CHEM 222L Final Exam

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Eluent

"carrier" portion of mobile phase

What is oxidation state of C=O in camphor?

+2

Functional groups on fluorene and fluorenone?

-H, =O

Which chemical species acts as Bronsted base? Which acts as a Lewis base?

-OH is both. Accepts proton from HCl H2O Donates electron to methyl salicylate form hydroxyl bond

What is oxidation state of C-OH carbon in isoborneol?

0

Typical mp range of pure compound?

0.5 to 2.0°C

A mixture of fluorene, fluorenone and fluorenol is examined by TLC and gives the following Rf values: 0.3, 0.5, 0.8. Identify each spot and rationalize the relative Rf values.

0.8 is fluorene, 0.5 is fluorenone, 0.3 is fluorenol. Fluorenol is an alcohol, so it is more polar than the ketone fluorenone, giving it a lower Rf value.

How many asymmetric C atoms in isoborneol

1

Purposes of TLC analysis?

1) assess progress of a reaction 2) assess purity of a compound 3) provide information about identity of a compound

Synthesis of salicylic acid: role of NaOH

1. deprotonates phenol group of methyl salicylate 2. attacks carbonyl carbon of methyl ester group to give disodium salicylate

What do you do if crystals don't form?

1. scratch with glass stir rod 2. try adding seed crystal 3. evaporate some solvent

Potassium salicylate + sulfuric acid rxn

2RCOO⁻K⁺ + H₂SO₄ → 2RCOOH + K₂SO₄

What might happen if the bulb of the thermometer is above the branch in the distillation head?

Above: will read as too low temperature, will possibly reach BP of compound with higher BP → imperfect separation

What happens when HCl is added to flask 1? (purpose of HCl)

Acidifies sodium benzoate and neutralizes remaining HCl. Produces benzoic acid (insoluble in water), which is filtered

How would you separate mixture of 4-methylbenzoic acid (p-toluic acid) and anthracene (organic)?

Add TBME and NaOH(aq) to create aqueous and organic layers, use separatory funnel. Aqueous: add HCl to react away NaOH, filter Organic: wash with NaCl, dry with CaCl2, evaporate TBME

Distinguish aldehyde from ketone using IR

Aldehyde has C-H peak at 2900-2800

Organic solvent in face

Alert TA and lab mates, take off glasses, use eyewash for 10-15min

If student drops beaker

Alert TA, use dust-pan and brush, dispose in broken glass container

Rank all functional groups from most to least polar.

Amide > Acid > Alcohol > Amines > Ketone ~ Aldehyde, esters > Ethers, halocarbons > Aromatic hydrocarbons > Alkenes > Alkanes

Why is oxone preferable to bleach for oxidation of isoborneol to camphor?

Bleach has widely varying concentrations and does not generate consistent yield

Explain electrophilicity of the carbonyl carbon in methyl salicylate

Bonded to two oxygen atoms (both are more electronegative), making the carbonyl carbon more electropositive

Synthesis of benzyhydrl-1-propyl ether: what species is the electrophile in this reaction?

C carbocation linking aromatic groups

Distinguish carboxylic acid from ketone using IR

CA has C-O peak at 1300-1000

Given that compound A can be recrystallized from CH2Cl2 and ethyl acetate, which would you choose and why?

CH2Cl2 is a carcinogen. Choose EtOAc: only hazard is flammability

Oxidation states of CH₄, CH₂O, H2CO₃

CH4: -4 CH2O: 0 H2CO3: +4

Name three common drying agents

CaCl2, Na2SO4, magnesium sulfate

Purpose of CaCl2 pellets?

Chemical drying, remove last remnants of dissolved water in organic solution

Difference between chemical hazard and handling precaution, and example of each

Chemical hazard: qualities of chemical reagent (flammable, skin irritant) Handling precaution: actions of experimenter (use fume hood, use gloves)

What the features of a good drying agent?

Chemically stable/chemically inert, high capacity, high efficiency

In oxidation rxn, what serves as catalyst?

Cl-

TLC use to judge completeness of reaction

Compare TLC of product to TLC of starting material (and model product if possible)

Why does 1-propanol give higher yields than does cyclohexanol?

Cyclohexanol is a bulky nucleophile

How does TLC reveal purity of given compound?

