Download 3 Properties Alcohols GOB Structures

13.3 Physical Properties of Alcohols,
Phenols, and Ethers
In an alcohol-containing
sanitizer, the amount of
ethanol is typically
60% (v/v) but can be as
high as 85% (v/v). Because
alcohols are flammable,
hand sanitizers are a fire
hazard in the home.
Hand sanitizers that contain ethanol
are used to kill bacteria on the hands.
Learning Goal Describe the classification of alcohols;
describe the boiling points and solubility of alcohols,
phenols, and ethers.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Classification of Alcohols
Alcohols are classified
• by the number of alkyl groups attached to the
carbon bonded to the hydroxyl.
• as primary (1°), secondary (2°), or tertiary (3°).
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Classify each alcohol as primary, secondary, or tertiary.
OH
A. CH3 —CH
CH2
CH3
B. CH3—CH2—CH2—OH
C.
OH
CH3 —CH2—C—CH2—CH3
CH3
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Classify each alcohol as primary, secondary, or tertiary.
OH
A. CH3 —CH
CH2
CH3
B. CH3—CH2—CH2—OH
C.
OH
CH3 —CH2—C—CH2—CH3
CH3
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
secondary
primary
tertiary
© 2016 Pearson Education, Inc.
Boiling Points
Because there is a large electronegativity difference between the oxygen
and hydrogen atoms in the — OH group,
• the oxygen has a partially negative charge.
• the hydrogen has a partially positive charge.
• hydrogen bonds form between the oxygen of one alcohol and hydrogen
in the — OH group of another alcohol.
Small alcohol and
ether molecules
are soluble in water
because they form
hydrogen bonds.
Hydrogen bonds form between alcohol molecules but not between ether molecules.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Boiling Points
• Hydrogen bonds cannot form between ether molecules
because there are not any polar — OH groups.
• Alcohols with similar mass have higher boiling points
than do ethers because alcohols require higher
temperatures (more energy) to break their
hydrogen bonds.
• The boiling points of ethers are similar to those of
alkanes because neither can form hydrogen bonds.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Boiling Points of Alcohols: Ethers
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solubility: Alcohols and Ethers
Alcohols
• contain polar — OH groups
and form hydrogen bonds with
other alcohol molecules and
with water.
• that have one to three carbons
are soluble in water.
The solubility of alcohols in water
decreases with increasing number
of carbons.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solubility: Alcohols and Ethers
Ethers
• can form hydrogen bonds with water.
• form fewer hydrogen bonds than alcohols
with water.
• are only slightly soluble in water when they have
fewer than four carbon atoms.
• are not soluble in water if they have five or more
carbon atoms.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solubility: Phenols
Phenols, once used as antiseptics,
• are slightly soluble in water.
• have an — OH group that can form hydrogen bonds
with water.
• can react with water to produce phenoxide ions.
In water, the — OH group of phenol ionizes slightly,
which makes it a weak acid (Ka = 1 × 10−10).
+ H2O
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
+ H3O+
© 2016 Pearson Education, Inc.
Phenol and Antiseptics
Antiseptics, substances applied to the skin to kill microorganisms
that cause infection,
• were once made of dilute solutions of phenol.
• were once used to disinfect wounds to prevent post-surgical
infections such as gangrene.
• are now used in Lysol, used to disinfect surfaces, and contain the
antiseptics 2-phenylphenol and 2-benzyl-4-chlorophenol.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health:
Hand Sanitizers
Hand sanitizers containing ethanol as their active ingredient
• kill most bacteria and viruses that spread colds and flu.
• are approximately 60% (v/v) but can be as high as 85% (v/v).
• are highly flammable and produce a transparent, blue flame.
• may also contain triclosan, which can accumulate in the
environment, promoting growth of antibiotic-resistant bacteria.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Indicate whether each of the following is soluble in water
and explain why.
A. CH3—CH2—CH2—CH2—CH2—CH2—OH
B. CH3—CH2—OH
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Indicate whether each of the following is soluble in water
and explain why.
A. CH3—CH2—CH2—CH2—CH2—CH2—OH
not soluble
Alcohols with long carbon chains (nonpolar) are not
soluble.
B. CH3—CH2—OH
soluble
Short-chain alcohols form hydrogen bonds with water.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.