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chemistry
organic chemistry

Questions and Answers of Organic Chemistry

Of the two anomers of methyl 2, 3-anhydro-d-ribofuranoside, I, the b form has a strikingly lower boiling point. Suggest an explanation using their structural formulas.
The following reaction sequence represents an elegant method of synthesis of 2-deoxy-d-ribose, IV, published by D. C. C. Smith in 1955:(a) What are the structures of II and III? (b) Propose a
The 1H NMR data for the two anomers included very comparable peaks in the d 2.0-5.6 region but differed in that, as their highest δ peaks, anomer V had a doublet at d 5.8 (1H, J = 12 Hz) while
How would you convert D-glucose to a mixture of ethyl a-d-glucopyranoside and ethyl β-D-glucopyranoside? Show all steps in the mechanism for their formation.
(a) Would you expect d-glucaric acid to be optically active?(b) Write the open-chain structure for the aldaric acid (mannaric acid) that would be obtained by nitric acid oxidation of d-mannose.(c)
D-Glucaric acid undergoes lactonization to yield two different g-lactones. What are their structures?
What products would you expect to be formed when each of the following compounds is treated with an appropriate amount of periodic acid? How many molar equivalents of HIO4 would be consumed in each
How many chirality centers are contained in (a) The aldotetrose (b) The ketopentose just given? (c) How many stereoisomers would you expect from each general structure?
Show how periodic acid could be used to distinguish between an aldohexose and a ketohexose. What products would you obtain from each, and how many molar equivalents of HIO4 would be consumed?
(a) Would you expect d-glucitol to be optically active? (b) Write Fischer projection formulas for all of the d-aldohexoses that would yield optically inactive alditols.
Although d-fructose is not an epimer of d-glucose or d-mannose (d-fructose is a ketohexose), all three yield the same phenylosazone. (a) Using Fischer projection formulas, write an equation for the
(a) What are the structures of L-(+)-threose and L-(+)-erythrose? (b) What aldotriose would you use to prepare them in a Kiliani-Fischer synthesis?
(a) Outline a Kiliani-Fischer synthesis of epimeric aldopentoses starting with D-(-)- erythrose (use Fischer projections). (b) The two epimeric aldopentoses that one obtains are D-(-)-arabinose and
Subjecting D-(-)-threose to a Kiliani-Fischer synthesis yields two other epimeric aldopentoses, D-(+)-xylose and D-(-)-lyxose. D-(+)-Xylose can be oxidized (with nitric acid) to an optically inactive
There are eight aldopentoses. In Practice Problems 22.14 and 22.15 you have arrived at the structures of four. What are the names and structures of the four that remain?
The aldohexose D-(+)-galactose can be obtained by hydrolysis of lactose, a disaccharide found in milk. When D-(+)-galactose is treated with nitric acid, it yields an optically inactive aldaric acid.
Fischer actually had to subject both g-lactones of d-glucaric acid (Practice Problem 22.8) to the procedure just outlined. What product does the other g-lactone yield?
Direct oxidation of an aldose affects the aldehyde group first, converting it to a carboxylic acid, and most oxidizing agents that will attack 1o alcohol groups will also attack 2o alcohol groups.
Write three-dimensional formulas for each aldotetrose and ketopentose isomer in Practice Problem 22.1 and designate each as a d or l sugar.
Give appropriate structural formulas to illustrate each of the following: (a) An aldopentose (b) A ketohexose (c) An l-monosaccharide (d) A glycoside (e) An aldonic acid (f) An aldaric acid (g) An
Draw conformational formulas for each of the following: (a) A-d-allopyranose, (b) Methyl b-d-allopyranoside, (c) Methyl 2, 3, 4, 6-tetra-O-methyl-b-d-allopyranoside.
Draw structures for furanose and pyranose forms of d-ribose. Show how you could use periodate oxidation to distinguish between a methyl ribofuranoside and a methyl ribopyranoside.
