Questions and Answers of Organic Chemistry 6th

A sample of (S)-2-butanol has an observed rotation of 12.18° at 20 °C. The measurement was made with a 2.0 M solution of (S)-2-butanol in methanol solvent in a sample container that is 10 cm long.
Determine the isomeric relationship between the following two molecules: CH3CH₂ H CH₂CH3 H H C=C CH3CH₂ CH₂CH3 H
Show the planes and centers of symmetry (if any) in each of the following achiral objects.(a) The methane molecule (b) A cone (c) The ethylene molecule (d) The trans-2-butene molecule (e) The
Your lab partner tells you that a sample of (1)-2-butanol has an apparent specific rotation of 113.8 degrees mL g–1 dm–1 and is known to be a mixture of the two enantiomers with EE = 94%.How much
Draw line-and-wedge representations for each of the following chiral molecules. Use models if necessary. (D 5 deuterium = 2H, a heavy isotope of hydrogen.) Note that several correct structures are
Indicate whether the asymmetric atom in each of the following compounds has the R or S configuration. H с. www. CH3 OH (b) NH₂ alanine НО www. ОН | CH₂ H OH malic acid О Me I ***** Pr
Suppose a sample of an optically active substance has an observed rotation of 110°. The scale on the analyzer of a polarimeter is circular, so 110° is the same as 2350° or 1370°. How would you
(a) The specific rotation of sucrose (table sugar) in water is 166.1 degrees mL g–1 dm–1. What is the observed optical rotation in a 1 dm path of a sucrose solution prepared from 5 g of sucrose
(a) Identify the asymmetric carbon of thalidomide.(b) Draw a structure of the teratogenic S enantiomer of thalidomide using lines, a wedge, and a dashed wedge to indicate the stereochemistry of this
A 0.1 M solution of an enantiomerically pure chiral compound D has an observed rotation of 10.20° in a 1 dm sample container. The molecular mass of the compound is 150.(a) What is the specific
A chemist has developed a new synthesis of ibuprofen and has reported that she has prepared the (S)-(1)-enantiomer in 90% EE, and that this material has a measured specific rotation of 151.7 degrees
Use the known stereochemistry of the starting alkene (from this section) to assign the stereochemical configuration of the product, which was found by experiment to be levorotatory.
Explain how you would use the alkene starting material in Problem 6.13 to determine the absolute configuration of the dextrorotatory enantiomer of the following hydrocarbon:Indicate what reaction you
Explain why the following compound has two meso stereoisomers. ОН ОН ОН | | | H3C-CH-CH-CH-CH3
Taking the anti conformation of butane as an isolated structure, determine whether it has any stereocenters. If so, identify them.
Which of the following compounds could in principle be resolved into enantiomers at very low temperatures? Explain.(a) Propane (b) 2,3-dimethylbutane (c) 2,2,3,3-tetramethylbutane
Arsenic (As) is below nitrogen and phosphorus in Group 5A of the periodic table. In an arsine (R3As;) the R—As—R bond angles are about 92°. How would you expect the inversion rate of arsines to
Identify all of the asymmetric carbon atoms (if any) in each of the following structures. (a) (b) CH₂CH₂CH- T CH3 CH3CH₂CH- T CH3 CH3 (c) H₂C-CH-CH₂OH T CH₂OCH3 (d)
As described in the previous account, Pasteur discovered two stereoisomers of tartaric acid. Draw their structures [you cannot tell which is (1) and which is (2)]. Which stereoisomer of tartaric acid
Think of Pasteur’s enantiomeric resolution of racemic acid in terms of the “resolving agent” idea discussed in Sec. 6.8. Did Pasteur’s resolution involve a resolving agent? If so, what was it?
For each of the following compounds, draw a line-andwedge structure in which all carbon–carbon bonds are in the plane of the page.(a) (3R,4R)-3,4-hexanediol (b) meso-3,4-hexanediol(c)
Ephedrine has been known in medicine since the Chinese isolated it from natural sources in about 2800 BC. Its structure has been known since 1885. Ephedrine can be used as a bronchodilator (a
Draw the structure of the chiral alkane of lowest molecular mass not containing a ring.
Indicate whether each of the following statements is true or false. If false, explain why.(a) In some cases, constitutional isomers are chiral.(b) In every case, a pair of enantiomers have a mirror
Imagine substituting, in turn, each hydrogen atom of 3-methylpentane with a chlorine atom to give a series of isomers with molecular formula C6H13Cl. Give the structure of each of these isomers.
