April 13, 2021, 02:36:45 AM
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Topic: Ring Strain Energy Calculations  (Read 183 times)

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Offline CompletelyIrrational

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Ring Strain Energy Calculations
« on: April 03, 2021, 03:31:24 PM »
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.




Offline Orcio_Dojek

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Re: Ring Strain Energy Calculations
« Reply #1 on: April 03, 2021, 04:24:54 PM »
Quote
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).

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