A to Z Directory – Virginia Commonwealth University
Chapter 10
• Classification
o Alcohols are classified much like alkyl halides - 1°, 2°, and 3°
• Nomenclature
o Alcohols have precedence over alkenes and alkynes
▪ Get to the hydroxyl first!
• You do have to say “1” with straight-chain alcohols
[pic]
• When the alcohol is the highest-priority group on a cyclic molecule, then the “1” is implied so you leave it off.
▪ Don’t worry about the sections naming diols and phenols
• You do need to name diols as “diol,” you just don’t need to call them glycols or anything else weird.
• When you name a cyclic diol, you do need to say the “1”
[pic]
• Physical Properties
o Hydrogen bonding causes higher boiling points
o Solubility – small alcohols are miscible with water; larger alcohols are not terribly soluble
• Solubility
o Smaller alcohols are miscible with water
o The larger the nonpolar piece, the less soluble the alcohol is in water
o You know this!
• Acidity
o pka – 15-18
o phenol - pka – 10
▪ Why? The conjugate base, phenoxide, is resonance stabilized
[pic]
• Formation of Alkoxides
o Acid/base
▪ Alcohol + very strong base (NaH, NaNH2) → Alkoxide
• If you just use hydroxide or an alkoxide, you will get an equilibrium mixture.
• The hydroxide or alkoxide is not strong enough to quantitatively deprotonate an alcohol (unless it’s a phenol)
o Redox
▪ Alcohol + alkali metal → Alkoxide
▪ This is one of the few times when you see Na or K and it’s significant.
• Synthesis Review
o SN2
▪ -OH added to primary or methyl alkyl halides
▪ See Chapter 6 Review
o SN1
▪ Water added to secondary or tertiary alkyl halides
▪ See Chapter 6 Review
o Acid-catalyzed hydration of alkenes
▪ Markovnikov addition of water with rearrangement
▪ See Chapter 8 Review
o Oxymercuration-demercuration
▪ Markovnikov addition of water without rearrangement
▪ See Chapter 8 Review
o Hydroboration-oxidation
▪ Anti-Markovnikov addition of water
▪ See Chapter 8 Review
o Addition of OsO4 or KMnO4 to alkenes
▪ Syn addition of two hydroxyls
▪ See Chapter 8 Review
o Acid-catalyzed ring-opening of epoxides
▪ Results in two hydroxyls added anti to one another
▪ See Chapter 8 Review
o Addition of acetylide ions to carbonyls
▪ See Chapter 9 Review
• Grignards/Organometallics
o Formation of Grignards and alkyl lithiums
▪ Magnesium inserts between carbon and halogens
▪ Lithium replaces the halogen
▪ This is one time where an sp3-hybridized carbon acts the same as an sp2-hybridized carbon.
• This means that this works on any carbon-halogen bond
▪ Solvent
• There cannot be any acidic protons in the solvent, as the Grignard is such a strong base.
• There cannot be any pi bonds in the solvent as those are sites of reactivity that the Grignard will attack.
▪ From here on, I will use Grignard to refer to both Grignard reagents and organolithiums, as they do the same things
▪ The carbon-metal bond is so strongly polar that it’s fine to think of it as ionic.
• Because of this, it’s often easiest to cross out the Li or MgBr and call the R-group an R-
Ex. [pic]
o Grignards as nucleophiles in SN2 reactions
▪ Grignards are strong bases/nucleophiles, so they will participate in both SN2 and E2 reactions
• SN2 with methyl and primary alkyl halides
[pic]
• E2 with secondary and tertiary alkyl halides – no point in using this strong of a base
o Grignards attacking carbonyls
▪ The negatively charged carbon of the Grignard is attracted to the partially positive carbon of the carbonyl
▪ In the following schemes, A and B are just the alkyl pieces attached to the carbonyl-containing molecules and C is the Grignard or other strong nucleophile (such as an acetylide ion)
▪ Addition of to ketones and aldehydes
[pic]
▪ Addition to esters
[pic]
▪ Addition to Acid Chlorides
[pic]
o Addition of Grignards to epoxides
▪ Grignards (and other strong bases) attack the less substituted side of epoxides in an SN2-like mechanism
[pic]
• Catalytic hydrogenation of Ketones and Aldehydes
o Just adds two hydrogens across the pi bond, much like it did with alkenes
• Reductions of Carbonyls with NaBH4 and LiAlH4
o NaBH4 (sodium borohydride) and LiAlH4 (lithium aluminum hydride) are sources of H- which has been covalently bonded to boron and lithium respectively
▪ H- serves as a nucleophile and reduces carbonyls
▪ Bonding the hydride to the boron or aluminum reduces the basicity of the hydride ion.
|Class of compound |NaBH4 |H2/Pt, Pd, or Ni |LiAlH4 |
|Aldehydes |Primary Alcohol |Primary Alcohol |Primary Alcohol |
|Ketones |Secondary Alcohol |Secondary Alcohol |Secondary Alcohol |
|Carboxylic Acids |NR |NR |Primary Alcohol |
|Esters |NR |NR |2 Alcohols |
o The mechanism of how LiAlH4 reduces an acid
[pic]
▪ You’re not responsible for this!
• That said, the ACS does expect you to know which hydrogen comes from NaBH4 or LiAlH4 or the water in these reactions.
o See the ACS review book for examples of this.
• Thiols
o Contain –SH instead of –OH
o They smell bad
▪ When you smell a skunk, you are smelling a thiol.
• Your TA loves the smell of skunk. She’ll be driving along in the country, smell a skunk, and become instantly happy.
o This does NOT mean you should spray her with skunk extract.
o pKa about 8-10
▪ Why?
• Weak S-H bond
• Sulfur is larger than oxygen, so the negative charge of the conjugate base is spread out over a larger orbital
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