During geometry optimization it is suggested that one should use 2S+1 formula to get the multiplicity number for example if your molecule has 1 unpaired electron that your multiplicity will be (2*1/2)+1 = 2 end up having doublet. However when I run my input it gives an error that looks like you cant have 48 electrons and a doublet multiplicity. I get it I mean even number of electrons would not give unpaired electron. But in the input the electron number is 47 and still gives the error. MP2/6-31+G(d) Opt=(Redundant) SCF=( tight, maxcyc=500) Geom=PrintInputOrient, this is the route and -1 is charge 2 is the multiplicity.
Please share your complete input otherwise it is difficult to say what is the problem.
%chk=geom_opt.chk
%nproc=1
%mem=1GB
# MP2/6-31G* Opt=(Redundant) SCF=Tight Geom=PrintInputOrient
Geometry optimization
-1 2
O1 12.930000305175781 38.472999572753906 15.069000244140625
O2 12.949000358581543 37.611000061035156 18.235000610351563
O3 10.895000457763672 37.5989990234375 17.229999542236328
C4 12.817000389099121 37.262001037597656 15.854999542236328
C5 14.196999549865723 36.6349983215332 15.954999923706055
C6 12.161999702453613 37.54100036621094 17.2450008392334
H7 12.151000022888184 36.582000732421875 15.309000015258789
H8 14.562000274658203 36.35599899291992 14.961000442504883
H9 14.923999786376953 37.34400177001953 16.367000579833984
H10 14.187000274658203 35.7400016784668 16.583999633789063
H11 13.118000030517578 38.18600082397461 14.163000106811523
I just don't understand, I mean it is so clear that in the carboxylic group one hydrogen is missing, in carboxylate form. Resonance structure should be observed but gaussview draws it as if the both oxygen has double bonds with the oxygen.
The system is anion and singlet. Use -1 and 1 for charge and multiplicity.In optimized geometry you will see both the C-O bond equal.
Thank you for your answer I will do so but can you explain why multiplicity is 1 ?
It is a closed shell molecule no unpaired electron. Read about the Lewis structure of carboxylate anion.
Dear Zeki Zeybek,
First this is close shell molecule with no unpaired electron and second you have to have assign charge of -1 (carboxylate ion) and multiplicity 1. Please take care while drawing the input molecule.
- Forgive my ignorance but how this molecule has no unpaired electron. I mean is it because of the resonance in carbkxylate ion. Normally one hydrogen is missing in single bonded oxygen in the carboxyl group so that oxygen cannot form its octet. Thank you for your attention by the way
Dear Zeki Zeybek,
Loss of proton (hydrogen without electron) leads to the formation of carboxylate ion. It means electron is with the oxygen and not with the hydrogen.
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