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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