Alcohols contain an
OH group attached to a saturated carbon. The common names for alcohols are
based on the name of the alkyl group.
The systematic nomenclature for alcohols adds the ending -ol to the name of
the parent alkane and uses a number to identify the carbon that carries the OH group. The systematic name for
isopropyl alcohol, for example, is 2-propanol.
Methanol, or methyl alcohol, is also known as wood alcohol because it was
originally made by heating wood until a liquid distilled. Methanol is highly toxic, and
many people have become blind or died from drinking it. Ethanol, or ethyl alcohol, is the
alcohol associated with "alcoholic" beverages. It has been made for at least
6000 years by adding yeast to solutions that are rich in either sugars or starches. The
yeast cells obtain energy from enzyme-catalyzed reactions that convert sugar or starch to
ethanol and CO2.
The method of choice for determining whether an individual is DUIdriving under the influence or DWI driving while intoxicated is the Breathalyzer, for which a patent was issued to R.
F. Borkenstein in 1958. The chemistry behind the Breathalyzer is based on the reaction
between alcohol in the breath and the chromate or dichromate ion.
Measurements taken with the Breathalyzer are reported in units of percent blood-alcohol concentration (BAC). In most states, a BAC of 0.10% is sufficient for a DUI or DWI conviction. (This corresponds to a blood-alcohol concentration of 0.10 grams of alcohol per 100 mL of blood.)
Ethanol is oxidized to CO2 and H2O by the alcohol dehydrogenase enzymes in the body. This reaction gives off 30 kilojoules per gram, which makes ethanol a better source of energy than carbohydrates (17 kJ/g), and almost as good a source of energy as fat (38 kJ/g). An ounce of 80-proof liquor can provide as much as 3% of the average daily caloric intake, and drinking alcohol can contribute to obesity. Many alcoholics are malnourished, however, because of the absence of vitamins in the calories they obtain from alcoholic beverages.
As a general rule, polar or ionic substances dissolve in polar solvents; nonpolar substances dissolve in nonpolar solvents. As a result, hydrocarbons don't dissolve in water. They are often said to be immiscible (literally, "not mixable") in water. Alcohols, as might be expected, have properties between the extremes of hydrocarbons and water. When the hydrocarbon chain is short, the alcohol is soluble in water. There is no limit on the amount of methanol (CH3OH) and ethanol (CH3CH2OH), for example, that can dissolve in a given quantity of water. As the hydrocarbon chain becomes longer, the alcohol becomes less soluble in water, as shown in the table below. One end of the alcohol molecules has so much nonpolar character it is said to be hydrophobic (literally, "water-hating"). The other end contains an -OH group that can form hydrogen bonds to neighboring water molecules and is therefore said to be hydrophilic (literally, "water-loving"). As the hydrocarbon chain becomes longer, the hydrophobic character of the molecule increases, and the solubility of the alcohol in water gradually decreases until it becomes essentially insoluble in water.
Alcohols are classified as either primary (1), secondary (2), or tertiary (3) on the basis of their structures.
Ethanol is a primary alcohol because there is only one alkyl group attached to the
carbon that carries the OH
substituent. The structure of a primary alcohol can be abbreviated as RCH2OH,
where R stands for an alkyl group. The isopropyl alcohol found in rubbing alcohol is a
secondary alcohol, which has two alkyl groups on the carbon atom with the OH substituent (R2CHOH).
An example of a tertiary alcohol (R3COH) is tert-butyl (or t-butyl)
alcohol or 2-methyl-2-propanol.
Another class of alcohols are the phenols, in which anOH group is attached to an aromatic
ring, as shown in the figure below. Phenols are potent disinfectants. When antiseptic
techniques were first introduced in the 1860s by Joseph Lister, it was phenol (or carbolic
acid, as it was then known) that was used. Phenol derivatives, such as o-phenylphenol,
are still used in commercial disinfectants such as Lysol.
As a result, alcohols have boiling points that are much higher than alkanes with
similar molecular weights. The boiling point of ethanol, for example, is 78.5ºC, whereas
propane, with about the same molecular weight, boils at -42.1ºC.
OH group attached to a saturated carbon. The common names for alcohols are
based on the name of the alkyl group.| CH3OH | Methyl alcohol | ||
| CH3CH2OH | Ethyl alcohol | ||
| CH3CHOHCH3 | Isopropyl alcohol |
OH group. The systematic name for
isopropyl alcohol, for example, is 2-propanol. Practice Problem 6:More than 50 organic compounds have
been isolated from the oil that gives rise to the characteristic odor of a rose. One of
the most abundant of these compounds is known by the common name citronellol. Use
the systematic nomenclature to name this alcohol, which has the following structure.  |
C6H12O6(aq) 
2 CH3CH2OH(aq)
+ 2 CO2(g)
When the alcohol reaches a concentration of 10 to 12% by volume, the yeast cells die.
