engineering chemistry unit3

7/21/2019 Engineering Chemistry Unit3

1/39

Stereoisomerism

Optical isomerism

Plane polarized light

Condition for optical activity: -

The necessary condition for a compound to exhibit optical activity is that it should be asymmetric or

dissymmetric and geometric structure of the molecule should not super-imposable on its mirror

image. Further it should not contain any of the following elements of symmetry.

Elements of symmetry

Plane of symmetry: -

plane which divides the molecules into e!ual and identical halves which are super imposable mirror

images of each other.

These compound are called meso and optically inactive.

a

b

b

c

a

c

2. Centre of symmetry: -"t is an imaginary point in the centre of molecule from which if lines are

drawn on any group# on both the sides two and e!ual distance then it divides the molecules into two

e!ual halves which are mirror images of each other.


2/39

C C

CC

H

COOH

H

COOH

H

COOHCOOH

H

3. Alternating axis of symmetry: -

"t should posses one or more chiral carbon atom.

$ight direction% - dextro rotatory &'( &d(

)eft direction% - )eavo rotatory &-( &)(

*xample of optically active compound

1. +ontaining one chiral +-atom% -

OH C

COOH

CH3

H H C

COOH

CH3

OH

$acimic ,ixture% - n e!uilibrium mixture of dextro-rotatory )ebo rotary. "t is optically inactive.

. /hat is optical isomerism0

Show optical isomer of lactic acid.

2. Containing two chiral c-atom: -


3/39

OH

OHC

C

COOH

H

COOH

H H

HC

C

COOH

OH

COOH

OH H

OHC

C

COOH

H

COOH

OH

( + d ) T a r t a r i c a c i d ( + l ) T a r t a r i c a c i d m e s o T a r t a r i c a c i d

Enantiomer and diasteromers: -

*nantiomers are the optically active compound having no super imposable mirror images.

1iastereomers are optically inactive compound which are not mirror images of each other.

OH

Br

CH3

H

CH3

H H

H

CH3

Br

CH3

OH

( + ) d 1 ( - ) l 2

H

Br

CH3

H

CH3

OH OH

H

CH3

Br

CH3

H

( + ) d 3 ( - ) l 4


4/39

+ompound 2 3# 4 5 are enantiomer.

+ompound 2 4# 3 5 are diastereomers

Only one +hiral +-atom present then no existing diasteromers.

The physical or chemical properties of enantiomer same except% - the angle of rotation toward left or

right.

The physical properties of diastereomer are di6erent and the chemical properties are similar but not

identical.

peci!c rotation: -

The measurement of optical activity is denoted in terms of speci7c rotation. "t is constant for a

compound and is the characteristic properties.

The observed angle of rotation produces by a solution of concentration 2gm8ml ta9en in a tube of

length 2dm &cm(

"#estion: -:ive the example of no carbon chiral atom

$ptical activity witho#t chirality:-

llene derivatives% -

*xample% 2# 4- diphenyl propadiene


5/39

H5C6

C C C

C6H5H

H H

C C C

HH5C6

C6H5

*xp% - "n allene the central carbon is s-p hybridized and the terminal carbon are Sp3 carbohydradized.

The +entral carbon forms two Sp-Sp sigma covalent bonds. The central carbon also has p-orbitals

which are mutually perpendicular and form pi bond with the terminal carbon. s a result the

substituent of one end the molecule is perpendicular to the other. So the compound exists in two

forms which are non super-imposable mirror images. ;ence they are optically active.

3. %iphenyl derivates: -


6/39

3. Presence of bul9y groups at ortho position which prevents the free rotation of two benzene

rings. Therefore the molecular wire prefers a conformation in which rings will be perpendicular

to each other and if it will be devoid of elements of symmetry. /hen both the double bond of

allene are replaced4. Spirans by rings the resulting compound is 9nown as spiro compound or spirans

The double bond may be replaced by 5# > or ? member ring. The two replaced rings areperpendicular to each other and hence substrate ' attaching reagent- product

bC

CH2

C

CH2

Ca

CH2 CH2ba

aC

CH2

C

CH2

Cb

CH2 CH2ab

#&stit#tion reaction: -

The replacement of an atom or group directly attached to carbon in the substrate molecule byanother atom or group is called substitution reaction.

CH3OH + HBr CH3Br + H2O

+ Br2

Br

+ HBr


7/39

'#cleophic s#&stit#tion reaction (' reaction): - Substitution reaction brought about by

nucleophiles is 9nown as nucleophic substitution.

