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chemistry
organic chemistry
Questions and Answers of
Organic Chemistry
Galactose, a sugar related to glucose, contains a six-membered ring in which all the substituents except the ?OH group indicated below in red are equatorial. Draw galactose in its more stable chair
Draw the two chair conformations of menthol, and tell which is morestable.
There are four cis—transisomers of menthol (Problem 4.37), including the one shown. Draw the other three.
Identify each pair of relationships among the ? OH groups in glucose (red?blue, red?green, red?black, blue?green, blue?black, green?black) as cis or trans.
A Draw 1, 3, 5-trimethy1cyclohexane using a hexagon to represent the ring. How many cis—Tran’s stereoisomers are possible?
From the data in Figure and Table, estimate the percentages of molecules that have their substituents in an axial orientation for the following compounds: (a) Isopropylcyclohexane (b)
A Assume that you have a variety of cyclohexanes substituted in the positions indicated. Identify the substituents as either axial or equatorial. For example, a 1, 2-cis relationship means that one
The diaxial conformation of cis-1, 3—dimethylcyclohexanc is approximately 23kJ/mol (5.4kcal/mol) less stable than the diequatorial conformation. Draw the two possible chair conformations, and
Approximately how much steric strain does the 1, 3-diaxial interaction between the two methyl groups introduce into the diaxial conformation of cis-1, 3-dirnethylcyclohexanc?
In light of your answer to Problem 4.44, draw the two chair conformations of 1, 1, 3-trimcthylcyclohexanc, and estimate the amount of strain energy in each. Which conformation is favored?
We saw in Problem 4.20 that cis-decalin is less stable than trans-decalin. Assume that the 1, 3-diaxial interactions in trans-decalin are similar to those m axial methylcyclohexane [that is, one
Using molecular models as well as structural drawings explain why trans-ans decalin is rigid and cannot ring-flip, whereas cis-decalin cans easily ring-flip.
Trans-Decalin is more stable than its cis isomer, but cis-bicyclo [4.1.0] heptane is more stable than its transisomer.Explain.
Myo-lnositol, one of the isomers of 1, 2, 3, 4, 5, 6-hexahydroxvcyclohexane, acts as a growth factor in both animals and microorganisms. Draw the most stable chair conformation ofmyo-inositol.
How many cis—trans stereoisomers of myo-inositol (Problem 4.49) are there? Draw the structure of the most stable isomer.
One of the two chair structures of cis-1-chloro-3-methylcyclohexane is more stable than the other by 15.5kJ/mol (3.7kcal/mol). Which is it? What is the energy cost of a 1, 3-diaxial interaction
The German chemist J. Bredt proposed in 1935 that bicycloalkenes such as 1-norbornene, which have a double bond to the bridgehead carbon, are too strained to exist. Make a molecular model of
Tell whether each of the following substituents on a steroid is axial or equatorial. (A substituent that is ?up? is on the top face of the molecule as drawn, and a substituent that is ?down? is on
Amantadine is an antiviral agent that is active against influenza A infection and against some strains of H5N1 avian flu. Draw a three-dimensional representation of amantadine showing the chair
Ketones react with alcohols to yield products called acetals. Why does the allcis isomer of 4-tert-butyl-l, 3-cyclohexanediol react readily with acetone and an acid catalyst to form an acetal while
Alcohols undergo an oxidation reaction to yield carbonyl compounds on treatment with CrO3. For example, 2-tert-butylcyclohexanol gives 2-tert-butylcyclo- hexanone. If axial ?OH groups are generally
Classify each of the following reactions as an addition, elimination, substitution, or rearrangement:(a) CH3Br + KOH → CH3OH + KBr(b) CH3CH2Br → H2C = CH2 + HBr(c) H2C = CH2 + H2 → CH3CH3
Radical chlorination of alkanes is not generally useful because mixtures of products often result when more than one kind of C—H bond is present in the substrate. Draw and name all monochloro
Using a curved fishhook arrow, propose a mechanism for formation of the cyclopentane ring of prostaglandin H2. What kind of reaction isoccurring?
Which of the following species is likely to be a nucleophile and which anelectrophile?
An electrostatic potential map of boron trifluoride is shown. Is BF3 likely to be a nucleophile or an electrophile? Draw a Lewis structure for BF3, and explain youranswer.
What product would you expect from reaction of cyclohexene with HBr? With HC1
Reaction of HBr with 2-methyipropenc yields 2-hromo-2-methylpropane, what is the structure of the carbocation formed during the reaction? Show the mechanism of the reaction.
Add curved arrows to the following polar reactions to indicate the flow of electrons in each:
Predict the products of the following polar reaction, a step in the citric acid cycle for food metabolism, by interpreting the flow of electrons indicated by the curve darrows:
Which reaction is more energetically favored, one with ΔG° = —44kJ/mol or one with ΔG° -t-44 kJ/mol?
Which reaction is likely to be more exergonic, one with Keq = 1000 or one with Keq = 0.001?
Which reaction is faster, one with ΔG++ = +45 kJ/mol or one with ΔG++ = +70kJ/mol?
