all labs

stereochemistry

involves the study of molecules in 3D space

stereoisomers

isomers that differ ONLY in spatial arrangement of atoms

bond angles of tetrahedral atom

109.5 degrees

chiral center

carbon atom with 4 different groups bonded to it

chemical and physical properties of enantiomers vs. diastereomers

• enantiomers

  • almost identical chemical and physical properties

  • differ in stereochemistry

• diastereomers

  • differ in stereochemistry, chemical properties, and physical properties

eclipsed vs. staggered conformers

• eclipsed - hydrogens brought as close together as possible

  • lower energy and more stable

• staggered - hydrogens are far away from one another

  • higher energy and less stable

2 preferred conformations of a cyclohexane

chair and boat

• chair is ore stable

• in chair conformation, all C-H bonds are either axial or equatorial

which carbon is achiral

• carbon B

which of the following are the two chiral structures for 1-chloro-2-bromopropane

I and II

are the two following structures identical, enantiomers, stereoisomers, structural isomers?

• stereoisomers and structural isomers

are these identical, enantiomers, stereoisomers, and/or structural isomers?

structural isomers

• they show different bonding

are these structures identical, enantiomers, stereoisomers, and/or structural isomers

• enantiomers and stereoisomers

  • since they are mirror images of each other

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

• since they are not superimposable and not mirror images of each other

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

• sincee they are not superimposable and not mirror images

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

enantiomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

enantiomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

enantiomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

diastereomers and stereoisomers

are these structures identical, enantiomers, diastereomers, stereoisomers, and/or structural isomers?

identical

which of the alkenes is in its Z geometric isomer form?

C

which of the following are axial bonds on the cyclohexane

B and D

which of the following is a correct statement

1. bonds A and C are 1,2-cis

2. bonds A and B are 1,3-cis

3. bonds C and B are 1,3-cis

4. bonds A and D are 1,3-trans

5. bonds C and D are 1,2-trans

4. bonds A and D are 1,3-trans

why does the crude caffeine isolated from the tea have a yellowish or greenish tinge (colour)?

because the presence of small amounts of flavonoid pigments and chlorophyll (which have a brown colour) are also extracted

There is an alternative procedure for removing the tannins and gallic acid which involves heating the tea leaves in an aqueous mixture containing calcium carbonate. Calcium carbonate reacts with the tannins and gallic acid to form insoluble calcium salts of these acids. If this procedure were used which of the following additional steps would be needed in order to obtain an aqueous tea solution?

filter the extract to isolate an aqueous tea solution from the insoluble salts

• because tannis and gallic acid react with calcium carbonate to form insoluble salts

The extraction of 8.0 g of a particular organic compound dissolved in 100 ml of water into diethyl ether proceeds with a distribution coefficient of 5. How much of the compound is extracted after three separate extractions using 50 ml of diethyl ether each time?

7.8 g of solute is extracted from the aqueous phase

The extraction of 8.0 g of a particular organic compound dissolved in 100 ml of water into diethyl ether proceeds with a distribution coefficient of 5. How much of the compound is extracted after one extraction using 150 ml of diethyl ether?

one extraction with 150mL of diethyl ether extracts 7.1 g of solute

tannins (and 2 major types)

a water soluble component of tea leaves

• have 2 major types:

  • group with esters of gallic acid and glucose

  • group of condensation polymers of catechin of varying sizes

is ethyl acetate a low or high boiling point liquid

low boiling point

why was sodium carbonate added? (give 3 reasons why)

• as a base, sodium carbonate converts tannins and gallic acids to salts so they are more soluble in water

  • caffeine can be extracted into the organic phase in a purer form

• a base ensures the caffeine is non-protonated so that it will be more organic soluble for the extraction

• salting out

  • by saturating the aqueous phase with any salt, extraction efficiency of the organic solvent for an organic solute will be increased

formula for calculating for partition (distribution) coefficient

K = C2 / C1

example of calculating distribution coefficient

extraction of 8.0g of a particular compound dissolved in 100mL of water into diethyl ether proceeds with a distribution coefficient of 5. Demonstrate that three 50mL extractions yields 7.8g of the compound extracted into ether, while one 150mL extraction yields 7.1g

(FLIP CARD FOR ANSWER)

check photo

general equation for the hydrolysis of the tannins that are esters of gallic acid and glucose

• (DONT NEED TO BALANCE THE EQUATION)

• indicated reactants and products by structure

check photo

caffeine structure

check photo

draw structure of tannins of esters of gallic acid and glucose (and draw catechin)

what does this graph tell us about extraction of caffeine

• shows us that caffeine' is extremely soluble at boiling temp. (100*C)