Three parts% - Substrate# =u# Solvent

Substrate% l9yl group# leaving group

,echanism% - S=2and S=3

S=2% @nimolecular reaction#


8/39

S=3%


9/39

CH3 C

CH3

CH3

BrS l o w

CH3 C+

CH3

CH3

Br-+

Step 3

CH3 C+

CH3

CH3

OH -

+ CH3 C

CH3

CH3

OH : OH C

CH3

CH3

CH3

5 0 5 0 ! a c i m i c " i # t $ r e

F a s t

:

tero-chemistry of '1 *echanism

S=2mechanism leads to retention of con7guration and form a racimic mixture

'2 *echanism

C % ++ & C & %

/hen rate of the reaction is proportional to the concentration of substrate as well as nucleophlic # the


10/39

reaction proceeds by a S=3 mechanism.

*echanism: -"t is a one step reaction in which the nucleophie denotes a pair of electrons to the

group# simultaneously the group withdraws the electron pair through the formation of transitory state.

C % ++ &-

& C % %-

& C

T r a ' s i t i o ' s t a t e ' e r t e d * r o d $ c t

Stero chemistry of S=3 ,echanism

S=3 reaction proceeds via inversion of con7guration and forms the invented product &/alden

inversion(

++ OH -

HO C

H

H

Br

H

Br-

OH C

H

H

H

T r a ' s i t i o ' s t a t e ' e r t e d * r o d $ c t

CH3 Br

uestion% - /hy S=3- -reaction gives a inverted product% - due to bac9 side attac9.

S=2 S=3

@nimolecular


11/39

Energy pro!le diagram

'1

:raph

'2

:raph

'arreaction: -('#cleophilic s#&stit#tion reaction in orgomatic system)

The reactions do not occur easily in halogens because +-B bond in heloal9enes. lso the low pair ofelectron in halogens participates in delocalozation with the pi electron of benzene rings. 1rastic

condition such as high temperature high pressure and highly concentrated reagents are used to carry

out =ucleophilic substitution in hello--- The reaction follows elimination addition mechanism via the

formation of intermediate benzyne.

Cl

+ aH 2 aClH i g h t e m p e r a t u r e p r o c e s s

N H3

H2

+

, ' i l i ' e

*echanism of this reaction: -

The reaction ta9e place in two steps% -

tep 1: -The elimination reaction with the formation of benzyne intermediate.


12/39

Cl

H

+ H2- + H3 + Cl

-

B e ' . ' e i ' t e r m e d i a t e

Step 3% - ddition reaction ta9es place% -

+ H3H2

H

Or

+ H3

H2

H

Electrophilic orometic s#&stit#tion reaction: -

/hen substitution occurs in the benzene ring due to the attac9 of an electrophils is called elctrophilic

aromatic substitution reaction.

+ %-

/

+/ %

/ l e c t r o * i l i c r e a e ' t

,echanism% -

tep 1: -Formation of an electrophile


13/39

/ %C a t a l y s t

%-+/

+

/ l e c t r o * i l e

tep 2: - *lectrophile attac9s on bezene ring to form a carbocation intermediate

+

/H

+

/H

+

/H

+

/H

+/

+

C a r b o c a t i o '

tep: 3The carbocation loses a proton to the base to form the 7nal substitution product.

i ' a l * r o d $ c t

/H

+ + %-

/

*xample% - Friedel craft reaction# ;elogination# sulphonation# nitration


14/39

+riedal carft reaction

The reaction in which benzene reacts with al9yle8acylhalide in the presence of catalyst l+l4to form

al9yl8acyl benzene

l9ylation% l9yl halide

+ CH3Cl + ,lCl3

CH3

+ HCl

" e t . l c l o r i d e

,echanism% -

Step 2% -

Step 3

+

CH3H

+

CH3H

+

CH3H

+ CH3Cl

CH3H

+ C a r b o c a t i o n


15/39

Step 4% -

CH3H

+ + ,lCl4-

CH3

+ HCl ,lCl3+

Acylation: -Acylhalide

+ CH3OCl ,lCl3+

COCH3

+ HCl ,lCl3+

Step 2% -

CH3OCl ,lCl3+ CH3CO+

+ ,lCl4-

Step 3% -

CH3CO+

+

CH3COH

+

Step 4


16/39

CH3COH

+ + ,lCl4-

CH3CO

+ HCl ,lCl3+

,alogenation

+

Cl

+ HCl ,lCl3+Cl ClA l C l

3/ F e C l

3

Step 2

Cl Cl + ,lCl3 + ,lCl4-

Cl+

C l o r i ' i $ m i o '

