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chemistry
organic chemistry

Questions and Answers of Organic Chemistry

Which compound has the greatest rate of hydrolysis: benzamide, o-carboxybenzamide, o formylbenzamide, or o-hydroxybenzamide?
The following reaction occurs by a general-acid-catalyzed mechanism:Propose a mechanism for this reaction.
Indicate the type of catalysis that is occurring in the slow step in each of the following reaction sequences:a.b.
The deuterium kinetic isotope effect (kH2O/kD2O) for the hydrolysis of aspirin is 2.2. What does this tell you about the kind of catalysis exerted by the ortho-carboxyl substituent? (It is easier to
Draw the pH-activity profile for an enzyme with one catalytic group at the active site. The catalytic group is a general-acid catalyst with a pKa of 5.6.
A Co2+ complex catalyzes the following hydrolysis of the lactam shown:Propose a mechanism for the metal-ion catalyzed reaction.
There are two kinds of aldolases. Class I aldolases are found in animals and plants; Class II aldolases are found in fungi, algae, and some bacteria. Only Class I aldolases form an imine. Class II
Propose a mechanism for the following reaction. (The rate of the reaction is much slower if the nitrogen atom is replaced by CH.)
The hydrolysis of the ester shown here is catalyzed by morpholine, a secondary amine. Propose a mechanism for this reaction. (The pKa of the conjugate acid of morpholine is 9.3, so morpholine is too
The enzyme carbonic anhydrase catalyzes the conversion of carbon dioxide into bicarbonate ion (Section 1.20). It is a metalloenzyme, with Zn2+ coordinated at the active site by three histidine
At pH = 12 the rate of hydrolysis of ester A is greater than the rate of hydrolysis of ester B. At pH = 8, the relative rates reverse. (Ester B hydrolyzes faster than ester A.) Explain these
2-Acetoxycyclohexyl tosylate reacts with acetate ion to form 1,2-cyclohexanediol diacetate. The reaction is stereospecific; the stereoisomers obtained as products depend on the stereoisomer used as a
Staphylococcus nuclease is an enzyme that catalyzes the hydrolysis of DNA. The overall hydrolysis reaction is as follows:Recall that the nucleotides in DNA have phosphodiester linkages. The reaction
Proof that an imine was formed between aldolase and its substrate was obtained by using D fructose-1,6-diphosphate, labeled at the C-2 position with 14C as the substrate. NaBH4 was added to the
3-Amino-2-oxindole catalyzes the decarboxylation of Î±-keto acids.a. Propose a mechanism for the catalyzed reaction.b. Would 3-aminoindole be equally effective as a catalyst?
a. Explain why the alkyl halide shown here reacts much more rapidly than do primary alkyl halides, such as butyl chloride and pentyl chloride, with guanine residues.b. The alkyl halide can react with
Triosephosphate isomerase catalyzes the conversion of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate. The enzyme's catalytic groups are Glu 165 and His 95. In the first step of the
The mechanism for hydroxide-ion-promoted ester hydrolysis is shown in Section 17.12. What catalytic role does hydroxide ion play in this mechanism?
The following reaction occurs by a mechanism involving general-base catalysis:Propose a mechanism for this reaction.
Although metal ions increase the rate of decarboxylation of dimethyloxaloacetate, they have no effect on the rate of decarboxylation either of the monoethyl ester of dimethyloxaloacetate or of
The hydrolysis of glycinamide is catalyzed by [Co(ethylenediamine)2]2+ Propose a mechanism for this reaction.
How does the metal ion in carboxypeptidase A increase its catalytic activity?
TPP is a coenzyme for transketolase, the enzyme that catalyzes the conversion of a ketopentose (xylulose-5-phosphate) and an aldopentose (ribose-5-phosphate) into an aldotriose
An unfortunate effect of drinking too much alcohol-a hangover-is attributable to the acetaldehyde formed when ethanol is oxidized. There is some evidence that vitamin B1 can cure a hangover. How can
Taking into account the pathway for phenylalanine degradation, answer the following questions: a. What coenzyme and what other organic compound are needed by tyrosine aminotransferase? b. What bond
Î±-Keto acids other than Î±-ketoglutarate can be used to accept the amino group from pyridoxamine in enzyme-catalayzed transaminations. What amino acids are formed from the
Propose a mechanism for a PLP-catalyzed α,β-elimination.
Which of the following compounds is more easily decarboxylated?
Explain why the ability of PLP to catalyze an amino acid transformation is greatly reduced if a PLP-requiring enzymatic reaction is carried out at a pH at which the pyridine nitrogen is not
Explain why the ability of PLP to catalyze an amino acid transformation is greatly reduced if the OH substituent of pyridoxal phosphate is replaced by an OCH3.
