CHEM 232 Exam 3 with Accurate
Solutions
aldol - ANS-Contains both aldehyde and alcohol functional groups.
ether - ANS-
alcohol -> R-X and P=O formation - ANS-PBr3, PCl3
inversion occurs
no carbocation
alcohol -> R-OMs , R-OTs , R-OSOCF3 - ANS-ClMs, ClTs, TfOTf and pyridine
no inversion
LG: Cl or OSOCF3
unhindered alkyl halide + metal alkoxide -> ether - ANS-WILLIAM ETHER SYNTHESIS
(SN2)
reagent examples: ClCH2CH3 + NaO(CH2)4CH3
OH-C's-X -> ether rings - ANS-INTRAMOLECULAR WILLIAM SYNTHESIS:
Good Nu/strong base
1.acid/base
2.ring closure 3>5>6>4>7,8
2 similarly alpha substituted alcohols -> symmetric ether - ANS-SYMMETRIC ETHER
SYNTHESIS WITH ACID:
H2SO4, H2O
1°-> SN2 + acid/base
2°, 3° -> SN1 + acid/base
less substituted alcohol: NU
more substitute alcohol: E
Ring + 1 eq H-X -> Open Ring
Open Ring + Excess H-X -> Open Ring with 2 X's - ANS-ETHER CLEAVAGE
oxonium, H-X, H2S04,
X= Br, I, Cl
1°-> SN2
2°, 3° -> SN1
, halohydrin(alcohol + x) -> epoxide - ANS-INTRAMOLECULAR WILLIAMSON:
good nu, strong base
Ring Closure
epoxide + SCH3 -> opened epoxide - ANS-BASIC CONDITIONS:
-use ether solvents
-SN2 + acidic workup (INVERSION!!!)
-attack least substituted C
epoxide + poor nu -> opened epoxide - ANS-ACIDIC CONDITIONS:
-activate O first
-lengthening bond, weakens bond-> opens backside
-SN2 + acid/base
-attack most substituted C
special nu for epoxide opening - ANS-USE ETHER SOLVENTS
LiAlH4 (hydride)
LiR, RMgBr, R-C-CNA (organometallic)
ester -> 1° alcohol - ANS-2x LiAlH4
reduction
carboxylic acid -> 1° alcohol - ANS-2x LiAlH4
reduction
aldehyde -> 1° alcohol - ANS-NaBH4 or LiAlH4
reduction
ketone -> 2° alcohol - ANS-NaBH4 or LiAlH4
reduction
HYDRIDE REDUCING: LiAlH4 - ANS--addition + acidic workup
-use ether solvents
-aldehydes/ketones -> ROH
-opens epoxides, deprotonates alcohols
-replaces halogens/sulfonate esters (SN2)
-reduces esters/carboxylic acids (SnAc -> 1° OH)
HYDRIDE REDUCING: NaBH4 - ANS--more selective, weak base, use alcohol solvents
-addition + acid/base
-aldehydes/ketones -> ROH ONLY
ester -> 3° alcohol - ANS-2x organometallic
reduction
aldehyde-> 2° alcohol - ANS-organometallic
Solutions
aldol - ANS-Contains both aldehyde and alcohol functional groups.
ether - ANS-
alcohol -> R-X and P=O formation - ANS-PBr3, PCl3
inversion occurs
no carbocation
alcohol -> R-OMs , R-OTs , R-OSOCF3 - ANS-ClMs, ClTs, TfOTf and pyridine
no inversion
LG: Cl or OSOCF3
unhindered alkyl halide + metal alkoxide -> ether - ANS-WILLIAM ETHER SYNTHESIS
(SN2)
reagent examples: ClCH2CH3 + NaO(CH2)4CH3
OH-C's-X -> ether rings - ANS-INTRAMOLECULAR WILLIAM SYNTHESIS:
Good Nu/strong base
1.acid/base
2.ring closure 3>5>6>4>7,8
2 similarly alpha substituted alcohols -> symmetric ether - ANS-SYMMETRIC ETHER
SYNTHESIS WITH ACID:
H2SO4, H2O
1°-> SN2 + acid/base
2°, 3° -> SN1 + acid/base
less substituted alcohol: NU
more substitute alcohol: E
Ring + 1 eq H-X -> Open Ring
Open Ring + Excess H-X -> Open Ring with 2 X's - ANS-ETHER CLEAVAGE
oxonium, H-X, H2S04,
X= Br, I, Cl
1°-> SN2
2°, 3° -> SN1
, halohydrin(alcohol + x) -> epoxide - ANS-INTRAMOLECULAR WILLIAMSON:
good nu, strong base
Ring Closure
epoxide + SCH3 -> opened epoxide - ANS-BASIC CONDITIONS:
-use ether solvents
-SN2 + acidic workup (INVERSION!!!)
-attack least substituted C
epoxide + poor nu -> opened epoxide - ANS-ACIDIC CONDITIONS:
-activate O first
-lengthening bond, weakens bond-> opens backside
-SN2 + acid/base
-attack most substituted C
special nu for epoxide opening - ANS-USE ETHER SOLVENTS
LiAlH4 (hydride)
LiR, RMgBr, R-C-CNA (organometallic)
ester -> 1° alcohol - ANS-2x LiAlH4
reduction
carboxylic acid -> 1° alcohol - ANS-2x LiAlH4
reduction
aldehyde -> 1° alcohol - ANS-NaBH4 or LiAlH4
reduction
ketone -> 2° alcohol - ANS-NaBH4 or LiAlH4
reduction
HYDRIDE REDUCING: LiAlH4 - ANS--addition + acidic workup
-use ether solvents
-aldehydes/ketones -> ROH
-opens epoxides, deprotonates alcohols
-replaces halogens/sulfonate esters (SN2)
-reduces esters/carboxylic acids (SnAc -> 1° OH)
HYDRIDE REDUCING: NaBH4 - ANS--more selective, weak base, use alcohol solvents
-addition + acid/base
-aldehydes/ketones -> ROH ONLY
ester -> 3° alcohol - ANS-2x organometallic
reduction
aldehyde-> 2° alcohol - ANS-organometallic