Draw the structures of all compounds with the formula C6H12Cl2 that can exist as meso compounds. Indicate how many meso compounds are possible for each structure.
Explain why compound A in Fig. P6.39 can be resolved into enantiomers but compound B cannot. CH3 1. Ph−N#CH_–CH=CH, CI CH,Ph Figure P6.39 A CH3 T Ph–N–CH,–CH=CH2 B
Construct sawhorse and Newman projections (Sec. 2.3A) of the three staggered conformations of 2-methylbutane (isopentane) that result from rotation about the C2—C3 bond.(a) Identify the
(a) Which of the compounds shown in Fig. P6.40 can in principle be resolved into enantiomers? Explain why or why not.(b) Omeprazole can be separated into two enantiomers that do not interconvert at
The specific rotation of the R enantiomer of the following alkene is [a]25D 5 179 degrees mL g–1 dm–1, and its molecular mass is 146.2.(a) What is the observed rotation of a 0.5 M solution of
(S)-(1)-Aspartic acid is one of the naturally occurring a-amino acids.Over time in the environment or in aqueous solution, aspartic acid can undergo racemization very slowly (by a process that we
The two most common forms of glucose, α-D-glucopyranose and β-D-glucopyranose, can be brought into equilibrium by dissolving them in water with a trace of an acid or base catalyst.The specific
(a) 2,3,4-Trichloropentane has two meso stereoisomers.Starting with the template below for each, complete line-and-wedge structures for the two meso stereoisomers.(b) Show the symmetry element in
(a) Give the stereochemical relationship (enantiomers, diastereomers, or the same molecule) between each pair of compounds in the set shown in Figure P6.46. Assume that internal rotation is rapid.(b)
From the outcome of the transformation shown in Fig. P6.48, indicate whether the levorotatory enantiomer of the product has the R or S configuration. Draw a structure of the product that shows its
(a) Explain why an optically inactive product is obtained when (2)-3-methyl-1-pentene undergoes catalytic hydrogenation.(b) What is the absolute configuration of (1)-3-methylhexane if catalytic
Which of the salts shown in Fig. P6.49 should have identical solubilities in methanol? Explain. Ph HC H.C H + NH3 A Figure P6.49 H;C **** + Ph C
Draw the structures of the possible stereoisomers for the compound below, assuming in turn (a) Tetrahedral, (b) Square planar, (c) Pyramidal geometries at the carbon atom. For each of these
Two stereoisomers of the compound (H3N)2Pt(Cl)2 with different physical properties are known. Show that this fact makes it possible to choose between the tetrahedral and square planar arrangements of
In 1914, the chemist Emil Fischer carried out the following conversion in which optically active starting material was transformed into a product with an identical melting point and an optical
Fischer also carried out the following pair of conversions. Again, no bonds to the asymmetric carbon were broken. Explain why this pair of conversions (but not either one alone) and the associated
Make a model of chair cyclohexane corresponding to the leftmost model in Fig. 7.4. Raise carbon-4 so that carbons 2–5 lie in a common plane. This is the half-chair conformation of cyclohexane, and
Given that the twist-boat form is 15.9 kJ mol–1 (3.8 kcal mol–1) higher in standard free energy than the chair form of cyclohexane, calculate the percentages of each form present in a sample of
The ΔG° difference between the axial and equatorial conformations of methylcyclohexane (7.4 kJ mol–1, 1.74 kcal mol–1; see Fig. 7.9) is about the same as the ΔH° difference. Calculate the
(a) The axial conformation of fluorocyclohexane is 1.0 kJ mol–1 (0.25 kcal mol–1) less stable than the equatorial conformation.What is the energy cost of a 1,3-diaxial interaction between
(a) Show that trans-1,3-dimethylcyclohexane is chiral. (b) For the 1R,3R stereoisomer, draw the two chair conformations.(c) What is the relationship between the two chair conformations of this
Determine the relative energies of the two chair conformations of trans-1,2-dimethylcyclohexane. Which conformation is more stable?
For each of the following compounds, draw the two chair conformations that are in equilibrium.(a) Cis-1,3-dimethylcyclohexane (b) Trans-1-ethyl-4-isopropylcyclohexane
What stereoisomeric products could be formed in the addition of bromine to cyclohexene? Which should be formed in the same amounts? Which should be formed in different amounts?