The starting material for a commercial synthesis of vitamin C is l-sorbose (see the following reaction); it can be synthesized from d-glucose through the following reaction sequence:The second step
What two aldoses would yield the same phenylosazone as l-sorbose (Problem 22.24)?In problem 22.24
In addition to fructose (Practice Problem 22.12) and sorbose (Problem 22.24), there are two other 2-ketohexoses, psicose and tagatose. D-Psicose yields the same phenylosazone as D-allose (or
A, B, and C are three aldohexoses. Compounds A and B yield the same optically active alditol when they are reduced with hydrogen and a catalyst; A and B yield different phenylosazones when treated
Xylitol is a sweetener that is used in sugarless chewing gum. Starting with an appropriate monosaccharide, outline a possible synthesis of xylitol.a
Although monosaccharides undergo complex isomerizations in base (Section 22.5A), aldonic acids are epimerized specifically at C2 when they are heated with pyridine. Show how you could make use of
Draw the Î²-pyranose form of (a) in its lowest energy chair conformation, and a Fischer projection for (b).(a)(b)
The most stable conformation of most aldopyranoses is one in which the largest group, the iCH2OH group, is equatorial. However, d-idopyranose exists primarily in a conformation with an axial --CH2OH
(a) Heating d-altrose with dilute acid produces a nonreducing anhydro sugar (C6H10O5). Methylation of the anhydro sugar followed by acid hydrolysis yields 2, 3, 4-tri-O-methyl- D-altrose. The
Show how the following experimental evidence can be used to deduce the structure of lactose (Section 22.12D): 1. Acid hydrolysis of lactose (C12H22O11) gives equimolar quantities of D-glucose and
Deduce the structure of the disaccharide melibiose from the following data: 1. Melibiose is a reducing sugar that undergoes mutarotation and forms a phenylosazone. 2. Hydrolysis of melibiose with
Trehalose is a disaccharide that can be obtained from yeasts, fungi, sea urchins, algae, and insects. Deduce the structure of trehalose from the following information: 1. Acid hydrolysis of trehalose
Outline chemical tests that will distinguish between members of each of the following pairs:(a) D-Glucose and d-glucitol(b) D-Glucitol and d-glucaric acid(c) D-Glucose and d-fructose(d) D-Glucose and
A group of oligosaccharides called Schardinger dextrins can be isolated from Bacillus macerans when the bacillus is grown on a medium rich in amylose. These oligosaccharides are all nonreducing. A
Isomaltose is a disaccharide that can be obtained by enzymatic hydrolysis of amylopectin. Deduce the structure of isomaltose from the following data: 1. Hydrolysis of 1 mol of isomaltose by acid or
Stachyose occurs in the roots of several species of plants. Deduce the structure of stachyose from the following data: 1. Acidic hydrolysis of 1 mol of stachyose yields 2 mol of D-galactose, 1 mol of
(a) How many stereoisomers are possible for 9, 10-dibromohexadecanoic acid? (b) The addition of bromine to palmitoleic acid yields primarily one set of enantiomers, (±)-threo-9,
Show how you might convert cholesterol into each of the following compounds: (a) 5α, 6β-Dibromocholestan-3β-ol (b) Cholestane-3β, 5α, 6β-triol (c) 5α-Cholestan-3-one (d)
Under suitable conditions all of the ester (and ether) linkages of a phosphatide can be hydrolyzed. What organic compounds would you expect to obtain from the complete hydrolysis of (Table 23.5)(a) A
How would you convert stearic acid, CH3(CH2)16CO2H, into each of the following?(a) Ethyl stearate,(b) tert-Butyl stearate, (c) Stearamide, (d) N, N-Dimethylstearamide, (e) Octadecylamine, (f)
How would you transform tetradecanal into each of the following?(a)(b) (c) (d)
Using palmitoleic acid as an example and neglecting stereochemistry, illustrate each of the following reactions of the double bond: (a) Addition of bromine (b) Addition of hydrogen (c)
When oleic acid is heated to 180-200 8C (in the presence of a small amount of selenium), an equilibrium is established between oleic acid (33%) and an isomeric compound called elaidic acid (67%).
When limonene (Section 23.3) is heated strongly, it yields 2 mol of isoprene. What kind of reaction is involved here?
