Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: CompletelyIrrational on April 03, 2021, 03:31:24 PM
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Hello there
I am currently doing ring strain calculations on Oxirane using estimated energy values calculated by Turbomole using different methods (HF / DFT using def-SV(P) and def2-TZVP optimizations). I have retrieved several energy values to perform these calculations using homodesmotic, isodesmic, and group theory approaches.
I am looking for some clarification on the calculations involved. From what I know, the calculated ring strain is the difference between the unstrained and strained molecule in question, the same as enthalpy calculations.
Here is my set up for Isodesmic:
Ethane + (2) Methanol --> Oxirane + (2) Methane + Water
Calculated energies rounded are:
-79 + -229 --> -152 + -80 + -75
When calculating the difference as:
((-79)+(-229)) - ((-152)+(-80)+(-75)
This is equal to 0.03, which is not correct. Is there something I am doing wrong with the calculations? I feel as though I am missing something?
Thank you.
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Here is my set up for Isodesmic:
Ethane + (2) Methanol --> Oxirane + (2) Methane + Water
Calculated energies rounded are:
-79 + -229 --> -152 + -80 + -75
When calculating the difference as:
((-79)+(-229)) - ((-152)+(-80)+(-75)
This is equal to 0.03, which is not correct.
Difference should be energy of products minus energy of substrates.
Of course value -0,3 (kJ, kcal ???) will be even worse (no energy strain).