Orgo Lab 223L Review
What would reaction between NaBH4 and solvent be?
CH3OH + NaBH4 --> Ch3OBH3(-)Na(+) + H2
Describe transition state of diels alder reaction
sigma overlap of the p-orbitals of the diene and dienophile
What do with solutions of NaCl, NaHCO3
sink under steady flow of water
hazards of anthraquinone? Sulfuric acid?
slight irritation on hands sulfuric acid is corrosive, burns hands
Danger of NaOH
strong caustic base
What species serves as catalyst in reaction?
sulfuric acid
What does adding substituents to benzophenone aromatic rings do?
- improve solubility of the ketone and improve ability to absorb UV light
Why s-cis and not s-trans
- in s-trans conformation, the p-orbitals of the diene and dienophile are too far apart to react in cyclic transition state
Concerted mechanism
- in the transition stat, bonds are simultaneously made and broken
What happens in reduction reaction?
- increase in the number of C-H bonds
What does vertical axis of IR spectrum give?
- intensity of the IR absorption bands in % transmission (T)
How is product recrystallized?
- is less soluble than the reactants and precipitates from solution
Phosphorane
- the phosphorus ylide that is required in a Wittig Reaction
What happens when %T is 100?
- there is no absorption of IR radiation
What does this mean in terms of IR radiation
- these stronger bonds absorb IR radiation of higher frequency and higher energy
Antracene, describe it
- three rings, conjugated because has delocalized pi electrons along ring -
Purpose of BLANK cuvette
- to zero/calibrate the UV Spectrometer
How does the catalyst impact the position of equilibrium? Rate of reaction?
- towards product, allows reaction to go faster
What forms for Diels Alder rxn (general mech)
- two new carbon-carbon sigma bonds and a cyclohexene ring
Assign oxidation states for methane
CH4, each H has +1, C has -4 state, because overall uncharged - C has lowest possible oxidation state here
What does stretching vibration depend on?
depends on the masses of the two molecules bound and the strength of the bond between them
What is role of sulfuric acid in reaction?
protonates the Oxygen to form positively charged carbonyl, leading to attack by lone pairs on oxygen
If reaction A has Keq of 2 and reaction B has Keg of 6, which favors pdt?
reaction B because more pdt formed
What is temperature of reaction kept below during addn of NaBH4? WHy?
- under 45 degrees C - in order to minimize the reaction between sodium borohydride and the solvent
As add oxygen to C atoms what happens to oxidation state on C?
- undergoes oxidation reaction, so lose electrons, C oxidation state becomes more positive
How will oxidize benzoin next time?
- use copper II acetate
Why is benzophenone used as sunscreen?
- very good at absorbing UV radiation
Bonds with stronger bonds vibrate high or low frequency?
- vibrate with higher frequency
How to clean IR plates?
- was with methylene chloride
When can you remove reaction flask from reflux?
- when all brown gas has evacuated the flask
What is peak at 2400 cm^-1
CO2
What is Lewis Base?
NaBH4 H because acts as nucleophile and donates electrons
How was excess acetic acid removed at end of reaction
NaCl deprotonates acetic acid (if didnt react with H2SO4) so it joins aqueous layer, then can be funneled out for extraction
How determine which method is better
- % yield and purity of compound - also reaction times and safety
What is typical concentration of substance for UV-Vis
- 10^-4 concentration
How many pi electrons does anthracene in product have? What does three separate benzene rings have
- 12 pi electrons, 18 pi electrons
Bond angle of carbonyl
- 120 degrees
How many electrons does anthracene have prior to rxn?
- 14 electrons
How reduce carbonyl
- Add H to carbonyl carbon, push electrons to Oxygen to grab H, form alcohol
What is reduced, what is oxidized? general and specific
- Benzoin is oxidized, nitric acid is reduced - C loses electrons, so oxidized - N gains electrons, reduced
What reagent in the reaction is the Lewis Acid?
- Benzophenone is the Lewis Acid
Compare C-O and C=O, why?
- C=O has higher bond order, higher stretching frequency
What should you do if spots of interest travel with the solvent front?
- get a less polar solvent
What do with methylene chloride waste?
- halogenated waste
What is an ylide?
