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organic chemistry

Questions and Answers of Organic Chemistry

Does increasing the energy barrier to an SN2 reaction increase or decrease the magnitude of the rate constant for the reaction?
At 600 °C, the ratio of the relative rates of formation of a tertiary, a secondary, and a primary radical by a chlorine radical is 2.6:2.1:1. Explain the change in the degree of regioselectivity
How many allylic substituted bromoalkenes are formed from the reaction of 2-pentene with NBS? Ignore stereoisomers.
Take the same alkanes whose percentages of monochlorination products you calculated in Problem 6, and calculate what the percentages of monobromination products would be if bromination were carried
If cyclopentane reacts with more than one equivalent Cl2 of at a high temperature, how many dichlorocyclopentanes would you expect to obtain as products?
In 1935, J. Bredt, a German chemist, proposed that a bicycloalkene cannot have a double bond at a bridgehead carbon unless one of the rings contains at least eight carbon atoms. This is known as
A solution of 4-methyl-3-penten-2-one in ethanol shows an absorbance of 0.52 at 236 nm in a cell with a 1-cm light path. Its molar absorptivity in ethanol at that wavelength is 12,600. What is the
List the following dienes in order of decreasing reactivity in a Diels–Alder reaction:
a. When HBr adds to a conjugated diene, what is the rate-determining step?b. When HBr adds to a conjugated diene, what is the product-determining step?
The triphenylmethyl cation is so stable that a salt such as triphenylmethyl chloride can be isolated and stored. Why is this carbocation so stable? C. triphenylmethyl chloride
Are the following pairs of structures resonance contributors or different compounds?a.b. CH3CH=CHĊHCH=CH2 and CH3ĊHCH=CHCH=CH2c.d.e. CH3C+HCH=CHCH3 and CH3CH=CHCH2C+H2 and
Draw resonance contributors for the following ions:a.b.c.d.
Which of the following compounds have delocalized electrons?a.b.c.d.e. CH2=CHCH2CH=CH2f.g.h. CH3CH2NHCH2CH=CHCH3i. CH3CH2NHCH=CHCH3j.k. CH2-CHCH3
Which of the following would you predict to be the stronger acid? -С-ОН or N- C-OH
Which of the following pairs are keto–enol tautomers?a.b.c.d.e. CH;CH,CH=CHCH,OH and CH;CH,CH,CH,CH
A chemist wants to synthesize 4-decyne but cannot find any 1-pentyne, the starting material used in the synthesis just described. How else can 4-decyne be synthesized?
When fumarate reacts with D2O in the presence of the enzyme fumarase, only one isomer of the product is formed. Its structure is shown. Is the enzyme catalyzing a syn or an anti addition of D2O? OOC
Sherry O. Eismer decided that the configuration of the asymmetric carbons in a sugar such as D glucose could be determined rapidly by simply assigning the R configuration to an asymmetric carbon with
a. Using the wedge-and-dash notation, draw the nine stereoisomers of 1,2,3,4,5,6-hexachlorocyclohexane.b. From the nine stereoisomers, identify one pair of enantiomers.c. Draw the most stable
A solution of an unknown compound (3.0 g of the compound in 20 mL of solution), when placed in a polarimeter tube 2.0 dm long, was found to rotate the plane of polarized light 1.8° in a
a. Is the reaction of 2-butene with HBr regioselective?b. Is it stereoselective?c. Is it stereospecific?d. Is the reaction of 1-butene with HBr regioselective?e. Is it stereoselective?f. Is it
What percent of naproxen is obtained as the S enantiomer in the above synthesis?
Which of the following is true?a. If two compounds have the same relative configuration, they will have the same absolute configuration.b. If two compounds have the same relative configuration and
What is the absolute configuration of the following?a. (-)-glyceric acidb. (+)-isoserinec. (-)-glyceraldehyded. (+)-lactic acid
(S)-(-)-2-Methyl-l-butanol can be converted to (+)-2-methylbutanoic acid without breaking any of the bonds to the asymmetric carbon. What is the configuration of (-)-2-methylbutanoic acid?
