Solved: Propose structures for molecules that meet the following descriptions. Assume

Each of the following substances can be prepared by a nucleophilic addition reaction between an aldehyde or ketone and a nucleophile. Identify the reactants from which each was prepared. If the substance is an acetal, identify the carbonyl compound and the alcohol; if it is an imine, identify the carbonyl compound and the amine; and so forth.

The following molecular model represents a tetrahedral intermediate resulting from addition of a nucleophile to an aldehyde or ketone. Identify the reactants, and write the structure of the final product when the nucleophilic addition reaction is complete.

The enamine prepared from acetone and dimethylamine is shown in its lowest-energy form. (a) What is the geometry and hybridization of the nitrogen atom? (b) What orbital on nitrogen holds the lone pair of electrons? (c) What is the geometric relationship between the p orbitals of the double bond and the nitrogen orbital that holds the lone pair? Why do you think this geometry represents the minimum energy?

Draw structures corresponding to the following names: (a) Bromoacetone (b) (S)-2-Hydroxypropanal (c) 2-Methyl-3-heptanone (d) (2S,3R)-2,3,4-Trihydroxybutanal (e) 2,2,4,4-Tetramethyl-3-pentanone (f) 4-Methyl-3-penten-2-one (g) Butanedial (h) 3-Phenyl-2-propenal (i) 6,6-Dimethyl-2,4-cyclohexadienone (j) p-Nitroacetophenone

Draw and name the seven aldehydes and ketones with the formula C5H10O. Which are chiral?

Give IUPAC names for the following compounds: C (a) (b) (c) (d) (e) (f) CH3 CH3CHCCH2CH3 O O CH3CHCH2CH OH O CH3 H OH CH2OH CHO O CHO OHC

Draw structures of compounds that fit the following descriptions: (a) An a,b-unsaturated ketone, C6H8O (b) An a-diketone (c) An aromatic ketone, C9H10O (d) A diene aldehyde, C7H8O

Predict the products of the reaction of (1) phenylacetaldehyde and (2) acetophenone with the following reagents: (a) NaBH4, then H3O1 (b) DessMartin reagent (c) NH2OH, HCl catalyst (d) CH3MgBr, then H3O1 (e) 2 CH3OH, HCl catalyst (f ) H2NNH2, KOH (g) (C6H5)3PPCH2 (h) HCN, KCN

Show how you might use a Wittig reaction to prepare the following alkenes. Identify the alkyl halide and the carbonyl components.

How would you use a Grignard reaction on an aldehyde or ketone to synthesize the following compounds? (a) 2-Pentanol (b) 1-Butanol (c) 1-Phenylcyclohexanol (d) Diphenylmethanol

How might you carry out the following selective transformations? One of the two schemes requires a protection step. (Recall from Section 19.4 that aldehydes are more reactive than ketones toward nucleophilic addition.) CH3CCH2CH2CH2CH CH3CCH2CH2CH2CH2OH (a) O O O CH3CCH2CH2CH2CH CH3CHCH2CH2CH2CH

How would you prepare the following substances from 2-cyclohexenone? More than one step may be needed. (a) (b) (c) (d) (Two ways)

How would you synthesize the following substances from benzaldehyde and any other reagents needed? (a) CH (b) (c) 2CHO C CH2

Carvone is the major constituent of spearmint oil. What products would you expect from reaction of carvone with the following reagents? Carvone O (a) (CH3)2Cu2 Li1, then H3O1 (b) LiAlH4, then H3O1 (c) CH3NH2 (d) C6H5MgBr, then H3O1 (e) H2/Pd (f ) CrO3, H3O1 (g) (C H ) PCHCH 6 5 3 3  (h) HOCH2CH2OH, HCl

How would you synthesize the following compounds from cyclohexanone? (a) 1-Methylcyclohexene (b) 2-Phenylcyclohexanone (c) cis-1,2-Cyclohexanediol (d) 1-Cyclohexylcyclohexanol

At what position would you expect to observe IR absorptions for the following molecules? OHC (a) (c) (b) (d) 4-Androstene-3,17-dione 1-Indanone O O O O O H H CH3 CH3

Acid-catalyzed dehydration of 3-hydroxy-3-phenylcyclohexanone leads to an unsaturated ketone. What possible structures are there for the product? At what position in the IR spectrum would you expect each to absorb? If the actual product has an absorption at 1670 cm21, what is its structure?

