Quantum Project 3

8/9/2019 Quantum Project 3

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QUANTUM CHEMISTRY PROJECT, DR. REETA KAKKAR

BenzeneEfect o s!st"tents on Benzene #"n$

Avisekh Dandapat (14), Komal (15), Vinita (20), Rupashree Das (13)

!i"k the date#

%e &'(e st)"e) t&e Mo*ec*'# O#!"t'*s o Benzene 'n) efect o )"fe#ents!st"tents *"+e e*ect#on "t&)#'"n$ - e*ect#on )on't"n$ $#os on Benzene#"n$.


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BENZENE

Benzene is a six membered hydrocarbon ring. All carbon carbonbond lengths are equal & intermediate between single and doblebonds in Benzene. If benzene actually ossessed three single and

three double bonds! as in a "e#ule structure! we would exect to findthree short bonds $%.' A( and three long bonds $%.') A! robably! asin %!*butadiene(. Actually! x*ray diffraction studies show that the sixcarbon*carbon bonds in benzene are equal and ha+e a length of %.,A! and are thus intermediate between single and double bonds.Bondlength of carbon carbon double bond is %., and carbonhydrogen bond length is %.-).

/he "e#ule structures I and II! we now immediately recognize! meetthe conditions for *resonance0 structures that differ only in thearrangement of electrons Benzene is a hybrid of I and II. 1ince I & IIae exactly equi+alent! and hence of exactly the same stability! they


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ma#e equal contributions to the hybrid. And! also since I and II areexactly equi+alent! stabilization due to resonance should be large.

234E564A7 37BI/A41 38 BENZENE1ince each carbon in benzene is bonded to three other atoms! it usess9 orbitals . /hese lie in the same lane! that of the carbon nucleus!and are directed toward the corners of an equilateral triangle. If wearrange the six carbons and six hydrogens of benzene to ermitmaximum o+erla of these orbitals we can see the molecular orbitalo+erlaing in it./he orbital aroach re+eals the imortance of the lanarity of thebenzene ring. /he ring is flat because the trigonal $s9( bond anglesof carbon :ust fit the %9- angles of a regular hexagon; it is this flatnessthat ermits ihe o+erla of the orbitals in both directions! with theresulting delocalization and stabilization.


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OMO-LUMO ENERGY LEVELS OF BENZENE

Figure: HOMO-LUMO energy levels of benzene

8rontier 2olecular orbital theory is an alication of 23 theory describing

>323 $>I?>E1/ 37BI/A4 234E564A7 37BI/A4( @ 4623

$43E1/ 37BI/A4 234E564A7 37BI/A4( interactions. It is based on

main obser+ations of 23*theory as 9 molecules interact as!


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/he occuied orbital of different molecules reel each other. ositi+e charges of % molecule attract the negati+e charges of other. /he occuied orbital of % molecule and the unoccuied orbital of the other

$secially >323*4623( interact with each other osing attraction.

p- ORBITAL CLOUD STRUCTURE FOR OMO

ENERGY LEVELS OF BENZENE


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Figure: Degenerate HOMO energy levels of benzene molecule

p- ORBITAL CLOUD STRUCTURE FOR LUMO

ENERGY LEVELS OF BENZENE


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Figure: Degenerate LUMO energy levels of Benzene molecules

PRO!DUR! OF F"#D"#$ OU% %H! HOMO-LUMO!#!R$& L!'!L( OF B!#)!#! MOL!UL! B& U("#$

H&P!RH!M (OF%*+R!

%.8irst of all we constructed a benzene ring.9.e geometrically otimized the molecule.

./hen we noted the binding energy of the molecule.'./hen we went to orbitals .C./hen we selected the homo and lomo energy le+els to draw the homo and

lumo orbitals in benzene ring.


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SUBSTITUTIONS IN BEN/ENE RIN0

2ono substituted benzenes ha+e a tendency to substitute its one or more >*

atom$s( with other grou or atom. /his is generally #nown as the substitution in

the benzene ring. Now theoretically it is easy to redict which substitution is

ossible for which benzene ring. Now we used the >yerchem* software to

redict the electrohilic character of some grous towards the benzene ring.

1ubstituents already attached to benzene exert an influence on additional atomsor grous attemting to bond to the benzene ring +ia electrohilic aromaticsubstitution reactions. An atom or grou already attached to a benzene ring maydirect an incoming electrohile to either the ortho*ara ositions or the meta

osition. Atoms or grous that ma#e the benzene molecule more reacti+e by

increasing the ringDs electron density are called activating grou,sActi+atinggrous ser+e as ortho*ara directors when they are attached to a benzene ring!meaning that they direct an incoming electrohile to the ortho or ara ositions.An atom or grou that ma#es the benzene molecule less reacti+e by remo+ingelectron density from the ring acts as a .eactivating grou,


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$%&$'('%'()* )+ ,-,.'R)*

/('0DR /(*1 1R)%! )*

&,*2,*, R(*1

SUBSTITUTION TO NITRO1BEN/ENE


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8igure @a$show the molecule of nitrobenzene(

2"$#e 31 ! 4 t&e c&'#$es on )"fe#ent 'to5s "n

n"t#o!enzene6


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In 7$#e 4!6 e &'(e n"t#o $#o 'tt'c&e) to ' Benzene

#"n$. N"t#o $#o "s 'n e*ect#on "t&)#'"n$ $#o )e to

&"c& "t s&os ne$'t"(e 5eso5e#"c efect o# #eson'nce

efect 45eso5e#"c efect "s ' e#5'nent efect o "

e*ect#on s&"t"n$ #o5 5*t"*e !on) to 'to5 o# #o5

5*t"*e !on) to s"n$*e !on) o# #o5 *one '"# to s"n$*e

!on)6 "n c'se o con8$'te) s9ste5 . 2#o5 t&"s 7$#e e

$ot to +no t&'t 't 5et' os"t"on "t& #esect to ' c'#!on

&"c& "s 'tt'c&e) to ' n"t#o $#o "s 5o#e ne$'t"(e*9

c&'#$e) 's co5'#e) to ot&e# os"t"ons . Hence

e*ect#o&"*e c'n e's"*9 'tt'c+ to ' &"$&*9 ne$'t"(e s"te

&"c& "s 5et' os"t"on "n n"t#o!enzene.

