Crystal structure of phenyl-substituted cyclopentenes

Article abstract of DOI:10.1023/A:1009566010200

The crystal structures of two stereoisomers of tetraphenyl-and pentaphenyl-substituted cyclopentenes 1 and 2 have been determined by X-ray analysis. An envelope conformation ¹E has been ascertained for the cis isomer 1a, whereas the cis, cis isomer 2a, which crystallizes in two different space groups, P1, and P2₁/n, displays a twisted ²T₁ conformation. The phenyl substituents are all tilted with respect to the cyclopentene ring in both structures. Compound 1a crystallizes in the space group P2₁/a with a = 18.553(3), b = 6.006(2), c = 19.355(5), β = 102.67(4)°, and V = 2104.2(g) A³ for Z = 4; compound 2a¹ crystallizes in P2₁/n with a = 10.064(2), b = 20.756(5), c = 12.245(3) A, β = 95.21(2)°, and V = 2547(1) A³ for Z = 4; compound 2aII crystallizes in P1 with a = 10.117(3), b = 11.750(2), c = 12.359(2) A, α = 111.25(2), β = 94.84(2), γ = 108.78(2)°, and V = 1262.3(6) A³ for Z = 2.

Full text of DOI:10.1023/A:1009566010200

Journal of Chemical Crystallography, Vol. 29, No. 10, 1999
Crystal structure of phenyl-substituted cyclopentenes
Franco Benetollo,(1)* Vilma Busetti,(2) and Franco Marcuzzi(3)
Received September 10, 1999
The crystal structures of two stereoisomers of tetraphenyl- and pentaphenyl-substituted
cyclopentenes 1 and 2 have been determined by X-ray analysis. An envelope conformation
1E has been ascertained for the cis isomer 1a, whereas the cis, cis isomer 2a, which crystallizes
in two different space groups, P1, and P21/n, displays a twisted 2T1 conformation. The phenyl
substituents are all tilted with respect to the cyclopentene ring in both structures. Compound
1a crystallizes in the space group P21/a with a ϭ 18.553(3), b ϭ 6.006(2), c ϭ 19.355(5), ͱ
3
I
˚
ϭ 102.67(4)Њ, and V ϭ 2104.2(g) A for Z ϭ 4; compound 2a crystallizes in P21/n with a ϭ
3
˚
˚
10.064(2), b ϭ 20.756(5), c ϭ 12.245(3) A, ͱ ϭ 95.21(2)Њ, and V ϭ 2547(1) A for Z ϭ 4;
compound 2aII crystallizes in P1 with a ϭ 10.117(3), b ϭ 11.750(2), c ϭ 12.359(2) A, Ͱ ϭ
111.25(2), ͱ ϭ 94.84(2), Ͳ ϭ 108.78(2)Њ, and V ϭ 1262.3(6) A for Z ϭ 2.
˚
3
˚
KEY WORDS: Crystal structure; phenyl-substituted cyclopentenes.
Introduction
It is quite difficult, in many cases, to predict the
phenyl-substituted cyclopentenes 1 and 2, which are
the products of monoreduction of 1,2,3,4-tetraphe-
nylcyclopentadiene and 1,2,3,4,5-pentaphenylcyclo-
pentadiene, respectively.
behavior of sterically crowded organic molecules in
solution. For example, the assignment of the config-
uration by routine spectroscopic techniques (e.g.,
NMR) may be complicated by the existence of differ-
ent conformations, which, being all roughly compati-
ble with the same spectroscopic parameters, make
the assignment very uncertain. In such cases, it is
necessary to resort to X-ray crystallographic analyses
to solve the problem. We faced this kind of problem
during a study on the dependence of the stereochem-
istry of the reduction of phenyl-substituted cyclopen-
tadienes on the specific mechanism followed by the
reaction;1 in order to identify precisely the reaction
products, we had to grow single crystals suitable for
X-ray analysis. Typically, this was the case of the
These compounds can exist in different configura-
tions, depending on the relative position occupied by
the phenyl groups. For compound 1, two stereoiso-
mers are possible, i.e., the cis 1a and the trans 1b.
We were able to obtain good crystals of compound 1a.
(1) ICTIMA - CNR, Corso Stati Uniti 4, 35127 Padova, Italy.
