Chapter 6

The Flavor of Our World: The Oxygen-Containing Organic Compounds We Drink, Smell, and Taste

Review Questions

  1. Today, diethyl ether is used in chemistry laboratories as a solvent for organic compounds. Historically, diethyl ether was used as an anesthetic.
  1. MTBE, or methyl tert-butyl ether, is used as a fuel additive.
  1. MBTE is added to gasoline as a replacement for some of the hydrocarbon content. It introduces oxygen into the fuel making it burn more completely and decreases the production of carbon monoxide.
  1. A functional group is an atom or bonded collection of atoms that occur in organic molecules.
  1. a) This molecule has the general structure represented by R-O-R, where an oxygen atom is bonded to two carbon atoms. Thus, the functional group in this molecule is an ether. The general structure of an ether is given below.

b) This compound is an aldehyde. The carbon atom must form four bonds. Thus, the –COH group is bonded to the CH2 group by a single bond, the oxygen by a double bond, and the hydrogen by a single bond. The structure of an aldehyde group is given below.

c) This molecule has the characteristic –COOH, or carboxylic acid functional group.

  1. The proof value of an alcoholic beverage is defined as two times the percent by volume of ethanol in the ethanol-water solution.
  1. The LD50 value is a commonly used measure of the toxicity of a substance. It is defined as the minimum dose of the substance that is lethal to 50% of the population.
  1. The subscript value for the LD designation indicates the percent of the population. Thus, a LD50 indicates the minimum dose that is lethal to 50% of the population, while a LD10 indicates the minimum dose that is lethal to 10% of the population. The LD50 value should be greater than the LD10 value.
  1. Consumption of alcohol significantly increases an individual’s risk of death from cancer and liver disease. Drinking excessive amounts of alcohol at one time can lead to brain injury and even death.

10. Fetal alcohol syndrome is a condition frequently found in children born to women who consumed alcohol during their pregnancy. Some of the adverse developmental abnormalities associated with this condition involve the incomplete or improper development of nerve cells in the fetus, and result in children with attention disorders, hyperactivity, aggression, and possible mental retardation. Alcohol consumption during pregnancy also interferes with the physical development of limbs, facial features, and other normal growth patterns.

  1. Metabolic processes are chemical reactions that occur in the body that ultimately alter the chemical nature of substances present in the body.
  1. Metabolic processes affected by drinking alcoholic beverages include enzymatic processes in the liver that metabolize the alcohol to CO2 and H2O, normal neuronal functions in the brain, and fluid balance in the body.
  1. Denatured alcohol is ethanol mixed with a small amount of pyridine, methanol, or other organic compound to make it undrinkable.
  1. a) The common name for methanol is wood alcohol.

b) The common name for ethanol is grain alcohol.

  1. Ethanol can be used as a fuel because it undergoes combustion in oxygen to produce heat.
  1. Ethanol undergoes combustion in oxygen to produce carbon dioxide, water and heat. The chemical equation for this process is given below.

C2H5OH + 3 O2 2 CO2 + 3 H2O + heat

  1. Ethanol is called a renewable fuel because its supply can be continually renewed and there is no net carbon dioxide release during its production-combustion cycle.
  1. Hydrogen bonding is an interaction between a hydrogen atom with a partial positive charge and a nearby atom that has both a negative charge and at least one pair of non-bonding electrons.
  1. Ethanol and water are miscible because of hydrogen bonding interactions between the molecules. Ethanol and water will dissolve in one another in all proportions to form homogeneous solutions.
  1. Hydrophilic molecules are “water-loving” molecules. They generally have some polar character and can frequently hydrogen bond with water. Hydrophobic molecules are “water-hating” molecules. These are frequently very non-polar organic molecules, such as fats and oils.
  1. Concentrated solutions (70% and higher) of ethanol are antiseptics. These solutions tend to denature the proteins and disrupt the lipid structures of infection-causing bacteria.
  1. THC is tetrahydrocannibinol. THC exerts a psychoactive effect on the body by binding to receptors in the brain. The structure of THC is given below.
  1. Phenol, glycerol, and THC are all classified as alcohols because they all contain free hydroxyl, or –OH, groups. The structures of THC, glycerol, and phenol are given below.
  1. Dehydrating agents are substances, such as sulfuric acid, that can remove water from molecules.
  1. Formaldehyde is harmful to humans and other living organisms. It causes eye, nose, throat, and skin irritation in humans and is toxic in high concentrations. It has also been classified as a “probable human carcinogen” having expected cancer sites in the respiratory system, including the nose.
  1. Dicarboxylic acids are molecules containing two carboxylic acid, -COOH, groups. Carboxylic acids generally only contain a single carboxylic acid group.
  1. In the body, ethanol is first converted into acetaldehyde and then into acetic acid before being oxidized to CO2 and H2O. The oxidation of acetaldehyde, however, takes place relatively slowly in the body. While acetaldehyde is in the bloodstream, it produces the effects associated with a hangover. It dilates the blood vessels in the scalp and around the brain producing a headache and a feeling of nausea.
  1. An intermediate in a chemical reaction is a substance that is produced during the initial stages of a sequence of reactions and is completely consumed later in the sequence.
  1. a) 2. Formic acid is a chemical found in ant stings. It is also a component of the sting of bees and wasps.