There are two stable isotopes of nitrogen, 14N and 15N. How many protons and neutrons does each isotope have?
Which of the following are chiral?
Which of the following compounds has a stereoisomer that is a meso compound?a. 2,4-dibromohexaneb. 2,4-dibromopentanec. 2,4-dimethylpentane d. 1,3-dichlorocyclohexanee. 1,4-dichlorocyclohexanef.
a. Stereoisomers with two asymmetric carbons are called _____ if the configuration of both asymmetric carbons in one isomer is the opposite of the configuration of the asymmetric carbons in the other
a. Stereoisomers with two asymmetric carbons are called _____ if the configuration of both asymmetric carbons in one isomer is the opposite of the configuration of the asymmetric carbons in the other
A solution prepared by mixing 10 mL of a 0.10 M solution of the R enantiomer and 30 mL of a 0.10 M solution of the S enantiomer was found to have an observed specific rotation of +480°. What is the
(S)-(+)-Monosodium glutamate (MSG) is a flavor enhancer used in many foods. Some people have an allergic reaction to MSG (headache, chest pains, and an overall feeling of weakness). "Fast food" often
a. Is (R)-lactic acid dextrorotatory or levorotatory?b. Is (R)-sodium lactate dextrorotatory or levorotatory?
Indicate whether each of the following structures has the R or the S configuration:a.b.c.d. CH(CH3)2 CH;CH, CH,Br CH3 t.
Which of the compounds in Problem 4 can exist as enantiomers?Problem 4Which of the following compounds have asymmetric carbons?a.b.c.d. CH3CH2OHe.f. CH;CH,CHCH3 ČI
Tetracycline is called a broad-spectrum antibiotic because it is active against a wide variety of bacteria. How many asymmetric carbons does tetracycline have?
Which of the following compounds have asymmetric carbons?a.b.c.d. CH3CH2OHe.f. CH;CH,CHCH3 ČI
Starting with an alkene, indicate how each of the following compounds can be synthesized:a.b.c. CI
The same alkane is obtained from the catalytic hydrogenation of both alkene A and alkene B. The heat of hydrogenation of alkene A is 29.8 kcal mol (125 kJ mol), and the heat of hydrogenation of
Which of the following carbocations would you expect to rearrange?a.b. CH2 CH3 CH3 e. CH;CHCHCH3 с.
Tell whether each of the following compounds has the E or the Z configuration:a.b.c.d. H3C CH2CH3 C=C CH3CH2 CH2CH2CI
The rate constant for a reaction can be increased by _____ the stability of the reactant or by _____ the stability of the transition state.
For each of the following compounds, tell how many of its carbon atoms lie in the same plane:a.b.c.d. CH3
Determine the degree of unsaturation for the hydrocarbons with the following molecular formulas:a. C10H16b. C20H34c. C8H16d. C12H20e. C40H56
Which of the following structures represents a cis isomer? CH3 CH, CH3 CH3 -CH, CH3 CH3 CH3 D B A
Ansaid® and Motrin® belong to the group of drugs known as nonsteroidal anti-inflammatory drugs (NSAIDs). Both are only slightly soluble in water, but one is a little more soluble than the other.
a. How many primary carbons does the following structure have?b. How many secondary carbons does the structure have?c. How many tertiary carbons does it have? CH2CH3 CH,CHCH3 CH3
a. Which of the following compounds will form hydrogen bonds between its molecules?1. CH3CH2CH2COOH2. CH2CH2N(CH3)23. CH3CH2CH2CH2Br4. CH3CH2CH2NHCH35. CH3CH2OCH2CH2OH6. CH3CH2CH2CH2Fb. Which of the
As long as the pH is greater than __________, more than 50% of a protonated amine with a pKa of 10.4 will be in its neutral, nonprotonated form.
a. Which of the halide ions (F-, Cl-, Br-, I-) is the strongest base?b. Which is the weakest base?
HCl is a weaker acid than HBr. Why, then, is ClCH2COOH a stronger acid than BrCH2COOH?
