experiment 8a oral report

8/18/2019 Experiment 8A Oral Report

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Experiment 8AQualitative Analysis (A to D)


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Objectives

The objectives of the experiment includetesting the samples for the determination ofdierent functional groups, as ell as the

positions of these functional groups in thecompound! Thus, the exact structure of thecompound could be determined!

The saturation and aromaticity of compoundsare also tested in this experiment, as ell as theacidity, basicity and presence of al"yl halides inthe compounds!


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IntroductionQualitative Analysis (A to D)


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Qualitative analysis

#is a set of procedures and techni$ues used toidentify and $uantify the chemical composition ofa given sample of a substance! %t relies on certainchemical reactions to detect particular functional

groups in a compound!


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Qualitative analysis

There are four general schemes of analysisuseful for identifying the nature of an un"noncompound!

• preliminary test,• physical constants• solubility tests• functional group classi&cation test

''This experiment hoever only focuses on theon the tests for identifying the functional groups a

compound is classi&ed!


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Functional groups

#are classi&ed chemical groups attached to aparent chain, hich could react and determine

the chemical and physical properties of acompound, and the reactions that are

characteristic of certain compounds


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Functional groups

A visible reaction indicates the presenceof a functional group! The presence offunctional groups is identi&ed by reactingthe compound to a reagent hich gives aspeci&c visible result! ome of these testsinclude

• *nsaturation• Aromaticity• Acidity and basicity•

Al"yl halides!


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Saturated compound

#is a compound that has single bonds only,ith no delocali+ing electrons, and containsas many hydrogen atoms as possible!

ompounds of this "ind are called al"anes!


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Unsaturated compound

#contains double or triple bonds, and thushas less hydrogen atoms than a saturated

compound of the same number of carbonatoms! ompounds of this type are calledal"enes, for those ith double bonds, and

al"ynes, for those ith triple bonds


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Aromaticity

#is a chemical property in hich aconjugated ring of unsaturated bonds, lone

pairs, or empty orbitals exhibit astabili+ation of conjugate alone!

#refers to the property of compounds to

release aroma or odor!


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Aromaticity

There are certain re$uirements for acompound to be aromatic

(-)yclical(.)planar

(/)has delocali+ed, conjugated double or pibonds(0)follos 1uc"el2s rule here the number

of pi electrons 3 0n 4 .


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Acid

#is de&ned as a compound hose p1 is less than5, and can turn blue litmus paper to red, such asacetic acid or vinegar!#has three types

• Arrhenius (increases the concentration of 14 ions in an a$ueous solution)

•

6eis (accepts electron pairs)• 7ronsted#6or acids donates rotons


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Base

#is de&ned as a compound hose p1 is greaterthan 5, and can turn red litmus paper to blue,such as sodium hydroxide or lye!

has three types • Arrhenius (increases the concentration of

81# ions in an a$ueous solution)• 6eis (release electron pairs)• 7ronsted#6ory acids (accepts protons)


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Alyl !alides

#have a general form of 9#: here 9 istypically an al"yl group and : is a halogen

replacing one of the hydrogens!


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Qualitative AnalysisA! Test for *nsaturation


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Test for*nsaturation

"reparationo# Acetylene

a.

(s) 4 .1.

8(l) .

1.

(g) a(81).

(a$)


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$eaction%it! Brominein &et!ylene

'!loride

Acetylene 7en+ene(; )

1exane(; )

tyrene(; )

( drops o# )* SO+U,IO- OF B$O&I-EI- &E,./+E-E '.+O$I0E


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'!loride

,estSample

1isible $esults Structure2Formula o# 'ompoundresponsible #or

t!e visibleresult

Acetylene ormation of dar"orange layer

(bottom) and lightorange layer (top)

Ben3ene ?o change (7lood

red solution)

Styrene


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'!loride4Unsaturatio

n5

Acetylene(4)

7en+ene(#)

1exane(#)

tyrene(4)


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'!loride

ReactionMechanism


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'!loride

The reaction involved iselectrop!ilic addition (halogenation)ith 7r. acting as the electrophile,

because the• bromine adds to each carbon of the

bond,• pi bond converts into a sigma bond• compound become saturated!• an 81 group is then added to each

carbon at each end of a multiplebond

• the multiple bonds become

saturated!