b) 5. Benzaldehyde is also known as the “oil of almond.”

c) 1. Lactic acid is an intermediate compound produced during the oxidation of glucose.

d) 4. Citric acid is found in oranges and other citrus fruits.

e) 3. Formaldehyde is used as a preservative for biological specimens.

f) 6. Phenol is an alcohol used as a floor disinfectant in hospitals.

30. Carboxylic acids and alcohols react to produce esters by a reaction known as a condensation reaction.

  1. A condensation reaction is a reaction between two compounds that removes a water molecule from the two reactants.

Understanding Concepts

  1. The following two compounds are isomers with the chemical formula C2H6O. One of the compounds is an ether and the other is an alcohol.
  1. Because MTBE introduces oxygen into the fuel mixture, it makes gasoline burn more completely and produce less carbon monoxide. Moreover, since MTBE has an octane rating of 116, it is able to replace some of the aromatic hydrocarbons in gasoline, thereby reducing benzene emissions.
  1. Methanol and ethanol dissolve completely in water because of the presence of hydrogen bonding between the molecules of water and the –OH groups on the alcohol. A molecular depiction of this interaction for methanol is given below.

or

36. The consumption of relatively small amounts of methanol can produce blindness due to the production of formaldehyde. Unlike ethanol, which is metabolized to acetaldehyde, acetic acid, and then carbon dioxide and water, methanol is first oxidized by the liver to formaldehyde, a compound believed to attach the optic nerve. Formaldehyde is further oxidized by the liver to formic acid and then to carbon dioxide and water. While ethanol is less toxic to the body than methanol, both can be lethal if ingested in large quantities.

  1. a)

b) The alcohol isomer of the ether in (a).

38.The condensed formula for an ether that is the isomer of butanol (CH3CH2CH2CH2OH) is given below.

Diethyl ether: CH3-CH2-O-CH2-CH3

  1. The subscript of the M symbol indicates the percent, by volume, of methanol present. Thus, the M symbol for a solution that is 8% methanol and 92% gasoline is M8. Similarly, the M symbol for a solution that is 90% methanol and 10% gasoline is M90.

40. The proof value is defined as two times the percent by volume of ethanol in an ethanol-water solution. Thus, if a material is 100% ethanol, then it is 200 proof. Similarly, 90 proof whiskey has an ethanol content of 45%, by volume.

  1. Since the proof value is defined as two times the percent by volume of ethanol in an ethanol-water solution, wine that has a 9% alcohol content is 18 proof. The alcohol content of a strong ale that has a proof value of 14 is 7%, by volume.
  1. LD50 values provide the minimum dose that is lethal to 50% of the population. The lower the LD50 value, the more lethal the material. (That is, a lower dose is lethal to 50% of the population). Thus, the rank of the substances from most toxic to least toxic is nicotine (230), acetaminophen (338), Naproxen (1,234), and Ibuprofen (1,255).
  1. In the process of fermentation, microscopic organisms called yeasts, catalyze the anaerobic (without oxygen) conversion of small organic molecules into ethanol. Since yeast is not active at alcoholic concentrations above about 12%, products with higher alcoholic content are not produced directly by the process of fermentation. Rather, the products of fermentation are distilled to produce solutions with higher concentrations of ethanol.

44. a) acetic acid and methanol

b) butyric acid and ethanol

c) acetic acid and pentanol

  1. The greater the attractive forces between the molecules of a liquid, the more energy required to convert the liquid to a vapor. Thus, the higher the temperature at which a liquid boils, the greater the attractive forces between the molecules.
  1. In an aldehyde, the carbon atom bound to the oxygen atom (called the carbonyl carbon) is attached to one carbon atom and one hydrogen atom. In a ketone, the carbonyl carbon is attached to two carbon atoms. The general structures for an aldehyde and a ketone are given below.

