ethers, epoxides, sulfides, aldehyes, ketones Flashcards
What is the oxygen hybridization in an ether?
Sp3
What are two main differences between the bonding in ethers and alcohols?
C-O bond is longer in Ether and the C-O-C bond angle is greater (~112º)
Where are the lone pairs on the oxygen in ethers located?
In the sp3 orbital
Why are ethers good solvents?
Their polarity and low reactivity, no H bonding is possible
What other compound are ether boiling points similar to?
Alkanes due to their inability to form hydrogen bonds
What are the conditions for a Williamson ether synthesis? What are rules regarding the conditions?
Reactant: alkoxide RO-
Conditions R-X (must be CH3 or 1º)
Product: ether
How do you prepare an alkoxide?
Alcohol treated with Na, K, or NaH
What are two ways to prepare epoxides? How are they added?
- Use peroxyacid or MCPBA
- Use halohydrin formation (Br2, H2O) with subsequent NaOH
Added via syn addition
Both on alkenes
Are ethers reactive?
No, stable to reagents making them good solvents
What are cleavage reactions? What are the conditions?
Reactant: ROR’
Conditions: (xs) HX, heat
Product: Mixture of ROH, RX, R’OH, R’X
Why do we use excess HX in cleavage reactions?
To allow ROH product to from RX and not a mixture (R’X and RX)
What occurs in reactions of epoxides?
Very reactive towards nucleophile, opening epoxied relives ring strain
What is the reactivity of HX in cleaving reactions? What are the conditions?
Most acidic HI>HBr>HCl least acidic. Occur under acidic conditions
Under what conditions do reactions of epoxides occur?
Acidic, basic sometimes neutral. Will influence the side of the nucleophile attack
In unsymmetrical epoxides where will the nucleophile attach under acidic and basic conditions?
Acidic conditions: Nu attacks more hindered side
Basic conditions: Nu attacks less hindered side
What are the conditions for a ring opening epoxide reaction?
Reactant: Nucleophile
Conditions: 1. epoxide, ether 2. H3O+
Product: Alcohol (enantiomers)
What are good nucleophile for ring opening reactions of epoxides?
C,O,S,N with -OR, -SR, -CN, -CR3, -alkene, -alkyne, -H, NH3
What are the conditions for an acid catalyzed ring openings?
Reactants: epoxides
Conditions: H2SO4| EtOH
Product: alcohol
How do you make oxygen a good leaving group?
Protinate it
How do you prepare alkyl sulfonates?
Reactants: alcohol, sulfonate
Conditions: pyridine
Product: alkyl sulfate (R-OTs group)
What are 4 reactions to make aldehydes and ketones?
- 2ºOH to K via PCC| CH2Cl2
- 1ºOH to A via PCC| CH2Cl2
- Ozonolysis of alkene via 1.O3 2. Zn, H2O
- Fiedel Craft Acylation of benzene with acyl chloride or acyl anhydride
What are the reaction conditions of gringard and organolithium to aldehyde or ketone?
Reactant: aldehyde or ketone
Conditions: 1. R-MgBr (R-Li), ether 2. H3O+
Products: alcohol + new R group. 1º (A) or 2º (K)
What are the reaction conditions of an aldehyde and ketone reduction?
Reactants: aldehyde or ketone
Conditions: 1. LAH, ether 2. H2O or H2,Pt, NaBH4|CH3OH
Product: alcohol 1º (A) or 2º (K)
What are the hybridizations present in carbonyl bond? Is there any resonance?
O and C are sp2 hybridized. Resonance is possible to create nucleophilic base of oxygen and electrophilic carbon
What is the relative stability of aldehydes and ketones?
(Most stable) ketone > aldehyde > formaldehyde
How is stability increased for carbonyl groups? How is this done?
Increasing the number of alkyl groups attached to the carbonyl group since they are able to donate electrons and increase stability of the C+
What are the reaction conditions of nucleophilic addition (hydration) of aldehydes or ketones?
Reactants: aldehyde/ ketone and water
Conditions: acid (H3O+) or base (-H or -OH)
Products: hydrate, 2 OH on same C
How is equilibrium determine or influenced in aldehyde and ketone reactions?
Carbonyl structure (electric, steric effects)
Hydrate structure (steric)
How does carbonyl structure influence equilibrium in aldehyde and ketone reactions?
Alkyl groups stabilize carbon, increase R groups = decrease in C reactivity. Halogenated alkyl groups are electron withdrawing and destabilize carbonyl C which increases reactivity
How does hydrate structure influence equilibrium in aldehyde and ketone reactions?
Increasing size of alkyl groups = decrease in stability of hydrate due to steric crowding = not formed easily = decreased reactivity of C
What are the reaction conditions for cyanohydrin formation?
Reactants: aldehyde and ketone
Conditions: NaCN (KCN)| H2O, H2SO4 or KCl
Product: cyanohydrin (OH and CN on same group)
What is the special condition regarding aldehyde and ketone reactions?
They go both ways
What are the reaction conditions to go from aldehyde/ketone to acetal?
Reactant: aldehyde/ ketone
Conditions: 2 eq of R-OH, H+
Products: acetal
Forms hemiacetal intermediate
Reaction conditions to form intramolecular hemiacteal?
H+. O from C=O bonds to H to form OH then OH from aldehyde/ketone bonds to C+
Reaction conditions to form cyclic acetals?
Reactant: aldehyde/ketone
Conditions: ethane-1,2 diol|TsOH, benzene
Product: cyclic acetal
*Adds two C
Why would you use ethane diol and tosic acid in synthesis?
Can be used as a protecting group of aldehyde and make it un reactive to bases and nucleophile
What are the reaction conditions to “deprotecting” synthesis?
H2O, HCl
What are the reaction conditions for imine formation?
Reactant: aldehyde/ketone
Conditions: R-NH3 or NH3
Product: imine (C=N-R)
*forms hemiaminal intermediate
Reaction conditions to form enamine?
Reactant: aldehyde/ketone
Conditions: 2º amine (R2NH)
Product: enamine ( has C=C and C-NR)
*has hemiaminal intermediate
What are the conditions for the witting reactions?
Reactant: ylide + aldehyde/ketone
Conditions: none
Product: Alkene between C=P of ylide and C=O of aldehyde/ketone
Reaction conditions for ylide preparation
Reactant: PhP: + alkyl halide (1º or 2º)
Conditions: n-BuLi, ether
Product: ylide