- has a positive charge and negative charge on two adjacent atoms but an overall neutral charge
What type of electrophilic aromatic substitution reaction occurs at end of mech?
- Friedel Crafts acylation - electrons in benzyl attack carbocation to form ring
What would second step of NaBH4 reaction be (react with H2O)
- H2O + NaBH4 --> Na(+)BH3OH(-) + H2
How would benzoic acid be detected by TLC, IR, NMR compared to Benzil?
- IR: benzoic acid has carboxylic acid group, benzil has two ketone - TLC: benzil is nonpolar, benzoic acid is polar, so in non polar solvent, benzil goes all way up but benzoic acid binds to silica gel - if polar solvent, pulls benzoic acid up as well NMR: Benzoic acid has hydrogen on carboxylic acid, benzil only has H on aromatic rings
What is LAH used for? What is NaBH4 used for?
- LAH is used to reduce carboxylic acids and esters - NaBH4 is used to reduce only ketones and aldehydes
For maleic anhydride, normal carbonyl peaks are 1850 and 1778. What should final peaks be at?
- Loss of conjugation so peaks should be at slightly higher frequency
How about MP
- Mp would be broader in range and overall lower
Give oxidation states for nitric acid
- N has +5 state, then gains electrons to +3 state
Is reversible?
- NO
WHy is NaBH4 easier to work with?
- NaBH4 can be massed on open bench and can be dissolved in low molecular weight alcohols like ethanol
Is there conjugation in the final product?
- No
Does Diels Alder need a catalyst?
- No because if have good diene and dienophile, will react quickly
Oxidation states of CO2?
- O has -2, so C has +4 state, highest oxidation state for C
What species is nucleophilic? Electrophilic?
- OH is nucleophile - diphenylacetone is electrophile 2nd time: benzil is electrophile, and diphenylacetone is nucleophile
WHat is purpose of solvent xylenes
- high boiling solvent that provides E needed for reaction to occur
What can UV-Vis do?
- UV-Vis can measure these energy transitions between orbitals
How oxidize benzoin this time?
- Use Nitric acid
Max wavelength
- Wavelength at which the maximum light is absorbed, corresponds to molar absorptivity
How is reaction facilitated/What can dienophile have that makes rxn happen faster? How?
- When dienophile bears electron withdrawing group like cyano, nitro, ester, or ketone/aldehyde group, since this lowers the energy of the dienophile and brings LUMO closer to HOMO
When does the reaction take place most readily?
- When the energy difference between the HOMO of the diene and the LUMO of the dienophile is not too large
Maleic acid in conjugation?
- Yes because of presence of double bond and lone pair electrons in sp3 orbital of oxygen
Le Chatelier's Principle
- a change in any factor that determines the position of equilibrium causes the system to adjust in order to offset the change
How is Le Chateliers principle used to increase yield?
- add more starting material acetic acid - water, a product of esterification synthesis, can be removed by distillation or by addition of a drying agent like molecular sieves - both adding SM and removing pdt pushes reaction toward right, toward product
Where should OH be added for diene to increase reaction speed?
- add on end because is electron withdrawing so lone pair of electrons can be in conjugation with pi electrons
What is reaction of carbonyl compound with metal hydride reducing agent considered?
- addition reaction
What should check for for hood to be sure are working?
- air flow
What is aldehyde reduced to? Ketone?
- aldehyde is reduced to primary alcohol - ketone is reduced to secondary alcohol
What reaction is used here?
- aldol condensation reaction
Benzoin
- an alpha hydroxy ketone that can be oxidized by a variety of agents to yield diketone benzil - has one ketone and one alcohol and two phenyl rings
Anhydrides and IR
- anhydrides give two peaks for IR that are ~60 cm^-1 apart - due to two difference stretching modes - one is symmetric and other is asymmetric stretching modes
Lithium Aluminum hydride
- another commonly used metal hydride reducing agent
Correlate bond order and stretching frequency, why?
- as bond order increases (bond becomes stronger), stretching frequency increases - higher bond order requires more energy to stretch the bond, therefore higher frequency since energy is proportional to energy
Relate energy gap and conjugation
- as conjugation increases, the energy gap decreases
Why is NaBH4 preferred?
- because LAH is difficult to work with
WHy is maleic anhydride a good dienophile?
