Orgo Lab Midterm

Describe Recrystallization

a purification technique for organic solids

allows the organic molecules to self-assemble into a crystal lattice that forms pure crystals

Describe the proper solvent for recrystalization

solvent must DISSOLVE BOTH UNDESIRED AND DESIRED WHEN HEATED (both soluble)

DESIRED compound must be INSOLUBLE when the solvent is cold, but the impurities must remain soluble after cooling

Describe the technique for hot gravity filtration

used to remove insoluble components like charcoal from solution

use a STEMLESS funnel because it allows for quick filtration, keeping it hot

the solution must be kept HOT to keep desired compound in soln.

Describe the reflux technique

this technique prevents organic solvents from evaporating from the reaction vessel

How do you calculate theoretical yield?

TY = (moles limiting reagent)(molecular weight of product)

How do you calculate percent yield?

actual yield (in g or mol)

----------------------------

theoretical yield (in g or mol)

Why did WES for acetophenetidin NOT work?

no heat, so rxn proceeded slowly

maybe would have worked if we left it overnight

What are the 2 types of extraction

(liquid-liquid) and (solid-liquid)

The 2 solvents chosen for liquid-liquid extraction must be _________________

immiscible

(for most, one is nonpolar organic, and one is polar)

The compounds being extracted must have _________________ ______________________ for the 2 solvents

different affinities

In liquid liquid extraction which phase is on top and which phase is on bottom?

non polar (organic) on top

polar (aqueous) on bottom

EDG direct substituents on an aromatic ring during EAS to which position?

Ortho and Para

EWG direct substituents on an aromatic ring during EAS to which position?

Meta

EDG are ring ___________, and ______________ nucleophilic

activating, more

EWG are ring _________________ and _______________ nucleophilic

deactivating, less

Describe Thin Layer Chromatography

TLC is a separation technique that uses the concept of "like dissolves like" to separate the different parts of a mixture

Describe the mobile phase of TLC

aka the "Eluent"

liquid phase - the solvent in the chamber

What is the stationary phase of TLC

The TLC plate

coated with adsorbent - silica gel

*MOST POLAR COMPONENT

many site for H bonding

How does the eluent move up the TLC plate?

capillary action

What is the point of filter paper in the developing chamber for TLC?

increases surface area for evaporation, increases solvent vapor

keeps stationary phase from drying out

Rf values for polar component is __________

Rf values for nonpolar components is ___________

polar - small

nonpolar - large

What is the formula for calculating Rf values?

distance from origin to center of spot

------------------------------------------

distance from origin to solvent front

How do impurities change a compound's melting point?

impurities lower a compounds melting point and broaden the range

Impurities must be ______________ to affect melting point range

soluble

NOT IMPURITIES:

sand

glass

decolorizing carbon

How do you differentiate 2 compounds using MP?

do a mixed MP:

grind equal portions of each sample, see if the MP range is sharp or lowered and broad

if MP is sharp= identical substances

if MP is low and broad= different subsances

What must you do to ensure you get a reliable MP?

sample must be finely powdered

proper amount must be firmly packed in tube

sample must be completely dry

describe IR spectroscopy

Utilizes infrared light to excite molecules

signals arise from changes in dipole moments when bonds vibrate

IR spec. gives info about ____________________

while

NMR spec. gives info about ______________

IR spec gives info about what functional groups are present in the molecule

NMR spec gives info about the structure and bonding in a molecule

Give the formula for IDH (degrees of unsaturation)

Degrees of unsat. =

C + (N-H)

----------- +1

2

H= HYDROGENS AND HALOGENS

What is Elemental Analysis (CHN)?

used to determine the molecular formula of a compound

you burn an organic compound in an oxygen atmosphere and measure the amount of combustion produced.

**assume leftover mass is oxygen

Describe general mech. for amide synthesis of acetophenetidin

1) amide attacks Proton, gets protonated

2) sodium acetate deprotonates aminium ion

3) amide attacks carbonyl of acetic anhydride

4) O anion snaps back in and kicks of rest of group

5) acetic anhydride deprotonates amine group again

What is the purpose of adding p-phenetidine to dilute HCl in the amide synthesis of acetophenetidin?

the purpose of adding p-phenetidin to dilute HCl is to increase the solubility of p-phenetidin in water by making the anime salt

salt is more soluble in polar H2O

because HCl protonates the amine group

What is the point of the decolorizing carbon in amide synthesis of acetophenetidin?

decolorizing carbon removes the impurities caused by air oxidation of the animo functional group

- impurity causes reddish-brown color of sample

pure, unoxidized p-phenetidin is clear

**only can use SMALL AMOUNT OF DECOLORIZING CARBON or else it will remove all the organic compounds

What is the point of the sodium acetate in the amide synthesis of Acetophenetidin?

sodium acetate is used to deprotonate the aminium ion

then acetic anhydride is immediately added to react with the reformed free amine to give the acetophenetidin product

What is the overall reaction of the amide synthesis of acetophenetidin?

p-phenetidine + acetic anhydride -----------> acetophenetidin + HOAc

reagents: HCl and NaOAc

adds on a carbonyl to the amine group of p-phenetidin

When using a reflux condenser - what must you make sure of?