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$eaction o#unsaturatedcompounds

%it! Brominein &et!ylene

'!loride

General Mechanism:


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'!loride

• 7r. 4 3 dibromoal"ane

•

7r. 4 B

tetrabromoal"ane

Chen this reaction occurs• molecular bromine is consumed• its characteristic dar" red#bron

color disappears (if bromine is notadded in excess)

• positive test for unsaturation!


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'!loride

4dra%bacs5

• ?egative results if electron#ithdraing groups are present inthe vinylic position! @osition slosdon bromine addition to the point

that a negative test is erroneouslyproduced!

• tertiary amines (li"e pyridine) formperbromides upon treatment ith

bromine hich can lead to falsepositive tests• aliphatic and aromatic amines

discharge the bromine color ithoutthe evolution of 17r gas even ith

the absence of multiple bonds!


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Baeyer,est #or

Unsaturation

Acetylene 7en+ene(; )

1exane(; )

tyrene(; )

( drops o# 6* AQUEOUS SO+U,IO- OF7&nO


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Baeyer ,est#or

Unsaturation

,estSample

1isible $esults Structure2Formula o#

'ompoundresponsible

#or t!e visible

resultAcetylene

Dar" bronprecipitate in

bron solution

En8.

Ben3ene >ormation of redviolet layer

(bottom) and redlayer (top)

En80

#

Styrene 9ed bronprecipitate inclear solution

En8.

.exane >ormation of

violet layer(bottom) and En80

#


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Baeyer ,est#or

Unsaturation

Acetylene(4)

7en+ene(#)

1exane(#)

tyrene(4)


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Baeyer ,est#or

Unsaturation

Reaction Mechanism


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Baeyer ,est#or

Unsaturation

General Mechanism:9


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Baeyer ,est#or

Unsaturation

• 9edox reaction• 8xid! Agent FEn80 (e# acceptor)• 8xidation En80

# (purple soln) En8.

(bron ppt)• The disappearance of the characteristic

color of the permanganate ion is thenconsidered a positive test for unsaturation!


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Baeyer ,est#or

Unsaturation

•Does not or" on al"anes and aromaticcompounds

• 7en+ene and hexane did not sho thebron precipitate because of ben+ene2saromatic stability and hexane2s lac" of pi

bonds!


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Baeyer ,est#or

Unsaturation

4dra%bacs5

• 8ther easily oxidi+ed compounds containing

other functional groups also give a positivetest! Eost aldehydes, phenols, aryl amines,impure alcohol, formic acid and its esters,ould give a positive test!

• 7ron precipitate often fails to form, instead

turning the solution reddish#bron, becauseater insoluble compounds formed aredissolved in ethanol, methanol, or acetone


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Ignition ,est

Acetylene 7en+ene(. )

1exane(. )

tyrene(. )


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Ignition ,est

,estSample

1isible$esults

Structure2Formula o#

'ompoundresponsible

#or t!e visibleresult

Acetylene 7lue#yelloGame H

soot

(s) 4 8.(g)

Ben3ene Iello

orangeGame H

soot

(s) 4 8.(g)

Styrene 8rangeGame H

soot

(s) 4 8.(g)

.exane Iello 8.( )


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Ignition ,est4Unsaturatio

n andAromaticity5

Acetylene(4)

7en+ene(4)

1exane(#)

tyrene(4)


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Ignition ,est

General Mechanism:

Equation 5

AromaticH*nsatd 4 8.(g) J (s) 4 8.(g)

4 1.8

Equation 6

Aliphatic 4 8.(g) J 8.(g) 4 1.8


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Ignition ,est

• Dierentiate aromatic unsaturated

compounds from aliphatic hydrocarbons• @ositive yello sooty Game K the yello

color of the Game is due to the presence ofcarbon hile the soot is a result of thedeposition of a carbon from multiple bonds!

