Ch. 9 - Alcohols, Ethers & Related Compounds (Week 1) Flashcards
Why are alcohols (basic)? What can they act as?
functional group that contains hydroxyl group bonded to sp3 carbon
- can act as nucs. bases or weak acids (pKa = 15)
What are enols and phenols?
enols and phenols have OH bonded to sp2 carbon
- undergo different reactions
- enols have OH bonded to C double bond
- phenols have OH bonded to benzene ring
What are ethers? What is their reactivity?
two alkyl groups bonded to an oxygen
- relatively unreactive (polar aprotic solvent)
What is a symmetrical ether vs an unsymmetrical ether?
sym: same alkyl groups
unsym: diff alkyl groups
What are epoxides/oxiranes? What is their reactivity?
ethers with ozygen atom in 3-membered ring
- highly reactive due to highly strained 3-mem ring that wants 109.5 deg tetra angles but is stuck with 60 deg angles
What is the electron geometry of O in alc/eth/epox?
tetrahedral
What is the molecular geometry of alcohols and ethers?
bent, bond angles are 109.5º
What is the bond angle of an epoxide? What are the consequences of this bond angle?
60º, consequences are angle strain which makes epoxides more reactive
Which are polar: alc/eth/epox?
all are polar and exhibit dipole-dipole, alcohols capable of H-bonding
How are alcohols named using IUPAC?
1) find longest carbon chain bearing -OH group
2) number carbon chain to give -OH the lower number and apply normal nomenclature names
How are rings with alcohols named?
number ring beginning with OH group then give next lowest number to substituent
** “1” in name is omitted for OH
When are common names used for alcohols? How are they named?
simple alcohols
1) name carbon atoms of a molecule as if single alkyl group
2) add “alcohol” separated by space
How are common names assigned for ethers (simple ethers)?
1) name both alkyl groups bonded to O
2) arrange groups alphabetically and add “ether”
How are IUPAC names assigned for ethers?
1) name simpler alkyl group and oxygen as alkoxy sub and change ending of alkyl group to -oxy (ex. methoxy)
2) name remaining alkyl group as an alkane w/ alkoxy group as sub bonded to this chain (ex. 4-ehtoxyoctane)
What is a heterocycle?
any cyclic compound containing heteroatom (ex. THF)
How are epoxides named as epoxyalkanes?
1) name alkane chain/ring to which O is attacked
2) use prefix “epoxy” to name epoxide as sub
3) use two numbers to designate location of O
ex. 1,2-epoxycyclohexane
What does a bent structure mean in terms of IMFs for alcohols and ethers?
dipole-dipole interactions
What affects solubility of alcohols/eth/epox?
- if they have less than or equal to 5 carbons, they are soluble in water (due to hydrogen bonding with O**check!)
- if they have more than 5 carbons, they are insolubel in H2O
- all are soluble in organic solvents regardless of size
T/F: A structure can be classified as an alcohol if it has OH bonded to an sp2 carbon.
False, alcohols must have OH bonded to an sp3 carbon.
T/F: Alcohols and ethers are common products of nuc sub reactions.
True
What is the conjugate base of an alcohol called?
alkoxide
What is an aromatic alcohol called?
phenol
What is an alkoxide?
R-O- (an alcohol without the hydrogen on OH), the conjugate base of an alcohol
What happens in a Williamson ether synthesis?
An alcohol reacts with sodium hydride and then an alkyl halide to give an ether.
What is the general mechanism for WES?
1) acid-base reaction btw alcohol and NaH
2) Sn2 btw alkoxide and alkyl halide
What is a halohydrin?
an organic compound that has a hydroxy group and a halogen on two opposide but adjacent carbons, participates in intramolecular version of WES
What is the base, nucleophile and electrophile in WES?
base = NaH (generates alkoxide) nuc = alkoxide elec = 1º or 2º alkyl halide or alkyl tosylate
What is solvent type for WES?
polar aprotic (DMSO, MeCN, THF, DMF, acetone)
What stereochemistry needs to be considered for WES?
Sn2 rules
- inversion if carbon w/ LG is stereocenter
- NO RXN on sp2 carbon w/ LG
- no stereochem change at a-carbon of alcohol
Is the hydroxyl group of an alcohol a good leaving group?
No, the LG would be -OH which is a strong base! Good leaving groups are weak bases
What must happen for an alcohol to participate in substitution?
conversion of OH to a good leaving group by protonating OH to become H2O
What is required for alcohol protonation?
strong acid such as HCl or H2SO4
Do ethers and epoxides have a good LG?
No, neither, but epoxides are so strained reactions are favorable to open the ring and reduce strain
What is a intramolecular WES of halohydrins?
A halohydrin reacts with NaH to form an epoxide . (One molecule reacts with itself essentially)
What is the mechanism of intramolecular WES epoxide synthesis?
1) acid-base reaction btw alcohol and NaH
2) Sn2 reaction w/ itself
* note that Sn2 backside-attack requires anti-periplanar configuration btw hydroxyl and LG
What type of conformation does WES epoxide synthesis require for the halohydrin to react?
anti-periplanar, may need a 180º rotation
this is required for Sn2 backside attack
What is the base/nuc/electrophile in WES epoxide synthesis?
base = NaH (deprotonation to make alkoxide)
nuc = alkoxide (1º, 2º, 3º)
elect = 1º or 2º alkyl halide (on same molecule, or tosylate)
** no sp2C-LG
What type of solvent is needed for intramolecular WES epoxide synthesis?
polar aprotic (DMSO, MeCN, THF, DMF, acetone)
What are the stereochemical considerations for WES epoxide synthesis?
must be anti-pp to react for Sn2 backside attack!
What are dehydration reactions of alcohols?
removal of H2O from an alcohol in the presence of a strong acid to form an alkene
What types of alcohols (subst.-wise) are most likely to react/dehydrate?
more substituted alcohols (3º)
What happens in an alcohol dehydration alkene synthesis reaction?
an alcohol reacts with tosic acid (TsOH) or sulfuric acid to make an alkene
What is the mechanism for alcohol dehyd alkene synth?
2º and 3º = protonation + E1
1º = protonation + E2
How is dehydration catalyzed?
acid-catalyzed
What is acid/alcohol of alcohol dehyd alkene synthesis?
acid = must have non-nucleophilic conj. base (otherwise could cause Sn1 to compete) alcohol = carbon must be sp3
What is the solvent for alcohol dehyd alkene synth?
acid is the solvent
What are the stereochemical considerations for alcohol dehyd alkene synth?
alpha carbon is irrelevant and trans-alkene are major
In which reactions can carbocation rearrangement occur?
alcohol dehydration alkene synthesis
What are regioisomers?
constitutional isomers arising from a common starting material or intermediate
What is the goal of carbocation RAR?
carbocation stability
What is a 1,2-hydride shift? When does it occur?
carbocation RAR where 2º carbocation shifts to adjacent carbon that is 3º before proceeding with reaction to stabilize carbocation
*can occur any time there is a 2º carbocation!