Gadoleic acid (C20H38O2), a fatty acid that can be isolated from cod-liver oil, can be cleaved by hydroxylation and subsequent treatment with periodic acid to CH3(CH2)9CHO and OHC(CH2)7CO2H. (a)
Î±-Phellandrene and Î²-phellandrene are isomeric compounds that are minor constituents of spearmint oil; they have the molecular formula C10H16. Each compound has a UV
Vaccenic acid, a constitutional isomer of oleic acid, has been synthesized through the following reaction sequence:Propose a structure for vaccenic acid and for the intermediates A-E.
(a) Show the isoprene units in each of the following terpenes.(b) Classify each as a monoterpene, sesquiterpene, diterpene, and so on.
w-Fluorooleic acid can be isolated from a shrub, Dechapetalum toxicarium, that grows in Africa. The compound is highly toxic to warm-blooded animals; it has found use as an arrow poison in tribal
Give formulas and names for compounds A and B:
The initial steps of a laboratory synthesis of several prostaglandins reported by E. J. Corey (Section 7.15B) and co-workers in 1968 are outlined here. Supply each of the missing
A useful synthesis of sesquiterpene ketones, called cyperones, was accomplished through a modification of the following Robinson annulation procedure (Section 19.7B). Write a mechanism that accounts
A Hawaiian fish called the pahu or boxfish (Ostracian lentiginosus) secretes a toxin that kills other fish in its vicinity. The active agent in the secretion was named pahutoxin by P. J. Scheuer, and
The reaction illustrated by the equation below is a very general one that can be catalyzed by acid, base, and some enzymes. It therefore needs to be taken into consideration when planning syntheses
What products would you expect to obtain if each of the following terpenes were subjected to ozonolysis and subsequent treatment with dimethyl sulfide? (a) Myrcene (b) Limonene (c) a-Farnesene (d)
Give structural formulas for the products that you would expect from the following reactions:(a)(b) (c) (d)
Draw the two basic ring systems given in Fig. 23.6 for the 5a and 5b series showing all hydrogen atoms of the cyclohexane rings. Label each hydrogen atom as to whether it is axial or equatorial.
(a) Androsterone, a secondary male sex hormone, has the systematic name 3a-hydroxy- 5a-androstan-17-one. Give a three-dimensional formula for androsterone. (b) Norethynodrel, a synthetic steroid that
Designate with asterisks the eight chirality centers of cholesterol.
What form of glutamic acid would you expect to predominate in
Treating oxytocin with certain reducing agents (e.g., sodium in liquid ammonia) brings about a single chemical change that can be reversed by air oxidation. What chemical changes are involved?
What classes of reactions are involved in the cleavage of the Fmoc group with piperidine, leading to the unprotected amino acid and the fluorene by-product? Write mechanisms for these reactions.
Show all steps in the synthesis of GVA using the tert-butyloxycarbonyl (Boc) group as a protecting group.
Tche csynthesis of a polypeptide containing lysine requires the protection of both amino groups.(a) Show how you might do this in a synthesis of the dipeptide KI using the benzyloxycarbonyl group as
One type of insoluble support used for SPPS is polymer-bound 4-benzyloxybenzyl alcohol, also known as "Wang resin," shown in Fig. 24.8. The 4-benzyloxybenzyl alcohol moiety serves as a linker between
Outline the steps in the synthesis of the tripeptide KFA using the SPPS procedure.
(a) Which amino acids in Table 24.1 have more than one chirality center? (b) Write Fischer projections for the isomers of each of these amino acids that would have the l configuration at the a
(a) What product would you expect to obtain from treating tyrosine with excess bromine water? (b) What product would you expect to be formed in the reaction of phenylalanine with ethanol in the
(a) On the basis of the following sequence of reactions, Emil Fischer was able to show that L-(-)-serine and L-(+)-alanine have the same configuration. Write Fischer projections for the intermediates
The guanidino groupof arginine is one of the most strongly basic of all organic groups. Explain.
(a) dl-Glutamic acid has been synthesized from diethyl acetamidomalonate in the following way. Outline the reactions involved.(b) Compound G has also been used to prepare the amino acid dl-ornithine
Synthetic polyglutamic acid exists as an a helix in solution at pH 2-3. When the pH of such a solution is gradually raised through the addition of a base, a dramatic change in optical rotation takes
Bradykinin is a nonapeptide released by blood plasma globulins in response to a wasp sting. It is a very potent pain-causing agent. Its constituent amino acids are 2R, G, 2F, 3P, S. The use of 2,
Complete hydrolysis of a heptapeptide showed that it has the following constituent amino acids:2A, E, L, K, F, VDeduce the amino acid sequence of this heptapeptide from the following data.1.