Propose structures for molecules that meet the following descriptions. Assume that the kinds of carbons (1, 2, 3, or 4) have been assigned by DEPT-NMR. (a) C6H12O; IR: 1715 cm21; 13C NMR: 8.0 d (1), 18.5 d (1), 33.5 d (2), 40.6 d (3), 214.0 d (4) (b) C5H10O; IR: 1730 cm21; 13C NMR: 22.6 d (1), 23.6 d (3), 52.8 d (2), 202.4 d (3) (c) C6H8O; IR: 1680 cm21; 13C NMR: 22.9 d (2), 25.8 d (2), 38.2 d (2), 129.8 d (3), 150.6 d (3), 198.7 d (4)

Compound A, C8H10O2, has an intense IR absorption at 1750 cm21 and gives the 13C NMR spectrum shown. Propose a structure for A.

Propose structures for ketones or aldehydes that have the following 1H NMR spectra: (a) C4H7ClO IR: 1715 cm21

Aldehydes can be prepared by the Wittig reaction using (methoxymethylene)- triphenylphosphorane as the Wittig reagent and then hydrolyzing the product with acid. For example, (Methoxymethylene)- triphenylphosphorane O + (C6H5)3P CHOCH3 + H OCH3 C H3O+ CHO (a) How would you prepare the necessary phosphorane? (b) Propose a mechanism for the hydrolysis step.

When 4-hydroxybutanal is treated with methanol in the presence of an acid catalyst, 2-methoxytetrahydrofuran is formed. Explain. O CH3OH HOCH2CH2CH2CHO HCl OCH3

The SN2 reaction of (dibromomethyl)benzene, C6H5CHBr2, with NaOH yields benzaldehyde rather than (dihydroxymethyl)benzene, C6H5CH(OH)2. Explain.

Reaction of 2-butanone with HCN yields a chiral product. What stereochemistry does the product have? Is it optically active?

One of the steps in the metabolism of fats is the reaction of an unsaturated acyl CoA with water to give a b-hydroxyacyl CoA. Propose a mechanism. H2O RCH2CH2CH CHCSCoA Unsaturated acyl CoA -Hydroxyacyl CoA O O RCH2CH2CH CH2CSCoA

The amino acid methionine is biosynthesized by a multistep route that includes reaction of an imine of pyridoxal phosphate (PLP) to give an unsaturated imine, which then reacts with cysteine. What kinds of reactions are occurring in the two steps?

Each of the following reaction schemes contains one or more flaws. What is wrong in each case? How would you correct each scheme? (a) 1. LiAIH4 2. H3O+ 1. CH3MgBr 2. H3O+ H+, CH3OH (b) CrO3 H3O+ H3O+ O CH3 O CH3 C6H5CH CHCH2OH HCN, KCN Ethanol CH3CCH3 C6H5CH CHCHO CHCH(OCH3) C6H5CH 2 O CH3CCH3 (c) OH CN CH3CCH3 OH CH2NH2

6-Methyl-5-hepten-2-one is a constituent of lemongrass oil. How could you synthesize this substance from methyl 4-oxopentanoate? CH3CCH2CH2COCH3 Methyl 4-oxopentanoate

Aldehydes and ketones react with thiols to yield thioacetals just as they react with alcohols to yield acetals. Predict the product of the following reaction, and propose a mechanism: + 2 CH3CH2SH ? H+ catalyst

Ketones react with dimethylsulfonium methylide to yield epoxides. Suggest a mechanism for the reaction. CH2S(CH3)2 (CH3) + + 2S O Dimethylsulfonium methylide

When cyclohexanone is heated in the presence of a large amount of acetone cyanohydrin and a small amount of base, cyclohexanone cyanohydrin and acetone are formed. Propose a mechanism. OH + + CH3CCH3

Tamoxifen is a drug used in the treatment of breast cancer. How would you prepare tamoxifen from benzene, the following ketone, and any other reagents needed? (CH3)2NCH2CH2O C O ? CH2CH3 (CH3)2NCH2CH2O C C Tamoxifen