(2) Universita` di Padova, Dipartimento di Chimica Organica, via
Marzolo 1, 35131 Padova, Italy.
(3) Universita` di Padova and C.N.R., Dipartimento di Chimica Or-
ganica and Centro di Studio sui Meccanismi di Reazioni Organ-
iche, via Marzolo 1, 35131 Padova, Italy.
* To whom correspondence should be addressed. E-mail: benetol-
lo@ictr.pd.cnr.it.
1127
1074-1542/99/1000-1127$16.00/0  1999 Plenum Publishing Corporation

1128
Benetollo, Busetti, and Marcuzzi
For compound 2 three stereoisomeric configurations
are possible, the cis,cis 2a, the cis,trans 2b, and the
trans,trans 2c.
1H NMR spectra of the second order, which do not
allow an unambiguous assignment of their configura-
tion, at least with routine spectrometers and tech-
niques. We report here the results of the determina-
tion of the crystal structure of compounds 1a and
2aI, 2aII.
Chemical preparation
We obtained by crystallization compound 2a, which
crystallized from different solvents, in two different
space groups, P21/n and P1, 2aI and 2aII, respectively,
with the same configuration. All these isomers display
The stereoisomer 1a was obtained by catalytic
hydrogenation (acetic acid as a solvent, 10% Pd on
charcoal as a catalyst, H2 pressure 1 bar, temperature
60ЊC, for 67 h) of 1,2,3,4-tetraphenylcyclopentadiene.
Table 1. Crystallographic Data and Summary of Intensity Data Collection and Structure Refinement
1a 2aI
C29H24 C35H28
2aII
Compound
C35H28
CCDC deposit no.
Color/shape
Mol wt
CCDC-1003/5686
Colorless/prism
372.5
CCDC-1003/5687
Colorless/prism
448.6
CCDC-1003/5688
Colorless/prism
448.6
Space group
Temp.; ЊC
P21/a
293(2)
P21/n
293(2)
P1
293(2)
Crystal system
Monoclinic
Monoclinic
Triclinic
Cell constanta
˚
a, A
18.553(3)
6.006(2)
19.355(5)
10.064(2)
20.756(5)
12.245(3)
10.117(3)
11.750(2)
12.359(2)
˚
b, A
˚
c, A
Ͱ, Њ
ͱ, Њ
Ͳ, Њ
111.25(2)
94.84(2)
108.78(2)
1262.3(6)
102.67(4)
95.21(2)
3
˚
Cell Volume, A
2104.2(9)
2547(1)
Formula units/unit cell
4
4
2
Dcalc g cmϪ3
1.176
0.66
1.170
0.66
1.180
0.66
Ȑ cmϪ1
Transmission factors
Diffractometer/scan
Scan width
0.93-1
Philips PW1100/␪-2␪
0.90-1
Philips PW1100/␪-2␪
1.5
0.93-1
Philips PW1100/␪-2␪
1.2
1.5
Standard reflections
Decay of standards, %
Reflections measured
2␪-range, deg
212; 401
Ϯ2
4178
6-50
234; 132
Ϯ2
5385
6-52
Ϫ331; 2-31
Ϯ2
5234
6-52
No. observed [I Ն 3␴(I)]b
Computer programs
2479
4155
4205
SIR 922
SIR 922
SIR 922
SHELX 933
SHELX 933
SHELX 933
PARST4
PARST4
PARST4
ORTEP II5
ORTEP II5
ORTEP II5
No. of parameters varied
Weight
359
429
429
1/[␴2(Fo2) ϩ (0.0P)2 ϩ 2.97Pc]
1/[␴2(Fo2) ϩ (0.0P)2 ϩ 1.43Pc]
1/[␴2(Fo2) ϩ (0.0P)2 ϩ 0.59Pc]
R (on F)
0.076
0.149
1.42
0.059
0.133
1.27
0.052
0.116
1.23
Rw (on F2)
GOF
a Least-squares refinement of (sin ␪/␭)2 values of 30 reflections with ␪ Ͼ 10Њ.
b Corrections: Lorentz-polarization; absorption (␺ scan).6
c P ϭ max(Fo2 Ϫ Fc2)2/3.

