Chapter 13 605300-MHz 1H NMR spectrum ppm ( )1 H1 H1 H3 HDTransmittance (%)01004000 3500

Draw the structures of the molecules with the following names. (a) 1-Chloro-1-butyne (b) (Z)-4-Bromo-3-methyl-3-penten-1-yne (c) 4-Hexyn-1-ol

Name each of the compounds below, using the IUPAC system of nomenclature. (a) Cl (b) OH (c) OH (d) (e) (f) %

Compare C H bond strengths in ethane, ethene, and ethyne. Reconcile these data with hybridization, bond polarity, and acidity of the hydrogen.

Compare the C2 C3 bonds in propane, propene, and propyne. Should they be any different with respect to either bond length or bond strength? If so, how should they vary?

Predict the order of acid strengths in the following series of cationic species: CH3CH2NH3 1, CH3CH NH2 1, CH3C q NH1. [Hint: Look for an analogy among hydrocarbons (Section 13-2).]

The heats of combustion for three compounds with the molecular formula C5H8 are as follows: cyclopentene, DHcomb 5 21027 kcal mol21; 1,4-pentadiene, DHcomb 5 21042 kcal mol21; and 1-pentyne, DHcomb 5 21052 kcal mol21. Explain in terms of relative stability and bond strengths.

Rank in order of decreasing stability. (a) 1-Heptyne and 3-heptyne (b) CqCCH3, CH2CqCH, and (Hint: Make a model of the third structure. Is there anything unusual about its triple bond?)

Deduce structures for each of the following. (a) Molecular formula C6H10; NMR spectrum A; no strong IR bands between 2100 and 2300 or 3250 and 3350 cm21. (b) Molecular formula C7H12; NMR spectrum B; IR bands at about 2120 and 3330 cm21. (c) The percentage composition is 71.41% carbon and 9.59% hydrogen (the remainder is O), and the exact molecular mass is 84.0584; NMR and IR spectra C (next page). The inset in NMR spectrum C provides better resolution of the signals between 1.6 and 2.4 ppm. 4 H 6 H 2.0 1.5 1.0 0.5 0.0 A 300-MHz 1H NMR spectrum ppm () 1H NMR (CH3)4Si 2 H 1 H 2 H 4 H 3 H 2.0 1.5 1.0 0.5 0.0 300-MHz 1H NMR spectrum ppm () B (CH3)4Si 1H NMR Chapter 13 601 2 H 2 H 1 H 1 H 2 H IR Transmittance (%) 0 Wavenumber

The IR spectrum of 1,8-nonadiyne displays a strong, sharp band at 3300 cm21. What is the origin of this absorption? Treatment of 1,8-nonadiyne with NaNH2, then with D2O, leads to the incorporation of two deuterium atoms, leaving the molecule unchanged otherwise. The IR spectrum reveals that the peak at 3300 cm21 has disappeared, but a new one is present at 2580 cm21. (a) What is the product of this reaction? (b) What new bond is responsible for the IR absorption at 2580 cm21? (c) Using Hookes law, calculate the approximate expected position of this new band from the structure of the original molecule and its IR spectrum. Assume that k and f have not changed.

Write the expected product(s) of each of the following reactions. (a) CH3CH2CHCHCH2Cl CH3 Cl 3 NaNH2, liquid NH3 A A (b) CH3OCH2CH2CH2CHCHCH3 Br 2 NaNH2, liquid NH3 A Br A (c) meso-CH3CHCH2CHCHCH2CHCH3 CH3 Cl NaOCH3 (1 equivalent), A A CH3OH CH3 A Cl A (d) (4R,5R)-CH3CHCH2CHCHCH2CHCH3 CH3 NaOCH3 (1 equivalent), CH3OH A CH3 A Cl A Cl

(a) Write the expected product of the reaction of 3-octyne with Na in liquid NH3. (b) When the same reaction is carried out with cyclooctyne (Problem 33b), the product is cis-cyclooctene, not trans-cyclooctene. Explain, mechanistically.