Aldehyde:

Ketone:

  1. Acetone has the chemical formula C3H6O. Its aldehyde isomer is propionaldehyde.
  1. The condensation reaction between ethanol and propanoic acid would produce ethyl propanoate.
  1. The acid and alcohol that are combined to produce butyl butanoate are butanoic acid and butanol, respectively.
  1. Some fragrant oils are soluble in ethanol. These oils are frequently classified as relatively non-polar esters or very long hydrocarbon chain alcohols. In general, these compounds have very low solubility in water, but are soluble in ethyl alcohol due to its hydrocarbon nature.
  1. Hard contact lenses are made from a polymer known as poly(methyl methacrylate), or PMMA. This polyester material is a hard, clear, colorless plastic with an optical clarity very close to glass. Soft contact lenses are composed of a variation of PMMA in which one hydrogen atom of the ester group is replaced with an –OH group. Hydrogen bonding by this –OH group allows the lens to absorb water making the plastic act like a thin film of water.

Synthesizing Ideas

  1. In order to calculate the lethal doses of caffeine and aspirin from the LD50 values, you need to determine the average weight of a person (154 lb.) in Kg.

154 lb. x 1 Kg = 70 Kg

2.2 lb.

Caffeine: 70 Kg x 127 mg = 8890 mg or 8.890 grams

1 Kg

Aspirin: 70 Kg x 1100 mg = 77,000 mg or 77 grams

1 Kg

  1. Probably the easiest way to determine the relative vapor pressures of different perfumes is to place equal volumes of the liquid at the same temperature and determine which evaporates first. The material that evaporates first has the highest vapor pressure. Alternatively, one could determine the boiling points of the compounds. The lower the boiling point, the higher the vapor pressure.
  1. It is generally accepted that a blood alcohol level of 0.05% begins to cause mental impairment. Given the average weight of a person to be 150 pounds, this corresponds to approximately 1.2 fluid ounces of ethanol. This is approximately the amount of alcohol in two small 6-oz. glasses of table wine.
  1. A renewable fuel is defined as a fuel having both a continually renewable supply and no net carbon dioxide release during its production-combustion cycle. Renewable fuels include ethanol, methanol, hydrogen, and oils from food products such as soy. Other “non-organic” renewable sources of energy include geothermal, solar, water, and wind.
  1. Ethanol: CH3CH2OH

1 hydrogen bond to another ethanol molecule

Acetaldehyde: CH3CHO

0 hydrogen bonds to another acetaldehyde molecule

Acetic Acid: CH3COOH

2 hydrogen bonds to another acetic acid molecule

Based upon the number of intermolecular hydrogen bonds possible, the boiling points of the compounds should be in the order: acetaldehyde < ethanol < acetic acid. This is because the greater the intermolecular bonding, the higher the boiling point. The observed boiling points of acetaldehyde (20.1oC), ethanol (78.3oC), and acetic acid (117.9oC) confirm this analysis.

  1. In order to calculate this concentration, first determine the weight of an average 150-lb. person in ounces.

150 lb. x 16 oz = 2400 oz

1 lb.

Next, determine the weight of ethanol in the blood. (Note: 0.01% = 0.0001)

2400 oz x 0.0001 = 0.24 oz

Convert the ounces of alcohol to milligrams.

0.24 oz x 28.4 grams = 6.8 grams or 6800 milligrams

1 oz

Divide the number of milligrams of ethanol in the body by the weight of the body in kilograms (150 lb. = 68 Kg)

6800 milligrams of ethanol = 100 mg/Kg body weight

68 Kg person

  1. For a 70-Kg person, the LD50 value for ethanol is approximately 700 grams. Each 12-ounce bottle of beer contains 14 grams of ethanol. Thus, you would need to consume 50 bottles of beer to achieve the LD50 dose. Drinking one bottle less or one bottle more would not likely alter the course of events. The LD50 value represents a dose that is lethal to 50% of the population. Thus, around this value your chances of living or dying are about equal.
  1. Propylene glycol
  1. Using a linear unbranched 5-carbon backbone, one unique aldehyde and two unique ketone structures can be drawn.
  1. Isopropyl alcohol is metabolized to acetone, a ketone, in the body.
  1. Alpha-hydroxy acids, or AHAs, are typically listed on cosmetic labels as glycolic acid, malic acid, lactic acid, citric acid, alpha-hydroxy ethanolic acid, alpha-hydroxy octanoic acid, alpha-hydroxy caprylic acid (hydroxy caprylic acid), mixed fruit acids, tri-alpha hydroxy fruit acids, triple fruit acid, sugar or cane extract. Most alpha-hydroxy acids are derived from fruit and milk sugars, and work by causing exfoliation or shedding of the surface skin. This loss of the dead cell layer of skin is believed to result in increased sensitivity to ultraviolet radiation.

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