- because has electron withdrawing groups with ketones (anhydride)
1,3-butadiene is colorless but has absorption max wavelength value in visible range. How?
- because is conjugated absorbs max light at longer wavelength than expected (lower frequency, less E) - so absorbs visible light even though colorless
Why is anthracene a good diene?
- because it is cis conjugated cyclic molecule - also has electron donating double bonds, electron rich
What does benzaldehyde oxidize to?
- benzoic acid
How can IR distinguish between benzoin, benzil and benzaldehyde?
- benzoin: ketone and alcohol - Benzil: two alcohols - Benzaldehyde: Has aldehyde
What was reaction to synthesize benzhydrol?
- benzophenone is reduced by using sodium borohydride to give benzhydrol (diphenylmethanol)
What is rxn scheme
- benzyl acetate is prepared by direct esterification of acetic acid with benzyl alcohol in the presence of sulfuric acid
More deshielding leads to what
- higher chemical shift, more downfield
What is used to recrystallize the crude benzil product?
- hot ethanol
How are copper oxides removed?
- by gravity filtration
Molar absorptivity, E
- calculated at the wavelength of maximum absorbance - how strongly a sample absorbs light at a certain wavelength
Anthraquinone danger
- can be absorbed through skin, wear gloves
Why are alpha hydrogen atoms acidic
- can form enolate which is stabilized b/c O is electronegative and stabilized by resonance
What can diene have that makes rxn happen faster?
- can have electron donating group like OH to induce reaction and donation of electrons to dienophile
What is oxidized, what is reduced in Copper II acetate reaction?
- carbon in benzoin is oxidized - copper is reduced from Cu2+ to Cu+
What is the electrophile in reaction? WHy0
- carbonyl Carbon, wants e-, partial pos charge
Maleic anhydride safety?
- caustic so use gloves, clean after spills
Molecular vibrational motion
- chemical bonds constantly stretching and compressing at particular frequency
How is this Diels Alder adduct produced
- combining anthracene and maleic anhydride
Why
- compounds with more extensive conjugation absorb light at longer wavelengths (lower energy)
What is more stable: conjugated or nonconjugated double bonds?
- conjugated because have electron delocalization/orbital hybridization - lowers the energy
What factors shift the band to a lower frequency
- conjugation
What is meant by anhydrous?
- contains no water
What do these electronic transitions that have energy gaps correspond to?
- correspond to electromagnetic radiation in the UV-Vis range
Benzophenone uses
- cosmetics industry as UV stabilizer and as sunscreen
What happens in oxidation reaction?
- decrease in number of C-H bonds
What does spectrometer do?
- detects the absorption bands and determines the relative strength of the absorptions
diene and dienophile?
- diene contains two (or more) carbon double bonds, donates electrons to dienophile in this case is anthracene - dienophile is the substituted alkene, accepts electrons from diene here is maleic anhydride
What should you do if plate has big streaky spots?
- dilute it with more spotting solvent
How would use recrystallization to separate the two?
- dissolve benzoic acid in polar solvent, then do filtration because benzil wont dissolve - OR can dissolve mixture in methylene chloride, then add NaOH to deprotonate acid and get into aqueous layer - then drain aqueous layer and reprotonate benzoic acid by adding HCl
If product were found to be contaminated with benzoic acid, what methods would be used to purify the product? Which not used?
- distillation not used because need liquids - Filtration: no because both solid - Extraction: no because both are organic layers - Column Chromatography: yes because polarities are different - Recrystallization: yes, followed by vacuum filtration
Diff between doublet doublet and quartet?
- doub-doub has 1:1:1:1 orientation - triplet has 1:3:3:1 orientation
Generalizations for shielding and deshielding of protons in molecule?
- electronegative atoms such as N, O, and halides deshield hydrogens because pull electrons away - electrons on aromatic ring, double bonded atoms, tripled bonded atoms deshield hydrogens b/c pull e density - Carbonyl group deshields - benzylic and allylic H are deshielded - Electron donated atoms, such as silicon, shield H
What hazards are associated with EtOH and KOH
- ethanol is flammable, KOH is corrosive
What must be added with reducing agent so reaction occurs
- ethanol, and acid (H3O+)
What happens when Energy by ultraviolet and visible radiation is absorbed by a molecule?