Compare the potential maps for methane, ammonia, and water. Which is the most polar molecule? Which is the least polar? electrostatic potential map for methane electrostatic potential map for ammonia
According to the potential map for the ammonium ion, which atom(s) is (are) most positively charged?
What orbitals are used to form the 10 covalent bonds in propane (CH3CH2CH3)?
Determine the partial negative charge on the oxygen atom in a C=O bond. The bond length is 1.22 Å* and the bond dipole moment is 2.30 D.
(a) The structures illustrated for the four DNA bases represent only the most stable tautomers. Draw one or more alternative tautomers for each of these heterocycles.(b) In certain cases, the
How many stereocenters are present in the small, naturally occurring protein glycylalanylalanine? (a) Zero; (b) One; (c) Two; (d) Three.
When an a-amino acid is dissolved in water and the pH of the solution adjusted to 12, which of the following species is predominant? (a)(b)(c)(d) RCHČOH NH2
Which one of the following five structures is a zwitterion? (a)(b) -O2CCH2CH2CO2-(c) H3N+CH2CO2- (d) CH3(CH2)16CO2 -K+ (e) 0,CCH,CNH,
The primary structure of a protein refers to: (a) Cross-links with disulfide bonds; (b) Presence of an a helix; (c) The a-amino acid sequence in the polypeptide chain; (d) The
Structure A (shown in the margin) is that of a naturally occurring a-amino acid. Select its name from the following list. (a) Glycine; (b) Alanine; (c) Tyrosine; (d)
Amino acids can be used as enantiomerically pure starting materials in organic synthesis. Scheme I depicts the first steps in the synthesis of a reagent employed in the preparation of
Sickle-cell anemia is an often fatal genetic condition caused by a single error in the DNA gene that codes for the b chain of hemoglobin. The correct nucleic acid sequence (read from the mRNA
The biosynthesis of oligosaccharides employs the chemical constituents of proteins and nucleic acids as well as carbohydrates. In the example shown, a disaccharide linkage is created between a
Hdroxyproline (Hyp), like many other amino acids that are not “officially” classified as essential, is nonetheless a very necessary biological substance. It constitutes about 14% of the amino
In addition to the conventional 20 amino acids in Tables 26-1 and 26-3, two others, selenocysteine (Sec) and pyrrolysine (Pyl), are incorporated into proteins using the nucleic acid–based cell
Factor VIII is one of the proteins participating in the formation of blood clots. A defect in the gene whose DNA sequence codes for Factor VIII is responsible for classic hemophilia. Factor VIII
The following molecule is thyrotropin-releasing hormone (TRH). It is secreted by the hypothalamus, causing the release of thyrotropin from the pituitary gland, which, in turn, stimulates the thyroid
Propose a synthesis of leu-enkephalin [see Problem 42(d)] from the component amino acids. Problem 42(d) OH CH2 O CH2 O CH,CH(CH3)2 HaN—CH—С—NH—СH2 —С-NH—СH2—С-NH—СH
Secreted by the pituitary gland, corticotropin is a hormone that stimulates the adrenal cortex. Determine its primary structure from the following information. (i) Hydrolysis by chymotrypsin
Secreted by the pituitary gland, corticotropin is a hormone that stimulates the adrenal cortex. Determine its primary structure from the following information. (i) Hydrolysis by chymotrypsin
The amino acid sequence of met-enkephalin, a brain peptide with powerful opiatelike biological activity, is Tyr-Gly-Gly-Phe-Met. What would be the products of step-by-step Edman degradation of
The polypeptide bradykinin is a tissue hormone that can function as a potent pain-producing agent. By means of a single treatment with the Edman reagent, the N-terminal amino acid in bradykinin is
What would be the outcome of reaction of gramicidin S with phenyl isothiocyanate (Edman degradation)?