Structure of phenyl-substituted cyclopentenes
1129
Table 3. Atomic Coordinates and Equivalent Isotropic Thermal
Parameters (A ϫ 10 ) with esd’s in Parentheses for Compound
After purification of the reaction mixture on a silica
gel column (eluant petroleum ether-dichloromethane
9:1), the product was obtained in a pure form. m.p.
126–127ЊC (acetone); m/z 372 (M, 90%), 281 (100),
2
3
˚
2aI, Ueq ϭ (1/3) ͚ ͚jUijai*aj*aiиaj
i
Atom
x
y
z
Ueq/iso
1
203 (48), 115 (32), 91 (50); H NMR (CDCl3 as a
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
0.8562(2)
0.7352(2)
0.8020(2)
0.9230(2)
0.9650(2)
0.9933(2)
1.0721(3)
1.0982(5)
1.0497(6)
0.9755(4)
0.9475(3)
1.0117(2)
1.1493(2)
1.2327(3)
1.1817(3)
1.0462(3)
0.9621(3)
0.7362(2)
0.6010(2)
0.5406(3)
0.6130(3)
0.7470(4)
0.8081(3)
0.6198(2)
0.6107(2)
0.5070(3)
0.4114(3)
0.4185(3)
0.5209(2)
0.8242(2)
0.8389(2)
0.8107(3)
0.7656(3)
0.7485(3)
0.7784(2)
0.894(2)
0.0692(1)
0.0592(1)
0.06136(9)
0.08929(9)
0.1042(1)
0.1745(1)
0.1896(2)
0.2536(3)
0.3024(2)
0.2877(2)
0.2239(1)
0.1070(1)
0.1120(1)
0.1303(2)
0.1441(2)
0.1400(2)
0.1224(1)
0.0298(1)
0.0378(1)
0.0048(2)
Ϫ0.0363(1)
Ϫ0.0450(1)
Ϫ0.0126(1)
0.1058(1)
0.1638(1)
0.2064(1)
0.1916(2)
0.1341(2)
0.0914(1)
0.0940(1)
0.0526(1)
0.0724(2)
0.1339(2)
0.1756(2)
0.1564(1)
0.025(1)
0.5890(2)
0.5005(2)
0.3947(2)
0.4078(2)
0.5274(2)
0.5532(2)
0.6497(3)
0.6765(4)
0.6082(6)
0.5121(5)
0.4836(3)
0.3225(2)
0.3481(2)
0.2694(3)
0.1648(3)
0.1378(3)
0.2157(2)
0.2949(2)
0.2628(2)
0.1734(2)
0.1146(2)
0.1447(2)
0.2348(2)
0.5073(2)
0.4508(2)
0.4631(2)
0.5323(3)
0.5882(3)
0.5749(2)
0.7002(2)
0.7891(2)
0.8925(2)
0.9081(2)
0.8204(2)
0.7176(2)
0.603(2)
39.8(7)
39.1(6)
37.0(6)
37.5(7)
40.0(6)
51.4(8)
75(1)
117(2)
134(2)
103(2)
67(1)
41.3(7)
50.7(8)
68(1)
78(1)
76(1)
57.1(9)
40.5(6)
50.8(8)
66(1)
71(1)
70(1)
54.4(8)
41.2(7)
49.0(8)
62.7(9)
70(1)
solvent, TMS as internal standard), AMX2 system,
ͳH (ppm) 2.09–2.16 (1H, dt, JAM 13.4 Hz, JAX 8.2 Hz,
HA), 3,17 (1H, dt, JAM 13.4 Hz, JMX 8.9 Hz, HM), 4.42
(2H, app. t, J 8.9 and 8.2 Hz, HX), 6.9–7.3 (20H, m,
arom.). Crystals for X-ray analysis were grown by
slow crystallization from acetone at room tempera-
ture, in a sealed cuvette, in about a month.
