Dear,

If you are familiar with Gaussian software, following instruction can be helpful.

Assume that, for simplicity, you are going to perform calculation for Acetone using HF/3-21g*.

First, you should perform optimization as follows:

# HF/3-21g opt freq

"freq" keyword is included in order to sure that your optimized structure is a true global minimum; i.e. there is no any imaginary frequencies in the corresponding calculation. Now, on the optimized structure, NBO calculation can be performed using following command:

#HF/3-21G pop=nbo

It should be noted that, in order to obtain more accurate results

, you can use larger basis set or even more accurate method; e.g. B3LYP/6-311G**. The part of output you are looking for will be as follows:

Second Order Perturbation Theory Analysis of Fock Matrix in NBO Basis

Threshold for printing: 0.50 kcal/mol

E(2) E(j)-E(i) F(i,j)

Donor NBO (i) AcceptorNBO (j) kcal/mol a.u. a.u.

=====================================================================================

within unit 1

1. BD ( 1) C 1 - O 2 / 17. RY*( 1) C 1 2.34 2.47 0.068

2. BD ( 2) C 1 - O 2 / 43. BD*( 1) C 3 - H 4 2.10 1.18 0.044

2. BD ( 2) C 1 - O 2 / 44. BD*( 1) C 3 - H 5 2.10 1.18 0.044

2. BD ( 2) C 1 - O 2 / 46. BD*( 1) C 7 - H 8 2.10 1.18 0.044

2. BD ( 2) C 1 - O 2 / 47. BD*( 1) C 7 - H 9 2.10 1.18 0.044

3. BD ( 1) C 1 - C 3 / 21. RY*( 1) O 2 1.44 2.91 0.058

3. BD ( 1) C 1 - C 3 / 32. RY*( 1) C 7 1.56 2.02 0.050

3. BD ( 1) C 1 - C 3 / 43. BD*( 1) C 3 - H 4 0.87 1.53 0.033

3. BD ( 1) C 1 - C 3 / 44. BD*( 1) C 3 - H 5 0.87 1.53 0.033

3. BD ( 1) C 1 - C 3 / 45. BD*( 1) C 3 - H 6 0.84 1.56 0.032

3. BD ( 1) C 1 - C 3 / 48. BD*( 1) C 7 - H 10 1.50 1.56 0.043

4. BD ( 1) C 1 - C 7 / 21. RY*( 1) O 2 1.44 2.91 0.058

4. BD ( 1) C 1 - C 7 / 25. RY*( 1) C 3 1.56 2.02 0.050

4. BD ( 1) C 1 - C 7 / 45. BD*( 1) C 3 - H 6 1.50 1.56 0.043

4. BD ( 1) C 1 - C 7 / 46. BD*( 1) C 7 - H 8 0.87 1.53 0.033

4. BD ( 1) C 1 - C 7 / 47. BD*( 1) C 7 - H 9 0.87 1.53 0.033

4. BD ( 1) C 1 - C 7 / 48. BD*( 1) C 7 - H 10 0.84 1.56 0.032

5. BD ( 1) C 3 - H 4 / 19. RY*( 3) C 1 0.71 1.72 0.031

5. BD ( 1) C 3 - H 4 / 39. BD*( 1) C 1 - O 2 2.07 1.53 0.050

5. BD ( 1) C 3 - H 4 / 40. BD*( 2) C 1 - O 2 5.78 0.90 0.065

5. BD ( 1) C 3 - H 4 / 44. BD*( 1) C 3 - H 5 0.58 1.37 0.025

5. BD ( 1) C 3 - H 4 / 45. BD*( 1) C 3 - H 6 0.68 1.40 0.028

6. BD ( 1) C 3 - H 5 / 19. RY*( 3) C 1 0.71 1.72 0.031

6. BD ( 1) C 3 - H 5 / 39. BD*( 1) C 1 - O 2 2.07 1.53 0.050

6. BD ( 1) C 3 - H 5 / 40. BD*( 2) C 1 - O 2 5.78 0.90 0.065

6. BD ( 1) C 3 - H 5 / 43. BD*( 1) C 3 - H 4 0.58 1.37 0.025

6. BD ( 1) C 3 - H 5 / 45. BD*( 1) C 3 - H 6 0.68 1.40 0.028

7. BD ( 1) C 3 - H 6 / 17. RY*( 1) C 1 0.71 1.72 0.031

7. BD ( 1) C 3 - H 6 / 39. BD*( 1) C 1 - O 2 1.03 1.53 0.036

7. BD ( 1) C 3 - H 6 / 41. BD*( 1) C 1 - C 3 0.68 1.30 0.027