Ethanolamine ammonia lyase, a coenzyme B12-requiring enzyme, catalyzes the followingreaction:Propose a mechanism for this reaction.
A fatty acid with an even number of carbon atoms is metabolized to acetyl-CoA, which can enter the citric acid cycle. A fatty acid with an odd number of carbon atoms is metabolized to acetyl-CoA and
FAD is obtained by an enzyme-catalyzed reaction that uses FMN and ATP as substrates. What is the other product of this reaction?
What is the source of the methyl group in thymidine?
Thiols such as ethanethiol and propanethiol can be used to reduce vitamin K epoxide back to vitamin KH2, but they react much more slowly than dihydrolipoate. Explain.
Answer the following questions: a. What six cofactors act as oxidizing agents? b. What are the cofactors that donate one-carbon groups? c. What three one-carbon groups are various tetrahydrofolates
Name the coenzymes that a. allow electrons to be delocalized b. activate groups for further reaction c. provide a good nucleophile d. provide a strong base
For each of the following reactions, name the enzyme that catalyzes the reaction and name the required coenzyme:a.b. c. d. e. f.
S-Adenosylmethionine (SAM) is formed from the reaction between ATP (Section 10.11) and methionine. The other product of the reaction is triphosphate. Propose a mechanism for this reaction.
Five coenzymes are required by Î±-ketoglutaate dehydrogenase, the enzyme in the citric acid cycle that converts to succinyl-CoA.a. Identify the coenzymes.b. Propose a mechanism for this
Give the products of the following reaction, where T is tritium:
Propose a mechanism for methylmalonyl-CoA mutase, the enzyme that converts methylmalonyl-CoA into succinyl-CoA.
When transaminated, the three branched-chain amino acids (valine, leucine, and isoleucine) form compounds that have the characteristic odor of maple syrup. An enzyme known as branched-chain α-keto
How many conjugated double bonds are there in a. FAD? b. FADH2?
When UMP is dissolved in T2O(T = tritium; see Problem 27), exchange of T for H occurs at the 5-position. Propose a mechanism for this exchange.
Dehydratase is a pyridoxal-requiring enzyme that catalyzes an Î±,Î²-elimination reaction. Propose a mechanism for this reaction.
In addition to the reactions mentioned in Section 25.6, PLP can catalyze Î²- substitution reaction. Propose a mechanism for the following PLP-catalyzed Î²-substitution reaction:
PLP can catalyze both Î±,Î²-eliminatin reactions (problem 31 and Î²,Î³-elimination reaction. Propose a mechanism for the following PLP-catalyzed
The glycine cleavage system is a group of four enzymes that together catalyze the following reaction:Use the following information to determine the sequence of reactions involved in the glycine
Nonenzyme-bound FAD is a stronger oxidizing agent than NAD+ How, then, can NAD+ oxidize the reduced flavoenzyme in the pyruvate dehydrogenase system?
FADH2 reduces Î±.Î²-unsaturated thioesters to saturated thioesters. The reaction is thought to take place by a mechanism that involves radicals. Propose a mechanism for this
Propose a mechanism for the reduction of lipoate by FADH2.
A common way for FAD to become covalently bound to its enzyme is by having a proton removed from the C-8 methyl group and a proton donated to N-1. Then a cysteine or other nucleophilic side chain of
Explain why the hydrogens of the methyl group bonded to flavin at C-8 are more acidic than those of the methyl group bonded at C-7.
Draw structures that show the similarity between decarboxylation of the pyruvate-TPP intermediate and decarboxylation of a β-keto acid.
Acetolactate synthase is another TPP-requiring enzyme. It also catalyzes the decarboxylation of pyruvate but transfers the resulting two-carbon fragment to another molecule of pyruvate, forming
Acetolactate synthase can also transfer the two-carbon fragment from pyruvate to Î±-ketobutyrate, forming Î±-aceto-Î±-hydroxybutyrate. This is the first step in
Explain the difference in the melting points of the following fatty acids: a. Palmitic acid and stearic acid b. Palmitic acid and palmitoleic acid c. Oleic acid and linoleic acid
Treating with PGA2 strong base such as sodium tert-butoxide followed by addition of acid converts it to PGC2. Propose a mechanism for this reaction.
Mark off the isoprene units in menthol, zingiberene, β-selinene, and squalene
One of the linkages in squalene is tail-to-tail, not head-to-tail. What does this suggest about how squalene is synthesized in nature?
Mark off the isoprene units in lycopene and β-carotene. Can you detect a similarity in the way in which squalene, lycopene, and β-carotene are biosynthesized?
Give the mechanism for the last step in the biosynthesis of isopentenyl pyrophosphate, showing why ATP is required.
