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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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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!loride
Acetylene 7en+ene(; )
1exane(; )
tyrene(; )
( drops o# )* SO+U,IO- OF B$O&I-EI- &E,./+E-E '.+O$I0E
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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!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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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!loride4Unsaturatio
n5
Acetylene(4)
7en+ene(#)
1exane(#)
tyrene(4)
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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!loride
ReactionMechanism
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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!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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Test for*nsaturation
$eaction o#unsaturatedcompounds
%it! Brominein &et!ylene
'!loride
General Mechanism:
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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!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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Test for*nsaturation
$eaction%it! Brominein &et!ylene
'!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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Test for*nsaturation
Baeyer,est #or
Unsaturation
Acetylene 7en+ene(; )
1exane(; )
tyrene(; )
( drops o# 6* AQUEOUS SO+U,IO- OF7&nO
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Test for*nsaturation
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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Test for*nsaturation
Baeyer ,est#or
Unsaturation
Acetylene(4)
7en+ene(#)
1exane(#)
tyrene(4)
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Test for*nsaturation
Baeyer ,est#or
Unsaturation
Reaction Mechanism
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Test for*nsaturation
Baeyer ,est#or
Unsaturation
General Mechanism:9
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Test for*nsaturation
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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Test for*nsaturation
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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Test for*nsaturation
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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Test for*nsaturation
Ignition ,est
Acetylene 7en+ene(. )
1exane(. )
tyrene(. )
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Test for*nsaturation
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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Test for*nsaturation
Ignition ,est4Unsaturatio
n andAromaticity5
Acetylene(4)
7en+ene(4)
1exane(#)
tyrene(4)
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Test for*nsaturation
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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Test for*nsaturation
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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Test for Acidityand 7asicity
Ag-O( ,est
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Test for Acidityand 7asicity
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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Test for Acidityand 7asicity
SilverAcetalde!yd
e ,est
,ollen9s
$eagent:-E ?1/
.M .Ag?8/
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Test for Acidityand 7asicity
SilverAcetalde!yd
e ,est
,estSample
1isible $esult
Structure2#or
mula o#compoundresponsible#or visible
result
Acetylene
loudy hitesolution ithyello crystals
Ag..
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Test for Acidityand 7asicity
SilverAcetalde!yd
e ,est
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Test for Acidityand 7asicity
SilverAcetalde!yd
e ,est
• @resence of terminal al"yne• diamminesilver(%) cation
(UAg(?1/).V4) Tollen2s reagent• ince this test only or"s for
al"ynes ith a hydrogen atomattached to a triple#bonded carbon,
this test could be used fordierentiating terminal al"ynes ithal"enes
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&et!odology! Test for Al"yl 1alides
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Test for Al"yl1alides
Alco!olicAg-O( ,est
P;ethanol
.M - min!
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,est Sample1isible$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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Test for Acidityand 7asicity
Alco!olicAg-O( ,est
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Test for Acidityand 7asicity
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