•

*nsaturated (positive) acetylene, ben+eneand styrene (e$! ;)• aturated (negative) hexane (e$! L)


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&et!odology7! Test for Aromaticity


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Test forAromaticity

-itration

onc! 1?8/ -M

drops

onc! 1.80 -M

drops

;m6 1.8(ice cold)

;Mo

;mins!

Toluene -Mdrops


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Test forAromaticity

-itration

,estSample

1isible$esults

Structure2Formula o# 'ompoundresponsible #or

t!e visible result

,oluene 8ily 6ight Iello color ontop of solutionhich is similar

to oil atermixture andsmells li"e

rugby


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Test forAromaticity

-itration

General Mechanism:


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Test forAromaticity

-itration

Reaction Mechanism


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Test forAromaticity

-itration

• electrophilic aromatic substitution• @ositive yello oily solution ith evolution

of odor

nitrotoluene• ulfuric acid as used to protonate the nitric

acid, hich then dehydrates to form thehighly electrophilic nitronium ion to be usedin the electrophilic substitution reaction! The

nucleophilic double bond attac"s the doublebond of the ben+ene ring attac"s thenitronium ion to produce mostly ortho# andpara#nitrotoluene


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Test forAromaticity

+e $osen,est

; drops 6e 9osenreagent

; drops xylene

%?6%?


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Test forAromaticity

+e $osen,est

General Mechanism:


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Test forAromaticity

+e $osen,est

• 6i"e nitration, but formaldehyde instead ofnitric acid

•


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&et!odology! Test for Acidity and 7asicity


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Test for Acidityand 7asicity

Ag-O( ,est

,est

Sample Observation

Acetic acidloudy hite solutionclear

"!enolloudy reddish#bronsolution

Aniline 6ight bron solutionBen3oicacid lear solution


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Ag-O( ,est


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Ag-O( ,est

• @resence of strong acids• The relative acidity and basicity of

organic chemistry can bedetermined by a general rule

9elative acidities

9881 N 181 N 981 N 1 R 1 N ?1 N 919elative basicities

988#

S 18#

S 98#

S 1 R #

S ?1.#

S 9#

• Acetic ben+oic positive• @henol aniline negative


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SilverAcetalde!yd

e ,est

,ollen9s

$eagent:-E ?1/

.M .Ag?8/


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SilverAcetalde!yd

e ,est

,estSample

1isible $esult

Structure2#or

mula o#compoundresponsible#or visible

result

Acetylene

loudy hitesolution ithyello crystals

Ag..


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SilverAcetalde!yd

e ,est


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SilverAcetalde!yd

e ,est

• @resence of terminal al"yne• diamminesilver(%) cation

(UAg(?1/).V4) Tollen2s reagent• ince this test only or"s for

al"ynes ith a hydrogen atomattached to a triple#bonded carbon,

this test could be used fordierentiating terminal al"ynes ithal"enes


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&et!odology! Test for Al"yl 1alides


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Test for Al"yl1alides

Alco!olicAg-O( ,est

P;ethanol

.M - min!


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,est Sample1isible$esult

Structure2#ormula o#

compoundresponsible#or visible

resultEt!ylc!loride

Chitelayer

Agl

Et!ylbromide

Eil"yhite(yello)

ppt

Ag7r

Et!yl iodide Iello ppt Ag%t;butylc!loride

rayishhite ppt

Agl, t#butylchloride

s;butylc!loride

rayishhite ppt

Agl

'!loroben3ene

learsolution

?HA (noreaction

Test for Al"yl1alides

Alco!olicAg-O( ,est


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Alco!olicAg-O( ,est


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Alco!olicAg-O( ,est

• @resence of halogens• t #butyl chloride N s#butyl chloride• hloroben+ene clear solution

(negative)


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uide Questions

Question =6

What test/s

could e usedto di!erentiatesaturated andunsaturated

h"drocarons#E$plain ho% the

test coulddi!erentiate

them#

&ns%er:

The decoloration of bromine solution test and7aeyer test dierentiate saturated from unsaturatedhydrocarbons! %n decoloration of bromine solutiontest, if the test compound is unsaturated, the red#bron color of the a$ueous bromine solution rapidlydisappears! 7romine adds to each of carbon of thebond then the pi bond converts into a sigma bondand thus become saturated!