Write the expected major product of reaction of 1-propynyllithium, CH3C q C2Li1, with each of the following molecules in THF. (a) CH3CH2Br (b) Cl (c) Cyclohexanone (d) CH OB (e) CH3CH CH2 O i f (f ) KK % CH3 O H

Write the mechanism and fi nal product for the reaction of 1-propynyllithium with trans-2,3- dimethyloxacyclopropane.

Which of the following methods is best suited as a high-yield synthesis of 2-methyl- 3-hexyne, ? (a) H2, Lindlar's catalyst (b) NaNH2, liquid NH3 Cl Cl (c) 1. Cl2, CCl4 2. NaNH2, liquid NH3 (d) Li  Br (e) Li  Br

Propose reasonable syntheses of each of the following alkynes, using the principles of retrosynthetic analysis. Each alkyne functional group in your synthetic target should come from a separate molecule, which may be any two-carbon compound (e.g., ethyne, ethene, ethanal). (a) (b) OH (c) OH (d) (CH3)3CCCH [Be careful! What is wrong with (CH3)3CCl 1 2:CCH?]

Draw the structure of (R)-4-deuterio-2-hexyne. Propose a suitable retro-SN2 precursor of this compound.

Reaction review. Without consulting the Reaction Road Map on p. 598, suggest reagents to convert a general alkyne RCqCH into each of the following types of compounds. (a) P R Br Br C C D G H D G (b) ROCOC Br Br O A A H Br Br A A (c) ROCOC H H O A A H (Markovnikov product)

Give the expected major product of the reaction of propyne with each of the following reagents. (a) D2, Pd CaCO3, Pb(O2CCH3)2, quinoline; (b) Na, ND3; (c) 1 equivalent HI; (d) 2 equivalents HI; (e) 1 equivalent Br2; (f ) 1 equivalent ICl; (g) 2 equivalents ICl; (h) H2O, HgSO4, H2SO4; (i) dicyclohexylborane, then NaOH, H2O2.

What are the products of the reactions of dicyclohexylethyne with the reagents in Problem 44?

Write the structures of the initially formed enol tautomers in the reactions of propyne and dicyclohexylethyne with dicyclohexylborane followed by NaOH and H2O2 (Problems 44, part i, and 45, part i).

Give the products of the reactions of your fi rst two answers to Problem 45 with each of the following reagents. (a) H2, Pd C, CH3CH2OH; (b) Br2, CCl4; (c) BH3, THF, then NaOH, H2O2; (d) MCPBA, CH2Cl2; (e) OsO4, then H2S.

Propose several syntheses of cis-3-heptene, beginning with each of the following molecules. Note in each case whether your proposed route gives the desired compound as a major or minor fi nal product. (a) 3-Chloroheptane; (b) 4-chloroheptane; (c) 3,4-dichloroheptane; (d) 3-heptanol; (e) 4-heptanol; (f) trans-3-heptene; (g) 3-heptyne.

Propose reasonable syntheses of each of the following molecules, using an alkyne at least once in each synthesis. P r o b l e m s (a) Br Cl (b) I I (c) meso-2,3-Dibromobutane (d) Racemic mixture of (2R,3R)- (e) Br H Cl Cl CH3 CH3 (f) O and (2S,3S)-2,3-dibromobutane (g) OH HO (h) H O (i)

Show how the Heck reaction might be employed to synthesize each of the following molecules. (a) B COCH3 O (b)

Propose a reasonable structure for calcium carbide, CaC2, on the basis of its chemical reactivity (Section 13-10). What might be a more systematic name for it?

