Questions and Answers of Organic Chemistry 6th

A compound contains carbon, hydrogen, oxygen, and one nitrogen. Classify each of the following fragment ions derived from this compound as an odd-electron or an even-electron ion. Explain.(a) The
In each of the following cases, the labeled protons are constitutionally equivalent. Determine whether the labeled protons in each case are expected to have identical or different chemical shifts.
Determine the structure of the compound with the formula C6H13Cl that has the NMR spectrum shown in Fig. 13.13. FIGURE 13.13 The NMR spectrum for Study Problem
A compound C8H18O2 with a strong, broad infrared absorption at 3293 cm–1 has the following proton NMR spectrum:(The resonance at d 1.96 disappears when the sample is shaken with D2O.) The
An unknown compound with the molecular formula C5H11Br has an NMR spectrum consisting of two resonances, one at δ 1.02 (relative integral 8378 units), and the other at δ 3.15 (relative integral
A compound C7H16O3 has the following 13C NMR-DEPT spectrum (the numbers in parentheses indicate the number of attached hydrogens):Propose a structure for this compound. 8 15.2 (3), 8 59.5 (2), 8
How would you use 13C NMR spectroscopy to differentiate the two isomers 1-chloropentane and 3-chloropentane?
(a) Consider entries 1 through 4 of Table 13.1. How does the chemical shift of a proton vary with the electronegativity of the neighboring halogen?(b) Compare entries 2, 5, and 6 of Table 13.1. How
Predict the NMR spectrum, including approximate chemical shifts, of the following compound. Explain your reasoning. OCH3 CH3O-CH₂-C-CH₂-OCH3 CH₂ OCH3
Propose a structure for a compound with the formula C7H14 with the NMR spectrum shown in Fig. 13.18. Explain in detail how you arrived at your structure.
Each of four bottles, A, B, C, and D, is labeled only “C6H12” and contains a colorless liquid. You have been called in as an expert to identify these compounds from their spectra:Compound A:NMR:
Suggest structures for each of the following compounds. (a) C4H₁0O; 8 1.27 (9H, s); 8 1.92 (1H, broad s; disappears after D₂O shake) (b) C5H₁O: 8 1.78 (3H, s); 8 1.83 (3H, s); 8 2.18 (1H, broad
Explain how the NMR spectra of (a) 3-methyl-2-buten-1-ol and (b) 1,2,2-trimethyl-1-propanol would change following a D2O shake.
Suggest structures for compounds with the following proton NMR spectra. (a) C₂H₁0O: 8 1.13 (3H, t, J = 7 Hz); 8 3.38 (2H, q, J = 7 Hz) 10 (b) C₂H5F₂Cl: 8 1.75 (3H, t, J = 17.5 Hz); 8 3.63
Suppose you were able to cool a sample of 1-bromo-1,1,2-trichloroethane enough that rotation about the carbon–carbon bond becomes slow on the NMR time scale. What changes in the NMR spectrum would
Indicate two things you would look for in their 13C NMR spectra to distinguish between 1,1-dichlorocyclohexane and cis-1,2-dichlorocyclohexane.
Suppose you wish to carry out the following reactions and you have the NMR spectrum of each starting material. In each case, explain what evidence you would look for in the NMR spectra to verify that
To which of the following compounds does the NMR spectrum shown in Fig. P13.46 belong? Explain your choice carefully. Once you have made your choice, explain why the resonance at δ 3.7 is so
What four primary types of information are available from an NMR spectrum? How is each used?
