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
H O Br (S,E) 4-bromohex-2-en-1-ol
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”
O H
Cl OH
2-chlorocyclohexan-1,3-diol
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
H - - O O O O O + H+ - -
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. CH3CH2MgBr CH3CH2MgBr 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
- CH3MgBr Br CH3
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
O 1) C 2) H+ O H A C A B B
. Addition to esters
O 1) C 2) H+ OH A C A OB C
. Addition to Acid Chlorides
O 1) C 2) H+ O H A C A Cl C o Addition of Grignards to epoxides
. Grignards (and other strong bases) attack the less substituted side of
epoxides in an SN2-like mechanism
O– + O H O H
R- R R