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
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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)
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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