Notizen: Cyclophanes, XXX The Crystal Structure of [2.4]Paracyclophane at —95°C

Abstract

The strong electronic interactions between the benzene rings of [2.2]-and [3.3]paracyclophane have fascinated many chemists, and have made these molecules the most thoroughly studied bridged aromatics to date [2 -4 ]. The proximity of the two rings not only has a pronounced influence on the various spectra of these molecules but also is the origin of some interesting chemical effects. It has been noted [5], for exam ple, that a carbonyl sub stituent at C-4 in [2.2]paracyclophane often directs an incoming electrophile into the so-called pseudogeminal position, viz. to a position of the unsubsti tuted ring exactly opposite the already substituted carbon atom.We are interested in investigating how far these directing effects extend, and therefore decided to study the chemical behaviour of the title compound. It is known from Cram 's classical papers [6] that the still higher-bridged phanes behave like conventional aromatic compounds. One would therefore expect that there should be no such directing effects in these ExperimentalFor the preparation of the title compound we fol lowed the procedure given in the literature [7], i.e. carried out a ring expansion of [2.2]paracyclophane with diethyl fumarate and subsequently decarboxylated and reduced the initially formed [2.4]paracyclophane diester. Crystals suitable for X-ray analy sis were obtained by recrystallization from ethanol. A room -tem perature structure determination proved unsatisfactory because of extreme thermal motion ef fects, especially in the longer bridge, and was th ere fore repeated at -95 °C. Crystal structure determinationCrystal data: C 18H 2n, Mr = 236.35, orthorhom bic, space group Pbca, a = 1151.5(5), b = 1832.9(7), c = 1304.1(4) pm, U = 2.752 nm3, Z = 8, D x = 1.14 M gm -3, F(000) = 1024. A (M oK a) = 71.069 pm, ju = 0.06 mm-1, T = -95 °C.Data collection and reduction: A colourless tablet ca. 0 .9 x 0 .5 x 0 .2 mm was m ounted on a glass fibre and transferred to a Nicolet P3 diffractometer fitted with an LT-2 low-temperature attachm ent. 2998 in tensities were registered to a maximum 2 6 of 50° (m onochrom ated M oKa radiation). Of 2411 unique reflections (R inl = 0.012), 1626 with F > 4a(F ) were used for all calculations (program system XLS). The orientation matrix was refined from setting angles of 44 reflections in the range 2 6 = 20-24°.Structure solution and refinement: The structure was solved by routine direct methods using the room tem perature data; the coordinates thus obtained were used as a starting point for the refinement of the low tem perature data. A fter anisotropic refine ment of all C atoms, the H atoms were identified in a difference Fourier synthesis; because of the m oder ate data/param eter ratio, they were placed in ideal ized positions and refined using a riding model. The final R value was 0.053, with R w = 0.047. The weighting scheme was w_1 = cr(F) -I-0.0003 F2. 163 param eters; S 1.6; max. A /o 0.001; max. A g 0.2X10"6 e p m " 3.Final atomic coordinates are presented in Table I, with derived bond lengths and an...

Neue Erkenntnisse Uber Die Chemie Der [M.N]PARACYCLOPHANE

“…MS m/z (%): 184 (M + , 87), 151(100), 137 (42), 117 (31), 115 (7), 105(10), 104 (37). Lithiumaluminiumhydrid in 500 ml abs.…”

“…UV(CH 3 CN): X m2a (lge)= 199 nm (4.64) MS m/z (%): 344 (M + , 100), 312 (27), 194(68), 162(31), 149 (38), 117( 51), 104 (32), 91 (42). 22), 250(100), 248 (17), 222( 39), 207 (12), 145 (18), 131 (37) -so 2…”

“…MS m/z (%): 392 (M + , 29), 376( 10), 328( 7), 309 (6), 264 (28), 236 (7), 221( 4), 207( 7), 145/18), 131 (28), 117 (30), 105 (47), 104(100). MS m/z (%): 430 (M + , 81 Br,5), 428 (M + , 79 Br,5), 302( 50), 300 (50), 221(44), 198(46), 196(49), 131 (12), 118 (42), 117(100), 115( 59), 105 (34), 104(68). 6), 416(10), 398( 5), 352(65), 337( 10), 324 (20), 320( 15), 293 (15), 220 (15), 204 (39), 131(41), 104(100).…”

“…MS m/z (%): 306 (M + , 85), 291(100), 288(67), 278 (19), 263(26), 171 (18), 145 (42), 131 (46), 117 (30), 105 (40). H-NMR (DMSO-D 6 ): δ = 1.…”

“…Br,100), 345 (15), 343 (15), 279( 5), 278 (19), 277 (30), 173 (25), 160 (55), 159 (27), 145 (21), 11 (37), 115 (30), 105 (22), 91( 22), 43 (50). , 79 Br,42), 279 (18), 247 (32), 175(100), 163(60), 144 (42), 131 (28), 117 (30), 115 (48). 2, 29.2, 33.8, 35.3, 35.5, 35.8 (t, C-l, C-2, C-3, C-10, C-ll, C-12), 129.1, 131.7, 132.2, 133.0, 133.5 (d, C-6, C-8, C-9, C-14, C-17, C-18), 124.7, 127.7, 137.4, 138.4, 140.7 (s, C-4, C-5, C-7, C-13, C-15, C-16), 167.9 (s, C-19).…”