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chemistry
organic chemistry
Questions and Answers of
Organic Chemistry
(a) A hydrocarbon isolated from fish oil and from plankton was identified as 2,6,10,14-tetramethyl-2-pentadecene. Write its structure. (b) Alkyl isothiocyanates are compounds of the type RN = C = S.
(a) The sex attractant of the Mediterranean fruit fly is (E)-6-nonen-1-ol. Write a structural formula or build a molecular model for this compound, showing the stereochemistry of the double
Which one of the following has the largest dipole moment (is the most polar)? Compare your answer with the calculated dipole moments on the Learning By Modeling CD.
Match each alkene with the appropriate heat of combustion: Heats of combustion (kJ/mol): 5293; 4658; 4650; 4638; 4632 Heats of combustion (kcal/mol): 1264.9; 1113.4; 1111.4; 1108.6; 1107.1 (a)
Choose the more stable alkene in each of the following pairs. Explain your reasoning. (a) 1-Methylcyclohexene or 3-methylcyclohexene (b) Isopropenylcyclopentane or allylcyclopentane
(a) Suggest an explanation for the fact that 1-methylcyclopropene is some 42 kJ/mol (10 kcal/mol) less stable than methylenecyclopropane
How many alkenes would you expect to be formed from each of the following alkyl bromides under conditions of E2 elimination? Identify the alkenes in each case. (a) 1-Bromohexane (e)
Write structural formulas for all the alkene products that could reasonably be formed from each of the following compounds under the indicated reaction conditions. Where more than one alkene is
Choose the compound of molecular formula C7H13Br that gives each alkene shown as the exclusive product of E2 elimination.
Give the structures of two different alkyl bromides both of which yield the indicated alkene as the exclusive product of E2 elimination. (a) CH3CHoeCH2 (c) BrCHoeCBr2 (b) (CH3)2CoeCH2
(a) Write the structures or build molecular models of all the isomeric alkyl bromides having the molecular formula C5H11Br. (b) Which one undergoes E1 elimination at the fastest rate? (c) Which one
(a) Write the structures or build molecular models of all the isomeric alcohols having the molecular formula C5H12O. (b) Which one will undergo acid-catalyzed dehydration most readily? (c) Write
Predict the major organic product of each of the following reactions. In spite of the structural complexity of some of the starting materials, the functional group transformations are all of the type
Evidence has been reported in the chemical literature that the reaction (CH3CH2)2CHCH2Br + KNH2 → (CH3CH2)2C = CH2 + NH3 + KBri Proceeds by the E2 mechanism . Use curved arrow notation to
The rate of the reaction (CH3)3CCl + NaSCH2CH3 → (CH3)2C = CH2 + CH3CH2SH + NaCl Is first-order in (CH3)3CCl and first-order in NaSCH2CH3 . Give the symbol (E1 or E2) for the most reasonable
Menthyl chloride and neomenthyl chloride have the structures shown. One of these stereoisomers undergoes elimination on treatment with sodium ethoxide in ethanol much more readily than the other.
The stereo selectivity of elimination of 5-bromononane on treatment with potassium ethoxide was described in Section 5.14. Draw Newman projections or make molecular models of 5-bromononane showing
In the acid-catalyzed dehydration of 2-methyl-1-propanol, what carbocation would be formed if a hydride shift accompanied cleavage of the carbon–oxygen bond in the alkyloxonium ion? What ion would
Each of the following carbocations has the potential to rearrange to a more stable one. Write the structure of the rearranged carbocation. (a) CH3CH2CH2+ (b) (CH3)2CHC_HCH3 (c) (CH3)3CCHCH3 (d)
Write a sequence of steps depicting the mechanisms of each of the following reactions:
We saw that acid-catalyzed dehydration of 2, 2-dimethylcyclohexanol afforded 1, 2-dimethylcyclohexene. To explain this product we must write a mechanism for the reaction in which a methyl shift
Acid-catalyzed dehydration of 2, 2-dimethyl-1-hexanol gave a number of isomeric alkenes including 2-methyl-2-heptene as shown in the following formula.