The proton NMR spectrum of valine methyl ester hydrochloride is summarized at the top of the next column.Note that protons He are not split by Hd (and vice versa) because protons He are rapidly
To which of the following compounds does the following 13C NMR-DEPT spectrum belong (attached protons in parentheses): 8 15.5 (3), 8 20.1 (3), 8 60.7 (2), 8 99.6 (1) CH3CH₂0-CH-OCH₂CH3
The two protons Ha and Hb in 1,2,3-trichloropropane have slightly different chemical shifts, and the splitting pattern of each is a doublet of doublets. For one proton, J 5 9.0 Hz and 4.9 Hz; for the
Propose a structure for the compound that has the following spectra:Mass spectrum: m/z = 152, 150 (equal intensity; double molecular ion) NMR: 81.28 (3H, t, J = 7 Hz); 8 3.91 (2H, q, J = 7 Hz); 8 5.0
The NMR spectrum of vitamin D3 is given in Fig. P13.58.Interpret the resonances marked with asterisks (*) by indicating the part of the structure to which they correspond.(Do not try to assign the
You work for a reputable chemical supply house. An angry customer, Fly Ofterhandle, has called, alleging that a sample of 2,5-hexanediol he purchased cannot be the correct compound. As evidence, he
A reaction has yielded a mixture of the following two stereoisomers. Explain how you would use proton NMR to determine which is which. CH3 HH. T Br A CH3 H Br B
Outline a synthesis of the following compound from acetylene and any other compounds containing no more than five carbons: CH3(CH₂)6, CH,CH,CH(CH3)2 C=C H H cis-2-methyl-5-tridecene
17O is a rare isotope that has a nuclear spin. The 17O NMR of a small amount of water dissolved in CCl4 is a triplet (intensity ratio 1 : 2 : 1). When water is dissolved in the strongly acidic
The NMR spectrum of iodocyclohexane was taken at 280 °C. At that temperature, the chair interconversion is slow and each chair conformation can be observed separately.The resonance of proton Ha is
Carbon–carbon splitting is not apparent in naturalabundance 13C NMR spectra because of the rarity of the 13C isotope. However, it can be observed in compounds that are enriched in 13C. A chemist,
Provide the substitutive name for each of the following compounds. Also provide common names for (a) and (b). (a)
A student consulted a well-known compilation of reference spectra for the proton NMR spectrum of propyne and was surprised to find that this spectrum consists of a single unsplit resonance at d 1.8.
Give the product that results from the addition of one equivalent of Br2 to 3-hexyne. What are the possible stereoisomers that could be formed?
Each of the following compounds protonates on nitrogen. Draw the conjugate acid of each. Which compound is more basic? Explain. HỌC–CH=NH H₂C-C=N: A B
(a) Ion A is more acidic than ion B in the gas phase. Is this the acidity order predicted by hybridization arguments? Explain.(b) Ion B is less acidic because it is stabilized by resonance, whereas
Explain why graduate student Choke Fumely, in attempting to synthesize 4,4-dimethyl-2-pentyne using the reaction ofwith tert-butyl bromide, obtained none of the desired product. What product did he
In the course of the synthesis of the sex attractant of the grape berry moth, both the cis and trans isomers of the following alkene were needed.(a) Outline a synthesis of the cis isomer of this
Propose a synthesis of 4,4-dimethyl-2-pentyne from an alkyl halide and an alkyne.
Outline two different preparations of 2-pentyne that involve an alkyne and an alkyl halide.
The following compound is an intermediate in one synthesis of the mating pheromone of the female Indian meal moth. Show how this compound can be converted into the pheromone in a single reaction.
Give the principal product(s) expected when 1-hexyne or the other compounds indicated are treated with each of the following reagents: (a) HBr (b) H₂, Pd/C (c) H₂, Pd/C, Lindlar catalyst (d)
A box labeled “C6H10 isomers” contains samples of three compounds: A, B, and C. Along with the compounds are the IR spectra of A and B, shown in Fig. P14.36. Fragmentary data in a laboratory
(a) Draw the structures of all enols that would spontaneously form the following ketone, including stereoisomers.(b) Would alkyne hydration be a good preparative method for this compound? If so, give
In each case, draw a structure containing only carbon and hydrogen that satisfies the indicated criterion.(a) A stable alkyne of five carbons containing a ring(b) A chiral alkyne of six carbon
You have just been hired by Triple Bond, Inc., a company that specializes in the manufacture of alkynes containing five or fewer carbons. The President, Mr. Al Kyne, needs an outlet for the
(a) When the reduction of alkynes to alkenes by Na in liquid ammonia is attempted with a 1-alkyne, every three moles of 1-alkyne give only one mole of alkene and two moles of the acetylenic
Arrange the following three carboxylic acids in order of increasing acidity (decreasing pKa). Explain your reasoning. H,C=CHCH,CO,H HC=CCH,CO,HCH,CH,CH,CO,H A B C
An optically active alkyne A (C10H14) can be catalytically hydrogenated to butylcyclohexane. Treatment of A with EtMgBr liberates no gas. Catalytic hydrogenation of A over Pd/C in the presence of
Give the structure of the diene and dienophile that would react in a Diels–Alder reaction to give the following product: CO₂CH3 CO₂CH3
Which of the following carbocations is more stable? + CH₂0-CH=CH-CH₂ or A :ÖCH, 1 H₂C=C-CH₂ B +
The conjugated triene (E)-1,3,5-hexatriene has six π molecular orbitals with relative energies ±1.80β, ±1.25β, and ±0.44β.(a) Sketch these MOs. Indicate which are bonding and which are
Predict the relative reactivity of the following two compounds in an SN1 solvolysis reaction. CH₂OCH₂CH₂Cl CH₂CH₂OCH₂Cl 1-chloro-2-methoxyethane (chloromethoxy)ethane A B
Calculate the delocalization energy for (E)-1,3,5-hexatriene.
