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organic chemistry

Questions and Answers of Organic Chemistry

Prednisolone acetate is an anti-inflammatory agent in clinical use. It is similar in structure to cortisol, with the following two differences: (1) Prednisolone acetate exhibits a double bond between
Draw the hypothetical ring-flip of trans-decalin, and explain why it does not occur. Use this analysis to explain why cholesterol has a fairly rigid three-dimensional geometry.
The following compounds are steroids. One is an anabolic steroid called oxymetholone and the other, called norgestrel, is used in oral contraceptive formulations. Identify these compounds based on
Would you expect glycerol to readily cross the membrane?
Octanol is more efficient than hexanol at crossing the cell membrane and entering a cell. Explain.
Draw the resonance structures of a fully deprotonated phosphatidic acid.
A cephalin was hydrolyzed to yield one equivalent of palmitic acid and one equivalent of oleic acid.(a) Draw two possible structures of the cephalin.(b) If the phosphodiester was located at C2 of the
A lecithin was hydrolyzed to yield two equivalents of myristic acid.(a) Draw the structure of the lecithin.(b) This compound is chiral, but only one enantiomer predominates in nature. Draw the
The conversion of triglycerides into biodiesel can be achieved in the presence of either catalytic acid or catalytic base. We have seen a mechanism for transesterification with catalytic acid. In
Draw the products obtained when triolein undergoes transesterification using isopropyl alcohol in the presence of catalytic sulfuric acid.
Draw a mechanism for the transesterification of tristearin using methanol in the presence of catalytic acid.
An optically inactive triglyceride was hydrolyzed to yield one equivalent of palmitic acid and two equivalents of lauric acid. Draw the structure of the triglyceride.
A triglyceride was treated with sodium hydroxide to yield glycerol and three equivalents of sodium laurate (the conjugate base of lauric acid). Draw the structure of the triglyceride.
Identify the products that are expected when the following triglyceride is hydrolyzed with aqueous sodium hydroxide.
Partial hydrogenation of triolein produces several different trans fats. Draw all possible trans fats that might be obtained in the process.
Triolein was treated with molecular hydrogen at high temperature in the presence of nickel. At completion, the reaction had consumed three equivalents of molecular hydrogen.(a) Draw the structure of
Identify each of the following compounds as a fat or an oil. Explain your answers.(a) A triglyceride containing one palmitic acid residue and two stearic acid residues(b) A triglyceride containing
Tristearin has a melting point of 72 °C. Based on this information, would you expect triarachadin to be classified as a fat or as an oil?
Arrange the following three triglycerides in order of increasing melting point. Tristearin, tripalmitin, and tripalmitolein
For each pair of triglycerides, identify the one that is expected to have the higher melting point. Consult Table 26.1 to determine which fatty acid residues are present in each triglyceride.(a)
One of the compounds present in lanolin was isolated, purified, and then treated with aqueous sodium hydroxide to yield an unbranched alcohol with 20 carbon atoms and an unbranched carboxylic acid
Waxes can be hydrolyzed to yield an alcohol and a carboxylic acid. Draw the products obtained when triacontyl hexadecanoate undergoes hydrolysis.
When the following compound is treated with concentrated HCl at 100ºC for several hours, hydrolysis occurs, producing one of the 20 naturally occurring amino acids. Identify which one. H,N,
We saw in Section 25.6 that DCC can be used to form a peptide bond. We explored the mechanism, and we saw that DCC activates the COOH moiety so that it readily undergoes nucleophilic acyl
Proton NMR spectroscopy provides evidence for the restricted rotation of a peptide bond. For example, N,N‑dimethylformamide exhibits three signals in its proton NMR spectrum at room temperature.
Consider a process that attempts to prepare tyrosine using a Hell‑Volhard‑Zelinski reaction:(a) Identify the necessary starting carboxylic acid.(b) When treated with Br2, the starting carboxylic
The side chain of tryptophan is not considered to be basic, despite the fact that it possesses a nitrogen atom with a lone pair. Explain.
When leucine is prepared with an amidomalonate synthesis, isobutylene (also called 2‑methylpropene) is a gaseous byproduct. Draw a mechanism for the formation of this byproduct.
Draw the alkyl halide that would be necessary to make the amino acid tyrosine using an amidomalonate synthesis. This alkyl halide is highly susceptible to polymerization. Draw the structure of the
Draw a mechanism for the following reaction:
A proline residue will often appear at the end of an α helix but will rarely appear in the middle. Explain why proline generally cannot be incorporated into an α helix.
Predict the major product(s) for each of the following reactions:(a)(b)(c) но. 1) Br2, PBr3 2) H20 3) Excess NH3 Н 1) NH,CI, NaCN 2) H30+
Show how racemic valine can be prepared by each of the following methods:(a) The Hell-Volhard-Zelinski reaction(b) The amidomalonate synthesis(c) The Strecker synthesis
Using an asymmetric catalytic hydrogenation, identify the starting alkene that you would use to make l-histidine.
