and ketones have dipoles more polar than those of alcohols, the elevation in boiling point is less than that in alcohols because no hydrogen bonding is present
why do aldehydes and ketones both act as electrophiles in reactions?
due to the electron-withdrawing properties of the carbonyl oxygen, which leaves a partial positive charge on the carbon
why are aldehydes generally more reactive toward nucleophiles than ketones are?
because they have less steric hindrance and fewer electron-donating alkyl groups
why does the carbonyl carbon have a dipole moment?
oxygen is more electronegative and pulls electrons away from the carbon, making the carbon electrophilic and a good target for nucleophiles
how can an aldehyde form?
the partial oxidation of a primary alcohol, only by PCC
how can a ketone form?
the oxidation of a secondary alcohol, which can be done using reagents ranging from sodium or potassium dichromate salts to chromium trioxide to PCC
why is there concern about oxidizing too far when oxidizing a primary alcohol, but not a secondary alcohol? what impact does this have on what oxidants can be used?
when oxidizing a secondary alcohol, there is no concern because the reaction will stop at the ketone stage
whereas, when oxidizing a primary alcohol, if the oxidant is stronger than PCC, primary alcohols would continue to be oxidized PAST aldehydes, all the way to carboxylic acids
why is the carbonyl carbon an electrophile, ripe for nucleophilic attack?
the C=O bond is polarized, with a partial positive charge on the carbonyl carbon and a partial negative charge on the oxygen
explain the basics of nucleophilic attack on a carbonyl carbon (4)
- when the nucleophile attacks, it forms a covalent bond to the carbon, breaking the pi bond in the carbonyl
- the electrons from the pi bond are pushed onto the oxygen atom
- oxygen happily accepts extra electrons due to its electronegativity
- breaking the pi bond forms a tetrahedral intermediate