Compound A (C4H10) gives two different monochlorides on photochemical chlorination. Treatment of either of these monochlorides with potassium tert-butoxide in dimethyl sulfoxide gives the same alkene
Compound A (C6H14) gives three different monochlorides on photochemical chlorination. One of these monochlorides is inert to E2 elimination. The other two monochlorides yield the same alkene B
What three alkenes yield 2-methylbutane on catalytic hydrogenation?
Match each alkene of Problem 6.1 with its correct heat of hydrogenation.
Write the structure of the major organic product formed in the reaction of hydrogen chloride with each of the following: (a) 2-Methyl-2-butene (b) 2-Methyl-1-butene (c) cis-2-Butene
Give a structural formula for the carbocation intermediate that leads to the major product in each of the reactions of Problem 6.3 (Section 6.5).
Addition of hydrogen chloride to 3, 3-dimethyl-1-butene gives a mixture of two isomeric chlorides in approximately equal amounts. Suggest reasonable structures for these two compounds, and offer a
Kharasch’s earliest studies in this area were carried out in collaboration with graduate student Frank R. Mayo. Mayo performed over 400 experiments in which allyl bromide (3-bromo-1-propene) was
Give the major organic product formed when hydrogen bromide reacts with each of the alkenes in Problem 6.3 in the absence of peroxides and in their presence.
Write a structural formula for the compound formed on electrophilic addition of sulfuric acid to cyclohexene (step 1 in the two-step transformation shown in the preceding equation).
Instead of the three-step mechanism of Figure 6.9, the following two-step mechanism might be considered: 1. (CH3)2C = CH2 + H3O+ → (CH3)3 C+ + H2O 2. (CH3)3C+ + HO- → (CH3)3COH This
The rates of hydration of the two alkenes shown differ by a factor of over 7000 at 25°C. Which isomer is the more reactive? Why?
Is the electrophilic addition of hydrogen chloride to 2-methylpropene the reverse of the E1 or the E2 elimination reaction of tert-butyl chloride?
Write the structure of the major organic product obtained by hydroboration–oxidation of each of the following alkenes: (a) 2-Methylpropene (b) cis-2-Butene (d) Cyclopentene (e)
Hydroboration–oxidation of pinene (page 213), like catalytic hydrogenation, is stereoselective. Addition takes place at the less hindered face of the double bond, and a single alcohol is produced
The mass 82 isotope of bromine (82Br) is radioactive and is used as a tracer to identify the origin and destination of individual atoms in chemical reactions and biological transformations. A sample
Arrange the compounds 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene in order of decreasing reactivity toward bromine.
Give the structure of the product formed when each of the following alkenes reacts with bromine in water: (a) 2-Methyl-1-butene (c) 3-Methyl-1-butene (b) 2-Methyl-2-butene (d) 1-Methylcyclopentene
Give the substitutive IUPAC name, including stereochemistry, for disparlure.
Give the structure of the alkene, including stereochemistry that you would choose as the starting material in a preparation of synthetic disparlure.
The same reaction that gave 2, 4, 4-trimethyl-2-pentene also yielded an isomeric alkene. This second alkene produced formaldehyde and 4, 4-dimethyl-2-pentanone on ozonolysis. Identify this alkene.
Write a series of equations describing a synthesis of 1-bromo-2- methyl-2-propanol from tert-butyl bromide.
The two dimers of 2-methylpropene shown in the equation can be converted to 2, 2, 4-trimethylpentane (known by its common name isooctane) for use as a gasoline additive. Can you suggest a method for
Write the structure of the major organic product formed in the reaction of 1-pentene with each of the following: (a) Hydrogen chloride (b) Hydrogen bromide (c) Hydrogen bromide in the presence of
Repeat Problem 6.22 for 2-methyl-2-butene.
Repeat Problem 6.22 for 1-methylcyclohexene.
Match the following alkenes with the appropriate heats of hydrogenation: (a) 1-Pentene (b) (E)-4, 4-Dimethyl-2-pentene (c) (Z)-4-Methyl-2-pentene (d) (Z)-2, 2, 5, 5-Tetramethyl-3-hexene (e) 2,
a) How many alkenes yield 2, 2, 3, 4, 4-pentamethylpentane on catalytic hydrogenation? (b) How many yield 2, 3-dimethylbutane? (c) How many yield methylcyclobutane?