Draw the s-cis and s-trans conformations of (2E,4E)-2,4-hexadiene and (2E,4Z)-2,4-hexadiene. Which diene contains the greater proportion of the gauche conformation? Why? (Use the s-cis conformation
Use the Frost circle to determine the energy levels and electron occupancies for the π MOs of benzene.
Decide whether each of the following compounds is aromatic. Explain your reasoning. (a) (d) -CH3 toluene (b)
Explain why there is a larger difference between the heats of formation of (E)-1,3 - pentadiene and 1,4-pentadiene (29.3 kJ mol–1 or 7.1 kcal mol–1) than between (E)-1,3- hexadiene and
What is the energy of light (in kJ mol–1 or kcal mol–1) with a wavelength of(a) 450 nm? (b) 250 nm?
(a) What percent of the incident radiation is transmitted by a sample when its absorbance is 1.0? When its absorbance is 0?(b) What is the absorbance of a sample that transmits one-half of the
(a) From the extinction coefficient of isoprene (10,750 M–1 cm–1) and its observed absorbance at 222.5 nm (Fig. 15.5), calculate the concentration of isoprene in mol L–1 (assume a 1 cm light
Predict λmax for the UV absorption of each of the following compounds. (a) Et H T H H T H Et (b) H T H CH3
Refer to Fig. 15.11. At what pH does the fluorescence of fluorescein have the greater quantum yield, pH = 9 or pH = 5? How do you know? relative absorbance 300 488 nm pH=9 pH = 5 400 wavelength,
One of the following compounds has an intense yellow fluorescence when irradiated with UV light. Which one do you think it is, and why? H₂C. CH3 0=S=O A NH₂ H₂C. N CH₂ 0=S=0 NH₂ B H₂C.
What products are formed in the Diels–Alder reactions of the following dienes and dienophiles? (a) (b) and H₂CO-C. and H₂C=C CO₂CH3 CO₂CH3
Give the diene and dienophile that would react in a Diels–Alder reaction to give each of the following products. (a) CN (b) CO₂CH3
(a) In the products of Eq. 15.14, the observed stereochemistry at the ring fusion is not specified. Show this stereo chemistry, assuming that the Diels–Alder reaction gives the endo product.(b)
(a) What product would be expected from the Diels–Alder reaction of 1,3-butadiene as the diene and ethylene as the dienophile?(b) This product is actually not observed under ordinary conditions
Complete the following Diels–Alder reaction. NC NC =C CN CN
A mixture of 0.1 mole of (2E,4E)-2,4-hexadiene and 0.1 mole of (2E,4Z)-2,4-hexadiene was allowed to react with 0.1 mole of TCNE. After the reaction, the unreacted diene was found to consist of only
(a) The allyl anion has an unshared electron pair on the allylic carbon:This anion has two more π electrons than the allyl cation. Use the molecular orbital diagram in Fig. 15.14b to decide which
In each of the following sets, show by the curved-arrow notation how each resonance structure is derived from the other one, and indicate which structure is more important and why. @ [:c=ö< :c=]
(a) Break down the following resonance interaction into four separate resonance structures (counting the two below), each connected to the next by one curved arrow.(b) Draw a hybrid structure
Suggest structures for the two constitutional isomers formed when 1,3-butadiene reacts with one equivalent of Br2. (Ignore any stereochemical issues.) Which of these products would predominate if the
The following isomers do not differ greatly in stability. Predict which one should react more rapidly in an SN1 solvolysis reaction in aqueous acetone. Explain. H C=C A CH3 H3C-CH-CH₂
(a) The following resonance-stabilized ion can protonate to give two different constitutional isomers. Give their structures and give the curved-arrow notation for their formation.(b) One of the
Use a Frost circle to determine the π-electron structure of (a) The cyclopentadienyl anion, which has a planar structure and six π electrons; and (b) The cyclopropenyl cation, which has two π
Furan is an aromatic compound. Discuss the hybridization of its oxygen and the geometry of its two electron pairs. furan (aromatic)
