Chem 219 Unit 5 Exam with Correct Solutions
Generic formula for alcohols - Answer -R-OH
phenol - Answer -hydroxy-substituted aromatic molecules (any compound with an -OH attached to a
benzene ring)
IUPAC system rules for naming organic alcohols - Answer -- organic alcohols are named by replacing the
suffix of the parent chain of the molecule with the suffix -ol
- The parent chain is numbered so as to give the hydroxyl group the lowest possible number. (examples:
1-propanol, and cyclohexanol)
- with unsaturated alcohols the -ol suffix comes last and takes priority when numbering the parent chain
(2-propene-1-ol)
- Molecules with more than one -OH group get a prefix describing the number of -OH groups added to
the IUPAC name. (ethane-1,2-diol)
Molecules with more than one -OH group - Answer -polyols
IUPAC rules for phenols - Answer -- the suffix for an alcohol substituted benzene is "phenol"
- start the numbering at the OH group (so OH is at the 1 position)
(examples: phenol, 3-methylphenol, 2,4-dinitrophenol)
Why can alcohols form strong hydrogen bonds? - Answer -Due to the presence of the hydroxyl group, as
the O-H bond is highly polarized by the electronegative oxygen atom. This polarization places a + charge
on the hydrogen atom and a - charge on the oxygen atom. The polarization in the O-H bond on one
alcohol molecule becomes attracted to the polarization in the O-H bond of another alcohol molecule.
Why do alcohols have much higher boiling points than other molecules of similar molecular weight? -
Answer -hydrogen bonding between alcohol molecules
, These attractions raise the amount of energy required to vaporize the liquid-phase molecules (boil),
which translates into increased boiling point temperatures.
Alcohol molecules can freely hydrogen bond to other molecules possessing what groups? - Answer -O-H,
N-H, or S-H functional groupings
How does the water solubility of alcohol molecules change as the molecular weight changes? - Answer -
Alcohol molecules of lower molecular weight are mostly soluble in water as a result of the ability to
hydrogen bond to OH, NH, or SH groups. As the molecular weight or carbon-chain length increases, the
alcohol molecules become correspondingly less soluble in water.
How do alcohols and phenols act as weak acids and weak bases? - Answer -- acts as an acid by donating
the O-H proton as H
- acts as a base by accepting H+ using a lone pair on the O atom
amphoteric substances - Answer -Substances that can act as both acids and bases (alcohols and phenols)
Why is acid dissociation for most alcohols unfavorable (lies towards the left)? - Answer -Dissociation
produces an alkoxide ion (the conjugate base of an alcohol), which is a very strong base.
How can you conduct acid-base reactions that favor the formation of weaker conjugate acids/bases? -
Answer -To promote (favor) the formation of the alkoxide ion, the alcohol can be treated with sodium or
potassium metal (Na or K) or a base that is stronger than the RO- ion produced.
protonation of an alcohol - Answer -When alcohols act as weak bases by using a lone pair on the oxygen
atom of the hydroxyl group, alcohols can accept a proton when they are placed in an acidic environment.
What is the product of the protonation of an alcohol called? - Answer -alkyloxonium ion
What is a Dehydration reaction for alcohols?
What happens during a dehydration reaction for alcohols? - Answer -- A specific type of elimination
reaction. In a dehydration reaction, an alcohol molecule will lose H2O to form an alkene. Alcohols
undergo a reaction known as dehydration when they are heated with strong mineral acids (like sulfuric
or phosphoric).
- the alcohol molecule loses the hydroxyl (OH) from one carbon (the α-carbon) and a hydrogen atom (H)
from an adjacent (β) carbon.
What is the function of an acid during a dehydration reactions? Why does it do what it does? - Answer -
To protonate the the OH group
Generic formula for alcohols - Answer -R-OH
phenol - Answer -hydroxy-substituted aromatic molecules (any compound with an -OH attached to a
benzene ring)
IUPAC system rules for naming organic alcohols - Answer -- organic alcohols are named by replacing the
suffix of the parent chain of the molecule with the suffix -ol
- The parent chain is numbered so as to give the hydroxyl group the lowest possible number. (examples:
1-propanol, and cyclohexanol)
- with unsaturated alcohols the -ol suffix comes last and takes priority when numbering the parent chain
(2-propene-1-ol)
- Molecules with more than one -OH group get a prefix describing the number of -OH groups added to
the IUPAC name. (ethane-1,2-diol)
Molecules with more than one -OH group - Answer -polyols
IUPAC rules for phenols - Answer -- the suffix for an alcohol substituted benzene is "phenol"
- start the numbering at the OH group (so OH is at the 1 position)
(examples: phenol, 3-methylphenol, 2,4-dinitrophenol)
Why can alcohols form strong hydrogen bonds? - Answer -Due to the presence of the hydroxyl group, as
the O-H bond is highly polarized by the electronegative oxygen atom. This polarization places a + charge
on the hydrogen atom and a - charge on the oxygen atom. The polarization in the O-H bond on one
alcohol molecule becomes attracted to the polarization in the O-H bond of another alcohol molecule.
Why do alcohols have much higher boiling points than other molecules of similar molecular weight? -
Answer -hydrogen bonding between alcohol molecules
, These attractions raise the amount of energy required to vaporize the liquid-phase molecules (boil),
which translates into increased boiling point temperatures.
Alcohol molecules can freely hydrogen bond to other molecules possessing what groups? - Answer -O-H,
N-H, or S-H functional groupings
How does the water solubility of alcohol molecules change as the molecular weight changes? - Answer -
Alcohol molecules of lower molecular weight are mostly soluble in water as a result of the ability to
hydrogen bond to OH, NH, or SH groups. As the molecular weight or carbon-chain length increases, the
alcohol molecules become correspondingly less soluble in water.
How do alcohols and phenols act as weak acids and weak bases? - Answer -- acts as an acid by donating
the O-H proton as H
- acts as a base by accepting H+ using a lone pair on the O atom
amphoteric substances - Answer -Substances that can act as both acids and bases (alcohols and phenols)
Why is acid dissociation for most alcohols unfavorable (lies towards the left)? - Answer -Dissociation
produces an alkoxide ion (the conjugate base of an alcohol), which is a very strong base.
How can you conduct acid-base reactions that favor the formation of weaker conjugate acids/bases? -
Answer -To promote (favor) the formation of the alkoxide ion, the alcohol can be treated with sodium or
potassium metal (Na or K) or a base that is stronger than the RO- ion produced.
protonation of an alcohol - Answer -When alcohols act as weak bases by using a lone pair on the oxygen
atom of the hydroxyl group, alcohols can accept a proton when they are placed in an acidic environment.
What is the product of the protonation of an alcohol called? - Answer -alkyloxonium ion
What is a Dehydration reaction for alcohols?
What happens during a dehydration reaction for alcohols? - Answer -- A specific type of elimination
reaction. In a dehydration reaction, an alcohol molecule will lose H2O to form an alkene. Alcohols
undergo a reaction known as dehydration when they are heated with strong mineral acids (like sulfuric
or phosphoric).
- the alcohol molecule loses the hydroxyl (OH) from one carbon (the α-carbon) and a hydrogen atom (H)
from an adjacent (β) carbon.
What is the function of an acid during a dehydration reactions? Why does it do what it does? - Answer -
To protonate the the OH group
