Ch 5 - Alcohols Flashcards
What is the general form of alcohols and how are they named?
- have general form of ROH
- named with suffix -ol
if they are not the highest priority, they are given the prefix hydroxy-
What are phenols and how are they named?
- benzene rings with hydroxyl groups (cyclic group with aromatic double bonds)
- named for the relative position of the hydroxyl groups: ortho - (adjacent carbons), meta- (separated by one carbon), or para- (on opposite sides of the ring)
How does hydrogen bonding affect alcohols?
- alcohols can H bond, raising their boiling and melting points relative to corresponding alkanes
- H bonding also increases the solubility of alcohols
Why are phenols more acidic than other alcohols?
because the aromatic ring can delocalize the charge of the conjugate base
How do electron-donating/withdrawing groups affect acidity?
- electron donating groups like alkyl groups decrease acidity because they destabilize negative charge
- electron withdrawing groups, such as electronegative atoms and aromatic rings, increase acidity because they stabilize negative charges
How are primary alcohols oxidized?
- primary alcohols can be oxidized to aldehydes only by pyridinium chlorochromate (PCC)
- they will be oxidized all the way to carboxylic acids by any stronger oxidizing agent
What will happen to secondary alcohols when oxidized by any common oxidizing agent
become ketones
Why are alcohols converted to mesylates or tosylates?
to make them better leaving groups for nucleophilic substitution reactions by increasing the stability of the product
- can also be used as protecting groups because many reagents (especially oxidizing reagents) that would react with an alcohol cannot react with these compounds
What is the difference between mesylates and tosylates?
- mes: contain the functional group -SO3CH3, which is derived from methanesulfonic acid
- tos: contain the functional group -SO3C6H4CH3, which is derived from toluenesulfonic acid
How can aldehydes and ketones be protected?
by converting them into acetals or ketals, which are less reactive (especially to reducing agents) and can thus protect the function group from reacting
What is an acetal and ketal and how are they formed?
- 2 equivalents of alcohol or a dialcohol are reacted with the carbonyl to form an acetal (a primary carbon with 2 -R groups and a H atom) or ketal (a secondary carbon with 2 -OR groups)
What is deprotection?
when the acetal or ketal is converted back to a carbonyl by catalytic acid with aqueous acid
What are quinones and how are they synthesized?
- resonance stabilized electrophiles
- synthesized through oxidation of phenols
- ex. vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones)
How are hydroxyquinones produced?
by oxidation of quinones, adding a variable number of hydroxyl groups
What is ubiquinone (coenzyme Q)?
- another biologically active quinone that acts as an electron acceptor in Complexes 1, 2, and 3 of the electron transporter chain
- reduced to ubiquinol
Which has a lower pKa and why: ethanol or p-ethylphenol
- phenols like p-ethylphenol have increased acidity due to resonance and the electron withdrawing character of the phenol aromatic ring
- because p-ethylphenol is the stronger acid than ethanol, it will have lower pKa
Rank the following by decreasing boiling point and explain: 1-pentanol, 1-hexanol, 1,6-hexanediol.
- 1,6-hexanediol will have the highest bp; a molecule with 2 hydroxyl moieties can have more H bonding
- 1-hexanol is next and then 1-pentanol
- 1-hexanol has the longer hydrocarbon chain meaning increased van der Waals forces
What chemical properties of ubiquinone allow it to carry out its biological functions?
- it has conjugated rings, which stabilize the molecule when accepting electrons
- the long alkyl chain in the molecule allows for lipid solubility, which allows the molecule to function in the phospholipid bilayer
Why is oxidizing tertiary alcohol difficult?
- they can be oxidized but only under extreme conditions because their substrate carbons do not have spare hydrogens to give up
- alcohol oxidation involves the removal of such a hydrogen so that carbon can instead make another bond to oxygen
- if not H is present, a carbon-carbon bond must be cleaved, which requires a great deal of energy and can only occur under extreme conditions
How does alkyl chain affect boiling point?
bp increases with increasing size of the alkyl chain because of increased van der Waals attractions
Which is more acidic between hexanol and cyclohexanol?
close, but the hydroxyl hydrogen of hexanol is slightly more acidic because the ring structure of cyclohexanol is slightly electron donating, which makes its hydroxyl hydrogen slightly less acidic