  • caffeine’s solubility in water is temp, dependent

  • which is why we boil the compound in water in order to dissolve caffeine

criteria for successful recrystallization

• compound to be purified must be:

  • soluble in hot solvent

  • insoluble in cold solvent

• impurities must be either:

  • soluble in cold solvent

    • so that it will remain in the filtrate during cold filtration while compound to be purified is isolated on the filter paper

  • OR insoluble in hot solvent

    • so that it will remain on filter paper during hot filtration while the compound to be purified remains in the filtrate

During hot filtration of a mixture of crude product (acetanilide, sand and salt) dissolved in hot solvent (water) it must be kept warm/hot because:

the desired product (acetanilide) will crystallize before passing through the filter paper if the mixture is cold

How much acetanilide (Solubility of acetanilide is 5.5 g/100 ml water at 90 °C, solubility of acetanilide is 0.53 g/100 ml water at 0 °C) is recovered from 5 g of impure acetanilide (containing 3 g of acetanilide, 1 g of salt and 1 g of sand) when it is heated (dissolving the salt and acetanilide) and filtered to remove the sand and then cooled (recrystallizing the acetanilide and keeping the salt dissolved) and filtered to retrieve the acetanilide? (Assume a constant 100 ml recrystallizing volume)

• AND HOW MUCH ACETANILIDE IS DISCARDED?

2.47 g

How much acetanilide (Solubility of acetanilide is 5.5 g/100 ml water at 90 °C, solubility of acetanilide is 0.53 g/100 ml water at 0 °C) is recovered from 8 g of impure acetanilide (containing 6 g of acetanilide, 1 g of salt and 1 g of sand) when it is heated (dissolving the salt and acetanilide) and filtered to remove the sand and then cooled (recrystallizing the acetanilide and keeping the salt dissolved) and filtered to retrieve the acetanilide? (Assume a constant 100 ml recrystallizing volume)

4.97 g

can acetanilide be separated from the impurities (sand, salt, sucrose, and sawdust)

No, salt, sucrose, and acetanilide will all remain in the filtrate

• thus, acetanilide will not be separated

does hot or cold filtration removes sand, sawdust, salt, and/or sucrose?

• hot filtration removes:

  • sand, sawdust

• cold filtration removes:

  • salt, sucrose

2 major reasons for measuring melting point

• to identify a compound

• to give an indication of a compound’s purity

what holds the molecules in a solid organic compound together

intermolecular forces that bind individual molecules into a crystal lattice

why will rinse-water wash away some of the product (from the reaction of p-phenetidine with cyanate)

due to amine solubility

what is the solubility of acetanilide at 90*C and 0*C

• at 90*C

  • 5.5 g / (100 mL of water)

• at 0*C:

  • 0.53 g / (100 mL of water)

what is the solubility of salt at 0*C

35 g / (100 mL of water)

recrystallization and why its important

used to purify crude solid compounds by removing impurities

describe recrystallization procedure

• principle: organic solids are a lot more soluble in hot solvents than in cold solvents

• steps:

1. dissolve impure solid in a small amount of hot solvent

2. hot filter to isolate from insoluble impurities

3. cool slowly to room temp. then place on ice to form crystals

• pure crystals form while soluble impurities remain in the liquid

4. cold filter (using a Buchner funnel) to isolate the pure crystals from the liquid

why a lot of dulcin might be lost during recrystallization

2 possible errors:

• using excess solvent

  • keeps too much compound dissolved even when its cold

• washing crystals with warm solvent

  • this redissolves the recovered crystals

how can loss of dulcin from recrystallization be minimized?

remember the 3 most important rules:

1. dissolved crude solid in minimal volume of hot solvents hot

2. allow flask to cool SLOWLY at room temp. before icing

3. wash the final crystals with minimal amount of ice-cold solvent

dulcin is known to be an artificial sweetener but it is not used as one today. Why not?

it is chemically modified in the body to p-aminophenol which is toxic

Draw ethanol

What’s the overalll reaction for fermentation to ethanol

What is ethanol best known as (not in lab manual)

A type of alcohol in beverages, solvent for thermometers and as fuel

What are the three fold representations of matter (not on lab manual)

1. Macroscopic

2. Microscopic

3. Symbolic level

In terms of the three folds of matter representation describe ethanol on all levels (not in lab manual)

1. Macro - bottle of alcohol

2. Micro - distillation process of ethanol and water

3. Symbolic - using chemical symbols, formulas and equations to describe the reaction

What occurs when you ferment sugar

Sucrose converts to ethanol and carbon dioxide, carried out by yeast and tap water

What is fermentation to ethanol

Series of reactions, each requiring an enzyme as a catalyst, certain ions and co catalysts

