ch. 13 questions

Match the carbonyl compounds described with the type of reaction that each undergoes. Aldehydes and ketones: carbonyl compounds with leaving groups:

Aldehydes and ketones: nucleophilic addition carbonyl compounds with leaving groups: nucleophilic substitution

Select all the statements that correctly describe organometallic reagents.

These reagents contain a polar carbon-metal bond. Organometallic reagents are good nucleophiles and strong bases. Reason: Organometallic reagents are a source of nucleophilic carbon.

Select all statements that correctly describe the role of NADH in biological reduction.

Biological reductions with NADH proceed with 100% enantioselectivity. NADH is a coenzyme that donates H:- to the carbonyl group. Pyruvic acid may be reduced by NADH to lactic acid.

Which of the following compounds could be used to deprotonate the hydrogen from a terminal alkyne?

CH3Li NaNH2

Which of the following compounds could be used to convert 1-octyne to the corresponding acetylide anion?

CH3MgBr NaH

Select all statements that correctly describe the reducing agents given below.

DIBAL-H has two bulky isobutyl groups, which make this reagent less reactive than LiAlH4. LiAlH[OC(CH3)3]3is less nucleophilic than LiAlH4.

Select all the statements that correctly describe the mechanism of 1,4-addition of a nucleophile to an α,β-unsaturated carbonyl compound.

Protonation of the enolate oxygen atom produces an enol. In the first step a resonance-stabilized enolate is formed. The 1,4-product is produced directly from protonation of carbon end of the enolate, or by tautomerization of the enol.

True or false: R2CuLi is much less reactive than either RLi or RMgX toward carbonyl groups.

True The polarity of the R-M bond determines the reactivity of the reagent. The R-Cu bond is much less polar than either the R-Li or R-MgX bond.

Reduction results in a(n) _____ in the number of C-O bonds or a(n) _____ in the number of C-H bonds.

decrease, increase

The mechanism for 1,4-addition to an α,β-unsaturated carbonyl compound involves _____ attack at the _____ carbon resulting in an enolate, which is then protonated.

nucleophilic, β

Which of the following reagents will reduce acid chlorides and esters to primary alcohols?

LiAlH4

Select all the statements that correctly describe the mechanism for the LiAlH4 reduction of an aldehyde or ketone.

LiAlH4 serves as a source of hydride ion (there are no free hydride ions present). The oxygen atom of the C=O group is protonated in Step 2, after the nucleophile attacks. The π bond of the C=O group is cleaved in the first step of the reaction. The reaction intermediate has tetrahedral geometry.

From the list below, select the reagent that will reduce an ester to an aldehyde, and select the reagent that will reduce an acid chloride to an aldehyde. LiAlH4 LiAlH[OC(CH3)3]3 NaBH4 DIBAL-H

LiAlH[OC(CH3)3]3 DIBAL-H

Select all reagents that may be used to reduce aldehydes and ketones to alcohols.

NaBH4 LiAlH4

Which of the following statements are correct? Organometallic reagents are strong nucleophiles, but they can also be strong bases. When using organometallic reagents, N-H and O-H bonds must be protected. Organometallic reagents will react with carbonyls before they deprotonate an O-H bond.

Organometallic reagents are strong nucleophiles, but they can also be strong bases. When using organometallic reagents, N-H and O-H bonds must be protected.

Which of the following statements correctly describe protecting groups? Select all statements that apply.

Protecting groups must be easily removed (deprotection) to regenerate the original functional group. A reactive functional group is converted into another functional group that does not interfere with the desired reaction.

Select all of the statements that correctly describe the process of nucleophilic acyl substitution.

The carbonyl group is preserved in this reaction. This reaction does not require protonation as the final step. The electronegative atom attached to the carbonyl group acts as a leaving group.

Select all the statements that correctly describe the mechanism of the reaction between an organometallic reagent and an aldehyde or ketone.

The intermediate of the reaction is a tetrahedral species. The carbon group of the organometallic reagent acts as the nucleophile. The final step of the reaction involves protonation of the alkoxide oxygen. The organometallic reagent adds to the carbonyl carbon

Select all statements that correctly describe the reactions of organometallic reagents.

The polarity of the R-M bond determines the reactivity of the organometallic reagent. After an organometallic reagent adds to a C=O group, the fate of the intermediate depends on the presence or absence of a leaving group. Organometallic reagents attack electrophilic carbon atoms, especially the carbonyl group.

Select all the statements that correctly explain why ketones are less reactive than aldehydes.

The two alkyl groups of a ketone stabilize the partial charge on the carbonyl C, making it less reactive. An aldehyde is less sterically crowded, allowing nucleophilic attack to occur more easily.

A Grignard reagent is prepared by reacting a(n) ______ with Mg metal in anhydrous ether.

alkyl halide

Organometallic reagents are very strong bases and readily abstract a proton from which of the following? Select all that apply.

amines water alcohols

Grignard reagents react with _____ to give carboxylic acids after protonation of the resulting carboxylate anion.

carbon dioxide

The mechanism for the reaction of Grignard reagents with aldehydes and ketones proceeds by ___ attack at the carbonyl carbon to form a tetrahedral alkoxide intermediate followed by___ of the alkoxide upon addition of water or aqueous acid.

nucleophilic, protonation

Esters react with two equivalents of Grignard reagent to produce ______ alcohols.

tertiary

When a Grignard reagent reacts with an unsymmetrical epoxide, the Grignard group attacks ______

the least substituted carbon from the back side.

During reduction of an acid chloride _____ equivalent(s) of H:- is/are delivered by LiAlH4. The leaving group Z is _____ and a _____ alcohol is formed.

two, chloride, primary

A mixture of CrO3/H2SO4/H2O may be used to convert a(n) _____ into a(n) _____.

1° alcohol, carboxylic acid

Select all statements that correctly describe the mechanism of the reduction of acid chlorides and esters with a metal-hydride reducing agent.

An aldehyde is produced in Step 2 of the mechanism. In Step 2 the π bond is re-formed. In Step 2 of ester reduction, an alkoxide leaving group is expelled from the tetrahedral intermediate.

Organolithium and Grignard reagents react with aldehydes and ketones forming a new carbon-carbon bond and resulting in the formation of a(n) ___ after aqueous workup (protonation).

alcohol

When the OH group of an ______ is reacted with TBDMSCl/imidazole, the resulting TBDMS ether is known as a ______ group.

alcohol, protecting

In cells, NADH donates a ______ to a carbonyl and acts as a ______ agent.

hydride, reducing