Different compounds form different spots on TLC plate b/c move diff distances If more than one compound present, will see more than one spot on TLC plate

What type of intermolecular forces are present in benzoic acid?

Dipole-dipole interactions (-OH group)

Intermolecular interactions in sample of hexane

Dispersion

What makes ethyl acetate a useful solvent for this reaction?

EtOAc can dissolve the substrate without dissolving oxone and NaCl so that the reaction can take place at the interface of two phases. Also, it makes the reagents easier to be removed.

Camphor, ethyl acetate, water and sodium chloride(aq) are in a separatory funnel. Where is each?

EtOAc: upper layer, contains camphor H2O: lower layer, contains NaCl

What hazard do most organic solvents share?

Flammable

What hazard do ethyl acetate, camphor, and isoborneol share in common?

Flammable solid

Imagine that the TLC of flask 3, following column chromatography to separate fluorene and fluorenone, shows two spots with Rf 0.4 and 0.6. Identify the spots and comment on the success of separation procedure.

Fluorenone is 0.4, fluorene is 0.6 Unsuccessful separation

Relative Rf of flourene and fluorenone

Fluorenone is more polar (ketone), has lower Rf value than fluorene (alkene/aromatic)

Why does separation with NaOH work?

Good use of pKa values, NaOH is stonger base than sodium salicylate so reaction proceeds forward

At the end, how is excess basic solvent removed?

HCl is added, neutralizes NaOH

Why should one avoid making acid and base solutions in graduated cylinders?

Heat of dissolution will cause expansion (up and out)

Bond order and absorption of IR radiation

High bond order = absorb higher frequency IR radiation

Rank polarity of following solvents (high, intermediate, low): water, hexane, ethyl acetate, toulene, acetone, ethanol

High: Water Inter: ethanol, acetone, ethyl acetate Low: hexane, toulene

Main hazard with strongly basic solutions

Highly corrosive to skin and eyes

Hirsch vs Buchner funnel choice

Hirsch: a little bit of product Buchner: a lot of product

Why is the benzhydryl cation formed preferentially? (how does this work)

It is stabilized by resonance, double bonds move around (one goes onto C-C next to ether to start)

Two methods for IR prep for solid

KBr pellet Thin solid film

What the active oxidizing agent in Oxone?

KHSO₅

Impact of higher melting or high boiling impurity or solvent on mp of organic compound

Lower mp and broaden range

If salicylic acid is wet with water, what is the effect on mp?

Lowers mp, broadens range (disruption of crystalline structure)

Why might you get a % recovery of salicylic acid way under 100% (say 40%)?

Might not have added enough HCl, all salicylate didn't reprotonate to salicylic acid, reducing % recovery

Solvent better for recrystallization of 1,4-dimethoxybenzene: methanol, water, or a mixture?

Mixed solvent. Methanol dissolves the solute, water induces crystallization

column chromatography mobile and stationary phase

Mobile: solvent, analogous to TLC developing solution Stationary: alumina sand Al₂O₃

Order of elution in column chromatography: anthracene, 2-napthol, benzaldehyde, benzoic acid

Most polar will elute last Anthracene > benzaldehyde > 2-napthol > benzoic acid

NaOH + C6H5COOH (benzoic acid)

Na+C6H5COO- + H2O sodium benzoate and water

NaOH + HCl

NaCl + H2O

If Rf of starting material is 0.2 in 100% pentane, what change would you make to the solvent and why?

Need more polar solvent, maybe do 50/50 with ethyl acetate. Must compete with polarity of silica gel

Excess TBME and NaOH disposal

Neutralize with 5% acetic acid, organic waste container

Excess NaOH disposal

Neutralize with 5% acetic acid, wash down sink

Excess organic solvent contaminated with mineral acid

Neutralize with sodium bicarbonate, dispose in organic waste

If IR spectrums are identical, are two compounds identical?

No 1. Only detects functional groups 2. Doesn't detect stereochemistry (could be enantiomers or diastereomers) 3. IR can only detect polarizable bonds

(Exp 1) Imagine performing the experiment with sodium bicarbonate instead of sodium hydroxide. Will the experiment work?

No: pKa of NaHCO3 disfavors formation of sodium benzoate

What species is the nucleophile? (synthesis of benzyhydryl-1-propyl-ether)

O of 1-propanol

Why does one need to heat the reactants in this reaction?