Distillation

Process used for the separation of components of a liquid mixture, exploiting difference in boiling points of the components

• boiling liquid and condensing vapours at different temperatures results in seperation of liquids

• yields one theoretical plate

2 differences between distillation of a pure vs mixture liquid

• pure liquid has constant boiling temperatures while mixture has constantly rising temperature

• Pure liquid distillation also gives pure distillate where as mixture has changing composition of the distillate

Fractional distillation

• vapour has to rise through a fractioning column before entering the distillation head

• The fractionating column has a large internal surface area for the recondensation and redistillation of vapour

• Yields a seperation of several theoretical plates

What’s the standard yeast viable that should be resulted from the experiment

12-14%

Formula for % atom economy (AE)

AE% = ( molar mass of product / molar mass of all reactant) 100

Formula for RME

1. Based on mass

RME = (actual mass of desired product / total mass of reactants) 100

2. Based on yield and atom economy

RME = atom economy x percent yield / 100

Steps to calculating mols of ethanol and yeast viable

1. Convert sugar mass → mols

2. Mols sugar x 4/1 = mols ethanol (mol ratio)

3. Mols ethanol → grams of ethanol

4. Yeast viable = (grams of ethanol / vol h2O (mL) ) x 100

The maximum ethanol production possible during fermentation of 55g of sucrose in 250mL of water is…

29.6g

The maximum ethanol production possible during the fermentation of 75 g of sucrose in 250 ml of water is:

30.0g

When making a graph for boiling points, density and ethanol content what is on each axis

X - %ethanol

Y left side - boiling point celcius

Y right side - density g/ml

A 210 ml sample of the original ferment was collected which had a density of 0.979 g/ml. The ethanol content (in grams) of this sample is:

29.4g

A 38.0 ml sample of the simple distillate was collected which had a density of 0.969 g/ml. The ethanol content (in grams) in the simple distillate is:

7.98g

A 6.0 ml sample of the second fraction of fractional distillation was collected which had a density of 0.960 g/ml. The ethanol content (in grams) in the fractional distillate sample is:

1.62g

When is ethanol content highest

First fraction collected from fractional distillation

According to the diagram, reading the hygrometer what’re the density indicated at position a, b and c

A- 0.813g/ml

B- 0.830g/ml

C-0.879g/ml

Using the information, determine ethanol content in % and in g for each fraction collected. Assuming starting amount of 55g of sucrose, calculate yield and RME for ethanol in each of the ferment, simple distillate and combined fractional distillates. Also comment on ethanol content as a function of the distillation procedures employed

Idk… let’s figure it out tgt…

Name the alcohols used from lead to most toxic to the lettuce seeds

Methanol <isopropanol < ethanol

• ethanol most toxic

• Methanol least toxic

Relative to humans, are the toxicity results the same? Using this data how can we estimate human toxicity

No, the least toxic to humans which is ethanol is the MOST toxic for plants and vice versa for methanol

• thus to estimate human toxicity we know that if its more toxic to plants than it’s safe for humans

What is the goal for green chemistry

Design of materials and processes that are inherently safer for human health and the environment

Bruh

Chromatography

General term that refers to a number of related techniques used for analyzing, identifying or separating compounds

What do all chromatographic techniques have in common

A liquid or gaseous solution of the sample called the mobile phased that gets moved through a liquid or solid adsorbent called the stationary phase

• the greater the tendency of the chemical to remain in the mobile phased, the faster the chemical will move during the chromatographic seperation

Advantages of TLC

Sensitive, fast, simple and inexpensive

What are the similarities and differences between o-nitroaniline and p-nitroanaline

• Both have functional groups NH2 and NO2

• O-nitroanaline has intramolecular hydrogen bonding due to their functional groups being adjacent to one another thus its less polar compared to p-nitroanaline which are on opposite sides thus is more polar

On the TLC sheet if the dot doesnt move much, is it polar or less polar and why

The closer it is to the origin, the less polar the solvent is because that means it wasnt polar enough to interact with the solute and move it up, the solute is more polar that’s why it interacts with the stationary phase and remains close to the origin

On the column chromatography, does the polar substance come out first or last

Polar substance remains at the top, non polar comes out first

What does the RF value tell us about its polarity

Larger rf value means less polar

Formula for RF value

Rf = distance travelled by solute over distance of solvent

According to the TLC plate, the Rf for solute 2 is

A) 0.19

B) 5.26

C) 0.19 CM

D) 5.26 CM

A) because low Rf means less movement and Rf has no unit

Which of the solutes is least polar

5, because its non polar character decreases its affinity for the polar stationary phase thus making it move up the TLC plate faster

What can be concluded if solutes have different RF values

They are different compounds