At 600 °C, the ratio of the relative rates of

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 compared with what Dr. Al Cahall found in Problem 17.

Problem 17

Dr. Al Cahall wanted to determine experimentally the relative ease of removal of a hydrogen atom from a tertiary, a secondary, and a primary carbon by a chlorine radical. He allowed 2-methylbutane to undergo chlorination at 300 °C and obtained as products 36% 1-chloro-2-methylbutane, 18% 2-chloro-2-methylbutane, 28% 2-chloro-3-methylbutane, and 18% 1-chloro-3-methylbutane. What values did he obtain for the relative ease of removal of tertiary, secondary, and primary hydrogen atoms by a chlorine radical under the conditions of his experiment?

A. Stereoisomers with two asymmetric carbons are called _____ if

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 isomer.

b. Stereoisomers with two asymmetric carbons are called _____ if the configuration of both asymmetric carbons in one isomer is the same as the configuration of the asymmetric carbons in the other isomer.

c. Stereoisomers with two asymmetric carbons are called _____ if one of the asymmetric carbons has the same configuration in both isomers and the other asymmetric carbon has the opposite configuration in the two isomers.

Determine the amino acid sequence of a polypeptide from the

Determine the amino acid sequence of a polypeptide from the following results:

Acid hydrolysis gives Ala, Arg, His, 2 Lys, Leu, 2 Met, Pro, 2 Ser, Thr, Val.

Carboxypeptidase A releases Val.

Edman’s reagent releases PTH-Leu.

Cleavage with cyanogen bromide gives three peptides with the following amino acid compositions:

1. His, Lys, Met, Pro, Ser

2. Thr, Val

3. Ala, Arg, Leu, Lys, Met, Ser

Trypsin-catalyzed hydrolysis gives three peptides and a single amino acid:

1. Arg, Leu, Ser

2. Met, Pro, Ser, Thr, Val

3. Lys

4. Ala, His, Lys, Met

An unknown, foul-smelling hydrocarbon gives the mass spectrum and infrared

An unknown, foul-smelling hydrocarbon gives the mass spectrum and infrared spectrum shown.

(a) Use the mass spectrum to propose a molecular formula. How many elements of unsaturation are there?

(b) Use the IR spectrum to determine the functional group(s), if any.

(c) Propose one or more structures for this compound. What parts of the structure are uncertain? If you knew that hydrogenation of the compound gives n-octane, would the structure still be uncertain?

(d) Propose structures for the major fragments at 39, 67, 81, and 95 in the mass spectrum. Explain why the base peak is so strong.

A laboratory student added 1-bromobutane to a flask containing dry

A laboratory student added 1-bromobutane to a flask containing dry ether and magnesium turnings. An exothermic reaction resulted, and the ether boiled vigorously for several minutes. Then she added acetone to the reaction mixture and the ether boiled even more vigorously. She added dilute acid to the mixture and separated the layers. She evaporated the ether layer, and distilled a liquid that boiled at 143 °C. GC–MS analysis of the distillate showed one major product with a few minor impurities. The mass spectrum of the major product is shown here.

(a) Draw out the reactions that took place and show the product that was formed.

(b) Explain why the molecular ion is or is not visible in the mass spectrum, and show what ions are likely to be responsible for the strong peaks at m/z 59 and 101.

A (C-D) (carbon–deuterium) bond is electronically much like a C-H

A (C-D) (carbon–deuterium) bond is electronically much like a C-H bond, and it has a similar stiffness, measured by the spring constant, k. The deuterium atom has twice the mass (m) of a hydrogen atom, however.

(a) The infrared absorption frequency is approximately proportional to √k/m, when one of the bonded atoms is much heavier than the other, and m is the lighter of the two atoms (H or D in this case). Use this relationship to calculate the IR absorption frequency of a typical C-D bond. Use 3000 cm-1 as a typical C-H absorption frequency.

(b) A chemist dissolves a sample in deuterochloroform then decides to take the IR spectrum and simply evaporates most CDCl3. of the What functional group will appear to be present in this IR spectrum as a result of the impurity?

(a) When n-heptane burns in a gasoline engine, the combustion

(a) When n-heptane burns in a gasoline engine, the combustion process takes place too quickly. The explosive detonation makes a noise called knocking. When 2,2,4-trimethylpentane (isooctane) is burned, combustion takes place in a slower, more controlled manner. Combustion is a free-radical chain reaction, and its rate depends on the reactivity of the free-radical intermediates. Explain why isooctane has less tendency to knock than does n-heptane.

(b) Alkoxy radicals (R-O∙) are generally more stable than alkyl (R∙) radicals. Write an equation showing an alkyl free radical (from burning gasoline) abstracting a hydrogen atom from tert butyl alcohol, (CH3)3COH. Explain why tert-butyl alcohol works as an antiknock additive for gasoline.

(c) Use the information in Table 4-2 to explain why toluene (PhCH3) has a very high octane rating of 111. Write an equation to show how toluene reacts with an alkyl free radical to give a relatively stable radical.

Table 4-2

Consider the following compound, which has been synthesized and characterized:(a)

Consider the following compound, which has been synthesized and characterized:

(a) Assuming this molecule is entirely conjugated, do you expect it to be aromatic, antiaromatic, or nonaromatic?

(b) Why was this molecule synthesized with three tert-butyl substituents? Why not make the unsubstituted compound and study it instead?

(c) Do you expect the nitrogen atom to be basic? Explain. Why doesn’t nitrogen’s lone pair overlap with the double bonds to give a total of six electrons in the pi system?

(d) At room temperature, the proton NMR spectrum shows only two singlets of ratio 1:2. The smaller signal remains unchanged at all temperatures. As the temperature is lowered to -110°C, the larger signal broadens and separates into two new singlets, one on either side of the original chemical shift. At -110 °C, the spectrum consists of three separate singlets of areas 1:1:1. Explain what these NMR data indicate about the bonding in this molecule. How does your conclusion based on the NMR data agree with your prediction in part (a)?

The ribonucleosides that make up ribonucleic acid (RNA) are composed

The ribonucleosides that make up ribonucleic acid (RNA) are composed of D-ribose (a sugar) and four heterocyclic “bases.” The general structure of a ribonucleoside is 

The four heterocyclic bases are cytosine, uracil, guanine, and adenine. Cytosine and uracil are called pyrimidine bases because their structures resemble pyrimidine. Guanine and adenine are called purine bases because their structures resemble purine.

(a) Determine which rings of these bases are aromatic.

(b) Predict which nitrogen atoms are basic.

(c) Do any of these bases have easily formed tautomers that are aromatic? (Consider moving a proton from nitrogen to a carbonyl group to form a phenolic derivative.)

A new graduate student was studying the insecticidal properties of

A new graduate student was studying the insecticidal properties of a series of polycyclic epoxides. He epoxidized alkene A using two different methods. First he used MCPBA, which gave an excellent yield of an epoxide that he labeled B. Then he treated alkene A with bromine water to form the bromohydrin, followed by 2,6-dimethylpyridine (see page 647) to form an epoxide in fair yield. To his surprise, the second method produced an epoxide (C) with different physical and chemical properties from the first. In particular, C reacts with strong nucleophiles much faster than B. Propose structures for B and C, and propose mechanisms to show why different products are formed. Explain why C reacts so much faster with strong nucleophiles.