Step 3

+ Cl+

H Cl

+

+

CH3H

+

CH3H

+

CH3H

Step 4


17/39

H Cl

+ + ,lCl4-

Cl

+ HCl ,lCl3+

'itration: -

+ HO 3

O2

+ H2O H2SO4+C o n c . H

2S O

4

tep 1: -

HO 3 + 2H2SO4 O2+

+ H3O+

+ 2HSO 4-

tep 2: -

+ O2+

+

O2H

+

O2H

+

O2H

O2H

+

tep 3: -


18/39

O2H

+ + 2HSO4-

O2

+ H2O H2SO4+

Elimination eaction: -*limination reaction involves the removal of two atoms or grows attached to adCacent carbon atom in

a molecule to produce on unsaturated compound. One of the group of atoms commonly eliminated as

proton and other as an anion.

1ehydration of al9yl halide% -

+ + +CH3CH2

CH2

Br OHCH3

CH

CH2Br OH2

, l c o o l i c

+ + +OH % OH2, l c o o l i c

H

C C

%

C C

1ehydration of lcohol

+ OH2C C

OHH

C CH e a t A c i !

,echanism % -There are two types.

E1*echanism: -Two steps and unimolecular.


19/39

Tertiary al9yl halide

Step 2% The substrate undergo heterolysis to from halide anion and carbocation

C C

H

%

H

S l o w+ %

-

C a r b o c a t i o '

H a l i d e i o '

CH4

C+

C

HH

Step 3 The carbocation rapidly loses a proton to base and forms the al9ene.

C+

CH

HH+

B-

C C

HH

+ HB

" a s t

,olecularityD2 &unimolecular(


20/39

C

CH3

CH3 Br

CH3

CH3 C

CH3

CH2

++ OH -

OH2

E2 *echanism: -


21/39

"n dehydrohalogenation hydrogen is eliminated preferentially from the carbon atom which has less

number of hydrogen atoms and so the highly substituted al9ene is the maCor product.

+ OH -

CH3CH2

CHCH3

Br CH3CH2

CHCH2

CH3CH

CH

CH3

1-b$te'e

2-b$te'e

r e e r r e d * r o d $ c t

H e a t

+ OH -

CH2CH2

CH2CH2CH3

Br 2-*e'te'eH e a t CH3CH2

CHCH

CH3

*limination vs. substitution% -

"n the presence of strong bases &lcoholic EO;( the al9yl halide undergo elimination reaction# whereas

a! EO; wea9 bases favor the substitution reaction.

)ess polar solvent at high temperature favor elimination reaction while more polar solvent at lower

temperature favour the substitution.

"#estion: 1ehydration of alcohols &2# 3- elimination(

lcohols are converted into al9enes in dehydration with the removal of water molecule.

$e!uires the presence of an acid heat


22/39

C OH

CH3

CH3

CH3

H e a t H2

S O4

CH3

C CH2

CH3

T e r t i a r . b $ t . l a l c o o l s o b $ t e ' e

*echanism: -

Step 2

Step 3

This protonated alcohol dissociate into carbocation water

Step 4

+arbocation loses a proton on a base

+#el comstion


23/39

+#el: - fuel is any combustible substance containing carbon as main constituent# which on properburning gives large amount of heat which can be utilized economically for domestic and industry

purpose.

Comstion: -ny chemical process followed by the evolution of light and heat is calledcombustion

+lassi7cation of fuel

2. On the basis of occurrencea. =atural &primary fuel(b. rti7cial &secondary fuel# derived fuel(

3. On the basis of their physical statea. Solidb. )i!uidc. :aseous

Solid /ood# coal# biomass# cattle# dung ca9e

+o9e# charcoal

)i!uid fuels 2. =atural% crude oil

3. rti7cial%


24/39

The total !uantity of heat librated from the combustion of a unit mass8unit volume of the fuel in the

presence of air or oxygen

gnition temperat#re: -The mini or lowest temperature at which the fuel must be so pre heated so that it starts burning

easily is called ignition temperature.

