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chemistry
organic chemistry

Questions and Answers of Organic Chemistry

The 200-MHz 1H NMR spectrum of 1, 4-dimethylbenzene looks exactly like that of CH3OCH2CN except the chemical shifts of the two peaks are δ 2.2 ppm and δ 7.0 ppm. Assign the peaks to the
How many signals would you expect to find in the 1H NMR spectrum of each of the following compounds?M (a) 1-Bromobutane (c) Butane (b) 1-Butanol (d) 1, 4-Dibromobutane (e) 2,
How many signals would you expect to find in the 1H NMR spectrum of each of the following compounds? (a) Vinyl bromide (d) trans-1, 2-Dibromoethene (b) 1, 1-Dibromoethene (e) Allyl bromide (c)
Describe the appearance of the 1H NMR spectrum of each of the following compounds. How many signals would you expect to find, and into how many peaks will each signal be split? (a) 1,
Describe the appearance of the 1H NMR spectrum of each of the following compounds. How many signals would you expect to find, and into how many peaks will each signal be split? (a) ClCH2OCH2CH3 (b)
In addition to the proton marked Ha in m-nitrostyrene in Figure 13.18, there are two other vinylic protons. Assuming that the coupling constant between the two geminal protons in ArCHoeCH2 is 2 Hz
Describe the splitting pattern expected for the proton at (a) C-2 in (Z)-1, 3-dichloropropene (b) C-2 in CH3CHCH
How many signals would you expect to see in the 13C NMR spectrum of each of the following compounds? (a) Propylbenzene (d) 1, 2, 4-Trimethylbenzene (b) Isopropylbenzene (e) 1, 3,
Consider carbons x, y, and z in p-methylanisole. One has a chemical shift of δ 20 ppm; another has δ 55 ppm, and the third δ 157 ppm. Match the chemical shifts with the appropriate
To which of the compounds of Problem 13.12 does the 13C NMR spectrum of Figure 13.22 belong?
Which one of the following compounds is most consistent with the infrared spectrum given in Figure 13.31? Explain your reasoning.
Λmax for the π→π* transition in ethylene is 170 nm. Is the HOMO–LUMO energy difference in ethylene greater than or less than that of cis, trans-1,3-cyclooctadiene?
Which one of the C5H8 isomers shown has its Λmax at the longest wavelength?
Knowing what to look for with respect to isotopic clusters can aid in interpreting mass spectra. How many peaks would you expect to see for the molecular ion in each of the following compounds? At
The base peak appears at m/z 105 for one of the following compounds and at m/z 119 for the other two. Match the compounds with the appropriate m/z values for their base peaks.
How many rings are present in each of the following compounds? Each consumes 2 moles of hydrogen on catalytic hydrogenation. (a) C10H18 (d) C8H8O (b) C8H8 (e) C8H10O2 (c) C8H8CI2 (f) C8H9ClO
Each of the following compounds is characterized by a 1H NMR spectrum that consists of only a single peak having the chemical shift indicated. Identify each compound. (a) C8H18; δ 0.9 ppm
Each of the following compounds is characterized by a 1H NMR spectrum that consists of two peaks, both singlets, having the chemical shifts indicated. Identify each compound.(a) C6H8; δ 2.7 ppm (4H)
Deduce the structure of each of the following compounds on the basis of their 1H NMR spectra and molecular formulas: (a) C8H10; δ 1.2 ppm (triplet, 3H) δ 2.6 ppm (quartet,
From among the isomeric compounds of molecular formula C4H9Cl, choose the one having a 1H NMR spectrum that (a) Contains only a single peak (b) Has several peaks including a doublet at δ 3.4
Identify the C3H5Br isomers on the basis of the following information: (a) Isomer A has the 1H NMR spectrum shown in Figure 13.40.
Identify each of the C4H10O isomers on the basis of their 13C NMR spectra: (a) δ 18.9 ppm (CH3) (two carbons) (c) δ 31.2 ppm (CH3) (three carbons) δ 30.8 ppm (CH) (one carbon)
Identify the C6H14 isomers on the basis of their 13C NMR spectra: (a) δ 19.1 ppm (CH3) (d) δ 8.5 ppm (CH3) δ 33.9 ppm (CH) δ 28.7 ppm (CH3) (b) δ 13.7 ppm (CH3)
A compound (C4H6) has two signals of approximately equal intensity in its 13C NMR spectrum; one is a CH2 carbon at δ 30.2 ppm, the other a CH at δ 136 ppm. Identify the compound.
