Computational Assignment 5
Calculation of the NMR isotropic chemical shift for benzene
Use Gaussian software on sona to calculate the isotropic chemical shift for carbon and
hydrogen in benzene with respect to TMS (tetramethylsilane).
1. Benzene
Create the following input file:
%Chk=benzene
#T B3LYP/6-31G(d) Opt Test
Benzene Opt
0,1
C
C,1,CC
C,1,CC,2,120.
C,2,CC,1,120.,3,0.
C,3,CC,1,120.,2,0.
C,4,CC,2,120.,1,0.
H,1,CH,2,120.,4,180.
H,2,CH,1,120.,7,0.
H,3,CH,1,120.,7,0.
H,4,CH,2,120.,8,0.
H,5,CH,3,120.,9,0.
H,6,CH,4,120.,10,0.
CC=1.38617
CH=1.07561
--link1-%Chk=benzene
%NoSave
#T RHF/6-311+G(2d,p) NMR Geom=AllCheck Guess=Read Test
Benzene NMR
0,1
2. TMS
Create the following input file:
%Chk=TMS
#T B3LYP/6-31G(d) Opt Test
TMS Opt
0,1
C
Si,1,rsic
C,2,rsic,1,acsic
C,2,rsic,1,acsic,3,dtet
C,2,rsic,1,acsic,3,-dtet
H,1,rch,2,ach,3,d6
H,1,rch,2,ach,3,d7
H,1,rch,2,ach,3,d8
H,3,rch,2,ach,1,d9
H,3,rch,2,ach,1,d10
H,3,rch,2,ach,1,d11
H,4,rch,2,ach,1,d12
H,4,rch,2,ach,1,d13
H,4,rch,2,ach,1,d14
H,5,rch,2,ach,1,d15
H,5,rch,2,ach,1,d16
H,5,rch,2,ach,1,d17
variables
rsic=1.875
rch=1.115
ach=109.8
acsic=109.2
d6=0.
d7=120.
d8=-120.
d9=0.
d10=119.999999
d11=-119.999999
d12=0.
d13=119.999999
d14=-119.999999
d15=0.
d16=119.999999
d17=-119.999999
dtet=120.
--link1-%Chk=TMS
%NoSave
#T RHF/6-311+G(2d,p) NMR Geom=AllCheck Guess=Read Test
TMS NMR
0,1
Notes:
Please do not forget to leave a blank line at the end of each step
Submit your jobs by typing g03 inputfile.inp &, this allows you to run
more than one job at a time
Your jobs should take only few minutes
3. Calculate the chemical shift as,
Relative shift = - absolute shielding value (TMS) - absolute shielding value (benzene)
Notice that the absolute shielding value for each of carbon and hydrogen is the average of
the corresponding XX, YY, and ZZ values.
4. Compare your results with the experimental values