- excites an electron from one orbital to another - electrons in pi orbitals are promoted to higher vacant orbital pi*
What is the position of equilibrium with the carbanion?
- favors the ketone strongly but enough enolate is generated so that reaction proceeds in forward direction
Esters used how?
- flavors and fragrances of flowers and fruits
Why does aymmetric stretching mode have lower IR frequency
- for IR, measure IR required to change the dipole of the molecule - asymmetric has higher dipole, strong absorption at lower freq, and requires less E to move it
What happens when diphenylacetone is exposed to base?
- forms an enolate
How are IR spectra usually reported?
- frequency units called wavenumbers, calculated as 1/lambda, (cm^-1)
What is meant by reducing compounds
- gaining electrons, losing oxygen, gaining Hydrogen
Vitamin A
- generated by Wittig reaction
What is benzhydrol?
- low melting solid used in perfume industry and as IM in pharma syntheses
How does catalyst act?
- lowers the rate of reaction by lower activation energy, therefore increasing speed of reaction - are not consumed in reaction
How form s-cis conjugated formation?
- make a ring like anthracene then very reactive cis diene
What makes copper II acetate oxidation good? bad?
- mild reaction conditions, short reflux period, high yields of product - but yield can be much lower
WHy is LAH hard to work with?
- must be handled in anhydrous conditions because it reacts violently with water - also decomposes energetically when heated
Benzyl acetate
- natural product used for pleasing odor of flowers - is a food additive
WHich of LAH and NaBH4 reduces alkenes and alkynes
- neither
What should do with acidic filtrate that results from the filtration of crude product?
- neutralize to pH 6-8 by transferring it to large water beaker and then adding sodium bicarbonate until reaction ceases
Which is preferred and why? Why not so perfect though
- nitric acid because has shorter reaction time and higher yield - can be contaminated with benzoin
What does reactive metal hydride act as? WHy
- nucleophile, gives electrons (H
Explain basic mechanism of Wittig Reaction
- nucleophilic ylide adds to the electrophilic carbonyl carbon of the aldehyde/ketone - Yields an alkoxide intermediate that decomposes through a four-membered ring to give an alkene and triphenylphosphine oxide
alpha hydrogen atoms, what are they and what happens when next to ketone?
- on alpha position next to phenyl group - abstracted by strong bases to give enolate intermediate
What is a good dienophile
- one that has electron withdrawing groups attached like NO2, Cyano, Aldehyde, Ketone
anthraquinone
- pale yellow high melting solid of great stability - compound is used as pesticide and bird repellant near airports
Hydrogens on phenyl groups with electron donating group attached
- para H have least deshielding - ortho H have mid deshielding - meta H have most deshielding - because if draw res structures, get electron density on o and p positions and not on m, so most deshielding
What happens if too much sample for liquid film IR?
- peaks appear blunt or cut off at tips
What happens for IR solid sample if there is still solvent?
- peaks from solvent are visible on graph
What do with ethanol and TLC solvents?
- put in nonhalogenated organic waste
Oxidation-reduction reaction, redox reactions
- reactions that involve a transfer of electrons from one molecule to another
What reagents are used for reduction reactions?
- reducing agents - NaBH4 and other metal hydride reducing agents
Benzoin is what kind of alcohol?
- secondary alcohol
What do nitrogen oxides cause? What do you do about it?
- skin irritation, reaction under good with gloves
Why wash reaction mixture with sodium bicarbonate solution?
- sodium bicarbonate is an ionic salt - adding it to a solution reduces solubility of organic molecules in the aqueous solution and results in higher yield
polarization of C=O?
- strongly polarized to oxygen, pulls electrons from C
Which mode is at higher frequency? Why
- symmetric stretching is at higher frequency - asymmetric stretching is more intense and occurs at lower frequency
What was the reaction for Experiment 10?
- synthesize trans-9-(2-phenylethenyl) anthracene from 9-anthraldehyde with the Wittig Reagent benzyltriphenylphosphonium chloride under basic conditions
Conjugation
- system of connected p-orbitals with delocalized electrons in compounds with alternating single and double bonds - results in lowered overall energy of molecule and increased stability
What else must be recorded when taking UV-vis? WHy
- temperature, solvent and solvent concentration at which absorbance measurements were made - because these conditions impact absorbance
What is other factor to increase kinetics of Diels Alder Reaction?