A compound (C3H7ClO2) exhibited three peaks in its 13C NMR spectrum at δ 46.8 (CH2), 63.5 (CH2), and 72.0 ppm (CH). Excluding compounds that have Cl and OH on the same carbon, which are
From among the compounds chlorobenzene, o-dichlorobenzene, and p-dichlorobenzene, choose the one that (a) Gives the simplest 1H NMR spectrum (b) Gives the simplest 13C NMR spectrum (c) Has three
Compounds A and B are isomers of molecular formula C10H14. Identify each one on the basis of the 13C NMR spectra presented in Figure 13.41.
A compound (C8H10O) has the infrared and 1H NMR spectra presented in Figure 13.42. What is its structure?
Deduce the structure of a compound having the mass spectrum and 1H NMR spectrum presented in Figure 13.43.
Figure 13.44 presents several types of spectroscopic data (IR, 1H NMR, 13C NMR, and mass spectra) for a particular compound. What is it?
[18]-Annulene exhibits a 1H NMR spectrum that is unusual in that in addition to a peak at ? 8.8 ppm, it contains a second peak having a chemical shift ? of - 1.9 ppm. A negative value for the
19F is the only isotope of fluorine that occurs naturally, and it has a nuclear spin of + ½ (a) Into how many peaks will the proton signal in the 1H NMR spectrum of methyl fluoride be split? (b)
31P is the only phosphorus isotope present at natural abundance and has a nuclear spin of +- ½. The 1H NMR spectrum of trimethyl phosphite, (CH3O) 3P, exhibits a doublet for the ethyl protons with
We noted in section 13.13 that an NMR spectrum is an average spectrum of the conformations populated by a molecule. From the following data, estimate the percentages of axial and equatorial bromine
Infrared spectroscopy is an inherently “faster” method than NMR, and an IR spectrum is a superposition of the spectra of the various conformations, rather than an average of them. When 1,
Microwave spectroscopy is used to probe transitions between rotational energy levels in molecules. (a) A typical wavelength for microwaves is 10-2 m, compared with 10-5 m for infrared radiation. Is
The peak in the UV-VIS spectrum of acetone [(CH3)2C═O] corresponding to the n → π* transition appears at 279 nm when hexane is the solvent, but shifts to 262 nm in water. Which is
A particular vibration will give an absorption peak in the infrared spectrum only if the dipole moment of the molecule changes during the vibration. Which vibration of carbon dioxide, the symmetrical
Both of the following organometallic reagents will be encountered later in this chapter. Suggest a suitable name for each.
Write an equation showing the formation of each of the following from the appropriate bromide: (a) Isopropenyllithium (b) sec-Butyllithium
Write the structure of the Grignard reagent formed from each of the following compounds on reaction with magnesium in diethyl ether: (a) p-Bromofluorobenzene (c) Iodocyclobutane (b) Allyl
Butyllithium is commercially available and is frequently used by organic chemists as a strong base. Show how you could use butyllithium to prepare solutions containing (a) Lithium diethylamide,
Write the structure of the product of the reaction of propylmagnesium bromide with each of the following. Assume that the reactions are worked up by the addition of dilute aqueous acid.
Write the equation for the reaction of 1-hexyne with ethylmagnesium bromide as if it involved ethyl anion (CH3CH2) instead of CH3CH2MgBr and use curved arrows to represent the flow of electrons.
Suggest two ways in which each of the following alcohols might be prepared by using a Grignard reagent:
What combination of ester and Grignard reagent could you use to prepare each of the following tertiary alcohols?
Suggest a combination of organic halide and cuprate reagent appropriate for the preparation of each of the following compounds: (a) 2-Methylbutane (b) 1, 3, 3-Trimethylcyclopentene
What alkenes would you choose as starting materials in order to prepare each of the following cyclopropane derivatives by reaction with iodomethylzinc iodide?