Two alkenes undergo hydrogenation to yield a mixture of cis- and trans-1, 4-dimethylcyclohexane. A third, however, gives only cis-1, 4-dimethylcyclohexane. What compound is this?
Specify reagents suitable for converting 3-ethyl-2-pentene to each of the following: (a) 2, 3-Dibromo-3-ethylpentane (b) 3-Chloro-3-ethylpentane (c) 2-Bromo-3-ethylpentane (d)
(a) Which primary alcohol of molecular formula C5H12O cannot be prepared from an alkene? Why? (b) Write equations describing the preparation of three isomeric primary alcohols of molecular formula
All the following reactions have been reported in the chemical literature. Give the structure of the principal organic product in each case.
A single epoxide was isolated in 79–84% yield in the following reaction. Was this epoxide A or B? Explain your reasoning.
Suggest a sequence of reactions suitable for preparing each of the following compounds from the indicated starting material. You may use any necessary organic or inorganic reagents. (a) 1-Propanol
Two different compounds having the molecular formula C8H15Br are formed when 1, 6- dimethylcyclohexene reacts with hydrogen bromide in the dark and in the absence of peroxides. The same two compounds
On catalytic hydrogenation over a rhodium catalyst, the compound shown gave a mixture containing cis-1-tert-butyl-4-methylcyclohexane (88%) and trans-1-tert-butyl-4-methylcyclohexane (12%). (a)
Compound A undergoes catalytic hydrogenation much faster than does compound B. Why? Making molecular models will help.
Catalytic hydrogenation of 1, 4-dimethylcyclopentene yields a mixture of two products. Identify them. One of them is formed in much greater amounts than the other (observed ratio =10:1). Which one is
There are two products that can be formed by syn addition of hydrogen to 2,3-dimethylbicyclo[ 2.2.1]-2-heptene. Write or make molecular models of their structures.
Hydrogenation of 3-carene is, in principle, capable of yielding two stereoisomeric products. Write their structures. Only one of them was actually obtained on catalytic hydrogenation over platinum.
In a widely used industrial process, the mixture of ethylene and propane that is obtained by dehydrogenation of natural gas is passed into concentrated sulfuric acid. Water is added, and the solution
On the basis of the mechanism of acid-catalyzed hydration, can you suggest a reason why the reaction
As a method for the preparation of alkenes, a weakness in the acid-catalyzed dehydration of alcohols is that the initially formed alkene (or mixture of alkenes) sometimes isomerizes under the
When bromine is added to a solution of 1-hexene in methanol, the major products of the reaction are as shown:
The reaction of thiocyanogen (N ≡ CS ─SC ≡ N) with cis-cyclooctene proceeds by anti addition.
On the basis of the mechanism of cationic polymerization, predict the alkenes of molecular formula C12H24 that can most reasonably be formed when 2-methylpropene [(CH3)2CoeCH2] is treated with
On being heated with a solution of sodium ethoxide in ethanol, compound A (C7H15Br) yielded a mixture of two alkenes B and C, each having the molecular formula C7H14. Catalytic hydrogenation of the
Compound A (C7H15Br) is not a primary alkyl bromide. It yields a single alkene (compound B) on being heated with sodium ethoxide in ethanol. Hydrogenation of compound B yields 2, 4- dimethylpentane.
Compounds A and B are isomers of molecular formula C9H19Br. Both yield the same alkene C as the exclusive product of elimination on being treated with potassium tert-butoxide in dimethyl sulfoxide.
Alcohol A (C10H18O) is converted to a mixture of alkenes B and C on being heated with potassium hydrogen sulfate (KHSO4). Catalytic hydrogenation of B and C yields the same product. Assuming that
Reaction of 3,3-dimethyl-1-butene with hydrogen iodide yields two compounds A and B, each having the molecular formula C6H13I, in the ratio A:B = 90:10. Compound A, on being heated with potassium
Dehydration of 2, 2, 3, 4, 4-pentamethyl-3-pentanol gave two alkenes A and B. Ozonolysis of the lower boiling alkene A gave formaldehyde (CH2 = O) and 2, 2, 4, 4-tetramethyl-3-pentanone. Ozonolysis
Compound A (C7H13Br) is a tertiary bromide. On treatment with sodium ethoxide in ethanol, A is converted into B (C7H12). Ozonolysis of B gives C as the only product. Deduce the structures of A and B.