"gnition temperature =ormal# moderate

,oisture content% -)owest

=on combustible metal% - ,inimum

+ombustion rate% -moderate

Product of combustion should not be harmful+ombustion should be controllable

)ow storage cost

*asy to transport

"#estion: - +ompare a demerit merit of solid fuel li!uid fuel

Solid Fuel )i!uid fuel :ases fuel+ost +heap They are costly ery costlyStorage *asy They are stored in

closed container)ea9 proof container

+alori7c value )ow"gnitiontemperature

)owest

,oisture ;igh ,ini


25/39

+ombustion rate )ow ;igh ery high+ombustioncontrol

;ard &diGcult( +ontrol regwire *asy and large bystopping gas supply

Calori!c val#e of a f#el: -

;igher calori7c value8gross calori7c value &;+ or :+(

)ower calori7c value8=et calori7c value &=+ or )+(

"mp. The total !uantity of heat liberated or unit volume of the fuel in the presence of air or oxygen#

when product of combustion are allow to coat at room temperature it is called higher calori7c value.

)+ or =+

The total !uantity of heat liberated from the combustion of unit mass &unit volume( of the fuel in thepresence of air or oxygen when products of combustion are allowed to escape.

nit of heat: -

Calorie: -mount of heat re!uired raising the temperature of 2gm of water by one degree

centigrade


26/39

4ilo Calories: -mount of heat re!uired to raise the temperature of 2 9g of water by one degree is

called 9ilo calorie.

%ritish thermal #nit (%..):-

;eat re!uired to raise the temperature of one pound of water by one degree Fahrenheit

Centigrade thermal #nit (C,)

;eat re!uired to raise the temperature of one pound of water of one degree centigrade

uestion% - fuel sample contains H5I carbon# 2.>I sulphur# ?I =3#>.>I hydrogen and rest oxygen.

;+ of the fuel is H.4>? 9cal8gm. +alculate =+

Solution

5etermination of calori!c val#e

*xperimental determination of bomb calorimeter method


27/39

Theoretical calculation of calori7c value by 1ulongs formula

1iagram

6or7ing

bout J.>32 gm of the fuel sample is ta9en and clean the crucible which is then 7tted in bomb.

7ne ,g-gire touching the fuel is than stretched along the electrode.

The bomb lid is tightly screwed and 7lled with oxygen of about 3> to 4- atm pressure.

The bomb is then placed on copper calorimeter containing the 9nown mass of water.The initial temperature of water is noted after through stirring.

The electrodes are then connected to ? battery to complete the circuit.

The fuel sample burns and heat is librated which is transferred to water.

@niform steering of water is continuous and the maximum temperature is attained is noted.

Calc#lation: -

)et xD mass of fuel samples ta9en in the crucible/D ,ass of water ta9en in calorimeter

/D water e!uivalent of apparatus &+alorimeter steerer# thermometer etc# /K x speci7c heat of

apparatus T2 Dinitial temperature

T3D 7nal temperature

;D ;+ of fuel


28/39

Correction: -

To get more accurate results the following correction must be considered while calculating the

calori7c value.

+#se wire correction: -The heat liberated above includes the heat given out by the ignition of fuse

wire used. ;ence it must be subtracted from the total value.

Acid Correction: -Fuel containing sulphur and nitrogen are oxidized under high temperature andpressure of ignition to form ;3SO5 and ;=O4 respectively. The formation of these acid are exothermic

reaction. So the measured heat also include the heat given out during acid formation. "t should be

deduced from the total value.

Cooling correction: -Time ta9en to cool the water in calorimeter from max temperature is noted

from the rate of cooling &dT8min( and actual time ta9en for cooling &t-minutes( the cooling correction

of dTxt is added to rise in temperature.

Cotton thread correction: -The heat liberated from the cotton thread &if use( is deducted.


29/39

"#estion: - sample of coal containing HLI +# HI ;# 4I ash# when tested in liberated for it + in

bomb calorie meter the following data is obtained weight of coal burnt DJ.Hgm# weight of

waterD?>Jgm

ol#tion: -

heoretical calc#lation of calori!c val#e: -

The calori7c value can be of fuel approximate calculated by noting the amount of the constituent of

the fuel


30/39

The ;+ of the chief combustible constituent of a fuel are% -;ydrogen# carbon# suphur

Oxygen if present in the fuel is assumed to be present in combined form with hydrogen &7xed

hydrogen( in the form of . So the amount of hydrogen a variable for combustionD Total mass of

hydrogen in the fuel- 7xed hydrogen

Since H parts of O3combine with 2 parts of ;3to form L parts of water.

uestion% - coal sample contains +DH>I# ;DHI# SD2I# =D3I# ashD5I. +alculate ;+ and =+


31/39

"#estion: -

Comstion: -+alculation of air !uantities

"#estion: -+alculate the weight and volume of air re!uired for the complete combustion of 2Eg

carbon.