- the diene must adopt a s-cis conformation on the single bond that connects the two double bonds
What is one general limitation of Wittig Reaction
- the lack of stereochemical control - this means that both E and Z isomers are produced by reaction
Why does the middle ring of anthracene react?
- when the center ring reacts, the final product gives two aromatic rings one at each end, each with 6 pi electrons, so aromatic, very stable
What are the reagents refluxed in? WHy?
- xylenes, a high boiling solvent - won't boil off during reflux
Lab 8: Synthesis of Benzyl Acetate (Peach Oil) by Fischer Esterification
- yep
What does w/w mean?
1 gram of substrate for 1 gram of solvent
One equivalent of reducing agent can reduce how many equivalents of ketone
4
How prepare 5% w/w solution in water
5 g of substrate and 100 g of water solution
Where would 9-anthraldehyde and the desired product be on TLC plate? Which has the higher RF?
9- anthraldehyde has big polar aldehyde so will bind to silica and stay close to bottom desired product is less polar so will move up - desired product has higher RF
Beer's Law
A = ECL - A= absorbance, E = molar absorptivity in 1/cm x 1/M, C = concentration, M, L = path length, cm
Then what?
Aligning against the field requires more E than aligning with field - when sample is irradiated with radio waves, E is absorbed by nuclei and those aligned with field flip to align against field
By IR spec, how do you know if the transformation of anthraldehyde to the desired product was successful?
Anthraldehyde has a aldehyde group (1730) whereas the desired product has a C=C non-aromatic group (1600 cm)
What is the catalyst in reaction?
Base OH
If benzil were contaminated with benzoic acid, how would impact the reaction?
Benzoic acid would be electrophile partially as well as benzil because both have electrophilic carbonyl groups
Rationalize the positions of benzophenone vs diphenylmethanol on TLC plates
Benzophenone: nonpolar Benzhydrol: polar Solvent is mostly nonpolar so forces nonpolar to the top, therefore benzophenone is at the top of plate and benzhydrol is at the bottom
Compare butanal (not conjugated) and butenal (conjugated)
Butenal is conjugated so has electron delocalization in bonds and therefore is more stable and less E is required to stretch bonds, therefore has lower stretching frequency - Butanal is not conjugated, more E needed, higher frequency
electrophilic and nucleophilic parts of C=O
C is electrophilic b/c is + charged O is nucleophilic b/c is - charged
Compare C-C, C=C, C triple bond C in terms of energy and frequency (cm^-1)
C-C has lowest energy, lowest frequency (1450 cm^-1 C=C has mid E, mid frequency (1650 cm^-1) C triple bond C has highest E, highest frequency (2180 cm^-1)
What to do for liquid samples for IR analysis?
Called Liquid Film or Neat Sample - transfer drop of liquid to bottom salt plate - cover drop of sample with the top salt plate to make sandwich - perform IR scan
What to do for solid sample for IR analysis
Called Solid Sample or Thin Film - Place spatula tip of solid sample in push-top vial with enough methylene chloride to dissolve sample - Add one/two drops to open face of one salt plate and allow the solution to spread over the face of the plate - as solvent evaporates, thin film of solid is noted - Perform IR scan
What can assigning peaks in IR spec tell about molecule
Can determine what functional groups are present in the molecule
What info can be acquired form a graph of wavelength and absorbance
Can get wavelength at which max absorbance occurs - can calculate molar absorptivity
Hybridization from C=O to C-O if attacked by nucleophile, what is final geometry
Goes from sp2 to sp3, tetrahedral geometry
How would contamination with starting material be observed with NMR?
H on aldehyde
How distinguish pdt from reactant with NMR, IR, TLC
IR: reactant has carboxylic acid, pdt has 2 ketones NMR: reactant has H on carboxylic acid TLC: antraquinone is not polar, 2-benzoylbenzoic acid is polar - in nonpolar solvent, anthraquinone travels up and benzobenzoic acid stays down
When is diene more reactive?