OH- won't be able to attack the carbonyl carbon without heat

Excess TBME disposal

Organic waste container

Which has the higher vapor pressure, pentane or hexane? How does this affect BP?

Pentane (57.90kPa) > Hexane (17.60kPA), means that pentane has lower BP

What other reagent could be used for the same purpose?

Phosphoric acid (H₃PO₄)

Important info in SDS

Product Info, Hazards, Safe Handling, Physical & Chemical Properties

What is the role of sulfuric acid? What is its effect on reaction equilibrium and reaction rate?

Provide H+ for abstraction of water and formation of carbocation. Excess H+ shifts reaction to right

What is role of sodium bisulfite?

Quenches reaction by consuming excess oxidizing agent

Symmetrical vs. nonsymmetrical ether (with examples)

R-O-R vs. R-O-R* dibenzhydryl ether vs. benzhydryl-n-propyl ether

Benzoic acid + KOH rxn

RCOOH + KOH → RCOO⁻K⁺ + H2O

What is the equipment that returns solvent vapors to the reaction pot?

Reflux condenser

Synthesis of camphor: What is the purpose of the sodium bicarbonate wash?

Remove acidic impurities

Why is simple distillation performed?

Remove heptane solvent. Less time than fractional distillation

What is the purpose of adding magnesium sulfate to the organic layer? What other reagent could be used in its place?

Remove water/dry solution. Calcium chloride (CaCl₂), sodium sulfate (Na₂SO₄)

What factors contribute to the stability of the benzhydryl cation?

Resonance of two adjacent benzene rings

Which distillation technique, simple distillation (S) or fractional distillation (F) would be more suitable for the following operations? o Preparing drinking water from seawater? o Removing diethyl ether (BP 35°C) from para-dichlorobenzene (184°C)? o Separating benzene (BP 80°C) from toluene (BP 111°C)?

S, S, F

Water is a co-product of the reaction--how is it removed?

Separatory funnel + drying reagents

What's better/different about fractional distillation?

Slower, but better separation of similar BP liquids, uses fractional distillation column between flask and distillation head

What does (aq) mean?

Solution with water as the solvent

What to do with splash of strong acid?

Strip off gloves/lab coat, alert TA, wash affected area with water for 10-15 min

What does "neat" refer to when taking an IR spectrum?

The sample is prepared as a thin film, with no solvent present

What is the purpose of washing the organic layer with sodium bicarbonate?

To neutralize H+ present

What is the purpose of washing the organic layer with saturated sodium chloride?

To remove water

A separatory funnel contains water, diethyl ether, benzoic acid, naphthalene, and 2M sodium hydroxide. What are the layers?

Upper: TBME dissolving naphthalene Lower: water dissolving sodium benzoate and Na+ OH-

Safety issues of HCl and NaOH

Very caustic (skin & eyes)

Advantage of slowly grown large crystals over quickly grown small crystals

Will have better formed crystal lattice structure with fewer impurities

Would sulfuric acid be appropriate for the same purpose?

Yes, but need less since sulfuric acid has 2 acidic hydrogens

Rank the following solvents in order of polarity: diethyl ether, ethanol, acetic acid, toluene

acetic acid > ethanol > diethyl ether > toluene

Name a ketone encountered in this lab

acetone

Rank the following solvents in order of polarity: hexane, ethyl acetate, acetone, methanol

acetone > methanol > ethyl acetate > hexane

Drying agents: efficiency

amount of water left in the organic solution after drying

Name a carboxylic acid encountered in this lab

benzoic acid

Functional groups of benzoic acid and 1,4-dimethoxybenzene

benzoic acid (carboxylic acid, benzene ring) 1,4-dimethoxybenzene (2 esters)

Name an ether encountered in this lab

benzydryl-1-propyl-ether, dimethyl ether

Rank the following functional groups by Rf value: alcohol, aldehyde, carboxylic acid, aromatic ether

carboxylic acid < alcohol < aldehyde < aromatic ether

Stationary phase (column)

contains analyte/absorbent system, remains in column

Second crop

crystals recovered from mother liquor

Purpose of acetic acid in a solvent system?

decreases pH, suppresses ionization of any carboxylic acids present. Acidic compound can move along plate without streaking

