VBFile 4-4

return to Tutorial n°4 Two geometries are provided the planar and the twisted where a vinyl part C1 C5 has been twisted by 90°. this second moieties has its pi orbitals along the y direction.

Evaluation of the conjugaison

Planar geometry

$contrl maxit=200 scftyp=rhf runtyp=ENERGY DFTTYP=B3LYP ICHARG=0 $end $SYSTEM TIMLIM=600000 MEMORY=100000000 $END $BASIS GBASIS=N31 NGAUSS=6 NDFUNC=1 $END $DATA BLW-ED Analysis C1 C 6.0 0.0000000000 0.6097325637 1.7490045499 C 6.0 0.0000000000 0.6038280097 0.4085967284 C 6.0 0.0000000000 -0.6038307169 -0.4085950903 C 6.0 0.0000000000 -0.6097309803 -1.7490029472 H 1.0 0.0000000000 1.5343833559 2.3190652626 H 1.0 0.0000000000 -0.3149186339 2.3230080652 H 1.0 0.0000000000 1.5514513284 -0.1322302753 H 1.0 0.0000000000 -1.5514569088 0.1322266423 H 1.0 0.0000000000 -1.5343794820 -2.3190677945 H 1.0 0.0000000000 0.3149214640 -2.3230051413 $END Corresponding files are planar.inp and planar-deconj.inp

Localization of px-like pi orbitals to deconjugate keeping planar

BLW part
px-like pi orbitals on C1=C2 and on C3=C4 $BLW NBLOCK=3 ITER=50 $END $BLWDAT 2 8 0 3 7 13 14 18 22 28 29 2 8 0 33 37 43 44 48 52 58 59 26 56 -1 $END

Evaluation of the hyperconjugaison in the twisted form

Twisted (perpendicular) geometry

$contrl maxit=200 scftyp=rhf runtyp=ENERGY DFTTYP=B3LYP ICHARG=0 $end $SYSTEM TIMLIM=600000 MEMORY=100000000 $END $BASIS GBASIS=N31 NGAUSS=6 NDFUNC=1 $END $DATA BLW-ED Analysis C1 C 6.0 0.000000 -1.086858 2.236154 C 6.0 0.000000 0.000000 1.489418 C 6.0 0.000000 0.000000 0.000000 C 6.0 -1.086858 0.000000 -0.746736 H 1.0 0.967527 0.000000 -0.478451 H 1.0 0.000000 0.967527 1.967869 H 1.0 -2.072275 0.000000 -0.314213 H 1.0 -1.029400 0.000000 -1.820913 H 1.0 0.000000 -2.072275 1.803631 H 1.0 0.000000 -1.029400 3.310331 $END

In the BLW part we localize px-like pi orbitals of atoms C1=C2 and py-like orbitals for C3=C4 to avoid hyperconjugaison.

BLW-Localized part
$BLW NBLOCK=3 ITER=50 $END $BLWDAT 2 8 0 3 7 13 14 18 22 28 29 2 8 0 34 38 43 45 49 53 58 60 26 56 -1 $END Corresponding files are twisted.inp and twisted-blw.inp

We find

delocalized planar -155.8824504889

localized planar -155.8603462862 (13.9 kcal/mol)

Twisted -155.8695790387 ( 8.1 kcal/mol)

Twisted but local -155.8537320442 (18.0 kcal/mol)

Hence conjugaison is 13.9 kcal/mol, and the hyper conjugaison in the twisted form is as large as 9.9 kcal/mol