Give the mechanisms for the Claisen condensation and aldol addition that occur in the first two steps of the biosynthesis of isopentenyl pyrophosphate.
Propose a mechanism for the conversion of the E isomer of geranyl pyrophosphate to the Z isomer.
Propose mechanisms for the formation of α-terpineol and limonene from geranyl pyrophosphate.
In aqueous acidic solution, farnesyl pyrophosphate forms the following sesquiterpene:Propose a mechanism for this reaction.
If squalene were synthesized in a medium containing acetate whose carbonyl carbon were labeled with radioactive 14C which carbons in squalene would be labeled?
What products are formed when arachidonic acid reacts with excess ozone followed by treatment with H2O2?
Aldosterone is in equilibrium with its cyclic hemiacetal. Draw the hemiacetal form of aldosterone.
The acid component of a cholesterol ester is a fatty acid such as linoleic acid. Draw the structure of a cholesterol ester.
Are the three OH groups of cholic acid axial or equatorial?
Draw the individual 1,2-hydride and 1,2-methyl shifts responsible for conversion of the protosterol cation to lanosterol. How many hydride shifts are involved? How many methyl shifts?
An optically active fat, when completely hydrolyzed, yields twice as much stearic acid as palmitic acid. Draw the structure of the fat.
a. How many different triacylglycerols are there in which one of the fatty acid components is lauric acid and two are myristic acid? b. How many different triacylglycerols are there in which one of
Cardiolipins are found in heart muscles. Give the products formed when a cardiolipin undergoes complete acid-catalyzed hydrolysis.
Nutmeg contains a simple, fully saturated triacylglycerol with a molecular weight of 722. Draw its structure.
Do all triacylglycerols have the same number of asymmetric carbons?
Give the product that would be obtained from the reaction of cholesterol with each of the following reagents:a. H2O,H+b. BH3 in THF, followed by H2O2 + HO-c. H2, Pd/Cd. Br2 + H2Oe. Peroxyacetic
Dr. Cole S. Terol synthesized the following samples of mevalonic acid and fed them to a group of lemon trees:Which carbons in citronellal, which is isolated from lemon oil, will be labeled in trees
An optically active monoterpene (compound A) with molecular formula undergoes catalytic hydrogenation to form an optically inactive compound with molecular formula C10H20O (compound B). When compound
If junipers were allowed to grow in a medium containing acetate in which the methyl carbon was labeled with which carbons in α- terpineol would be labeled?
a. Propose a mechanism for the following reaction:b. To what class of terpene does the starting material belong? Mark off the isoprene units in the starting material.
5-Androstene-3,17-dione is isomerized to 4-androstene-3,17-dione by hydroxide ion. Propose a mechanism for this reaction.
Both OH groups of one of the following steroid diols react with excess ethyl chloroformate, but only one OH group of the other steroid diol reacts under the same conditions:Explain the difference in
The acid-catalyzed dehydration of an alcohol to a rearranged alkene is known as a Wagner-Meerwein rearrangement. Propose a mechanism for the following Wagner-Meerwein rearrangement:
Diethylstilbestrol (DES) was given to pregnant women to prevent miscarriage, until it was found that the drug caused cancer in both the mothers and their female children. DES has estradiol activity
Which has a higher melting point, glyceryl tripalmitoleate or glyceryl tripalmitate?
Draw the resonance contributors for the radical formed when a hydrogen atom is removed from C-10 of arachidonic acid.
A colony of bacteria accustomed to an environment at 25°C was moved to an identical environment, at 35°C. The higher temperature increased the fluidity of the bacterial membranes. What could the
a. Draw the structures of three different sphingomyelins. b. Draw the structure of a galactocerebroside.
The membrane phospholipids in animals such as deer and elk have a higher degree of unsaturation in cells closer to the hoof than in cells closer to the body. Explain how this trait can be important
In acidic solutions, nucleosides are hydrolyzed to a sugar and a heterocyclic base. Propose a mechanism for this reaction.
Using the D, A, and D/A designations in Problem 9, explain how base pairing would be affected if the bases existed in the enol form.
The 2Ê¹,3Ê¹ - cyclic phosphodiester, which is formed when RNA is hydrolyzed (Figure 27.8), reacts with water, forming a mixture of nucleotide and -phosphates. Propose a
Calculate the length of a turn in: a. A-DNA b. B-DNA c. Z-DNA
Using a dark line for parental DNA and wavy lines for DNA synthesized from parental DNA, show what the population of DNA molecules would look like in the fourth generation.
Assuming that the human genome, with its 3.1 billion base pairs, is entirely in a B-helix, how long is the DNA in a human cell?
Why doesn't DNA unravel completely before replication begins?
Why do both thymine and uracil specify the incorporation of adenine?

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