How many bonding MOs are there in a planar, cyclic, conjugated hydrocarbon that contains a ring of 10 carbon atoms? How many π electrons does it have? How many of the π electrons can be
Which of the following species should be aromatic by the Hückel 4n + 2 rule? (a) thiophene G O H H (d) N: isoxazole :0: B Et
Using the theory of aromaticity, explain the finding that A and B are different compounds, but C and D are identical. (That A and B are different molecules was established by Prof. Barry Carpenter
Which of the compounds or ions in Problem 15.38 are likely to be antiaromatic? Explain.Problem 15.38Which of the following species should be aromatic by the Hückel 4n + 2 rule? (a) thiophene G O H
The following molecule has a barrel shape (in which the benzene rings are the “walls” of the barrel). It forms a noncovalent complex with the iodide salt of acetylcholine in chloroform
Using the Hückel 4n + 2 rule, determine whether each of the following compounds is likely to be aromatic. Explain how you arrived at the π-electron count in each case. (a) (c) CO (b) -C=C- (d) :1
Give the principal product(s) expected, if any, when trans-1,3-pentadiene reacts under the following conditions. Assume one equivalent of each reagent reacts unless noted otherwise.(a) Br2 (dark) in
Which of the following molecules is likely to be planar and which nonplanar? Explain. :O: oxepin tropylium ion cyclooctatetraenyl dianion
A colleague, Ima Hack, has subjected isoprene to catalytic hydrogenation to give isopentane. Hack has inadvertently stopped the hydrogenation prematurely and wants to know how much unreacted isoprene
How would the color of b-carotene be affected by treatment of the compound with a large excess of H2 over a Pt/C catalyst? Explain.
Fluorescein was once used to color the Chicago River green on St. Patrick’s Day until it was subsequently replaced with a vegetable dye. One problem with fluorescein was that the green color
If a solution of fluorescein at pH = 9 is subjected to visible light at 488 nm, it has maximum fluorescence at 510 nm. Calculate the energy difference between the absorbed and fluorescing radiation
Draw as many resonance structures as you can for (a) The form of fluorescein present at pH = 9, and (b) The fluorescent group of the green fluorescent protein.Use the curved-arrow notation to
A chemist, I. M. Shoddy, has just purchased some compounds in a going-out-of-business sale from Pybond, Inc., a cut-rate chemical supply house. The company, whose motto is “You get what you pay
Account for the fact that the antibiotic mycomycin is optically active.
If a lysine residue and a phenylalanine residue are located close to each other in a protein structure, describe how you would expect them to be oriented for the most favorable interaction.
Following is a series of acid–base reactions that represent the individual steps in a known organic transformation, the replacement of —Br by —OH at a carbon bearing three alkyl groups.
Let pH - pKa = Δ. Starting with Eqs. 3.30c and 3.30d, derive Eqs. 3.31a and 3.31b. fA= = 10-PK₁ 10 PK + 10-PH (3.30c)
(a) Which acid is the strongest in Problem 3.13?(b) Which acid is the strongest in Problem 3.14?Problem 3.13What is the pKa of an acid that has each of the following dissociation constants?Problem
Acetic acid, CH3CO2H, is a carboxylic acid with pKa = 4.76. What is the fraction of acetic acid dissociated (fA) if 0.1 mole of acetic acid is dissolved in pure water?
A scientist at an Air Force Research Laboratory in California has studied “highly energetic materials” (explosive materials) and, more significantly, has lived to tell about it. In 2000, he and
Use the curved-arrow notation to derive resonance structures that convey the following ideas. In each case, draw a single hybrid structure using dashed lines and partial charges that conveys the same
Malonic acid has two carboxylic acid groups and consequently undergoes two ionization reactions. The pKa for the first ionization of malonic acid is 2.86; the pKa for the second is 5.70. The pKa of

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