Write the products of a single Edman degradation of the peptides in Problem 42. (a)
In your own words, outline the procedure that might have been followed by the researchers who determined which amino acids were present in vasopressin (Exercise 26-10). Exercise
Explain the following three observations. (a) Silk, like most polypeptides with sheet structures, is water insoluble. (b) Globular proteins such as myoglobin generally dissolve readily in
Of the 153 amino acids in myoglobin, 78 contain polar side chains (i.e., Arg, Asn, Asp, Gln, Glu, His, Lys, Ser, Thr, Trp, and Tyr). When myoglobin adopts its natural folded conformation, 76 of these
Identify as many stretches of α helix as you can in the structure of myoglobin (Figure 26-8C). Prolines are located in myoglobin at positions 37, 88, 100, and 120. How does each of these prolines
Silk is composed of β-sheets whose polypeptide chains consist of the repeating sequence GlySer-Gly-Ala-Gly-Ala. What characteristics of amino acid side chains appear to favor the β-sheet
Indicate which of the amino acids in Problem 32 and the peptides in Problem 42 would migrate in an electrophoresis apparatus at pH = 7 (a) Toward the anode (b) Toward the
Using the three-letter abbreviations for amino acids, write the peptide structures in Problem 42 in short notation. Data From Problem 42(a)
Identify each of the following structures as a dipeptide, tripeptide, and so forth, and point out all the peptide bonds. (a)
Devise a procedure for separating a mixture of the four stereoisomers of isoleucine into its four components: (+)-isoleucine, (-)-isoleucine, (+)-alloisoleucine, and (-2)-alloisoleucine (Problem 31).
The antibacterial agent in garlic, allicin, is synthesized from the unusual amino acid alliin by the action of the enzyme allinase. Because allinase is an extracellular enzyme, this process takes
(a) Illustrate the Strecker synthesis of phenylalanine. Is the product chiral? Does it exhibit optical activity? (b) It has been found that replacement of NH3 by an optically active amine in the
Using either one of the methods or a route of your own devising, propose a reasonable synthesis of each of the following amino acids in racemic form. (a) Val; (b) Leu; (c)
What amino acid would result from carrying out the following synthetic sequence on 1. CH3CH2O2Na+ , CH3CH2OH; 2. Br(CH2)4NHCOCH3; 3. H+, H2O, Δ. N-CH(CO,CH,CH3),?
Show how the use of a Strecker synthesis can give each of the following amino acids in racemic form: (a) Gly; (b) Ile; (c) Ala.
Show how Hell-Volhard-Zelinsky bromination followed by amination can be used to synthesize each of the following amino acids in racemic form: (a) Gly; (b) Phe; (c) Ala.
Show how the pI values for the amino acids in Problem 32 (see Table 26-1) are derived. For each amino acid that possesses more than two pKa values, give the reason for your choice when
Group the amino acids in Problem 32 according to whether they are (a) Positively charged, (b) Neutral, (c) Negatively charged at pH = 7.Data From Problem 32(a) Alanine at pH = 1, 7,
Draw the structure that each of the following amino acids would have in aqueous solution at the indicated pH values. (a) Alanine at pH = 1, 7, and 12;(b) Serine at pH = 1, 7, and 12; (c)
The abbreviation allo means diastereomer in amino acid terms. Draw allo-L-isoleucine, and give it a systematic name.
Draw stereochemically correct structural formulas for isoleucine and threonine (Table 26-1). What is a systematic name for threonine? Table 26-1 Natural (25)-Amino Acids (continued) pK, of
This reaction yields one main organic product. Which of the following compounds is it? (a)(b)(c)(d) SnCl,, CH,CCI 2-Phenylthiophene
Which of the following compounds would you expect to be the major organic product of the two-step sequence shown here? (a)(b)(c)(d) ÇH3 THF CH,CHI + (CH;CH),NLi
Pyrrole is a much weaker base than azacyclopentane (pyrrolidine) for which of the following reasons?(a) The nitrogen in pyrrole is more electropositive than that in pyrrolidine; (b) Pyrrole is a
The proton decoupled 13C NMR spectrum of pyridine will display how many peaks? (a) One; (b) Two; (c) Three;(d) Four; (e) Five.
This problem introduces two literature syntheses of indole derivatives, and you are asked to come up with plausible mechanisms for them. Divide your team in two, each group concentrating on one of

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