Conformations of 1,2-dicyano-1,1,2,2-tetraphenylethane and cyanodiphenylmethyl peroxide

Article abstract of DOI:10.1246/bcsj.74.1033

The solid-state structures of 1,2-dicyano-1,1,2,2-tetraphenylethane and cyanodiphenylmethyl peroxide are determined by X-ray crystallography. Both molecules adopt the trans conformation in the solid-state. Experimentally derived values of the energy diffe

Full text of DOI:10.1246/bcsj.74.1033

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Bull. Chem. Soc. Jpn., 74, 1033—1034 (2001) 1033
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Short Articles
and the valence angle spread.8
Conformations of 1,2-Dicyano-
1,1,2,2-tetraphenylethane and
Cyanodiphenylmethyl Peroxide
Earlier studies5 on the conformation of 1 show that the mol-
ecule exists almost entirely in the trans-configuration in the so-
lution-state with a ∆E value of 13.39–14.23 kJ molꢀ1. Since
no computational results exist which would represent the con-
formational preference of 1 in the gaseous state, we therefore
subjected our experimental conclusions to a computational
test. AMPAC calculations with AM1 parametrization and full
geometry optimization clearly showed that the trans rotamer
has a lower energy than the gauche form, differing from it by
10.66 kJ molꢀ1. The torsion angle of the gauche rotamer with
the lowest energy was found to be 62˚ and the Boltzmann dis-
tribution to be 97.4% trans and 2.6% gauche. These data com-
pare well with the results obtained in both solid- and solution-
state experiments.
Y. Lam et al.
01
33
34
SJA8
09-2673
0039
tober
Yulin Lam,* Gene-Hsiang Lee,† and Eping Liang
Department of Chemistry, National University of Singapore,
3 Science Drive 3, Singapore 117543
†Instrumentation Centre, National Taiwan University, Taipei
10764, Taiwan
00
01
(Received October 24, 2000)
Molecule 2 adopts a trans conformation. The presence of a
peroxide group appears to relieve some of the strong interac-
tions between the phenyl moieties. The phenyl groups are ar-
ranged in a propeller-like conformation, with rings A and B be-
The solid-state structures of 1,2-dicyano-1,1,2,2-tetra-
phenylethane and cyanodiphenylmethyl peroxide are deter-
mined by X-ray crystallography. Both molecules adopt the
trans conformation in the solid-state. Experimentally derived
values of the energy difference between the gauche and trans
rotamers and their population quotient are compared with
values predicted by semiempirical MO calculations.
.2
.3
Earlier works on the dicyano series of compounds have
shown contrasting results, with 1,2-dicyanoethane1 and 9,9′-di-
cyano-9,9′-bifluorenyl2 existing predominantly in the gauche
form, whilst other dicyano compounds containing phenyl and
alkyl substituents generally favor the trans conformation.3,4
Through the years, various studies on 1,2-dicyano-1,1,2,2-tet-
raphenylethane 1 have been carried out5–7 but no experimental
evidence has been published which would bear directly on the
conformational preference of the molecule in the solid-state.
We now report our findings on 1 and its peroxide analogue, cy-
anodiphenylmethyl peroxide 2, based on X-ray diffraction
measurements and semiempirical molecular orbital calcula-
tions.
Figure 1 depicts the structures and defines the atomic num-
bering of 1 and 2. The pair of central carbon atoms of mole-
cule 1 is slightly disordered and occupies two possible sites,
(C(1) and C(1′) and C(2) and C(2′), as shown in Fig. 1a), with
occupancy factors of 0.805(16):0.195(16). Since there is finite
movement of these central carbon atoms, the bond lengths,
bond angles and torsion angles involving them are consequent-
ly not physically significant.
Projection down the C(1)–C(2) bond clearly shows that 1
adopts a trans conformation, like meso-2,3-dicyano-2,3-
diphenylbutane3 and 1,1,2,2-tetraphenylethane,8 but in contrast
with its back-clamped analogue, 9,9′-dicyano-9,9′-bifluoren-
yl,2 which exists in the solid-state as a gauche structure with a
CN–C–C–CN torsion angle of ~56.5˚. This difference in con-
formational behavior between 1 and 9,9′-dicyano-9,9′-bifluo-
renyl confirms the manifestation of the effects of phenyl ring
stacking in 1; it is consistent with theory that there is a tenden-
cy for neighboring phenyl rings in an unclamped polyaryl-
ethane to nest or stack so as to diminish the geminal repulsions
Fig. 1.
(a) Thermal ellipsoid diagrams of 1 at 30% proba-
bility. (b) Thermal ellipsoid diagramas of 2 at 30% proba-
bility