The syn stereochemistry of dibromocarbene cycloaddition was demonstrated in experiments using cis- and trans-2-butene. Give the structure of the product obtained from addition of dibromocarbene to
Like nickel, iron reacts with carbon monoxide to form a compound having the formula M (CO)n that obeys the 18-electron rule. What is the value of n in the formula Fe (CO)n?
Write structural formulas for each of the following compounds. Specify which compounds qualify as organometallic compounds. (a) Cyclopentyllithium (d) Lithium divinylcuprate (b) Ethoxymagnesium
Dibal is an informal name given to the organometallic compound [(CH3)2CHCH2]2AlH, used as a reducing agent in certain reactions. Can you figure out the systematic name from which “dibal” is
Suggest appropriate methods for preparing each of the following compounds from the starting material of your choice. (a) CH3CH2CH2CH2CH2MgI (c) CH3CH2CH2CH2CH2Li (b) CH3CH2C≡CMgI (d)
Which compound in each of the following pairs would you expect to have the more polar carbon–metal bond? Compare the models on Learning By Modeling with respect to the charge on the carbon bonded
Write the structure of the principal organic product of each of the following reactions: (a) 1-Bromopropane with lithium in diethyl ether (b) 1-Bromopropane with magnesium in diethyl ether (c)
Using 1-bromobutane and any necessary organic or inorganic reagents, suggest efficient syntheses of each of the following alcohols: (a) 1-Pentanol (d) 3-Methyl-3-heptanol (b) 2-Hexanol (e)
Using bromobenzene and any necessary organic or inorganic reagents, suggest efficient syntheses of each of the following: (a) Benzyl alcohol (b) 1-Phenyl-1-hexanol (c) Bromodiphenylmethane (e)
Analyze the following structures so as to determine all the practical combinations of Grignard reagent and carbonyl compound that will give rise to each:
A number of drugs are prepared by reactions of the type described in this chapter. Indicate what you believe would be a reasonable last step in the synthesis of each of the following:
Predict the principal organic product of each of the following reactions:
Addition of phenylmagnesium bromide to 4-tert-butylcyclohexanone gives two isomeric tertiary alcohols as products. Both alcohols yield the same alkene when subjected to acid-catalyzed dehydration.
(a) Unlike other esters, which react with Grignard reagents to give tertiary alcohols, ethyl formate (HCOCH2CH3) yields a different class of alcohols on treatment with Grignard reagents. What
Reaction of lithium diphenylcuprate with optically active 2-bromobutane yields 2-phenylbutane, with high net inversion of configuration, When the 2-bromobutane used has the stereostructure shown,
Suggest reasonable structures for compounds A, B, and C in the following reactions:
The following conversion has been reported in the chemical literature. It was carried out in two steps, the first of which involved formation of a p-toluenesulfonate ester. Indicate the reagents for
Sometimes the strongly basic properties of Grignard reagents can be turned to synthetic advantage. A chemist needed samples of butane specifically labeled with deuterium, the mass 2 isotope of
Diphenylmethane is significantly more acidic than benzene, and triphenylmethane is more acidic than either. Identify the most acidic proton in each compound, and suggest a reason for the trend in
The 18-electron rule is a general, but not universal, guide for assessing whether a certain transition-metal complex is stable or not. Both of the following are stable compounds, but only one obeys
One of the main uses of the “linear σ-olefins” prepared by oligomerization of ethylene is in the preparation of linear low-density polyethylene. Linear low-density polyethylene is a
Each of the following ethers has been shown to be or is suspected to be a mutagen, which means it can induce mutations in test cells. Write the structure of each of these ethers. (a) Chloromethyl
The heats of combustion of 1, 2-epoxybutane (2-ethyloxirane) and tetrahydrofuran have been measured: one is 2499 kJ/mol (597.8 kcal/mol) the other is 2546 kJ/mol (609.1 kcal/mol). Match the heats of
Ethers tend to dissolve in alcohols and vice versa. Represent the hydrogen-bonding interaction between an alcohol molecule and an ether molecule.
What organic compound mentioned earlier in this chapter is a cyclic dimer of ─OCH2CH2─ units
Outline a reasonable mechanism for the formation of tert-butyl methyl ether according to the preceding equation.