16B1/I/6/I3N /3 BENZENE 164>67I5 A5I


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Figure: Benzene carbo/ylic aci. 0.ifferent atoms are s1o2n3

Figure: Benzene carbo/ylic aci. 0c1arges on .ifferent atoms are s1o2n3

In the abo+e figure Benzene is substituted with carboxylic acid. 5arboxylic acidgi+e negati+e mesomeric effect and inducti+e effect. >ere meta carbon with

resect to a carbon substituted with carboxylic grou has more negati+e charge

as comared to other osition .1o electrohile which is a ositi+ely charged

identity can easily attac# at highly negati+e site which is meta osition in

benzoic acid.


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16B1/I/6/I3N /3 BENZENE 5ANI


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In t&e '!o(e 2"$#e , Benzene #"n$ "s s!st"tte) "t&

c9'n")e $#o.C9'nn")e $#o s&o ne$'t"(e

5eso5e#"c 'n) "n)ct"(e efect. He#e 5et' c'#!on

"t& #esect to ' c'#!on &'("n$ c9'n")e $#o "s &"$&*9

ne$'t"(e*9 c&'#$e) "t& #esect to '#' o# o#t&o

os"t"on. Hence e*ect#o&"*e c'n 'tt'c+ 't 5et' os"t"on

.


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COMPARIN0 THE BEN/ENE

SUBSTITUTED %ITH E:ECTRON

%ITHDRA%IN0 0ROUPS

%&en e co5'#e t&e Benzene #"n$ s!st"tte) "t&

e*ect#on "t&)#'"n$ $#o41CN,1COOH,1NO;6 .2#o5

'!o(e )"scss"on e c'5e to +no t&'t c&'#$e )ens"t9

"s ('#9"n$ "t& ('#9"n$ t&e s!st"ttent on !enzene #"n$

.In N"t#o!enzene e see t&'t 5et' o "t "s &"$&*9

os"t"(e*9 c&'#$e) "n co5'#"son to !enzo"c 'c") 5et'os"t"on 'n) t&e !enzo"c 'c") 5et' os"t"on "s 5o#e

ne$'t"(e*9 c&'#$e) 's co5'#e) to t&e 5et' os"t"on

o !enzene &'("n$ c9'n")e $#o. So #o5 t&"s

)"scss"on e c'5e to +no t&'t e*ect#o&"*e c'n

'tt'c+ on t&ese s!st"tte) !enzene #"n$ "n t&e

o**o"n$ o#)e#31 CCC


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In t&"s 7$#e e &'(e &eno* &"c& &'s ' e*ect#on

)on't"n$ $#o on ' !enzene #"n$. P&eno* &'s '

os"t"(e 5eso5e#"c 'n) ne$'t"(e "n)ct"(e efect He#e

e see t&'t o#t&o 'n) 5et' os"t"on '#e 5o#e


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ne$'t"(e*9 c&'#$e) 's co5'#e) to 5et' os"t"on

,&ence 'n e*ect#o&"*e c'n e's"*9 'tt'c+ on o#t&o 'n)

'#' os"t"ons.


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In t&"s 7$#e e &'(e 5et&o?9 !enzene &"c& &'s '

5et&o?9 $#o &"c& "s o#t&o o# '#' )"#ect"n$ .He#e

e &'(e o#t&o 'n) '#' os"t"on "t& 5o#e ne$'t"(e

c&'#$e 's co5'#e) to 5et' .T&e#eo#e e*ect#o&"*"c

s!st"tt"on c'n occ# 't o#t&o o# '#' os"t"on.

SUBSTITUTION ON CH:OROBEN/ENE


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In t&"s 7$#e e &'(e c&*o#o!enzene 'n) c&*o#o $#o

"s 'n o#t&o o# '#' )"#ect"n$ .C&*o#"ne s&o os"t"(e

5eso5e#"c 'n) ne$'t"(e "n)ct"(e efect "n &"c&

os"t"(e 5eso5e#"c efect "** #e)o5"n'te )e to&"c& c&*o#o $#o "nc#e'se t&e e*ect#on )ens"t9 on

!enzene #"n$.He#e e &'(e o#t&o 'n) '#' os"t"on

"t& 5o#e ne$'t"(e c&'#$e 's co5'#e) to 5et'

.T&e#eo#e e*ect#o&"*"c s!st"tt"on c'n occ# e's"*9 't

o#t&o o# '#' os"t"on.

2I@E MEMBERED HETEROCYC:IC2I@E MEMBERED HETEROCYC:IC

COMPOUNDSCOMPOUNDS

2URAN


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In t&"s 7$#e e &'(e ' 7(e 5e5!e#e) &et#oc9c*"c

co5on) 2#'n. He#e e &'(e ' 'n) os"t"on

&"$&*9 ne$'t"(e*9 c&'#$e) )e to &"c& e*ect#o&"*e c'n

e's"*9 'tt'c+ on t&ese os"t"on.

Quantum Project 3

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