According to the experimental results in Eq. 7.33, is the addition of bromine to cis-2-butene a syn- or an anti-addition? H3C-CH=CH-CH3 cis trans Br₂ CH₂Cl2 Br Br 1
For each of the compounds in Problem 7.5, draw a boat conformation.Problem 7.5For each of the following compounds, draw the two chair conformations that are in equilibrium.(a)
Draw planar-ring structures for the following cyclic compounds.(a) Cis-1-bromo-3-methylcyclohexane (both enantiomers)(b) (1R,2S,3R)-2-chloro-1-ethyl-3-methylcyclohexane
Draw the two chair conformations of each compound in Problem 7.7.Problem 7.7Draw planar-ring structures for the following cyclic compounds.(a) Cis-1-bromo-3-methylcyclohexane (both enantiomers)(b)
Draw the planar-ring structure that results from each rotation of the following structure.(a) 180° about axis (a)(b) 120° counterclockwise about an axis (b) that runs through the center of the ring
Redraw the following chair conformations after 180° rotations about each of the axes shown. Use models if necessary. @ H₂C- Br F- (a) Br (a) (b) H₂C- (b) Br Br
Use their planar-ring structures to determine which of the following compounds are chiral. For any that are achiral, indicate whether their individual chair conformations are chiral. Tell how you
Determine whether each of the following compounds can be isolated in optically active form. Explain how you know.(a) Trans-1,2-dimethylcyclohexane(b) 1,1-dimethylcyclohexane(c)
(a) Does trans-1,4-dimethylcyclohexane contain any asymmetric carbons? If so, identify them.(b) Does trans-1,4-dimethylcyclohexane contain any stereocenters? If so, identify them.(c) Is
(a) The dipole moment of trans-1,3-dibromocyclobutane is 1.1 D. Explain why a nonzero dipole moment supports a puckered structure rather than a planar structure for this compound.(b) Draw a structure
Tell whether each of the following compounds is chiral.(a) Cis-1,2-dimethylcyclopropane (b) Trans-1,2-dimethylcyclopropane
Name the following compounds and tell whether each is a bridged or a fused bicyclic compound. (a) (b)
Without drawing their structures, tell which of the following compounds is a fused bicyclic compound and which is a bridged bicyclic compound, and how you know.bicyclo[2.1.1]hexane
How many 1,3-diaxial interactions occur in cis-decalin? In trans-decalin? Which compound has the lower energy and by how much?
Tell whether the two enantiomers of alkene A react at the same or different rates with each of the following reagents, and explain your reasoning. Give the products of the reaction in each case. H
What stereoisomeric products are possible when cis-2-butene undergoes bromine addition? Which are formed in different amounts? Which are formed in the same amounts?
Write all the possible products that might form when racemic 3-methylcyclohexene reacts with Br2. What is the relationship of each pair? Which compounds should in principle be formed in the same
Assuming the operation of the bromonium-ion mechanism, give the structure of the product(s) (including all stereoisomers) expected from bromine addition to cyclohexene.
What products, including their stereochemistry, should be obtained when each of the following alkenes is subjected to hydroboration–oxidation? (a) H₂C D C=C CH3 (b) H3C D D C=C D CH3
Give the structure of the products formed, including their stereochemistry, when (Z)-3-methyl-2-pentene undergoes hydroboration with BH3 in THF followed by oxidation with H2O2/NaOH. Tell whether any
Which of the following alcohols can be synthesized relatively free of constitutional isomers and diastereomers by (a) Hydroboration–oxidation; (b) Oxymercuration–reduction? Explain.
Suggest a reason that the energy difference between the two chair conformations of ethylcyclohexane is about the same as that for methylcyclohexane, even though the ethyl group is larger than the
Draw a conformational representation of the following steroid. Show the α-and β-faces of the steroid, and label the angular methyl groups. но. H₂C Bo Н B H H3C Н CH3 mu) H 0
Draw the two chair conformations of the sugar α-(1)-glucopyranose, which is one form of the sugar glucose. Which of these two conformations is the major one at equilibrium? Explain.
Provide an IUPAC substitutive name for each of the following compounds. (a) CH3CH₂CHCH3 (b) CH3CHCH=CHCHCH3 | ОН T ОН | CH₂CH₂SH
Give the common name for each of the following compounds, and tell whether each is a primary, secondary, or tertiary alkyl halide. (a) (CH3)₂CHCH₂-F -Br (d) (b)
Give the structure of each of the following compounds.(a) 2,2-dichloro-5-methylhexane(b) Chlorocyclopropane(c) 6-bromo-1-chloro-3-methylcyclohexene(d) Methylene iodide
Draw the structure of each of the following compounds.(a) sec-butyl alcohol (b) 3-ethylcyclopentanethiol (c) 3-methyl-2-pentanol(d) (E)-6-chloro-4-hepten-2-ol (e) 2-cyclohexenol
In which of the following solvents should 1-octene be least soluble: diethyl ether, dichloromethane, methanol, or 1-octanol? Explain.
