ch21 –ay 2013-2014 sem ii -- r.d. a. bolinas by protonating –oh in acid, we get an oxonium...
TRANSCRIPT
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
By protonating –OH in acid, we get an oxonium –OH2+ that can leave as H2O
E1/E2 depends on the nature of ROH, but usually E1 prevails, except for 1° alcohols (E2)
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
Predict the major product. Remember Zaitsev’s rule!
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
Predict the major product. Remember Zaitsev’s rule!
Alcohols can undergo E1/E1cB/E2 reactions to form alkenes
E1cB occurs in biological systems: the -OH group is two carbons away
from a carbonyl (C=O) group
Alcohols can be oxidized into carbonyls…
We use oxidizing agents: periodinane (with Iodine in +5 oxidation
state) PRIMARY R-OH TO ALDEHYDE ONLY
Alcohols can be oxidized into carbonyls…
We use oxidizing agents: Acidic CrO3/CrO4
2- (with Chromium in +6 oxidation state)
PRIMARY R-OH TO CARBOXYLIC ACID
The Williamson Ether synthesis uses an alkoxide and alkyl halide…
Ethers (R-O-R) SN2 reaction between R-X and R-O-
The Williamson Ether synthesis uses an alkoxide and alkyl halide…
SN2 reaction between R-X and R-O- WE NEED TO CONSIDER STERIC
HINDERANCE. This might lead to E2!
Backside attack is not favorable!
Methoxide is also a very strong base.
Phenols can sometimes react like alcohols in forming ethers.
CANNOT: be dehydrated with acid, convert into halides with HX
CAN: convert to ether via Williamson ether synthesis, react via EArS (review)The aromatic ring allows the
H+ to leave easily, making phenols ACIDIC.
Oxidation of phenols gives us QUINONES
Because they don’t have a hydrogen on the C-OH carbon, phenols become quinones
Ethers generally undergo only acidic cleavages.
Ethers are unreactive to most common reagents
Only strong acids can usually react with them: HI/HBr via SN1 or SN2
Ethers generally undergo only acidic cleavages.
Ethers are unreactive to most common reagents
Only strong acids can usually react with them: HI/HBr via SN1 or SN2
SN1
Cyclic ethers are also generally as unreactive, except for EPOXIDES.
Epoxides come from alkenes + peroxy acids
High angular strain induces reactivity.
SN2 attacks with H3O+ or HX lead to trans-diol or trans-halohydrins, other nucleophiles work too.
Cyclic ethers are also generally as unreactive, except for EPOXIDES.
SN2 attacks with H3O+ or HX lead to trans-diol or trans-halohydrins, other nucleophiles work too.
beta-blocker that is used for treatment of cardiac arrhythmias, hypertension, and heart attacks
Thiols can be made via SH- and RX, and can react via Williamson mechanismSN2 Synthesis:
Williamson thioether synthesis
Disulfides are formed via oxidation. Reduction to thiols can occur as well.
http://delight.spslinfotechpvtl.netdna-cdn.com/media/catalog/product/cache/1/image/650x650/9df78eab33525d08d6e5fb8d27136e95/r/e/rebonding.jpg
http://b.vimeocdn.com/ts/147/230/147230470_640.jpg
Disulfides are formed via oxidation. Reduction to thiols can occur as well.
http://delight.spslinfotechpvtl.netdna-cdn.com/media/catalog/product/cache/1/image/650x650/9df78eab33525d08d6e5fb8d27136e95/r/e/rebonding.jpg
For rebonding:
(1)Thioglycolate (acid-like) to convert disulfide bonds in hair protein to thiolates
(2)Hydrogen peroxide to oxidize the thiolates back to disulfides.
(3)Reforming the disulfides helps re-align amino acids and make hair straight
Disulfides are formed via oxidation. Reduction to thiols can occur as well.
http://b.vimeocdn.com/ts/147/230/147230470_640.jpg
“antioxidant” because it protects your cells from oxidative degradation.
Propose a synthetic route from 2-phenylethanol to make:
H2SO4 P
eri
od
inan
e
CrO3
KMnO4
1. H2SO4 2. H2/Pd