The stereoisomer 2a was obtained by cathodic
reduction on a Hg pool of 1,2,3,4,5-pentaphenylcyclo-
pentadiene, in DMF as a solvent and 0.1 M TBAP
as supporting electrolyte, in the presence of phenol
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
H(1)
Table 2. Atomic Coordinates and Equivalent Isotropic Thermal
2
3
˚
Parameters (A ϫ 10 ) with eds’s in Parentheses for Compound
1a, Ueq ϭ (1/3)͚ ͚j Uijai*aj*aiиaj
i
Atom
x
y
z
Ueq/iso
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
0.1395(3) Ϫ0.3056(9) 0.3099(2)
0.0822(2) Ϫ0.1998(8) 0.3464(2)
0.0285(2) Ϫ0.0878(7) 0.2845(2)
0.0398(2) Ϫ0.1568(7) 0.2219(2)
0.1024(2) Ϫ0.3251(8) 0.2302(2)
0.1563(2) Ϫ0.2931(8) 0.1828(2)
52(2)
43(1)
38(1)
40(1)
46(2)
47(2)
58(2)
72(2)
82(3)
78(3)
58(2)
43(1)
52(2)
60(2)
61(2)
62(2)
51(2)
42(1)
54(2)
68(2)
72(2)
66(2)
53(2)
40(1)
51(2)
62(2)
68(2)
70(2)
54(2)
74(12)a
54(13)a
45(11)a
39(10)a
72(1)
0.1960(3) Ϫ0.097(1)
0.2493(3) Ϫ0.072(1)
0.2632(3) Ϫ0.240(1)
0.2241(3) Ϫ0.434(1)
0.1847(3)
0.1452(3)
0.1025(3)
0.0982(3)
56.3(9)
41.9(7)
51.7(8)
67(1)
73(1)
63(1)
51.4(8)
34(5)a
38(5)a
39(5)a
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
H(1)
0.1710(3) Ϫ0.4604(9) 0.1384(3)
Ϫ0.0054(2) Ϫ0.1016(8) 0.1509(2)
Ϫ0.0164(2) Ϫ0.2619(9) 0.0976(2)
Ϫ0.0601(3) Ϫ0.217(1)
Ϫ0.0928(3) Ϫ0.013(1)
0.0311(2)
0.0164(3)
0.0681(3)
H(2)
H(5)
0.698(2)
1.053(2)
0.016(1)
0.080(1)
0.513(2)
0.550(2)
Ϫ0.0817(3)
Ϫ0.0384(3)
Ϫ0.0346(2)
Ϫ0.0240(3)
Ϫ0.0831(3)
Ϫ0.1538(3)
Ϫ0.1658(3)
0.149(1)
0.1064(9) 0.1348(2)
0.0460(7) 0.2973(2)
0.2468(8) 0.3337(3)
0.372(1)
0.298(1)
0.098(1)
a Isotropic.
0.3437(3)
0.3191(3)
0.2838(3)
as proton donor, followed by purification on column
chromatography (see reference1 for more experimen-
tal details); m.p. 217ЊC (acetone-acetonitrile); m/z
448 (M, 100%), 370 (90), 357 (67), 279 (68), 191 (60),
Ϫ0.1071(3) Ϫ0.0264(9) 0.2731(2)
0.1139(2) Ϫ0.0488(7) 0.4085(2)
0.1636(2)
0.1896(3)
0.1656(3)
0.1168(3)
0.1189(8) 0.4031(3)
0.2618(9) 0.4585(3)
0.243(1)
0.076(1)
0.5206(3)
0.5273(3)
1
91 (50); H NMR (AB2 system) ͳH 4.59 (1H, app. t,
JAB 10.0 Hz, HA), 4.73 (2H, app. d, JAB 10.0 Hz, HB),
6.0 and 6.9–7.3 (25H, m, arom.). Crystals of 2aI for
X-ray analysis were grown by slow evaporation of
the solvent at room temperature in a sealed cuvette.
Crystals of 2aII were recovered from the NMR tube
after complete evaporation of the CDCl3.
0.0913(3) Ϫ0.0686(9) 0.4717(2)
0.158(3)
0.183(2)
0.054(2)
0.081(2)
Ϫ0.453(8)
Ϫ0.200(7)
Ϫ0.318(7)
Ϫ0.478(7)
0.331(2)
0.316(2)
0.366(2)
0.223(2)
H(1A)
H(2)
H(5)
a Isotropic.

