Kaplan MCAT OChem Ch. 7: Alcohols and Esters

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alcohol

general formula is ROH

hydroxy group

OH

alcohol

water molecule loses a proton when it attaches to an alkyl grouop => restoring neutrality

alcohol

can be protic solvents

alcohol

OH has highest priority

alcohol naming

alkyl group + alcohol

phenol

alcohols attached be aromatic

phenol

ArOH

phenol

resonance of ring and lone pair of oxygen make H of alcohol more acidic that other alcohols

phys. prop. of alcohols

BP of alcohols higher than hydrocarbons, due to H bonding

phys. prop. of alcohols

more than one OH group => greater degree of H bonding

phys. prop. of alcohols

OH hydrogen weakly acidic

phys. prop. of alcohols

alcohols can dissociate into protons and alkoxy ions (like water does protons and hydroxide ions)

phys. prop. of phenols

OH hydrogen of this are more acidic => dist'n of neg charge throughout ring => stabilizing anion

phys. prop. of phenols

for intermolecular H bonds and relatively high MP and BP

phys. prop. of phenols

slight soluble in water as are some of its derivatives

phys. prop. of phenols

can form salts w/ inorganic bases such as NaOH

phys. prop. of phenols

presence of other sub affect acidity, BP, and MP of phenols

phys. prop. of phenols EWG

inc. acidity

along w/ resonance, it stabilizes the alkoxy anion => alcohol more acidic

phys. prop. of phenols EDG

dec acidity

as more alkyl groups (electron donating) attach -> destabilize alkoxide anion

phys. prop. of alcohol (aliphatic)

more alkyl groups => less acidic molecule

phys. prop. of alcohlols w/ carbocations

alkyl groups donate electron density => stabilize pos charge but destabilize neg. charge

Big Three Mechs for alcohol and ethers

1. Nu Su (Sn1 and 2)
-water to DB

2. Nu add to carbonyl

4. oxi-red (more oxygen bonded, more oxidized)

types of synthesis of alcohols

addition

substitution

reduction

phenol

addition synthesis of alcohol

prepared by adding organometallic compoundss to carbonyl groups

sub synthesis of alcohol

both sn1 and sn2 under proper conditions

reduction synthesis of alcohols

this of aldehydes, ketones, carb acids, or esters

reduction synthesis of alcohols

LAH or NaBH4 are two common this reagents

LAH

powerful reducing agent, just about anything

NaBH4

weaker than LAH, reduces aldehydes, ketones, or acyl chlorides, but CANNOT:

esters, carb acids, or amides

phenol synthesis of alcohols

maybe be from arylsulfonic acids w/ hot NaOH, however this is only useful only for phenol or its alkylated derivatives

phenol synthesis of alcohols

more versatile method is hydrolysis of diazonium salts

reducing agents

have a lot of Hs

oxidizing agents

have a lot of Os

alcohol rxns

elimination

substitution

oxidation

alcohol elimination

these can be dehydrated in strongly acidic solution (usually H2SO4) => alkene

alcohol elimination

mech of dehydration is E1 for secondary and tertiary these

alcohol elimination

mech of dehydration is E2 for primary these

alcohol elimination

OH group can be protonated and converted to a good LG

alcohol elimination

more stable alkene as major product

occurs via movement of proton (hydride shift)

alcohol elimination

milder method uses POCl3 (phos. oxychloride) => E2 mech for primary and secondary alcohols

OH as LG

alcohol sub rxn

OH group turns into water, a good LG for Sn1

alcohol sub rxn

this converted to tosylate (p-toluenesulfonate) group, making good LG for Sn2 reactions

alcohol sub rxn

convert this to alkyl halides, common is forming inorganic esters which undergo Sn2 reactions

alcohols + thionyl chloride => intermediate inorganic ester (chlorosulfite) and pyridine => Cl- backside carbon => SO2 and Cl-, making alkyl chloride w/ inversion of config

alcohol sub rxn

treated w/ PBr3 (pyridine) => alkyl bromide

OH turned into good LG

alcohol sub rxn

phenols undergo EAS since lone pair of O donate to ring -> OH strongly activating => ortho/para-directing