Propose two different syntheses of linalool, a terpene found in cinnamon, sassafras, and orange fl ower oils. Start with the eight-carbon ketone shown here and use ethyne as your source of the necessary additional two carbons in both syntheses. O ? OH Linalool

The synthesis of chamaecynone, the essential oil of the Benihi tree, requires the conversion of a chloroalcohol into an alkynyl ketone. Propose a synthetic strategy to accomplish this task. HO O Cl C CH ? Eventually KK KK O q C Chamaecynone CH

Synthesis of the sesquiterpene bergamotene proceeds from the alcohol shown here. Suggest a sequence to complete the synthesis. ? 0 HOH2C CH3 Bergamotene 0CH3

An unknown molecule displays 1H NMR and IR spectra D (next page). Reaction with H2 in the presence of the Lindlar catalyst gives a compound that, after ozonolysis and OO O B B B treatment with Zn in aqueous acid, gives rise to one equivalent of CH3CCH and two of HCH. What was the structure of the original molecule?

Chapter 13 605 300-MHz 1H NMR spectrum ppm ( ) 1 H 1 H 1 H 3 H D Transmittance (%) 0 100 4000 3500 3000 2500 2000

A synthesis of the sesquiterpene farnesol requires the conversion of a dichloro compound into an alkynol, as shown below. Suggest a way of achieving this transformation. (Hint: Devise a conversion of the starting compound into a terminal alkyne.) P r o b l e m s Cl Cl ? C C CH2 q O OH Eventually OH Farnesol

Your team is studying the problem of an intramolecular ring closure of enediyne systems important in the total synthesis of dynemicin A, which exhibits potent antitumor activity. H OH % BB AA AA BB AA AA O HN OH O OH O H COOH OCH3 CH3 Dynemicin A ~ % % One research group tried the following approaches to effect this process. Unfortunately, all were unsuccessful. Divide the schemes among yourselves and assign structures to compounds A through D. (Note: R9 and R0 are protecting groups.) 1. N B AA AA O OCH3 CH3O % CH3 OH OCH3 OCH3 H CH3SO2Cl, (CH3CH2)3N A LiNR2 ~ N B AA AA O OCH3 CH3O % CH3 OCH3 OCH3 % H ? ? 2. B RN 1. (CH3CH2CH2CH2)4NF, THF (removes R) 2. CH3SO2Cl, (CH3CH2)3N AA AA OCH3 % CH3 OH O ~ RNAA AA OCH3 % CH3 OH R ~ % % R OCH3 OCH3 ? OCH3 OCH3 ? C LiNR2 % RNAA AA OCH3 %CH3 H H O ~ % OCH3 OCH3 ? 3. RNA OCH3 % CH3 OH Br O D OH Mild base } % % LiNR2 % RNAA AA OCH3 %CH3 H H O ~ % H Chapter 13 607 A successful model study (shown here) provided an alternative strategy toward the completion of the total synthesis. CHO O O LDA OH

The compound whose structure is H C q C(CH2)3Cl is best named (IUPAC) (a) 4-chloro-1-pentyne; (b) 5-chloropent-1-yne; (c) 4-pentyne-1-chloroyne; (d) 1-chloropent-4-yne.

A nucleophile made by deprotonation of propyne is (a) 2:CH2CH3; (b) 2:HC CH2; (c) 2:C q CH; (d) 2:C q CCH3; (e) 2:HC CHCH3.

When cyclooctyne is treated with dilute, aqueous sulfuric acid and HgSO4, a new compound results. It is best represented as (a) O (b) OH (c) HO OH (d) (e)

From the choices shown below, pick the one that best describes the structure of compound A. A H3PO4, pH 2, 270C, 100 atm O CH3 (a) HOCH2CH(CH2)2OH CH3 A (b) HOCH2CHCH2OH CH3 A (c) CCHCH2OH CH3 HC A q (d) CCH2CHCH2OH CH3

From the choices shown below, pick the one that best describes the structure of compound A. CH3C CCH2OH A (A primary alcohol; %C  68.6, %H  8.6, and %O  22.9) 1-butanol Br2 (2 equivalents) Br A Br Br Br A A A O H2 (2 equivalents), Raney Ni (a) CH2PCHCH2CH2OH (b) CH2OH (c) CH3CqCCH2OH (d) CH3CHPCHOCHPCHOH (e) OH