Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1. Figure 1In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2.Figure 2Cotton is a natural fiber composed of cellulose, a polymer of glucose. Which of the compounds shown in Figure 1 would adhere to a cotton fiber via hydrogen bonding?
Answer(s): C
Hydrogen bonding occurs between OH groups and NH groups in any combination. Since the glucose monomer in cellulose has OH groups, cellulose should be capable of hydrogen bonding to either alizarin, with its two OH groups, or to aniline yellow, with its aromatic amine functionality. Malachite green, on the other hand, has no acidic protons available for hydrogen bonding due to the methylation of the nitrogen atoms.
Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.Figure 1In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2. Figure 2Nylon, Dacron, and many other synthetic fibers are produced via condensation reactions. Which of the following would be the best starting materials for the production of nylon 66?
Answer(s): D
Amides are produced by the condensation of amines with carboxylic acids:To produce a repeating chain, or polyamide, one would need to condense a diamine with a dicarboxylic acid.As indicated in figure 2, nylon 66 has a straight chain of six carbons between the two nitrogen atoms and six more carbon atoms, also unbranched, in the dicarbonyl portion of the monomer. As such, the amine starting material must therefore be 1,6-hexanediamine, while the carboxylate reactant is hexanedioic acid:Choice A is incorrect because cis-2-butenoic acid has only one carboxylate functionality and therefore would not condense on both ends, and it would produce a condensation product in which the butane double bond is still present. It also contains only four carbon atoms, rather than the required six.Choice B is incorrect since, while butanedioic acid can polymerize with the diamine, it would produce a polymer with only two methylene groups between the carbonyl carbons in each monomer. (This product would be called nylon 64.)Choice C is wrong on two counts: first, the hexanoic acid is a monocarboxylic acid, and thus will not combine with two amine molecules; second, any polyamide formed via condensation of an appropriate diacid and the suggested amine, 2,5-hexanediamine, would have two methyl group side chains.
Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.Figure 1In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2.Figure 2Azo dyes are synthesized via diazotization. The sequence of diazotization involves first treating an aromatic amine with NaNO2 in acidic solution, thereby converting it to the corresponding diazonium salt (with the general formula ArN2X-), then reacting with a second aromatic compound to form the azo dye. What is the structure of the azo dye produced by the reaction sequence below?
Aromatic diazonium salts have the general formula ArN2+X-. The second step of the diazotization reaction described is electrophilic aromatic substitution, with ArN2+ acting as the electrophile, thus one should predict that the nitrogen of the salt should attach to the second ring in the position dictated by the second ring's substituents. Since the second aromatic compound, p-nitroanisole, has two substituents, we need to examine the directing effect of each: the nitro group is a meta director, while the ether is an ortho/para director. The effects of these two groups should thus be additive, placing the new substituent ortho to the OCH3, as shown in choice D.Choices A and B are incorrect since the substitution reaction will take place at one of the ring protons rather than one of the substituent groups.Choice C is wrong because NO2 is meta directing but is forced here to be ortho directing.
Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.Figure 1In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2.Figure 2 Hydrogenation of alizarin over a specific rhodium catalyst results in the complete saturation of all the carbon- carbon bonds, but does not affect any other functional groups. Which of the following effects should also be expected?
As stated in the passage, color is the result of electronic transitions due to the delocalized system in the dye.If the two aromatic rings of alizarin are completely hydrogenated, the resulting compound will contain only the two isolated ketone double bonds; the system will thus no longer be delocalized, and color production will cease.Choice A is incorrect since the two OH groups would still be present in the hydrogenated product; it is this feature of the molecule which accounts for the affinity for Dacron, via hydrogen bonding.Choice B is wrong since solubility in aqueous base is mainly due to the presence of the two OH groups, and to a lesser extent to the polar carbonyl bonds, which will still be present in the hydrogenated product.Choice D is incorrect because it is not the aromatic nature of alizarin which accounts for its affinity, or lack thereof, for nylon 66. As the passage states, side chains are often necessary to provide a binding site; this is very likely to be the case between nylon and alizarin.
Hypoxia refers to a physiological condition in which the body lacks sufficient oxygen for normal cellular functioning. Prolonged hypoxia generally leads to an inhibition of mental capacity and a reduction in the work capacity of muscle. Severe cases of hypoxia can lead to coma or even death. Depending on the cause, hypoxia can be classified into four general types:Hypoxic hypoxia is a type of hypoxia that occurs when the partial pressure of oxygen in the blood is too low. For example, climbers at high altitude, where the air contains less oxygen, might experience hypoxic hypoxia because the partial pressure of oxygen in the air inhaled is very low, leading to insufficient partial pressure of oxygen in the blood.Anemic hypoxia describes a diminished ability of the blood to transport oxygen. Several factors can influence the oxygen-carrying capacity of the blood. Primary causes of anemic hypoxia include a lower than normal number of functional erythrocytes or an insufficient quantity of hemoglobin, the oxygen-carrying molecules of the blood. Abnormal hemoglobin can also decrease the blood's capacity to carry oxygen and lead to anemic hypoxia.Ischemic hypoxia is caused by a decreased delivery of blood to the tissues. Localized circulatory deficiencies, such as blood clots, and global circulatory deficiencies, such as heart failure, decrease the delivery of blood to the tissues, and can therefore cause ischemic hypoxia.Histotoxic hypoxia results from the inability of cells to utilize the oxygen available in the blood. Causes of histotoxic hypoxia include the poisoning of cellular enzymes involved in aerobic respiration, as well as the decreased metabolic capacity of the oxidative enzymes due to vitamin deficiency. Cyanide poisoning causes histotoxic hypoxia by blocking the action of cytochrome oxidase in the electron transport chain so that tissues cannot use oxygen even though it is available.Cigarette smoking causes emphysema, a condition in which the net surface area of the lungs is greatly decreased leading to a decrease in the diffusing capacity of the lungs. Emphysema leads to which type of hypoxia?
Answer(s): A
The passage states that hypoxic hypoxia is caused by any factor that leads to a decreased plasma pO2. Since emphysema decreases the diffusing capacity of the lungs, less oxygen will diffuse into the blood, leading to a lower pO2.Choice B is incorrect because anemic hypoxia is caused by a decreased oxygen carrying capacity of the blood.Emphysema affects the amount of oxygen in the blood, not the ability of the blood to carry oxygen.Choice C is incorrect because ischemic hypoxia is caused by a decreased delivery of blood to the tissues.Emphysema has no effect on blood circulation.Choice D is incorrect because histotoxic hypoxia is caused by the inability of the tissues to utilize oxygen.Emphysema does not affect the ability of the tissues to use oxygen.
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