alcohol oxi-red rxn

generally involves some form of chromium (VI) as oxidizing agent => reduced to chromium (III)

alcohol oxi-red rxn (PCC)

only mild (anhydrous) oxidant

alcohol oxi-red rxn (PCC)

partially oxidizes primary alcohols => aldehyde => stops since lacks water to hydrate aldehyde (aldehydes easily hydrated)

alcohols become better LG by

1. protonation

2. convert to tosylate

3. form an inorganic ester

electron donating sub

when lone pair from oxygen

alcohol oxi-red rxn aldehyde

when hydrated (gem diols or 1,1-diols) => can be oxidized to carb acids

alcohol oxi-red rxn (PCC)

form ketones from 2ndary

alcohol oxi-red rxn (PCC)

3rd alcohols already oxidized as can be, so don't react w/ any of oxidizing agents

alcohol oxi-red rxn (alkali dichromate salt)

fully oxidze primary and secondary alcohols

1 - to carb acids
2 - to ketones

alcohol oxi-red rxn (CrO3)

even strong oxidant

often dissolved w/ dilute sulfuric acid in acetone

alcohol oxi-red rxn (CrO3)

reaction called Jone's oxidation

alcohol oxi-red rxn (CrO3)

oxidizes:

1 - carb acids
2 - ketones

phenol oxi-red rxn

w/ oxidizing reagents => produce quinones

ether

two alkyl (two aryl) bonded to an oxygen atom

ether

important solvents, but are aprotic and unreactive

ether (naming)

alkyl alkyl ethers

ether (naming)

exception are cyclic ethers, as their aren't two diff. alkyl

ether (smaller rings)

more angle strain => less stable and more reactive

phys. prop. of ethers

don't H bond

phys. prop. of ethers

boil at low temp compared w/ alcohols, actually do at approx. same temp as alkanes of comparable MW

phys. prop. of ethers

only slightly polar => only slightly soluble in water

phys. prop. of ethers

inert to most organic reagents => freq. used as solvents

williamson ether synthesis

produce ether from rxn of metal alkoxides w/ primary alkyl halide or tosylates

williamson ether synthesis

alkoxides as Nu => displace halide or tosylate via Sn2 => ether

competes w/ E2

williamson ether synthesis

alkoxides w/ ONLY attack nonhindered halides

williamson ether synthesis of phenols

relatively mild rxn conditions, since acidity of these

williamson ether synthesis of phenols (cyclic ethers)

intramolecular rxns forced since rate and equilibrium of rxn affected by reagent conc.

reagents see fairly high conc. of each other

williamson ether synthesis of phenols (cyclic ethers)

oxidation of an alkene w/ a peroxy acid (gen. formula RCOOOH) like mcpba

reaction w/ ethers

peroxide formation

cleavage

peroxide formation

ethers react w/ oxygen => highly explosive peroxides

cleavage (straight-chain ethers)

under vigorous conditions, usually at high temp in presence HBr or HI

cleavage (straight-chain ethers)

initiated by protonation of ether oxygen

cleavage (straight-chain ethers)

can be sn1 or sn2, depending on conditions and structure of ether

cleavage (straight-chain ethers)

alcohols products usually react w/ second molecule of hydrogen halide => alkyl halide

SB

poor LG

cleavage (highly strained cyclic ethers)

epoxides ready to react and doe Sn2

cleavage (highly strained cyclic ethers)

catalyzed by acid treated or reacted w/ base (Nu)

cleavage (highly strained cyclic ethers)

symm. epoxides => either C can be Nu attacked

cleavage (highly strained cyclic ethers)

asymm. epoxides => most sub. C is Nu attack when catalyzed w/ acid; least sub C w/ Nu (basic conditions)

cleavage (highly strained cyclic ethers)

base (nu) this mostly Sn2 occurs at least hindered (least sub)

environment is basic, so better Nu than in acidic environment

cleavage (highly strained cyclic ethers)

acid-catalyzed is Sn1 and some Sn2

O is protonated => better LG

sub stabilizes charge, so more sub, good target for Nu attack

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