7. BD ( 1) C 3 - H 6 / 42. BD*( 1) C 1 - C 7 3.69 1.30 0.062

7. BD ( 1) C 3 - H 6 / 43. BD*( 1) C 3 - H 4 0.74 1.37 0.028

7. BD ( 1) C 3 - H 6 / 44. BD*( 1) C 3 - H 5 0.74 1.37 0.028

8. BD ( 1) C 7 - H 8 / 19. RY*( 3) C 1 0.71 1.72 0.031

8. BD ( 1) C 7 - H 8 / 39. BD*( 1) C 1 - O 2 2.07 1.53 0.050

8. BD ( 1) C 7 - H 8 / 40. BD*( 2) C 1 - O 2 5.78 0.90 0.065

8. BD ( 1) C 7 - H 8 / 47. BD*( 1) C 7 - H 9 0.58 1.37 0.025

8. BD ( 1) C 7 - H 8 / 48. BD*( 1) C 7 - H 10 0.68 1.40 0.028

9. BD ( 1) C 7 - H 9 / 19. RY*( 3) C 1 0.71 1.72 0.031

9. BD ( 1) C 7 - H 9 / 39. BD*( 1) C 1 - O 2 2.07 1.53 0.050

9. BD ( 1) C 7 - H 9 / 40. BD*( 2) C 1 - O 2 5.78 0.90 0.065

9. BD ( 1) C 7 - H 9 / 46. BD*( 1) C 7 - H 8 0.58 1.37 0.025

9. BD ( 1) C 7 - H 9 / 48. BD*( 1) C 7 - H 10 0.68 1.40 0.028

10. BD ( 1) C 7 - H 10 / 17. RY*( 1) C 1 0.71 1.72 0.031

10. BD ( 1) C 7 - H 10 / 39. BD*( 1) C 1 - O 2 1.03 1.53 0.036

10. BD ( 1) C 7 - H 10 / 41. BD*( 1) C 1 - C 3 3.69 1.30 0.062

10. BD ( 1) C 7 - H 10 / 42. BD*( 1) C 1 - C 7 0.68 1.30 0.027

10. BD ( 1) C 7 - H 10 / 46. BD*( 1) C 7 - H 8 0.74 1.37 0.028

10. BD ( 1) C 7 - H 10 / 47. BD*( 1) C 7 - H 9 0.74 1.37 0.028

11. CR ( 1) C 1 / 17. RY*( 1) C 1 0.79 12.16 0.088

11. CR ( 1) C 1 / 26. RY*( 2) C 3 1.67 12.17 0.127

11. CR ( 1) C 1 / 33. RY*( 2) C 7 1.67 12.17 0.127

12. CR ( 1) O 2 / 17. RY*( 1) C 1 10.63 21.12 0.425

12. CR ( 1) O 2 / 22. RY*( 2) O 2 1.02 21.99 0.133

13. CR ( 1) C 3 / 18. RY*( 2) C 1 2.00 12.19 0.139

13. CR ( 1) C 3 / 20. RY*( 4) C 1 0.53 12.70 0.074

13. CR ( 1) C 3 / 29. RY*( 1) H 4 1.47 11.97 0.118

13. CR ( 1) C 3 / 30. RY*( 1) H 5 1.47 11.97 0.118

13. CR ( 1) C 3 / 31. RY*( 1) H 6 1.57 11.97 0.122

14. CR ( 1) C 7 / 18. RY*( 2) C 1 2.00 12.19 0.139

14. CR ( 1) C 7 / 20. RY*( 4) C 1 0.53 12.70 0.074

14. CR ( 1) C 7 / 36. RY*( 1) H 8 1.47 11.97 0.118

14. CR ( 1) C 7 / 37. RY*( 1) H 9 1.47 11.97 0.118

14. CR ( 1) C 7 / 38. RY*( 1) H 10 1.57 11.97 0.122

15. LP ( 1) O 2 / 17. RY*( 1) C 1 26.05 1.96 0.202

15. LP ( 1) O 2 / 41. BD*( 1) C 1 - C 3 1.30 1.55 0.040

15. LP ( 1) O 2 / 42. BD*( 1) C 1 - C 7 1.30 1.55 0.040

16. LP ( 2) O 2 / 41. BD*( 1) C 1 - C 3 26.74 1.05 0.151

16. LP ( 2) O 2 / 42. BD*( 1) C 1 - C 7 26.74 1.05 0.151

For example, the last line indicates resonance (delocalization) of second lone pair of oxygen #2 with sigma star (sigma anti bonding orbital shown by BD*) of C1-C7 bond will lead to stabilization energy, E2 perturbation, as 26.74 kcal/mol.

I hope this simple example is helpful and can explain what you are looking for. If your problem is still remained unresolved, let me to know.

Best,

thanks Mr emamian... I want to calculate total resonance for my molecule from this calculations... I want to know... how sum(summation) this results for resonance???

I can not understand your mean properly. You can contact me via: [email protected] in order to more explanations.