Brandy, rum, gin, and the various whiskeys that have a higher concentration of alcohol are
prepared by distilling the alcohol produced by this fermentation reaction. Ethanol isn't
as toxic as methanol, but it is still dangerous. Most people are intoxicated at blood
alcohol levels of about 0.1 gram per 100 mL. An increase in the level of alcohol in the
blood to between 0.4 and 0.6 g/100 mL can lead to coma or death. 2 CH3CH2OH(aq)
+ 2 CO2(g) The method of choice for determining whether an individual is DUI
driving under the influence or DWI driving while intoxicated is the Breathalyzer, for which a patent was issued to R.
F. Borkenstein in 1958. The chemistry behind the Breathalyzer is based on the reaction
between alcohol in the breath and the chromate or dichromate ion.
3 CH3CH2OH(g) + 2 Cr2O72-(aq)
+ 16 H+(aq) 3 CH3CO2H(aq) + 4 Cr3+(aq)
+ 11 H2O(l)
The instrument contains two ampules that hold small samples of potassium dichromate
dissolved in sulfuric acid. One of these ampules is used a reference. The other is opened
and the breath sample to be analyzed is added to this ampule. If alcohol is present in the
breath, it reduces the yellow-orange Cr2O72- ion to the
green Cr3+ ion. The extent to which the color balance between the two ampules
is disturbed is a direct measure of the amount of alcohol in the breath sample.
Measurements of the alcohol on the breath are then converted into estimates of the
concentration of the alcohol in the blood by assuming that 2100 mL of air exhaled from the
lungs contains the same amount of alcohol as 1 mL of blood. 3 CH3CO2H(aq) + 4 Cr3+(aq)
+ 11 H2O(l)Measurements taken with the Breathalyzer are reported in units of percent blood-alcohol concentration (BAC). In most states, a BAC of 0.10% is sufficient for a DUI or DWI conviction. (This corresponds to a blood-alcohol concentration of 0.10 grams of alcohol per 100 mL of blood.)
Ethanol is oxidized to CO2 and H2O by the alcohol dehydrogenase enzymes in the body. This reaction gives off 30 kilojoules per gram, which makes ethanol a better source of energy than carbohydrates (17 kJ/g), and almost as good a source of energy as fat (38 kJ/g). An ounce of 80-proof liquor can provide as much as 3% of the average daily caloric intake, and drinking alcohol can contribute to obesity. Many alcoholics are malnourished, however, because of the absence of vitamins in the calories they obtain from alcoholic beverages.
As a general rule, polar or ionic substances dissolve in polar solvents; nonpolar substances dissolve in nonpolar solvents. As a result, hydrocarbons don't dissolve in water. They are often said to be immiscible (literally, "not mixable") in water. Alcohols, as might be expected, have properties between the extremes of hydrocarbons and water. When the hydrocarbon chain is short, the alcohol is soluble in water. There is no limit on the amount of methanol (CH3OH) and ethanol (CH3CH2OH), for example, that can dissolve in a given quantity of water. As the hydrocarbon chain becomes longer, the alcohol becomes less soluble in water, as shown in the table below. One end of the alcohol molecules has so much nonpolar character it is said to be hydrophobic (literally, "water-hating"). The other end contains an -OH group that can form hydrogen bonds to neighboring water molecules and is therefore said to be hydrophilic (literally, "water-loving"). As the hydrocarbon chain becomes longer, the hydrophobic character of the molecule increases, and the solubility of the alcohol in water gradually decreases until it becomes essentially insoluble in water.
Solubilities of Alcohols in Water
| Formula | Name | Solubility in Water (g/100 g) |
||
| CH3OH | methanol | infinitely soluble | ||
| CH3CH2OH | ethanol | infinitely soluble | ||
| CH3(CH2)2OH | propanol | infinitely soluble | ||
| CH3(CH2)3OH | butanol | 9 | ||
| CH3(CH2)4OH | pentanol | 2.7 | ||
| CH3(CH2)5OH | hexanol | 0.6 | ||
| CH3(CH2)6OH | heptanol | 0.18 | ||
| CH3(CH2)7OH | octanol | 0.054 | ||
| CH3(CH2)9OH | decanol | insoluble in water |
Alcohols are classified as either primary (1), secondary (2), or tertiary (3) on the basis of their structures.
OH
substituent. The structure of a primary alcohol can be abbreviated as RCH2OH,
where R stands for an alkyl group. The isopropyl alcohol found in rubbing alcohol is a
secondary alcohol, which has two alkyl groups on the carbon atom with the OH substituent (R2CHOH).
An example of a tertiary alcohol (R3COH) is tert-butyl (or t-butyl)
alcohol or 2-methyl-2-propanol. Another class of alcohols are the phenols, in which an
OH group is attached to an aromatic
ring, as shown in the figure below. Phenols are potent disinfectants. When antiseptic
techniques were first introduced in the 1860s by Joseph Lister, it was phenol (or carbolic
acid, as it was then known) that was used. Phenol derivatives, such as o-phenylphenol,
are still used in commercial disinfectants such as Lysol.
Water has an unusually high boiling point because of the hydrogen bonds
between the H2O molecules. Alcohols can form similar hydrogen bonds, as shown
in the figure below.
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