Aldehydes and Ketones Flashcards
What is an aldehyde?
An aldehyde is an organic molecule consisting of an alkane chain with a carbon-oxygen double bond on one terminal carbon of the chain.
All aldehydes are named by removing the -e from the end of the name of the parent alkane and replacing it with -al. The three carbon chain below is called propanal.
What is the name of this molecule?
This molecule is named pentanal.
To name an aldehyde, remove the -e from the end of the name of the parent alkane and replace it with -al. Since an aldehyde is a terminal group (always position 1) it’s unnecessary to write 1-pentanal.
What is the IUPAC name of the following molecule?
Methanal (common name: formaldehyde).
All aldehydes are named by removing the -e from the end of the name of the parent alkane and replacing it with -al.
What is a ketone?
An ketone is an organic molecule consisting of an alkane chain with a carbon-oxygen double bond on one of the internal carbons of the chain.
All ketones are named by removing the -e from the end of the name of the parent alkane and replacing it with -one. The three carbon chain below is called propanone, also known commonly as acetone.
What is the name of this molecule?
This molecule is named 2-pentanone.
To name an ketone, remove the -e from the end of the name of the parent alkane and replace it with -one. This will always be called 2-pentanone and never 4-pentanone.
What is the IUPAC name of the following molecule?
This molecule is named butanone.
All ketones are named by removing the -e from the end of the name of the parent alkane and replacing it with -one.
How will the boiling point for ketones and aldehydes compare to simple hydrocarbons of the same length? Why?
Ketones and aldehydes will have higher boiling points, due to dipole-dipole forces (hydrocarbons only have dispersion forces).
Ex: Propane has a boiling point of -42C, compared to propanal 50C and propanone 56C.
How will the boiling point for ketones and aldehydes compare to alcohols of the same length? Why?
Ketones and aldehydes will have lower boiling points, since alcohols can hydrogen bond (which is stronger than dipole-dipole).
Ex: Propanol has a boiling point of 97C, compared to propanal 50C and propanone 56C.
What atom in a ketone or aldehyde is most succeptible to nucleophilic attack? Why?
The C=O carbon.
Oxygen is very electronegative and pulls electron charge away from the carbon, leaving the carbon with a partial positive charge.
What is the product when an aldehyde and alcohol are reacted in the presence of an acid catalyst?
Hemiacetal (and water).
What is the product when a ketone and alcohol are reacted in the presence of an acid catalyst?
Hemiketal (and water).
What is an acetal?
An acetal is an aldehyde derivative, where the carbonyl has been replaced by two OR groups, where the R groups can be identical or different.
Acetals are formed via the reaction of an aldehyde molecule with two equivalents of alcohol.
What is the product when an aldehyde and excess alcohol are reacted in the presence of an acid catalyst?
Acetal (and water).
What is the product when a ketone or aldehyde and secondary amine are reacted in a condensation reaction?
Enamine (and water).
What is a ketal?
An ketal is a ketone derivative, where the carbonyl has been replaced by two OR groups, where the R groups can be identical or different.
Ketals are formed via the reaction of a ketone molecule with two equivalents of alcohol.
What is the product when a ketone and excess alcohol are reacted in the presence of an acid catalyst?
Ketal (and water).
What is the name of this functional group?
This functional group is an imine functional group.
Imine nomenclature is rarely tested on the MCAT; it is sufficient to know the identity of the functional group.
What would be the product if a carbonyl containing compound was reacted so that the oxygen from the C=O bond was replaced with an N-H group?
Imine.
What product will this reaction form?
Hemiketal
The -OR group from the alcohol is the nucleophile, the carbon from the ketone is the electrophile, and the oxygen accepts the H instead of reforming the carbonyl. A basic workup keeps the -OH from further protonating and creating a leaving group.
What product will this reaction form?
Hemiacetal
The -OR group from the alcohol is the nucleophile, the carbon from the aldehyde is the electrophile, and the oxygen accepts the H instead of reforming the carbonyl. A basic workup keeps the -OH from further protonating and creating a leaving group.
What product will this reaction form?
Ketal
The -OR group from the alcohol is the nucleophile, the carbon from the ketone is the electrophile, and the oxygen accepts the H instead of reforming the carbonyl. An acidic workup protonates the -OH into H2O, creating a leaving group and allowing a second -OR substitution to occur.
What product will this reaction form?
Acetal
The -OR group from the alcohol is the nucleophile, the carbon from the aldehyde is the electrophile, and the oxygen accepts the H instead of reforming the carbonyl. An acidic workup protonates the -OH into H2O, creating a leaving group and allowing a second -OR substitution to occur.
What product will this reaction form?
Chloroform (a type of haloform) and a terminal carboxylate group.
The strong base (OH-) removes a proton from the methyl group and Cl attaches in its place. This happens three times (exhaustive halogenation), and creates a stable leaving group. The base attacks, and chloroform leaves with the H, allowing the carbonyl bond to reform.
What product will this reaction form in the presence of heat?
An enone. (4-methyl-3-penten-2-one)
The enolate ion of propanone nucleophilicly attacks the carbonyl carbon of an original propanone, and protonates that original carbonyl oxygen. By shifting a beta proton, this creates H2O as a good leaving group, and subsequent condensation.
What stable resonance structure will a 1,3 dicarbonyl structure form?
An internal hydrogen bonded enol.
What product will this reaction form?
2-methyl-butanol.
A ketone reacting with an organometallic reagent will produce an alcohol on a tertiary carbon.
What product will this reaction form?
Propane (and nitrogen gas).
A ketone reacted with hydrazine will form an alkane segment (methylene) and nitrogen gas.
What product will this reaction form?
An alcohol on a secondary carbon.
The MgBr detatches and leaves back into solution.
What product will this reaction form after acid work up?
An alcohol on a tertiary carbon.
The OR group of the reactant is a good leaving group, so this will react with two equivalents of Grignard reagent, once as a substitution of R’ and once as an addition of R’.
Would the tert-Butyl groups on the following molecule affect a nucelophilic addition to the carbonyl carbon? If so, how would the groups affect reactivity?
Yes.
Reactivity would be decreased due to the steric hindrance of the tert-Butyl groups.
What product form(s) are possible after deprotonation of an alpha proton on a carbonyl compound?
A resonance stabilized carbanion, in both keto and enol forms.
What resonance structure(s) will an alpha, beta-unsaturated carbonyl form?
An enolate and a resonance structure with the double bond shifted to the beta-carbon.
What is the product of a strong nucelophilic attack on an alpha, beta-unsaturated carbonyl (such as the one below)?
A carbonyl with the nucleophile added to the beta position.
The nucleophile attacks at the beta position, causing the alpha, beta-unsaturated carbonyl to convert to the enol form. The enol then tautomerizes back to a carbonyl.
What product will this reaction form?
2-methyl-propene.
The oxygen from the carbonyl group will be replaced by a CH2 group, forming a terminal alkene.
What product will this reaction form?
2-butanone.
Aldehydes with a 2-carbon chain or longer will always form a product that contains a ketone.
