Ch 5 - Alcohols

Question 1

What is the general form of alcohols and how are they named?

Answer 1

• have general form of ROH
• named with suffix -ol
  if they are not the highest priority, they are given the prefix hydroxy-

Question 2

What are phenols and how are they named?

Answer 2

• 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)

Question 3

How does hydrogen bonding affect alcohols?

Answer 3

• alcohols can H bond, raising their boiling and melting points relative to corresponding alkanes
• H bonding also increases the solubility of alcohols

Question 4

Why are phenols more acidic than other alcohols?

Answer 4

because the aromatic ring can delocalize the charge of the conjugate base

Question 5

How do electron-donating/withdrawing groups affect acidity?

Answer 5

• 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

Question 6

How are primary alcohols oxidized?

Answer 6

• 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

Question 7

What will happen to secondary alcohols when oxidized by any common oxidizing agent

Answer 7

become ketones

Question 8

Why are alcohols converted to mesylates or tosylates?

Answer 8

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

Question 9

What is the difference between mesylates and tosylates?

Answer 9

• mes: contain the functional group -SO3CH3, which is derived from methanesulfonic acid
• tos: contain the functional group -SO3C6H4CH3, which is derived from toluenesulfonic acid

Question 10

How can aldehydes and ketones be protected?

Answer 10

by converting them into acetals or ketals, which are less reactive (especially to reducing agents) and can thus protect the function group from reacting

Question 11

What is an acetal and ketal and how are they formed?

Answer 11

• 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)

Question 12

What is deprotection?

Answer 12

when the acetal or ketal is converted back to a carbonyl by catalytic acid with aqueous acid

Question 13

What are quinones and how are they synthesized?

Answer 13

• resonance stabilized electrophiles
• synthesized through oxidation of phenols
• ex. vitamin K1 (phylloquinone) and Vitamin K2 (menaquinones)

Question 14

How are hydroxyquinones produced?

Answer 14

by oxidation of quinones, adding a variable number of hydroxyl groups

Question 15

What is ubiquinone (coenzyme Q)?

Answer 15

• another biologically active quinone that acts as an electron acceptor in Complexes 1, 2, and 3 of the electron transporter chain
• reduced to ubiquinol

Question 16

Which has a lower pKa and why: ethanol or p-ethylphenol

Answer 16

• 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

Question 17

Rank the following by decreasing boiling point and explain: 1-pentanol, 1-hexanol, 1,6-hexanediol.

Answer 17

• 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

Question 18

What chemical properties of ubiquinone allow it to carry out its biological functions?

Answer 18

• 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

Question 19

Why is oxidizing tertiary alcohol difficult?

Answer 19

• 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

Question 20

How does alkyl chain affect boiling point?

Answer 20

bp increases with increasing size of the alkyl chain because of increased van der Waals attractions

Question 21

Which is more acidic between hexanol and cyclohexanol?

Answer 21

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