Part of the evidence for restricted rotation about the carbon-nitrogen bond in a peptide linkage comes from 1H NMR studies done with simple amides. For example, at room temperature the 1H NMR
Starting with diethyl a-bromomalonate and potassium phthalimide and using any other necessary reagents, show how you might synthesize (a) dl-leucine, (b) dl-alanine, and (c) dl-phenylalanine.
(a) Outline a Strecker synthesis of dl-phenylalanine. (b) dl-Methionine can also be synthesized by a Strecker synthesis. The required starting aldehyde can be prepared from acrolein (CH2 == CHCHO)
The electron-withdrawing property of the 2, 4-dinitrophenyl group makes separation of the labeled amino acid very easy. Suggest how this is done.
(a) Write a reaction showing how 2, 4-dinitrofluorobenzene could be used to identify the N-terminal amino acid of VAG. (b) What products would you expect (after hydrolysis) when VKG is treated with
Write the reactions involved in a sequential Edman degradation of MIR.
Glutathione is a tripeptide found in most living cells. Partial acid-catalyzed hydrolysis of glutathione yields two dipeptides, CG and one composed of E and C. When this second dipeptide was treated
Give the amino acid sequence of the following polypeptides using only the data given by partial acidic hydrolysis:(a)(b)
Write the structures of other tautomeric forms of adenine, guanine, cytosine, thymine, and uracil.
The sense strand of a segment of DNA has the following sequence of bases:5' . . . T G G G G G T T T T A C A G C . . . 3'(a) What mRNA sequence would result from this segment?(b) Assume that the first
(a) Using the first codon given for each amino acid in Table 25.2, write the base sequence of mRNA that would translate the synthesis of the following pentapeptide:Arg · Ile · Cys · Tyr · Val(b)
Write the structure of the RNA dinucleotide G-C in which G has a free 59-hydroxyl group and C has a free 39-hydroxyl group.
Write the structure of the DNA dinucleotide T-A in which T has a free 59-hydroxyl group and A has a free 39-hydroxyl group.
The example of a silyl-Hilbert-Johnson nucleosidation reaction in Section 25.3 is presumed to involve an intermediate ribosyl cation that is stabilized by intramolecular interactions involving the C2
(a) Mitomycin is a clinically used antitumor antibiotic that acts by disrupting DNA synthesis through covalent bondforming reactions with deoxyguanosine in DNA. Maria Tomasz (Hunter College) and
As described in Section 25.5B, acid-base catalysis is believed to be the mechanism by which ribosomes catalyze the formation of peptide bonds in the process of protein translation. Key to this
The nucleosides shown in Figs. 25.4 and 25.5 are stable in dilute base. In dilute acid, however, they undergo rapid hydrolysis yielding a sugar (deoxyribose or ribose) and a heterocyclic base. (a)
Basing your answer on reactions that you have seen before, propose a likely mechanism for the condensation reaction in the first step of the preceding uridine synthesis.
(a) What kind of linkage is involved in the acetonide group of the protected nucleoside, and why is it susceptible to mild acid-catalyzed hydrolysis? (b) How might such a protecting group be
The following reaction scheme is from a synthesis of cordycepin (a nucleoside antibiotic) and the first synthesis of 29-deoxyadenosine (reported in 1958 by C. D. Anderson, L. Goodman, and B. R.
(a) There are approximately 3 billion base pairs in the DNA of a single human cell. Assuming that this DNA exists as a double helix, calculate the length of all the DNA contained in a human cell.
(a) The most stable tautomeric form of guanine is the lactam form (or cyclic amide, see Section 17.8I). This is the form normally present in DNA, and, as we have seen, it pairs specifically with
Mutations can also be caused chemically, and nitrous acid is one of the most potent chemical mutagens. One explanation that has been suggested for the mutagenic effect of nitrous acid is the
Write structural formulas showing how the keto form of uracil (Section 25.2) in mRNA can pair with adenine in DNA through hydrogen bond formation.

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