Using three-letter abbreviations, identify all possible acyclic tripeptides containing l-leucine, l methionine, and l-valine.
Draw the predominant form of Asp-Lys-Phe at physiological pH.
Draw a bond-line structure of the peptide that corresponds with the following sequence of amino acid residues, and identify the N terminus and C terminus:Trp-Val-Ser-Met-Gly-Glu
Methionine enkephalin is a pentapeptide that is produced by the body to control pain. From the sequence of its amino acid residues, draw a bond€‘line structure of
From its amino acid sequence, draw the form of aspartame that is expected to predominate at physiological pH:Asp-Phe-OCH3
Bradykinin has the following sequence:(N terminus) Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg (C terminus)Identify all fragments that will be produced when bradykinin, is treated with:(a) Trypsin (b)
Identify the N-terminal residue of a peptide that yields the following PTH derivative upon Edman degradation: N. HN- S.
Treatment of a tripeptide with phenyl isothiocyanate yields compound A and a dipeptide. Treatment of the dipeptide with phenyl isothiocyanate yields compound B and glycine. Identify the structure of
Glucagon is a peptide hormone produced by the pancreas that, with insulin, regulates blood glucose levels. Glucagon is comprised of 29 amino acid residues. Treatment with trypsin yields four
When the N terminus of a peptide is acetylated, the peptide derivative that is formed is unreactive toward phenyl isothiocyanate. Explain. Acetylation PEPTIDE PEPTIDE Н. N. N. н Zーエ
Predict the major product(s) of the reaction between l-valine and:(a) MeOH, H+(b) Di-tert-butyl-dicarbonate(c) NaOH, H2O(d) HCl
Show all steps necessary to make the dipeptide Phe-Ala from l-phenylalanine and l-alanine.
Draw all four possible dipeptides that are obtained when a mixture of l-phenylalanine and l alanine is treated with DCC.
Draw the structure of the protected amino acid that must be anchored to the solid support in order to use a Merrifield synthesis to prepare leucine enkephalin.(N terminus) Try-Gly-Gly-Phe-Leu
Identify all of the steps necessary to prepare the tripeptide Leu-Val-Ala with a Merrifield synthesis.
Identify the steps you would use to combine Val-Leu and Phe-Ile to form the tetrapeptide Phe Ile-Val-Leu.
The amidomalonate synthesis can be used to prepare amino acids from alkyl halides. When the amidomalonate synthesis is used to make glycine, no alkyl halide is required. Explain.
Under similar conditions, alanine and valine were each prepared with an amidomalonate synthesis, and alanine was obtained in higher yields than valine. Explain the difference in yields.
Show how you would use a Strecker synthesis to make valine.
A mixture of amino acids was treated with ninhydrin, and the following aldehydes were all observed in the product mixture:(a) Identify the structure and name all three amino acids in the starting
Draw the products that are expected when each of the following amino acids is treated with ninhydrin:(a) l-Aspartic acid (b) l-Leucine(c) l-Phenylalanine (d) l-Proline
A mixture containing l-glycine, l-glutamine, and l-asparagine was subjected to electrophoresis. Identify which of the amino acids moved the farthest distance assuming that the experiment was
Optically active amino acids undergo racemization at the α position when treated with strongly basic conditions. Provide a mechanism that supports this observation.
For each amino acid, draw the structure that predominates at the isoelectric point:(a) l-Glutamine (b) l-Phenylalanine(c) l-Proline (d) l-Threonine
Just as each amino acid has a unique pI value, proteins also have an overall observable pI. For example, lysozyme (present in tears and saliva) has a pI of 11.0 while pepsin (used in our stomachs to
Using the data in the following table, calculate the pI of the following amino acids:(a) l-Alanine (b) l-Asparagine(c) l-Histidine (d) l-Glutamic acid THE PK,VALUES FOR TWENTY NATURALLY
For each of the following amino acids, draw the form that is expected to predominate at physiological pH:(a) l-Isoleucine (b) l-Tryptophan(c) l-Glutamine (d) l-Glutamic acid
Draw the form of l-glutamic acid that predominates at each pH:(a) 1.9 (b) 2.4 (c) 5.8 (d) 10.4
Histidine possesses a basic side chain which is protonated at physiological pH. Identify which nitrogen atom in the side chain is protonated.
Arginine is the most basic of the 20 naturally occurring amino acids. At physiological pH, the side chain of arginine is protonated. Identify which nitrogen atom in the side chain is protonated.
Draw all stereoisomers of l-isoleucine. In each stereoisomer, assign the configuration (R or S) of all chirality centers.