1034 Bull. Chem. Soc. Jpn., 74, No. 6 (2001)
© 2001 The Chemical Society of Japan
C2/c, a ꢂ 17.310(7), b ꢂ 7.7679(16), c ꢂ 17.650(6) Å, β ꢂ
106.561(16)˚, V ꢂ 2274.9(13) Å3, Z ꢂ 4, Dcalc ꢂ 1.216 g cmꢀ3, µ
ꢂ 0.077 mmꢀ1, crystal size 0.40 ꢃ 0.40 ꢃ 0.36 mm, 6921 reflec-
tions measured (2θ ꢂ 58.3˚), 2824 independent reflections [I >
2σ(I)] used in the refinement; R ꢂ 0.0511, Rw ꢂ 0.1161 and GOF
ꢂ 1.093 for 185 parameters. Lists of final atomic coordinates,
bond lengths and angles, thermal parameters and torsion angles
have been deposited as Document No. 14030 at the Office of the
Editor of Bull. Chem. Soc. Jpn. Crystallographic data have been
deposited at the Cambridge Crystallographic Data Centre.
Calculations. Semiempirical molecular orbital calculations
were performed using the program11 AMPAC 6.51 with AM1 pa-
rametrization.12 Structural parameters were taken from our X-ray
diffraction results of the compounds. Full geometry optimization
was performed for each incremental value of the torsion angle
which were defined by the atoms CN–C–C–CN in 1 and C–O–O–
C in 2 according to the convention of Klyne and Prelog.13
ing oriented at 38.63(17)˚ and 51.87(16)˚ to the C(1)–C(13)–
O(1) and C(7)–C(13)–O(1) planes respectively.
AMPAC calculations of 2 show that the trans isomer with a
C–O–O–C torsion angle of 134˚ and the phenyl rings oriented
at 21.9˚ and 44.31˚ to the respective C(sp2)–C(sp3)–O plane is
the preferred structure. These results are in broad agreement
with our experimental values.
Experimental
Preparation of 1 and 2. To diphenylacetonitrile (2.90 g, 15
mmol) was added t-butyl peroxide (1.30 g, 8.9 mmol) and the re-
action was gently refluxed for 2 days. On cooling, solid was de-
posited in the yellow solution. The solution was decanted and the
solid washed thoroughly with hot methanol and then fractionally
recrystallized from benzene to give 1 (1.96 g, 5.1 mmol) and 2
(0.51 g, 1.2 mmol). Compound 1 is a white solid, mp 214–215 ˚C
(decomp) (from benzene ) (Ref. 9, 213–215 ˚C). Anal. Calcd for
C28H20N2: C, 87.45; H, 5.25; N, 7.30%; Mr, 384. Found: C, 87.42;
H, 5.33; N, 7.25%; Mꢁ, 384.2. Compound 2 is a white solid, mp
191 ˚C (from benzene). Anal. Calcd from C28H20N2O2: C, 80.77;
H, 4.81; N, 6.73%; Mr, 416. Found: C, 80.75; H, 4.78; N, 6.80%;
Mꢁ, 416.
References
1
R. J. W. LeFèvre, G. L. D. Ritchie, and P. J. Stiles, J. Chem.
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obtained from benzene–hexane mixtures. Crystallization of 1
proved extremely difficult because the crystals were often poorly
formed. In an attempt to obtain crystals more suitable for the de-
termination of the crystal structure, a saturated solution of 1 in
benzene–hexane was allowed to slowly evaporate at 5 ˚C.
2
Y. L. Lam, L. L. Koh, H. H. Huang, and L. Wang, J. Chem.
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Data collection of 1 was performed at 295 K on a NONIUS
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atoms and refined isotropically. Crystal data for 1: C28H20N2, Mr
ꢂ 384.46, monoclinic, space group P21/n, a ꢂ 9.390(2), b ꢂ
16.118(3), c ꢂ 13.598(3) Å, β ꢂ 90.53(2)˚, V ꢂ 2057.9(7) Å3, Z
ꢂ 4, Dcalc ꢂ 1.241 g cmꢀ3, µ ꢂ 0.073 mmꢀ1, crystal size 0.60 ꢃ
0.20 ꢃ 0.04 mm, 3624 reflections measured (2θ ꢂ 50.0˚), 3624
independent reflections [I > 2σ(I)] used in the refincement; R ꢂ
0.0795, Rw ꢂ 0.2148 and GOF ꢂ 1.102 for 290 parameters. Crys-
tal data for 2: C28H20N2O2, Mr ꢂ 416.46, monoclinic, space group
5
K. K. Chui, H. H. Huang, and P. K. K. Lim, J. Chem. Soc.,
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9
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