(wip)(#striketeam) Reproduction of gauche / anomeric effect

Owned by Hyesu Jang
Last updated: Sept 28, 2020
2 min read

1. Hyperconjugation effect (Gauche effect)

* Paul’s comment on the alkane torsion parameters

  • He found dramatically different torsion parameter signs for F-C-C-F and O-C-C-O;

  • Test calculation showed that F-C-C-F and O-C-C-O didn’t result in the gauche (60 degree) conformation as lowest energy.

>> with a negative k value of three-fold component, which seems counter-intuitive, with all the other factors, for example 1-4 non-bonded interactions and other torsion energy term, it still reproduce QM torsion profiles and gauche conformation.

(1) Parameters before and after the optimization

>> O-C-C-O

t5

[#8X2:1]-[#6X4:2]-[#6X4:3]-[#8X2:4]

initial

0.144*(1+cos(3* theta)) + 1.175*(1+cos(2*theta))

v1.1.0

-0.3014444642399*(1+cos(3* theta)) + 1.12459107565*(1+cos(2*theta))

v1.2.0

-0.04029961117620*(1+cos(3*theta)) + 0.5796570519069*(1+cos(2*theta))

>> F-C-C-F

t6

[#9:1]-[#6X4:2]-[#6X4:3]-[#9:4]

initial

0.0* (1 + cos(3* theta )) + 1.2 (1  + cos(2* theta-180))

v1.1.0

0.09287807122213*(1+cos(3* theta)) + 0.4123370893719*(1+cos(2* theta-180))

v1.2.0

-0.01988644358668*(1+cos(3*theta)) + 0.2143541237817*(1+cos(2* theta-180))

  • positive k vs negative k of three-fold torsion component:

(2) MM vs QM torsion profiles

 

(3) QM vs. MM optimized geometry

  • FDA set

     

  • hexafluoroethane