%n the permanganate test, unsaturatedcompounds reduce the purple permanganate ion(En80

#), forming a precipitate of bron manganese

(%O) oxide (En8.)! This then indicates that if acompound is positive for the presence ofunsaturation, potassium permanganate ill oxidi+ethe multiple bond resulting to the removal of itspurple color! This test ill not give a positive result ifthe sample tested is an al"ane or an aromatic

compound!


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uide Questions

Question =)

'o al("nes)i*e all tests%hich al(enese$hiit# Whattests could e

used todi!erentiate

them#

&ns%er:?o! The silver acetylide test could beused to dierentiate beteen anal"yne and an al"ene! %t only producesa positive test (formation of a silverprecipitate) on al"ynes!


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uide Questions

Question =(

+llustrate %ithequation the

reaction o, r 2

in meth"lenechloride %ithacet"lene.

&ns%er:

.1. 4 .7r. ##N .1.7r0


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uide Questions

Question =

'oes tolueneeha*e in thesame %a" li(e

the other

unsaturatedh"drocarons#

Wh"#

&ns%er:?o! Toluene does not behave in the same ayli"e other unsaturated hydrocarbons since it isan aromatic compound and because of thepresence of its ben+ene ring! The stable

structure due to resonance is less reactivethan the other saturated hydrocarbonsbecause the electrons in its double bonds aredelocali+ed and hence move freely about thering! The shared electrons in the saturated

bonds of the aromatic compound ring preventa$ueous bromine solution from reacting iththem!


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uide Questions

Question =?

ho% themechanism ,orthe ,ollo%in)reactions:

(a) ?itration(b) 6e 9osen

Test

4a5 -itration

4b5 +e $osen ,est


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uide Questions

Question =@

Gi*e theequation

in*ol*ed in thereaction o,

acet"lene %ithammoniacalsil*er nitrate.

&ns%er: .1. 4 Ag(?1/)?8/ .Ag. 4 1?8/


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uide Questions

Question =

E$plain %h" the

terminalh"dro)en inacet"lene is

acidic %hen in,act the

electrone)ati*e*alues o,h"dro)en and

caron arealmost the same.

&ns%er:

Terminal al"ynes are unusualhydrocarbons for they can bedeprotonated using an appropriatebase to generate carbanion! This is anacidic situation since terminal al"ynes

have an sp#hybridi+ed orbital ith ;Ms character, meaning it is a highlyelectronegative orbital, the electronpair shared ith 1(terminal and

directly attached to the unsaturation)is tightly held by the nucleus of ma"ing it electrostatically stabili+ed!o, The 14 no, to relieve the tensioncan leave o the chain! ince this is aositive 1 then terminal al" nes are


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uide Questions

Question=66

Wh" is theorder o,

reacti*it" o,al("lhalides

to%ardalcoholic sil*er

nitrate321#

&ns%er: Tertiary carbons formed by the

hetrolysis of al"yl halides are morestable due to #1 hyperconjugation!

The positive charge is distributed to agreater number of surrounding

hydrogen atoms compared to thesecondary and primary al"ylhalides! The primary carbonium ion is the leaststable since its positive charge isconcentrated only to the carbon atom!Also, ith increasing branching theelectron density of a moleculeincreases and the alcoholic silvernitrate hich is an electron pair

acceptor tends to be attracted more to


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uide Questions

Question =6)

+n the sil*ernitrate test ,orhalides e$plain%h" alcohol isused as the

sol*ent ,orsil*er nitrate

and not %ater.

&ns%er

Cater is not used as the solventbecause it is highly polar consideringthat the reaction proceeds ith ahydrocarbon!


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' l i


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'onclusion

• The functional groups of compounds could bedetermined by causing the reaction of thesamples ith certain "non compounds thatfollo a general mechanism! ome functionalgroups have dierent reactions and observableresults ith others, and these properties could beused to determine the identity of the compound!


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$ #


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$e#erences

Aromaticity! (n!d!)! 9etrieved fromhttpHHmhhe!comHphyssciHchemistryHcareyHstudentHolcHgraphicsHcareyM0ocHrefHch--aromaticity!html

experiment 8a oral report

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