Structures and Other Properties of Polyynes and their Isomers: Theoretical and Experimental Results - Polyynes: Synthesis, Properties, and Applications - page 384

TABLE 17.21
Fundamental Vibrational Frequencies of the C 5 H 2 Five-Rings (All This
Work)

Molecule F1 F2 F3 F4 F5 F6 F7 F8

5C1(s) 3216 3200 1364 1324 1254 1186 1180 1017

- [6.5]R [4.3]R [8.2]R [13]R [110]R [6.9]R [25]R [30]R

5C2(s) 3188 3119 1789 1599 1445 1153 1080 1009

- [0.8]R [2.0]R [136]R [28]R [2.8]R [12]R [5.1]R [28]R

Molecule F9 F10 F11 F12 F13 F14 F15

5C1(s) 931 870 852 790 669 392 312

- [99]R [16]R [30]R [54]E [17]R [7.89]R [53]R

5C2(s) 910 873 794 603 454 382 86

- [13]R [0.3]R [2.0]R [64]R [61]R [84]R [15]R

TABLE 17.22
Relative SCF Energy, Zero Point Energy (ZPE), and Dipole Moment of the
C 5 H 2 Four-Rings (All This Work)

"E SCF (kJ mol 1 ) ZPVE (kJ mol 1 )

Molecule Dipole (debye)

5C3(s) 147 109.9 4.05

5C4(s) 274 111.29 0.00

5C5(s) 279 108.17 4.23

5C6(s) 498 102.19 2.78

published results of semi-empirical calculations for some C 6 H 2 tetra-
dehydrobenzenes. Bettinger et al. [126] have computed energy separations
and vibrational frequencies of three cyclic C 6 H 2 isomers. Sattelmeyer and
Stanton [6] have computed equilibrium structures and properties of nine
C 6 H 2 molecules, four open and five cyclic. Their results offer a good
opportunity for comparison with computations for the same molecules with
our program. Obviously many more constructs of six carbon and two
hydrogen atoms are possible. A potentially interesting one can be derived
from 3C1(s) cyclopropenylidene by the substitution of

C 3 H for one of
the hydrogen atoms. However, the quantum chemical treatment of this
construct results in an open molecule with hydrogen atoms bonded to C2
and C6 and 224 kJ mol 1 above 6O1(s). E SCF ¼

Tables 17.29 , 17.30 and 17.31 list energy data for the C H

2 isomers. 6