Paraldehyde, a sedative and hypnotic agent, is prepared by treatment of acetaldehyde with an acidic catalyst. Propose a mechanism for the reaction. catalyst H+ CH3 H3C CH3 O 3 CH3CH O O O Paraldehyde

The MeerweinPonndorfVerley reaction involves reduction of a ketone by treatment with an excess of aluminum triisopropoxide, [(CH3)2CHO]3Al. The mechanism of the process is closely related to the Cannizzaro reaction in that a hydride ion acts as a leaving group. Propose a mechanism. CH3COCH3

Propose a mechanism to account for the formation of 3,5-dimethylpyrazole from hydrazine and 2,4-pentanedione. Look carefully to see what has happened to each carbonyl carbon in going from starting material to product. CH3CCH2CCH3 O O 2,4-Pentanedione 3,5-Dimethylpyrazole

In light of your answer to Problem 19.61, propose a mechanism for the formation of 3,5-dimethylisoxazole from hydroxylamine and 2,4-pentanedione. 3,5-Dimethylisoxazole

Trans alkenes are converted into their cis isomers and vice versa on epoxidation followed by treatment of the epoxide with triphenylphosphine. Propose a mechanism for the epoxide n alkene reaction. RCO3H (Ph)3P (Ph)3P O

Treatment of an a,b-unsaturated ketone with basic aqueous hydrogen peroxide yields an epoxy ketone. The reaction is specific to unsaturated ketones; isolated alkene double bonds do not react. Propose a mechanism. O H2O2 NaOH, H

One of the biological pathways by which an amine is converted to a ketone involves two steps: (1) oxidation of the amine by NAD1 to give an imine and (2) hydrolysis of the imine to give a ketone plus ammonia. Glutamate, for instance, is converted by this process into a-ketoglutarate. Show the structure of the imine intermediate, and propose mechanisms for both steps. NH3

Compound A, MW 5 86, shows an IR absorption at 1730 cm21 and a very simple 1H NMR spectrum with peaks at 9.7 d (1 H, singlet) and 1.2 d (9 H, singlet). Propose a structure for A

Compound B is isomeric with A (Problem 19.66) and shows an IR peak at 1715 cm21. The 1H NMR spectrum of B has peaks at 2.4 d (1 H, septet, J 5 7 Hz), 2.1 d (3 H, singlet), and 1.2 d (6 H, doublet, J 5 7 Hz). What is the structure of B?

The 1H NMR spectrum shown is that of a compound with formula C9H10O. How many double bonds and/or rings does this compound contain? If the unknown has an IR absorption at 1690 cm21, what is a likely structure?

The 1H NMR spectrum shown is that of a compound isomeric with the one in Problem 19.68. This isomer has an IR absorption at 1730 cm21. Propose a structure. [Note: Aldehyde protons (CHO) often show low coupling constants to adjacent hydrogens, so the splitting of aldehyde signals is not always apparent.]

Propose structures for ketones or aldehydes that have the following 1H NMR spectra: (a) C9H10O2 IR: 1695 cm21

Propose structures for ketones or aldehydes that have the following 1H NMR spectra. (a) C10H12O IR: 1710 cm21 TMS Intensity 10 0123456789 ppm0123456789 ppm Chemical shift () Chem. shift 1.01 2.47 3.66 7.28 Rel. area 1.50 1.00 1.00 2.50 (b) C6H12O3 IR: 1715 cm21 I TMS ntensity 10 0123456789 ppm0123456789 ppm Chemical shift ()

Primary amines react with esters to yield amides: RCO2R1RNH2 n RCONHR1ROH. Propose a mechanism for the following reaction of an a,b-unsaturated ester. O O O N + CH3NH2 + CH3OH CO2CH3

When crystals of pure a-glucose are dissolved in water, isomerization slowly occurs to produce b-glucose. Propose a mechanism for the isomerization. OH OH H -Glucose

When glucose (Problem 19.73) is treated with NaBH4, reaction occurs to yield sorbitol, a polyalcohol commonly used as a food additive. Show how this reduction occurs. H OH OH Glucose Sorbit

The Wharton reaction converts an epoxy ketone to an allylic alcohol by reaction with hydrazine. Propose a mechanism. (Hint: Review the WolffKishner reaction in Section 19.9.) CH3CO2 +Na CH3CO2H O O CH3 OH CH3 + H2NNH2 + N2