Is sensitive to substitution and is most reactive when it posses electron donating groups attached to the C=C bond - here is the other electrons in rings
Dienophile, when most reactive?
It is most reactive when it possesses electron withdrawing groups
What would happen to mp of pdt if were contaminated with benzoin? benzaldehyde?
MP range would broaden and overall MP would decrease - same thing
NMR: explain basics
Nuclei of atoms with odd number of protons have permanent magnetic moments and spin states - placing these types of atoms in a strong magnetic field separates them into two groups: those that align with applied field and those that align against field
What kinds of substituents could be added
OH, OCH3, SO3H
Vibrations of polar bonds give strong/weak IR bands? Give ex
OH, strong IR bands
How would you make methanol starting with a carbonyl compound?
Reduce formaldehyde with NaBH4 to get methanol
Why wash with saturated sodium chloride solution at end of reaction?
Removes trace amounts of water or anything else that is soluble from the organic layer
What is the expected change in IR spectra for product vs starting reagent
SM: has ketone, no alcohol Pdt: has alcohol, no ketone
Why is the product an excellent reagent for a Diels Alder reaction?
Several electron-withdrawing benzene ring attachments. Product is locked in an s-cis confirmation about the single bond; this aligns the pi orbitals so that the electrons can react in a cyclic transition state.
How does bond formation occur?
The HOMO (highest occupied molecular orbital) of the diene overlaps with the LUMO (lowest unoccupied molecular orbital) of the dienophile
Lab 3: Oxidation of Benzoin to Benzil using Nitric Acid Lab 4: Oxidation of Benzoin to Benzil using Copper II Acetate
WooHOo!!
Lab 6: A Diels Alder Reaction Using Maleic Anhydride and Anthracene
WooHoo!
Lab 7: Synthesis of Anthraquinone
WooHoo!
Lab 10: Wittig Reaction to Yield trans-9-(2-Phenylethenyl) Anthracene
Woohoo
Lab 2 Synthesis of Benzhydrol
Woohoo!
RECOGNIZE WHAT IS GOOD DIENE AND GOOD DIENOPHILE
Yep
What is reaction also called? Why
[4+ 2] cycloaddition reaction because 4 pi electron from the diene and two pi electrons from the dienophile interact
Induced Field
a field created by the electrons in the bond to the Hydrogen and the electrons in nearby pi bonds When induced field and applied field reinforce each other, a smaller field must be applied to flip the proton - this causes deshielding When the applied and induced fields oppose each other, a stronger field must be applied to flip the proton. In this state, the proton is shielded.
What is functional group
a specific group of atoms in a molecule responsible for characteristic physical and chemical properties
How can IR analysis of ester product be used to detect presence of unreacted acetic acid? Benzyl Alcohol?
acetic acid has carboxylic acid, not ester - ester is higher stretching frequency Benzyl alcohol has alcohol, has very high stretching frequency
Fischer Esterification
acid catalyzed reaction between a carboxylic acid and an alcohol
What are safety and waste issues related to use of acetic acid and copper II acetate
acid, so must neutralize if spilled - wash skin
What should do if sample contains carboxylic acid
add a few drops of acetic acid in developing solvent
What functional groups transform?
alcohol --> ketone
If any unreacted benzozylbenzoic acid remains, how is removed?
ammonia
So...
anthracene is not aromatic stabilized as is, so is reactive and wants to form stable aromatic compound
What species is electrophile? What else would have worked?
anthraldehyde with carbonyl C, ketone
What drives the reaction so that there is qualitative yield for reaction?
anthraquinone is very stable because is resonance stabilized and is also aromatic compound - benzoylbenzoic acid has two separated phenyl rings but anthraquinone is more stable
What is role of wittig reagent
attacks anthraldehyde at carbonyl to form 4 member ring
How is triphenylphosphine removed from the product?
both products are dissolved in hot 1-propanol and the desired product recrystallizes whereas the side product does not. then the desired product is collected via vacuum filtration - triphenylphosphine oxide is more soluble in propanol because it can hydrogen bond using its Oxygen atom, making it less likely to precipitate out of the solution with the desired product
Diketone Benzil
bright yellow solid that contains two ketones and two phenyl groups
Compare heat of formation for 1,3-butadiene (conjugated) and 1,4-pentadiene (not conjugated)?
butadiene is conjugated, is more stable, lower energy of formation
Diels Alder cycloaddition reaction
conjugated dienes react with alkenes to form new c-c bonds in cyclohexane product
What kind of reaction is used?
cyclodehydration reaction of 2-benzoylbenzoic acid in presence of sulfuric acid
How would NMR show contamination by diphenylacetone?
diphenylacetone has 2 two types of H, pdt only has 1
NMR for benzyl acetate
do it!
http://www.chem.ucla.edu/harding/ec_tutorials/tutorial51.pdf
do this quiz!