East Indian sandalwood oil contains a hydrocarbon given the name santene (C9H14). Ozonation of santene followed by hydrolysis gives compound A. What is the structure of santene?
Sabinene and Δ3-carene are isomeric natural products with the molecular formula C10H16. (a) Ozonolysis of sabinene followed by hydrolysis in the presence of zinc gives compound A. What is the
The sex attractant by which the female housefly attracts the male has the molecular formula C23H46. Catalytic hydrogenation yields an alkane of molecular formula C23H48. Ozonolysis yields
A certain compound of molecular formula C19H38 was isolated from fish oil and from plankton. On hydrogenation it gave 2, 6, 10, 14-tetramethylpentadecane. Ozonolysis gave (CH3)2C = O and a 16-carbon
The sex attractant of the female arctiid moth contains, among other components, a compound of molecular formula C21Hf40 that yields
Examine the following for stereogenic centers: (a) 2-Bromopentane (c) 1-Bromo-2-methylbutane (b) 3-Bromopentane (d) 2-Bromo-2-methylbutane
Identify the stereogenic centers, if any, in (a) 2-Cyclopenten-1-ol and 3-cyclopenten-1-ol (b) 1, 1, 2-Trimethylcyclobutane and 1, 1, 3-Trimethylcyclobutane
Locate any planes of symmetry or centers of symmetry in each of the following compounds. Which of the compounds are chiral? Which are achiral? (a) (E)-1, 2-Dichloroethene (c) cis-1,
Cholesterol, when isolated from natural sources, is obtained as a single enantiomer. The observed rotation _ of a 0.3-g sample of cholesterol in 15 mL of chloroform solution contained in a 10-cm
A sample of synthetic cholesterol was prepared consisting entirely of the enantiomer of natural cholesterol. A mixture of natural and synthetic cholesterol has a specific rotation [a] D 20 of _13°.
Does the molecular model shown represent (+)-2-butanol or (-)-2-butanol?
Assign absolute configurations as R or S to each of the following compounds:
Draw three-dimensional representations or make molecular models of
Write Fischer projections for each of the compounds of Problem 7.7.
Biological reduction of pyruvic acid, catalyzed by the enzyme lactate dehydrogenase, gives (+)-lactic acid, represented by the Fischer projection shown. What is the configuration of (+)-lactic acid
Draw Fischer projections or make molecular models of the four stereoisomeric 3-amino-2-butanols, and label each erythro or threo as appropriate.
One other stereoisomer of 3-amino-2-butanol is a crystalline solid. Which one?
A meso stereoisomer is possible for one of the following compounds. Which one? 2, 3-Dibromopentane; 2,4-dibromopentane; 3-bromo-2-pentanol; 4-bromo-2-pentanol
One of the stereoisomers of 1, 3-dimethylcyclohexane is a meso form. Which one?
Using R and S descriptors, write all the possible combinations for a molecule with three stereogenic centers.
A second category of six-carbon carbohydrates, called 2-hexuloses, has the constitution shown. How many stereoisomeric 2-hexuloses are possible?
Epoxidation of alkenes is a stereo specific syn addition. Which stereoisomer of 2-butene reacts with Peroxyacetic acid to give meso-2, 3-epoxybutane? Which one gives a racemic mixture of (2R, 3 R) -
Could the fact that hydrogenation of 2-methyl (methylene) cyclohexane gives more cis-1, 2-dimethylcyclohexane than trans- be explained on the basis of the relative stabilities of the two
There are two other stereoisomeric tartaric acids. Write their Fischer projections, and specify the configuration at their stereogenic centers.
Could the unusual, optically inactive form of tartaric acid studied by Pasteur have been meso-tartaric acid?
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