Solute

dissolved substance in a solution

Name an alcohol encountered in this lab

ethanol

Main hazard of organic solvents

flammable

Safety issues of TBME

flammable, skin/eye irritant

eluent

fluid running out of tip of column

Features of good recrystallization solvent?

good solvent at high temperature, but not good solvent at lower temperatures; lowest mp of the ones that work

Name an alkane encountered in this lab

heptane

Drying agents: chemical inertness

how well the agent avoids reacting with the solvent and chemical

Rf changes with increasing solvent polarity

larger Rf values: solvent pulls polar compounds up, kicks nonpolar compounds up

Which compound has highest Rf and why? benzhydrol, 1-propanol, benzhydryl-n-propyl ether

least polar: benzhydryl-n-propyl ether. Ether makes O less polar

Solvent

liquid in excess that dissolves a substance

mother liquor

liquid left after initial crystallization (solute still present)

Distillate

liquid product condensed from vapor during distillation

Miscible

liquids able to be mixed together (oil and water would be immiscible)

Forerun

liquids whose BPs are lower than that wanted, usually impurities

Conjugate base, and example

matching base to acid in acid/base rxn (salicylic acid -> sodium salicylate)

Drying agents: capacity

maximum # of moles of water the drying agent can bind

Given that compound B can be recrystallized from methanol, ethanol and water, which would you choose and why?

methanol - lowest BP, easiest to dry

Why might you get a % recovery of salicylic acid that is greater than 100%?

might not be enough water to dissolve all of the NaCl created, so some undissolved NaCl was filtered out with the salicylic acid

TLC solvent system

mixture of developing solvents for TLC (i.e. hexane and EtAc)

Molecular symmetry and melt point

more symmetrical = higher melt point

Which would have a higher Rf value: naphthalene or beta-naphthol?

naphthalene: B-naphthol has an -OH group, making it more polar

NaOH spill on bench

neutralize with 5% acetic acid, cover with spill pad, dispose in solid waste

"Like dissolves like"

nonpolar dissolves nonpolar, polar dissolves polar

In hydrolysis of ester group, what species is the nucleophile and which is the electrophile?

nucleophile: -OH electrophile: O of ester

Experiment 1: two layers develop, what is in each?

organic (upper, TBME, 1,4-dimethoxybenzene), aqueous (lower, H2O, sodium benzoate, excess NaOH)

What compounds can be observed under UV light, after TLC analysis?

organic compounds containing pi bonds

Rank the following functional groups by Rf value: ketone, ester, phenol, alkene

phenol < ketone < ester < alkene

How is IR of product distinct from starting materials? What if it was contaminated?

product has ether peak and C-H (CH3) peak if contaminated, would see alcohol (C-O and O-H) peaks

Purpose of NaOH

provides separation of organic and aqueous layers, deprotonates benzoic acid into sodium benzoate so it dissolves in aqueous layer

Definition of melt point

range of temperatures, solid to liquid

What is the purpose of adding HCl to the cooled reaction mixture of disodium salicylate?

reacts with excess NaOH, neutralizing the solution Acidic solution allows disodium salicylate to be protonated and precipitate as salicylic acid

% recovery vs. % yield

recovery: recrystallization yield: synthesis reaction

What's the purpose of the NaCl wash of the organic layer?

remove majority of excess water in organic layer

Name a phenol encountered in this lab

salicylic acid

What would an explanation for if the mp of salicylic acid is higher than expected?

sampling height is too high (more heat needed)

Mobile phase (column)

solvent systems that passes through the stationary phase

Filtrate

the liquid left after filtration

temperature plateau

the temperature peak at which distillation is signaled to be over, is the BP of the lower boiling compound

What does [O] mean?

unspecified oxidizing agent

What makes a good TLC spotting solvent?

very volatile, nonreactive, should not absorb UV radiation (i.e. EtOAc)

What hot solvent will best dissolve benzoic acid: pentane or water? (think about salicylic acid)

water, more polar

boiling

when vapor pressure = atmospheric pressure

Too far below the branch in the distillation head?

will read as too high temperature, won't get good separation (compound with lower BP won't actually get distilled off)

If product was contaminated by benzhydrol, what would TLC plate look like?

would have another spot below the benzhydryl-n-propyl ether, more polar (alcohol)

Can KOH be used in place of NaOH to same end result?

yes, even stronger base so rxn still goes forward


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