Top of condenser is OPEN

water goes in at bottom and out at top

vapor line should be between 1/4 and 1/2 way up condenser

What is superheating and how do you combat this?

superheating occurs when a liquid is heated above its boiling point in a clean, smooth container

always add a stir bar or boiling stone/stick

What do you do if no crystals form during recrystalization?

scratch inside of flask with glass stir rod to form site of nucleation

What is the point of reflux?

for synthesis we often need to heat solutions for long periods of time but dont want to lose volume (dont want it to boil away)

Why is dry ice a "green alternative"

it is solid CO2

it is carbon neutral

it is formed through capturing CO2 in atmosphere

Why do we use brine in extraction?

To dry the organic layer

How is the organic layer "dried" in extraction?

1) wash the organic layer with brine to remove dissolved water that may have gotten on it

2) dried further by placing it in contact with an anhydrous inorganic salt (usually mag. sulfate)

What is the difference between extracting and washing?

extracting: removing desired cmpd from a mixture such that the desired cmpd ends up in the aqueous phase (as an ion that will later be neutralized)

washing: leaves desired cmpd in organic phase and removes impurities to aqueous phase

When do you need to perform back extraction?

How do you do this?

you must back extract if precipitation of a neutral compound does not occur from aq. phase

extract compound from water using a fresh portion of organic solvent

Why can you not use glass tubes in solid-liquid extraction

CO2 pressure would cause it to shatter

What is an emulsion?

how do you fix this?

occurs when drops of one liquid become suspended in the other (during extraction)

not a clear separation

fix: make aq. layer more polar by adding brine

How do you find signal splitting?

(n+1) rule

number of neighbors + 1

What are the two basic steps of EAS?

1) the aromatic ring acts as a nuc. and attacks Electrophile

2) the aromatic ring is regenerated through the loss of a proton

How is aromaticity reestabilshed in an EAS reaction?

through SUBSTITUTION

What is the source of I in the EAS reaction?

(iodination of salicylamide)

Sodium iodide

(NaI)

For the iodination of salicylamide:

What is the purpose of bleach (NaOCI)

aka 6% hypochlorite solution

it is the oxidizing agent to react with NaI producing I+ in solution

Why do you cool the solution before the EAS reaction?

to slow the reaction rate and avoid unwanted secondary reactions

When and why is aq. sodium thiosulfate added to the EAS reaction?

At the end

the purpose of sodium thiosulfate is to react with the leftover, unreacted I+ in solution

also regenerates aromaticity by deprotonating the ring

In amide synthesis of acetophenetidin, how is the insoluble impurity of activated carbon removed?

through hot gravity filtration

for solid-liquid extraction:

solid CO2 _________________ and causes pressure buildup in tube so gaseous CO2 becomes liquid

sublimes

*heating tube speeds up process

for extraction:

organic compounds contain functional groups that can be ___________________ so that the compound becomes water soluble

ionized

for extraction:

weak bases will extract ______________

and strong bases will extract ___________

weak bases will extract strong acids

and strong bases will extract weak acids

for extraction:

what does the carboxylic acid react with?

what does the phenol react with?

carb acid- weak base sodium bicarb.

phenol- strong base NaOH

What must take place in extraction after the desired compound has been extracted into the aqueous phase?

neutralization

to regenerate the neutral compound

How do we perform neutralization in the extraction lab?

10% HCl is added to the aqueous layer containing the ionic species, converting it back to the neutral carboxylic acid (pH around 2)

describe the intermediate in the EAS reaction

the intermediate formed in EAS is a charged species stabelized be resonance

what is the overall reaction for the EAS experiment?

salicylamide --------------> Iodosalicylamide

reagents: NaI + NaOCl + ethanol

What is the purpose of using HCl in the EAS reaction?

to precipitate out the product iodosalicylamide

How do polar mobile phase bond with the solid phase in TLC?

Hydrogen bonding

what is the eluent in TLC?

the solvent that is used for the mobile phase

What is an ideal solvent for TLC?

a solvent system that moves the target compound about 1/3 of the total solvent path

Rf value between .25 and .35

define melting point

the temperature at which the solid phase is in equilibrium with the liquid phase