1130
Benetollo, Busetti, and Marcuzzi
˚
Table 4. Atomic Coordinates and Equivalent Isotropic Thermal
Parameters (A ϫ 10 ) with esd’s in Parentheses for Compound
Table 5. Selected Bond Lengths (A) and Angles (Њ) for the
2
3
˚
Compounds Ia, 2aI and 2aII
2aII, Ueq ϭ (1/3)͚ ͚jUijai*aj*aiиaj
i
1a
2aI
2aII
Atom
x
y
z
Ueq/iso
C(1)UC(2)
C(1)UC(5)
C(2)UC(3)
C(3)UC(4)
C(4)UC(5)
C(5)UC(6)
C(4)UC(12)
C(3)UC(18)
C(2)UC(24)
C(1)UC(30)
1.536(7)
1.550(6)
1.534(5)
1.340(6)
1.521(6)
1.510(7)
1.482(5)
1.485(6)
1.517(6)
1.569(3)
1.564(3)
1.515(3)
1.345(3)
1.519(3)
1.516(3)
1.480(3)
1.487(3)
1.519(3)
1.517(3)
1.566(3)
1.575(2)
1.516(2)
1.348(3)
1.523(3)
1.519(3)
1.484(2)
1.484(2)
1.519(3)
1.515(3)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
0.1567(2)
0.2346(2)
0.1107(2)
Ϫ0.0165(2)
Ϫ0.0025(2)
Ϫ0.0511(2)
Ϫ0.0838(2)
Ϫ0.1242(3)
Ϫ0.1349(3)
Ϫ0.1052(3)
Ϫ0.0646(2)
Ϫ0.1603(2)
Ϫ0.2838(2)
Ϫ0.4193(2)
Ϫ0.4350(2)
Ϫ0.3144(2)
Ϫ0.1793(2)
0.1387(2)
0.2453(2)
0.2730(3)
0.1969(3)
0.0923(3)
0.0630(3)
0.3323(2)
0.2845(2)
0.3758(3)
0.5166(3)
0.5651(2)
0.4751(2)
0.2373(2)
0.2995(2)
0.3814(3)
0.4009(3)
0.3388(2)
0.2584(2)
0.151(2)
0.4734(2)
0.4132(2)
0.3192(2)
0.2904(2)
0.3704(2)
0.2917(2)
0.3524(3)
0.2871(3)
0.1586(3)
0.0964(3)
0.1619(2)
0.1973(2)
0.2121(2)
0.1267(2)
0.0251(2)
0.0070(2)
0.0906(2)
0.2813(2)
0.2335(2)
0.2053(3)
0.2260(3)
0.2752(3)
0.3023(2)
0.3525(2)
0.2217(2)
0.1708(3)
0.2517(3)
0.3809(3)
0.4317(2)
0.5307(2)
0.6670(2)
0.7263(3)
0.6509(3)
0.5153(3)
0.4553(2)
0.551(2)
0.6366(2)
0.5401(2)
0.4336(2)
0.4647(2)
0.5964(2)
0.6697(2)
0.7777(2)
0.8494(2)
0.8138(2)
0.7067(2)
0.6344(2)
0.3881(2)
0.4218(2)
0.3511(2)
0.2455(2)
0.2113(2)
0.2816(2)
0.3121(2)
0.2811(2)
0.1689(2)
0.0856(2)
0.1147(2)
0.2262(2)
0.5769(2)
0.5602(2)
0.5986(2)
0.6556(2)
0.6726(2)
0.6330(2)
0.7651(2)
0.8262(2)
0.9417(2)
0.9987(2)
0.9402(2)
0.8241(2)
0.622(2)
43.0(7)
42.6(7)
41.1(7)
40.8(7)
42.2(7)
45.7(7)
59(1)
78(1)
83.1(1)
75(1)
56.3(9)
43.0(7)
51.2(8)
61.3(9)
60(1)
60.6(9)
52.4(9)
42.6(7)
60.0(9)
85(1)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
H(1)
C(2)UC(1)UC(5)
C(1)UC(2)UC(3)
C(1)UC(5)UC(4)
C(2)UC(3)UC(4)
C(3)UC(4)UC(5)
C(4)UC(5)UC(6)
C(1)UC(5)UC(6)
C(3)UC(4)UC(12)
C(5)UC(4)UC(12)
