Chapter 18: Aldehydes and Ketones - Nucleophilic Addition to the Carbonyl Group

In a mass spectrometer, aldehydes and ketones can undergo fragmentation to initially form an acyl _____

cation

A _____ effect causes α hydrogen(s) of a ketone to appear at a lower field than alkyl carbons

deshielding

Due to the polarization of the carbonyl group, the carbonyl C atom is _____ and readily react with _____

electrophilic; nucleophiles

The C=O group found in aldehydes and ketones is called the _____ group

carbonyl

Organize the steps involved in enamine formation in the correct order, beginning with the first at the top

1. nucleophilic attack 2. elimination of H2O/OH- 3. deprotonation at the former α C atom

Which of the following will hydrogen bond to an aldehyde?

-alcohol -water

In the biological oxidation of ethanol, two enzymes are employed. Match each enzyme to its function

-alcohol dehydrogenase: converts ethanol to ethanal -aldehyde dehydrogenase: converts ethanal to ethanoic acid

Match each type of starting material to the product formed in a reduction reaction using NaBH4 or LiAlH4

-aldehyde : primary alcohol -ketone : secondary alcohol

Match the starting material with the product in reactions of carbonyl containing compounds with Grignard reagents

-aldehyde: secondary alcohol -ketone: tertiary alcohol

Match each substrate shown with the typical position of the equilibrium when preparing an acetal

-aldehydes: equilibrium favors products -ketones: equilibrium favors reactants

Select all the statements that correctly describe a Wittig reagent

-an organophosphorous reagent -a species containing nucleophilic C

Match each functional group with the correct IR absorption

-carbonyl C=O : 1700 cm-1 -aldehyde C-H : 2700-2830 cm-1 -ketone C=O : 1715 cm-1 -aldehyde C=O : 1730 cm-1

Which of the following are typical solvents for use in a Wittig reaction?

-dimethyl sulfoxide -tetrahydrofuran

Designate the appropriate chemical steps that will prepare a ketone with a different number of carbons from an aldehyde

-first step: addition of a Grignard reagent -second step: oxidation of a secondary alcohol with Cr+6 -not used: reduction with LiAlH4; formation of an acetal

Select all the statements that correctly describe the mechanism of a Wittig reaction

-nucleophilic attack by the ylide at the carbonyl C occurs at the same time that the carbonyl O attacks the P of the ylide -step 2 involves eliminaton of Ph3P=O, and two new π bonds are formed at the same time

The correct suffix used to designate a ketone is _____

-one

Select the steps required (not necessarily in order) to generate a Wittig reagent

-reaction of a phosphonium salt with a strong base -reaction of an alkyl halide with Ph3P (triphenylphosphine)

Select all the reagents and/or reaction conditions under which acetals are stable

-reducing agents -oxidizing agents -aqueous base -nucleophilic attack

Which of the following options correctly describe the mechanism of acetal formation from an aldehyde or ketone?

-the alcohol acts as a nucleophile in the reaction -a hemiacetal is formed as an intermediate -the first step of the reaction is protonation of the carbonyl O atom

Select all the structural features that determine the chemical and physical properties of aldehydes and ketones

-the carbonyl C is an electrophilic center -the C=O group is polarized -the C and O of the C=O group are sp2 hybridized

Select all the statement that apply to the reaction of a carbonyl compound with H2O in the presence of either acid or base catalyst

-the product is called a hydrate -H an OH add across the C-O π bond

Which of the following options correctly describe the reactivity of the C=O carbon atom in aldehydes and ketones?

-this carbon atom is electrophilic due to the polarization of the C=O bond -since the carbonyl is relativity uncrowded, reactions at this site often involve nucleophilic addition reactions

The following steps are required to generate a Wittig reagent. Place them in the correct order, with the first at the top

1. an alkyl halide is reacted with Ph3P 2. a phosphonium salt is racted with a strong base

Order the steps of the Wittig reaction correctly, with the first at the top

1. concerted nucleophilic attack by both species to form an oxaphosphetene ring 2. elimination of Ph3P=O form an alkene

Rank the following in order of stability, with the more stable compound at the top

1. ketone carbonyl 2. aldehyde carbonyl

Place the steps involved in imine formation in the correct, beginning with the first

1. nucleophilic attack by amine 2. proton transfer to form an unstable hemiaminal 3. protonation of OH to give a good leaving group 4. elimination of H2O to form an iminium ion 5. loss of a proton to form the imine

Order the steps in the acid-catalysed hydration of an aldehyde or ketone, beginning with the first

1. protonation of the C=O oxygen 2. addition of water 3. deprotonation of oxygen

Hydration of aldehydes and ketones can occur both acidic and basic conditions. Match the following reaction characteristics with the mechanism associated with each

Basic conditions: nucleophilic attack occurs as the first step; the nucleophile is stronger, increasing the rate of reaction Acidic conditions: protonation of the carbonyl oxygen is the first step; the electrophilic character of the carbonyl C atom is increased, increasing the rate of reaction

If the Wittig reagent with a cyanide group is used to form an alkene, which stereoisomer of the alkene is likely to form?

E isomer

Which of the following is true regarding compounds that contain both aldehyde and alcohol functional groups?

They are named as aldehydes with hydroxyl substituents

Reaction of a aldehyde with two equivalents of an alcohol will produce a(n) _____

acetal

Which of the following provides a good protecting group for an aldehyde/ketone?

acetal

How can ketones and aldehydes be distinguished by IR spectroscopy?

aldehydes will have C-H stretching bands around 2720 and 2820 cm-1 that will not be present in a ketone

How can aldehydes and ketones be distinguished by NMR?

aldehydes will have a proton around 9-10 ppm that will not be present in ketones

In the Wittig reaction a(n) _____ is produced by reaction of an aldehyde/ketone with a Wittig reagent

alkene

A Wittig reagent is an example of an ylide, a species containing two oppositely charged atoms bonded to each other, both of which have full octets. In the Wittig reagent, a negatively charged _____ atom is bonded to a positively charged _____ atoms

carbon; phosphorous

The species formed when an aldehyde or ketone reacts with one equivalent of alcohol is a(n) _____

hemiacetal

Acetal formation is reversible, and an acetal can therefore be _____ to the original aldehyde or ketone using aqueous _____

hydrolyzed; acid

Since O _____ electronegative than C, the C=O is polarized and the C has _____ electron density than the O

more; less

What will be the product when an acetal is reacted with LiAlH?

no reaction

In terms of length and strength, the C=O bond of a carbonyl group is _____ and _____ than the C=C bond of an alkene

shorter; stronger

What is the hybridization of the oxygen atom of a carbonyl group?

sp2

What solvent is used when triphenylphosphonium salts are converted to ylides using an alkyllithium reagent as the base?

tetrahydrofuran

Which of the following statements correctly describe the numbering of a ketone parent chain?

the chain is numbered so that the carbonyl C has the lowest possible number

How can aldehydes and ketones be distinguished through C-NMR spectroscopy?

they cannot be easily distinguished; other characterization methods must be used

Ethylene glycol, HOCH2CH2OH, will react with an aldehyde or ketone to form an acetal. Since ethylene glycol has _____ OH group(s), it forms a(n) _____ acetal when reacted with a carbonyl compound

two; cyclic

An acetal is a compound _____

with one carbon singly bonded to two -OR groups