Draw the structure of each of the following compounds.(a) Ethyl propyl ether (b) Dicyclohexyl ether(c) Tert-butyl isopropyl sulfide (d) Allyl benzyl ether(e) Phenyl vinyl ether (f)
Using the data in Table 8.1, estimate the carbon–selenium bond length in H3C—Se—CH3. Increasing electronegativity TABLE 8.1 Bond Lengths (in Angstroms) in Some Methyl
(a) A chemist used the name 3-butyl-1,4-dioxane in a paper. Although the name unambiguously describes a structure, what should the name have been? Explain.(b) Give the structure of 2-butoxyethanol,
From the data in Fig. 8.1, tell which bonds have the greater amount of p character (Secs. 1.9B and 6.9B): C—O bonds or C—S bonds. Explain.Fig. 8.1 1.426 Á H₂C H₂C 109° 0.96 Å H 1.413
(a) The dipole moment of acetaldehyde is 2.7 D and that of propene is 0.5 D. Even though they have about the same molecular mass, they differ in boiling point by about 68°C (–47°C and 121°C).
The boiling points of the 1,2-dichloroethylene stereoisomers are 47.4°C and 60.3°C. Which stereoisomer has each boiling point? Explain.
Octane and 2,2,3,3-tetramethylbutane have boiling points that differ by about 20°C (106°C and 126°C). Which has the higher boiling point and why?
Label each of the following molecules as a hydrogen-bond acceptor, donor, or both. Indicate the hydrogen that is donated or the atom that serves as the hydrogen-bond acceptor. (a) H-Br: (b) H-F:
Within each set, arrange the compounds in order of increasing boiling point.(a) 4-ethylheptane, 2-bromopropane, 4-ethyloctane(b) 1-butanol, 1-pentene, chloromethane
Match the structures with the following melting points. Explain. 168–172°C; –74.5°C; 143–147°C; –157°C. (The alkenes are liquids at room temperature, and the carboxylic acids are solids.)
Use their structures and dielectric constants to classify each of the following substances according to their solvent properties (as in Table 8.2). (a) 2-methoxyethanol (E = 17) (b)
If the “sawtooth” pattern of melting point behavior is explained by the efficiency of crystal packing, what would we expect to find if we were to plot the density of the crystal (solid) form of
Use Eq. 8.6 to calculate the free energy of mixing of 1 mole of isotopically labeled hexane in 1 liter of ordinary hexane. The molecular mass of hexane is 114 g mol–1, and the density of hexane is
In each case, which distribution has the higher entropy? Explain.(a) Four coins in which two are heads and two are tails, or four coins in which one is heads and three are tails.(b) Six coins in
Dimethyl sulfoxide (DMSO, Table 8.2) has a very large dipole moment (4.0 D). Using structures, show the stabilizing interactions to be expected between DMSO solvent molecules and (a) A dissolved
Into a separatory funnel is poured 200 mL of dichloromethane (density = 1.33 g mL–1) and 55 mL of water. This mixture forms two layers. One milliliter of 2-octanol is added, and the mixture is
How would you expect the standard entropy of solution to change along a series of primary alcohols (for example, from methanol to 1-octanol) as the chain length increases? Explain.
(a) Triethylamine, Et3N;, is a liquid that is not soluble in water. When HCl is added to a stirred mixture of triethylamine and water, a solution is formed. Explain.(b) What could you add to the
Give the structure of (a) A phosphatidylserine; (b) A lecithin.
(a) Give the structures of all alcohols with the molecular formula C5H11OH.(b) Which of the compounds in part (a) are chiral?(c) Name each compound using IUPAC substitutive nomenclature.(d) Classify
(a) Give the structures of all ethers with the molecular formula C5H12O.(b) Which of the compounds in part (a) are chiral?(c) Name each compound using both common and IUPAC substitutive
Give a structure for each of the following compounds. (In some cases, more than one answer is possible.)(a) A chiral ether C5H10O that has no double bonds (b) A chiral alcohol C4H6O (c) A vicinal

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