Seventeen of the 20 naturally occurring amino acids (See the following table) exhibit exactly one chirality center. Of the remaining three amino acids, glycine has no chirality center, and the other
Draw a Fischer projection for each of the following amino acids:(a) l-Threonine (b) l-Serine(c) l-Phenylalanine (d) l-Asparagine
The 20 naturally occurring amino acids (See the following table) are all l amino acids, and they all have the S configuration, with the exception of glycine (which lacks a chirality center) and
Draw a bond‑line structure showing the zwitterionic form of each of the following amino acids:(a) l-Valine (b) l-Tryptophan(c) l-Glutamine (d) l-Proline
Below is the primary structure for a peptide. Identify the regions that are most likely to form β pleated sheets.Trp-His-Pro-Ala-Gly-Gly-Ala-Val-His-Cys-Asp-Ser-Arg-Arg-Ala-Gly-Ala-Phe
Identify the sequence of the tripeptide that would be formed from the following order of reagents. Clearly label the C terminus and N terminus of the tripeptide.
Identify all of the steps necessary to prepare each of the following peptides with a Merrifield synthesis.(a) Phe-Leu-Val-Phe (b) Ala-Val-Leu-Ile
Draw all of the steps and reagents necessary to prepare a pentapeptide with the sequence Leu Val-Phe-Ile-Ala.
Draw all of the steps and reagents necessary to prepare a tripeptide with the sequence Ile-Phe Gly.
Draw all of the steps and reagents necessary to prepare each of the following dipeptides from their corresponding amino acids.(a) Trp-Met (b) Ala-Ile (c) Leu-Val
Consider the structure of the following cyclic octapeptide. Would cleavage of this peptide with trypsin produce different fragments than cleavage with chymotrypsin? Explain. Phe Arg Arg Phe Phe Arg
The tetrapeptide Val-Lys-Ala-Phe is cleaved into two fragments upon treatment with trypsin. Identify the sequence of a tetrapeptide that will produce the same two fragments when treated with
A peptide with 22 amino acid residues is treated with trypsin to give four fragments, while treatment with chymotrypsin yields six fragments. Identify the sequence of the 22 amino acid residues in
Draw the structure of the initial PTH derivative formed when the tripeptide Ala‑Phe‑Val undergoes an Edman degradation.
Bacitracin A is produced by bacteria and therefore contains some residues that are not from the list of 20 naturally occurring amino acids (See the following figure).(a) Identify which amino acid
Aspartame is an artificial sweetener sold under the trade name NutraSweetTM. Aspartame is the methyl ester of a dipeptide formed from l‑aspartic acid and l-phenylalanine and can be summarized
Using a bond-line structure, show the tetrapeptide obtained when two molecules of Cys-Phe are joined by a disulfide bridge.
Draw the s-cis conformation of the dipeptide Phe-Phe and identify the source of steric hindrance.
It is believed that penicillin antibiotics are biosynthesized from amino acid precursors. Identify the two amino acids that are most likely utilized during the biosynthesis of penicillin antibiotics:
Green fluorescent protein (GFP), first isolated from bioluminescent jellyfish, is a protein containing 238 amino acid residues. The discovery of GFP has revolutionized the field of fluorescence
Propose two structures for a tripeptide that contains glycine, l-alanine, and l-phenylalanine but does not react with phenyl isothiocyanate.
How many different pentapeptides can be constructed from the 20 naturally occurring amino acids in the following table? Abbreviation Name Structure Abbreviation Name Structure Amino acids with polar
Draw the s-trans conformation of the dipeptide Phe- Leu and identify both the N terminus and the C terminus.
Compare the following tripeptides and determine whether they are constitutional isomers or the same compound.Ala-Gly-Leu and Leu-Gly-Ala
Determine which of the following peptides will have a higher molecular weight.Cys-Tyr-Leu or Cys-Phe-Ile
Using three- and one-letter abbreviations, show the sequence of amino acid residues in the following pentapeptide. Он ОН H2N SH
Draw the structure of each of the following peptides:(a) Leu-Ala-Gly (b) Cys-Asp-Ala-Gly (c) Met-Lys-His-Tyr-Ser-Phe-Val
Draw the α-N-glycoside and the β-N-glycoside formed when d-glucose is treated with aniline (C6H5NH2).
Draw the nucleoside formed from each of the following pairs of compounds and name the nucleoside:(a) 2-Deoxy-d-ribose and adenine(b) d-Ribose and guanine
Compound A is a d-aldopentose that is converted into an optically active alditol upon treatmentwith sodium borohydride. Draw two possible structures for compound A.
When d-glucose is treated with an aqueous bromine solution (buffered to a pH of 6), an aldonic acid is formed called d-gluconic acid. Treatment of d-gluconic acid with an acid catalyst produces a
When each of the d-aldohexoses assumes an apyranose form, the CH2OH group occupies an equatorial position in the more stable chair conformation. The one exception is d-idose, for which the CH2OH
Draw the product that is expected when the β-pyranose form of compound A is treated with excess ethyl iodide in the presence of silver oxide. The following information can be used to determine the
Explain why glucose is the most common monosaccharide observed in nature.
When d-glucose is treated with aqueous sodium hydroxide, a complex mixture of carbohydrates is formed, including d-mannose and d-fructose. Over time, almost all aldohexoses will be present in the

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