C(2)UC(3)UC(18)
C(4)UC(3)UC(18)
C(1)UC(2)UC(24)
C(3)UC(2)UC(24)
C(2)UC(1)UC(30)
C(5)UC(1)UC(30)
106.7(3)
105.2(2)
105.5(1)
102.3(1)
102.6(1)
112.4(2)
112.0(2)
116.1(2)
118.0(2)
128.6(2)
119.3(2)
119.1(2)
128.3(2)
115.5(2)
115.4(2)
116.0(2)
119.8(2)
102.7(3)
102.5(4)
111.5(3)
112.2(4)
116.3(4)
112.8(3)
126.9(4)
120.6(3)
120.6(3)
127.1(4)
115.1(4)
115.4(3)
102.1(2)
103.0(2)
112.3(2)
111.9(2)
115.3(2)
118.2(2)
128.3(2)
119.8(2)
119.4(2)
128.2(2)
115.3(2)
115.4(2)
116.8(2)
119.4(2)
93(1)
83(1)
59.3(9)
43.7(7)
53.1(8)
68(1)
77(1)
70(1)
56.9(9)
45.1(7)
50.9(8)
61.4(9)
67(1)
Table 6. Selected Torsion Angles (Њ) for the Compounds 1a, 2aI
and 2aII
1a
2aI
2aII
68(1)
53.8(9)
41(5)*
39(5)*
40(5)*
C(1)UC(2)UC(3)UC(4)
C(1)UC(2)UC(3)UC(18)
C(2)UC(1)UC(5)UC(6)
C(2)UC(1)UC(5)UC(4)
C(2)UC(3)UC(4)UC(5)
C(2)UC(3)UC(4)UC(12)
C(3)UC(4)UC(5)UC(1)
C(3)UC(4)UC(5)UC(6)
C(5)UC(1)UC(2)UC(24)
C(5)UC(1)UC(2)UC(3)
C(24)UC(2)UC(3)UC(4)
C(18)UC(3)UC(4)UC(5)
C(12)UC(4)UC(5)UC(1)
C(12)UC(4)UC(5)UC(6)
C(18)UC(3)UC(4)UC(12)
C(24)UC(2)UC(3)UC(18)
C(30)aUC(1)UC(2)UC(24)
C(30)aUC(1)UC(5)UC(6)
C(18)UC(3)UC(4)UC(12)
C(24)UC(2)UC(3)UC(18)
C(30)UC(1)UC(5)UC(4)
C(30)UC(1)UC(2)UC(3)
12.9(5)
Ϫ177.0(4)
145.9(4)
20.2(4)
Ϫ18.8(2)
156.7(2)
108.3(2)
Ϫ20.1(2)
6.2(2)
Ϫ172.4(2)
9.3(2)
Ϫ120.9(2)
Ϫ102.6(2)
23.2(2)
107.0(2)
Ϫ168.8(2)
Ϫ172.0(2)
57.8(3)
12.6(4)
Ϫ77.5(2)
32.4(3)
Ϫ17.9(2)
156.3(2)
109.3(2)
Ϫ19.7(2)
5.5(2)
Ϫ176.2(2)
9.4(2)
Ϫ120.8(2)
Ϫ103.6(2)
22.5(2)
108.4(2)
Ϫ168.1(2)
Ϫ169.1(2)
60.8(2)
10.2(3)
Ϫ77.4(2)
31.4(2)
H(2)
H(5)
0.298(2)
Ϫ0.065(2)
0.488(2)
0.424(2)
0.522(2)
0.604(2)
Ϫ0.1(5)
174.0(4)
Ϫ12.7(5)
Ϫ136.2(4)
Ϫ146.4(4)
Ϫ20.2(4)
138.9(4)
Ϫ169.4(4)
172.8(4)
49.3(5)
a Isotropic.
Structure determination and description
Crystal data, summary of intensity data collec-
tion and refinement are listed in Table 1. All non-
hydrogen atoms were refined with anisotropic ther-
mal parameters. The H-atoms were located from dif-
ference Fourier maps and refined isotropically. Final
atomic coordinates and equivalent isotropic tempera-
ture factors for non-hydrogen atoms and hydrogen
atoms of the cyclopentene rings of compounds 1a, 2aI
and 2aII are shown in Tables 2, 3 and 4, respectively.