Sketch an energy diagram for a two-step reaction with an endergonic first step and an exergonic second step. Label the parts of the diagram corresponding to reactant, product, and intermediate.
The following alkyl halide can be prepared by addition of HBr to two different alkenes. Draw the structures of both (reddish brown = Br).
The following structure represents the carbocation intermediate formed in the addition reaction of HBr to two different alkenes. Draw the structures ofboth.
Electrostatic potential maps of (a) Formaldehyde (CH2O) and (b) Methanethiol (CH3SH) is shown. Is the formaldehyde carbon atom likely to be electrophilic or nucleophiic? What about the Methanethiol
Look at the following energy diagram: (a) Is ?G? for the reaction positive or negative? Label it on the diagram. (b) How many steps are involved in the reaction? (c) How many transition states are
Look at the following energy diagram for an enzyme-catalyzed reaction: (a) How many steps are involved? (b) Which step is most exergonic? (c) Which step is the slowest?
Identify the functional groups in the following molecules, and show the polarity ofeach:
Identify the following reactions as additions, eliminations, substitutions, orrearrangements:
What is the difference between a transition state and an intermediate?
Draw an energy diagram for a one-step reaction with Keq < 1. Label the parts of the diagram corresponding to reactants, products, transition state, ΔG°, and ΔG++. Is ΔG° positive or negative?
Draw an energy diagram for a two-step reaction with Keq > 1. Label the overall ΔG°, transition states, and intermediate. Is ΔG° positive or negative?
Draw an energy diagram for a two-step exergonic reaction whose second step is faster than its first step.
Draw an energy diagram for a reaction with Keq = 1. What is the value of ΔG° in this reaction?
The addition of water to ethylene to yield ethanol has the following thermodynamic parameters: (a) Is the reaction exothermic or endothermic? (b) Is the reaction favorable (spontaneous) or
When a mixture of methane and chlorine is irradiated, reaction commences immediately. When irradiation is stopped, the reaction gradually slows down but does not stop immediately. Explain.
Radical chlorination of pentane is a poor way to prepare 1-chioropentane, but radical chlorination of neopentane, (CH3)4C, is a good way to prepare neopentyl chloride, (CH3)3CCH2C1. Explain.
Despite the limitations of radical chlorination of alkanes, the reaction is still useful for synthesizing certain halogenated compounds. For which of the following compounds does radical chlorination
An Add curved arrows to the following reactions to indicate the flow of electrons ineach:
A Follow the flow of electrons indicated by the curved arrows in each of the following reactions, and predicts the products thatresult:
When isopropylidenecyclohexane is treated with strong acid at room temperature, isomerization occurs by the mechanism shown below to yield 1-iso- propylcyclohexenc: At equilibrium, the product
Add curved arrows to the mechanism shown in Problem 5.32 to indicate the electron movement in each step.
2-Chloro-2-mcthylpropane reacts with water in three steps to yield 2-methyl- 2-propanol. The first step is slower than the second, which in turn is much slower than the third. The reaction takes
An Add curved arrows to the mechanism shown in Problem 5.34 to indicate the electron movement in each step.
The reaction of hydroxide ion with chloromethane to yield methanol and chloride ion is an example of a general reaction type called a nucleophilic sub- Situation reaction: HO- + CH3C1 ↔ CH3OH + C1-
Ammonia reacts with acetyl chloride (CH3COCI) to give acetamide (CH3CONH2). Identify the bonds broken and formed in each step of the reaction, and draw curved arrows to represent the flow of
The naturally occurring molecule ?-terpineol is biosynthesized by a route that includes the following step: (a) Propose a likely structure for the isomeric carbocation intermediate. (b) Show the
Predict the product(s) of each of the following biological reactions by interpreting the flow of electrons as indicated by the curvedarrows:
Reaction of 2-methylpropene with HBr might, in principle, lead to a mixture of two alkyl bromide addition products. Name them, and draw their structures.
Draw the structures of the two carbocation intermediates that might form during the reaction of 2-methylpropene with HBr (Problem 5.40). We’ll see that the stability of carbocation depends on the
Name the following aldehydes and ketones according to IUPAC rules:
Draw structures corresponding to the following names:(a) 3-Methylbutanal(b) 4-Chloro-2-Pentanone(c) Phenyl acetaldehyde(d) cis-3-tert-Butylcyclohexanecarbaldehyde(e) 3-Methyl-3-butenal(f)
How would you prepare pentanal from the following starting materials?(a) CH3CH2CH2CH2CH2OH(b) CH3CH2CH2CH2CH = CH2(c) CH3CH2CH2CH2CO2CH3
How would you carry out the following reactions? More than one step may be required.(a) 3-Hexyne → 3-Hexanone(b) Benzene → m-Bromo acetophenone(c) Bromobenzene → Acetophenone(d)
Treatment of an aldehyde or ketone with cyanide ion (–: C ≡ N), followed by proton-ation of the tetrahedral alkoxide ion intermediate, gives a cyanohydrins. Show the structure of the cyanohydrins
P-Nitrobenzaldehyde is more reactive toward nucleophilic additions than p-methoxy-benzaldehyde. Explain
When dissolved in water, trichloroacetaldehyde (chloral, CCl3CHO) exists primarily as chloral hydrate, CCl3CH (OH)2, better known as “knockout drops.” Show the structure of chloral hydrate.