Why is ester product treated with calcium chloride?
drying agent to remove water
How can aldol reactions be catalyzed? What is used here?
either acid or base catalyzed, this time KOH base is used
What kind of reaction is Fischer esterification?
equilibrium reaction that is affected by Le Chatelier's Principle
NMR Sample Preparation
filter sample so fits into capillary tubes of NMR probe - add 400 ul of solvent (CDCL3 with 1% TMS) to vial - add 20 uL of sample to vial
Xylene safety?
flammable
For NaBH4, how many reducing reactions can occur
four reducing reactions, one H for each reduction
UV absorbance, what produce
graph of absorbance v wavelength - then get wavelength of maximum absorbance and can calculate molar absorptivity value from data
Explain the change in bond order for the final C=O bond
in product, the C=O bond are no longer in conjugation, therefore have lower bonding order because of the delocalization of the electrons in the ring - decreased bond order corresponds to less energy required to stretch the bond and lower frequency of IR absorption bands
How could benzil product be separated from other reactant and side products
recrystallize in crude ethanol, dissolve in polar solvent then add water and allow nonpolar benzil to recrystallize out of solution - other polar compounds wont recrystallize
Why is benzil a reagent for an Aldol reaction with diphenylacetone than is acetone
ketone groups withdraw electrons and form enolate easier than acetone, stabilized by resonance, and then can react
Ketone or enolate equilibrium favored?
ketone is favored but there is still some enolate produced
Chemical shift
measure of deshielding - more deshielding, move further to left of graph
Why use NaOH? Can KOH be used? what about PhOH?
must be a strong base, KOH could be used because it is a strong base - PhOH could not be used b/c it is not a strong base
What substrates are appropriate for the WIttig Reaction
need the Wittig reagent and a carbonyl aldehyde or ketone
What is the approximate pKa of benzhydrol?
negative 13 (check this!), very acidic because stabilized by resonance, but irreversible because reduced
What happens when benzil is exposed to base?
nothing, won't form enolate because no lone H to remove
Oxidant vs reductant
oxidant = oxidizing agent does the oxidizing, is reduced itself (Copper II acetate and Nitric acid) reductant: = reducing agent does the reducing, is oxidized itself NaBH4
What happens when reduced/oxidized?
oxidized: lose electrons reduced: gain electrons
What is the wittig reagent
the phosphorus ylide, in this case is Phosphorane
What specifically does IR measure
the vibrational excitation of molecules - the frequency of these absorption lines depends on types of bonds present
For a bond to absorb IR light, what must happen?
the vibrational motion must cause a change in molecular dipole
What do with solid NaCl, NaHCO3, CaCl2?
trash
Aromatic splitting
triplet or doublet doublet, if H are attached to carbons in different environments
How many carbonyl stretching frequencies are expected for product?
two as well, one ketone and one carboxylic acid
How many carbonyl stretching frequencies for the product are expected?
two, symmetric and asymmetric modes, both ketones
What should you do if spots don't travel far from the original spotting point?
use a more polar solvent
Are the alkene products of Wittig reactions cis, trans, or both?
usually both cis and trans
Acidification
way to test filtrate to see if any starting benzoylbenzoic acid is present in filtrate - benzoylbenzoic acid reacts with base to form soluble carboxylic acid salt - when test with acid to tube with a few mL of filtrate, see if precipitate forms - if precipitate forms, then there is still some unreacted benzoylbenzoic acid in filtrate and must keep washing with ammonia - if no precipitate forms, then yield will be close to 100%
Lab 5: Benzil to 2,3,4,5-Tetraphenylcyclopentadienone (TPCD)
woohoo