4.7(7)
Ϫ51.0(5)
Ϫ29(3)
29(3)
Ϫ25.2(3)
12.6(4)
Ϫ77.5(2)
Ϫ153.7(2)
158.2(2)
Ϫ23.7(3)
10.2(3)
Ϫ77.4(2)
Ϫ152.7(2)
157.6(2)
a H in compound 1a.

Structure of phenyl-substituted cyclopentenes
1131
Fig. 3. ORTEP drawing of the compound 2aI.
Fig. 1. ORTEP drawing of the compound 1a.
rings, I, II, III and IV, tilted to the mean cyclopentene
plane by 90.8(2), 35.6(1), 60.0(2), and 85.7(1)Њ, respec-
tively; so, the symmetry plane through the atom C(1)
and the bond C(3)UC(4) is missed only by the differ-
ent bending of the two phenyls III and IV.
As mentioned above, compound 2a crystallizes
from two different solvents yielding crystals belong-
ing to two different space groups, 2aI and 2aII, re-
spectively, (see Figs. 3 and 4). In compound 2aII,
space group P1, there are two molecules in the unit
Fig. 2. Crystal packing of the compound 1a.
Selected bond lengths and angles are reported in
Table 5 and torsion angles in Table 6.
The main feature of the crystal structure of com-
pound 1a (see Figs. 1 and 2), is the envelope confor-
mation 1E of the cyclopentene ring, with parameters
Q ϭ 0.211(5) and ⌽ ϭ 0.4(1.2)Њ, with the four phenyl
Fig. 4. Overlap view of the two packing of 2aI (cell with dot lines)
and 2aII (cell with full lines). Origin of 2aI at 1/2 of the a axis of
2aII and c axis along ac diagonal of of 2aII.

1132
Benetollo, Busetti, and Marcuzzi
cell, related by the symmetry center; these two mole-
cules are doubled in 2aI, space group P21/n, by the
presence of the n glide plane perpendicular to the b
axis of the P1 space group, so, in the two space groups
there are only slight differences in the a and c axis
values and in P21/n there is a nearly doubling of the
b axis value of P1 space group. No differences in
bond lengths, bond angles and torsion angles are
apparent from the data collected in Tables 5 and 6
for compounds 2aI and 2aII: they display the same
pounds, the cyclopentene ring is not planar and the
crowding around it causes the phenyl substituents to
rotate to some extent to release the steric hindrance;
as a result, the delocalization of the ȏ electrons must
be not so efficient as one may expect and this can
have important consequences on the spectroscopic
behavior and on the physical and chemical properties
of the molecule; (iii) the crystal packing, in the ab-
sence of hydrogen bonding and of solvent molecules
of crystallization, does not display any particular solid
state motif. Finally, it is worthy to mention that crys-
tals belonging to two different space groups could be
isolated from different solvents in the case of com-
pound 2a.
2
twisted T1 conformation, with Q ϭ 0.230(2) and
⌽ ϭ Ϫ168.8(5)Њ. Now, the phenyl ring V is nearly
perpendicular to the cyclopentene ring, 97.0(1)Њ,
while the phenyls I and IV deviate more from orthog-
onality, 69.8(1)Њ and 78.9(1)Њ, respectively; the bend-
ing angles of the phenyls II and III are 18.6(1)Њ and
122.7(1)Њ, respectively.
References
1. Farnia, G.; Marcuzzi, F.; Sandona`, G. J. Electroanal. Chem.
1999, 460, 190.
2. Altomare, A.; Burla, M.C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr.
1994, 27, 435.
Conclusions
3. Sheldrick, G.M.: SHELX-93: Program for Crystal Structure
Determination; University of Go¨ttingen: Go¨ttingen, Ger-
many, 1993.
4. Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
5. Johnson, C.K.: ORTEP II, report ORNL-5138; Oak Ridge
National Laboratory: TN, 1976.
The main conclusions, which can be drawn from
this crystallographic study are the following: (i) the
determination of the configuration of compounds 1a
and 2a allows the assignment of the 1H NMR signals
unambigously, and this is of great help for the identi-
fication of the reaction products1; (ii) in both com-
6. North, A.C.T.; Philps, D.C.; Mathews, F.S. Acta Crystallogr.
1968, A24, 351.