The oxygen in water is primarily (99.8%) 16O, but water enriched with the heavy isotope 18O is also available. When an aldehyde or ketone is dissolved in 18O-enriched water, the isotopic label
Cyclohexanone forms cyanohydrins in good yield but 2, 2, 6-trimethylcyclo-hexanone does not. Explain.
Show the products you would obtain by acid-catalyzed reaction of Cyclohexanone with ethylamine, CH3CH2NH2, and with diethyl amine, (CH3CH2)2NH.
Imine formation is reversible. Show all the steps involved in the acid-catalyzed reaction of an imine with water (hydrolysis) to yield an aldehyde or ketone plus primary amine.
Draw the following molecule as a line-bond structure, and show how it can be prepared from a ketone and an amine.
Show how you could prepare the following compounds from 4-methyl-3-penten-2-one, (CH3)2C =CHCOCH3.
Show all the steps in the acid-catalyzed formation of a cyclic acetal from ethylene glycol and an aldehyde or ketone.
Identify the carbonyl compound and the alcohol that were used to prepare the following acetal:
What carbonyl compound and what phosphorus ylide might you use to prepare each of the followingcompounds?
?-Carotene a yellow food-coloring agent and dietary source of vitamin A, can be prepared by a double Witting reaction between 2 equivalents of ?-ionylideneacetaldehyde and a diylide. Show the
When o-phthalaldehyde is treated with base, o-(hydroxymethyl) benzoic acid is formed. Show the mechanism of this reaction.
What is the stereochemistry of the pyruvate reduction shown in figure, does NADH lose its pro-R or pro-S hydrogen? Does addition occur to the Si face or Re face of pyruvate?
Assign R or S stereochemistry to the two chirality centers in isocitrate, and tell whether OH and H add to the Si face or the Re face of the double bond.
Treatment of 2-cyclohexenone with HCN/KCN yields a saturated keto nitrile rather than an un-saturated cyanohydrins. Show the structure of the product, and propose a mechanism for the reaction.
How might conjugate addition reactions of lithium diorganocopper reagents be used to synthesize the following compounds?
How might you use IR spectroscopy to determine whether reaction between 2-cyclohexenone and lithium dimethylcopper gives the direct addition product or the conjugate product?
Where would you expect each of the following compounds to absorb in the IR spectrum?(a) 4-Penten-2-one(b) 3-Penten-2-one(c) 2, 2-Dimethylcyclopentanone(d) m-Chloro benzaldehyde(e) 3-Cyclohexenone(f)
How might you use mass spectrometry to distinguish between the following pairs of isomers?(a) 3-Methyl-2-hexanone and 4-methyl-2-hexanone(b) 3-Heptanone and 4-heptanone(c) 2-Methylpentanal and
Tell the prominent IR absorptions and mass spectral peaks you would expect for the following compound:
Each of the following substances can be prepared by a nucleophilic addition reaction between an aldehyde or ketone and a nucleophile. Identify the reactants from which each was prepared. It the
The following molecular model represents a tetrahedral intermediate resulting from addition of a nucleophile to an aldehyde or ketone. Identify the reactants, and write the structure of the final
The enamine prepared from acetone and dim ethylamine is shown here in its lowest-energy form. (a) What is the geometry and hybridization of the nitrogen atom? (b) What orbital on nitrogen holds the
Draw structures corresponding to the following names:(a) Bromoacetone(b) (S)-2-Hydroxypropanal(c) 2-Methyl-3-hcptanone(d) (2S, 3R)-2, 3, 4-Trihydroxybut anal(e) 2, 2, 4, 4-Tetramethvl-3-pentanone(f)
Draw and name the seven aldehydes and ketones with the formula C5H10O. Which are chiral?
Give IUPAC names (or the following structures:
Give structures that fit the following descriptions:(a) An α, β-un-saturated ketone, C6H8O(b) An α-dike tone(c) An aromatic ketone, C9H10O(d) A diene aldehyde, C7H8O
Predict the products of the reaction of (i) phenyl acetaldehyde and (ii) acetophenone with the following reagents:(a) NaBH4 then H3O+(b) Tollens’ reagent(c) NH2OH, HC1 catalyst(d) CH3MgBr, then
How would you prepare the following substances from 2-cyclohexcnone? More than one step may be required.
Show how the Wittig reaction might be used to prepare the following alkenes. Identify the alkyl halide and the carbonyl components that would he used.
How would you use a Grignard reaction on an aldehyde or ketone to synthesize the following compounds?(a) 2-Pentanol(b) 1-Butanol(c) 1-Phenylcyclohexanol(d) Diphenyl methanol
Aldehydes can be prepared by the Wittig reaction using (methoxymethylene)-triphenylphosphorane as the Wittig reagent and then hydrolyzing the product with acid. For example, (a) How would you prepare
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