Write equations describing two different ways in which benzyl ethyl ether could be prepared by a Williamson ether synthesis.
Only one combination of alkyl halide and alkoxide is appropriate for the preparation of each of the following ethers by the Williamson ether synthesis. What is the correct combination in each case?
Combustion in air is, of course, a chemical property of ethers that is shared by many other organic compounds. Write a balanced chemical equation for the complete combustion (in air) of diethyl ether.
A series of dialkyl ethers was allowed to react with excess hydrogen bromide, with the following results. Identify the ether in each case. (a) One ether gave a mixture of bromocyclopentane and
Adapt the mechanism shown in Figure 16.4 to the reaction:
Is either of the epoxides formed in the preceding reactions chiral? Is either epoxide optically active when prepared from the alkene by this method?
What is the principal organic product formed in the reaction of ethylene oxide with each of the following? (a) Sodium cyanide (NaCN) in aqueous ethanol (b) Sodium azide (NaN3) in aqueous
Given the starting material 1-methyl-1, 2-epoxycyclopentane, of absolute configuration as shown, decide which one of the compounds A through C correctly represents the product of its reaction with
Which product, compound A, B, or C, would you expect to be formed when 1-methyl-1, 2-epoxycyclopentane of the absolute configuration shown is allowed to stand in methanol containing a few drops of
Which alkene, cis-2-butene or trans-2-butene, would you choose in order to prepare meso-2, 3-butanediol by Epoxidation followed by acidcatalyzed hydrolysis? Which alkene would yield meso-2,
The p-toluenesulfonate derived from (R)-2-octanol and ptoluenesulfonyl chloride was allowed to react with sodium benzenethiolate (C6H5SNa). Give the structure, including stereochemistry and the
Verify, by making molecular models, that the bonds to sulfur are arranged in a trigonal pyramidal geometry in sulfoxides and in a tetrahedral geometry in sulfones. Is phenyl vinyl sulfoxide chiral?
What other combination of alkyl halide and sulfide will yield the same sulfonium salt shown in the preceding example? Predict which combination will yield the sulfonium salt at the faster rate.
There is another oxygen-stabilized cation of m/z 87 capable of being formed by fragmentation of the molecular ion in the mass spectrum of secbutyl ethyl ether. Suggest a reasonable structure for this
Write the structures of all the constitutionally isomeric ethers of molecular formula C5H12O, and give an acceptable name for each.
Many ethers, including diethyl ether, are effective as general anesthetics. Because simple ethers are quite flammable, their place in medical practice has been taken by highly halogenated
Although epoxides are always considered to have their oxygen atom as part of a threemembered ring, the prefix epoxy in the IUPAC system of nomenclature can be used to denote a cyclic ether of various
The name of the parent six-membered sulfur-containing heterocycle is thiane. It is numbered beginning at sulfur. Multiple incorporation of sulfur in the ring is indicated by the prefixes di-, tri-,
The most stable conformation of 1, 3-dioxan-5-ol is the chair form that has its hydroxyl group in an axial orientation. Suggest a reasonable explanation for this fact. Building a molecular model is
Outline the steps in the preparation of each of the constitutionally isomeric ethers of molecular formula C4H10O, starting with the appropriate alcohols. Use the Williamson ether synthesis as your
Predict the principal organic product of each of the following reactions. Specify stereochemistry where appropriate.
Oxidation of 4-tert-butylthiane with sodium metaperiodate gives a mixture of two compounds of molecular formula C9H18OS. Both products give the same sulfone on further oxidation with hydrogen
When (R)-(+)-2-phenyl-2-butanol is allowed to stand in methanol containing a few drops of sulfuric acid; racemic 2-methoxy-2-phenylbutane is formed. Suggest a reasonable mechanism for this reaction.
Select reaction conditions that would allow you to carry out each of the following stereospecific transformations:
The last step in the synthesis of divinyl ether (used as an anesthetic under the name Vinethene) involves heating ClCH2CH2OCH2CH2Cl with potassium hydroxide. Show how you could prepare the necessary
Suggest short, efficient reaction sequences suitable for preparing each of the following compounds from the given starting materials and any necessary organic or inorganic reagents:

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