$e!uirement of combustion of 29g +


32/39

"#estion: - Fuel sample +DM>I# ,D>.3I# OD23.32I# =D4.3I# ashD5.>I. +alculate the weight ofair re!uired for the complete combustion of 2 9g of the fuel &coal(

+alculation of O3is re!uired

Solution% -

2. +arbon


33/39

3. ;ydrogen

Coal: -+oal is highly carbonaceous &carbon containing ( matter# that has been formed as a result ofalteration of vegetable matter &plants( under certain favorable condition. "t is composed of carbon

hydrogen nitrogen and oxygen with some other non combustible inorganic metals.

Classi!cation of coal &y ran7

arious types of coal are commonly categorized on the commonly the basis of ran9 of degree of

alteration or coali7cation on the wood.

The process of formation of wood is called coali7cation.

Progressive transformation of wood to anthracite


34/39

5ecrease properties: -

,oisture content# ;ydrogen# =itrogen# Sulphur# Oxygen content# volatile matter

ncrease: -+arbon content# +alori7c value

)ignite% -"t is called brown coal soft and lowest ran9 coal# soft and lowest ran9 coal

%it#mino#s: -+ommon coal

Pitch bac9 to dar9 gray

+arbon% HJ-LJI

,oisture% + N H33-H>JJ 9cal89g

Anthracite: highest ran9 coal below 2JI moisture

L3-LHI weight

)owest moister and volatile matter hardest of all 9ind of coal

Analysis of coal: -

Proximate analysis: -to determine the !uality of coal

*oist#re: -bout 29g coal &7nely produced form ( &air dried( and weighed in crucible &silica(


35/39

8olatile *atter: -

Car&on

Car&on 9,ydrogen: -bout 2-3 gm accurately weighed coal sample is burnt in the presence ofoxygen in a combustion apparatus condition ; of the coal are converted into +O3 and ;3O

respectivelyThese gaseous products of combustion are absorbed respectively in EO and anhydrous +a+l tubes of

9nown weight. The increase in weight determines the amount of carbon of hydrogen.

=itrogen- 9Ceidene ,ethod

bout 2 gm of accurately weighed produced cool is heated with concentrated ;3SO5.


36/39

Conformation: -

The di6erent arrangements of atoms or groups in space which can be converted into one another by

rotation about +-+ single band in a molecule are called conformation.

*xample% +onformation of ethane

=ewmann proCection formula% -

.&dot( shows the bac9 carbon

6)ines emerging from dot# one substituent of bac9 carbon

+ircle% - shows the front carbon

)ine emerging from the circumference of the circle or the constituent of front carbon

Staggered conformation% -

,ore stable# less energy


37/39

H

HH

H

H H

$otation by ?Jo

HH

HH

HH

&*clipsed conformation(

4?Jorotation we get ? conformation three staggered and three eclipsed

+onformation of n-butane% - H

C C

HH

CH3

H

CH3


38/39

H CH

3

H CH

3

H

H

H

H

H

HH

HH

CH3

H CH

3

HH

HH

H CH

3 H CH

3

H

HH

H

H CH

3

H

HH

H

H CH

3H

CH3

H CH

3

H

H

HH

$ %o

$ %o

$ %o

$ %o

7 S t a g a r e d * . * c l i p s e d F S t a g g a r e d

. * c l i p s e d < S t a g g a r e d

CH3H

CH3H

HH$ %

o

+ . * c l i p s e d


39/39

:eometrical isomerism% - ;inged rotation of +D+ double bond

C C

b

a

b

a

C C

a

a

b

b

C i s T r a ' s

*ach doubly bonded carbon di6erent atom functional group

*-Q =otation% -

1ecided the priority of each doubly bonded carbon &using cahn invgold prelog priority rules( se!uence

rule.

"f similar priority are on the similar side of the double bond than the compound- Q isomer &cis(

"f similar priority are on the opposite side of the double bond than the compound *- isomer &trans(

Q% - Qussasmein &on same side(

*% -*ntigen &on opposite side(

engineering chemistry unit3

Documents