Single-crystal X-ray geometries and electron density distributions of cyclopropane, bicyclopropyl and vinylcyclopropane. I. Data collection, structure determination and conventional refinements

Abstract

Crystal structures of cyclopropane (CP) C3H 6, bicyclopropyl (BCP) C6HI0 and vinylcyclopropane (VCP) C5H s have been determined by accurate single-crystal X-ray measurements at T,~ 100 K. In addition to the conventional full-angle refinements [(sin0)/2< 1.15 A -~ for CP and < 1.

Preparation and Properties of Centrally Bridgehead‐Substituted Hexacyclo[4.4.0.02,1.03,5.04,8.07,9]decanes (“Diademanes”) and Related (CH)10Hydrocarbons

“…The other six cyclopropane bonds (1.502(4) ä) are shorter than the best calculated value and very close to the normal length of 1.499(1) ä in cyclopropane. [22] The experimentally determined value for bond d (1.559(4) ä) is the only one that almost completely agrees with the calculated value for diademane 1 a. The deviations between the experimentally determined bond lengths a ± d and the best available computed ones can be attributed to the influence of the substituent at C6 and to crystal packing effects.…”

“…the unsubstituted cyclopropane moiety are virtually the same as in unsubstituted cyclopropane itself (c 1.505(3) vs. 1.499(1) ä [22] ), but bond e in the unsubstituted cyclopropane moiety is significantly lengthened (1.534(3) ä); this must be caused by the b-donating effect of the trimethylsilyl group. [23] In the substituted cyclopropane moiety, however, p electron withdrawal comes to play its role, so that the two proximal (with respect to the SiMe 3 group) bonds b are lengthened Table 1.…”

Stereoselective Preparation of Six Diastereomeric Quatercyclopropanes from Bicyclopropylidene and Some Derivatives

“…The parent bicyclopropyl also has such a conformation in the crystal,30 whereas in the gas phase17, 31 and in the liquid16, 32 the synclinal ( gauche ) conformer predominates. From a structural point of view, meso ‐ 5 is essentially a linked combination of the structures of bicyclopropylidene ( 3 )18b and of bicyclopropyl 30a. Thus, the structures of both bicyclopropylidene units in meso ‐ 5 are actually undistorted in comparison with the parent bicyclopropylidene ( 3 ),18b and the bond length h between the two bicyclopropylidenes in meso ‐ 5 [1.494(1) Å] is essentially the same as the central bond length in bicyclopropyl [1.4924(4) Å], as measured at 100 K 30a.…”

Tetracyclopropylmethan: ein einzigartiger Kohlenwasserstoff mitS4-Symmetrie

“…Tricyclopropyl(2,2-dideuteriocyclopropyl)methan 7 b wurde auf die gleiche Weise aus 6 b hergestellt, welches aus 3 durch Reduktion mit LiAlD 4 und weitere Transformationen des resultierenden Alkohols 4 b entsprechend den für 4 a ausgearbeiteten Versuchsbedingungen erhalten wurde (Schema 1). [21] Doch ist die berechnete (B3LYP/6-31 G**) Rotationsbarriere der Cyclopropylgruppen in 7 a von 8.2 kcal mol À1 (298 K) höher als die für die Rotation um die zentrale Bindung in Hexacyclopropylethan (6.4 kcal mol À1 ), [20a] ähnelt aber der Barriere für die Rotation der Cyclopropylgruppen im Tricyclopropylmethylkation (8 ± 10 kcal mol À1 ). [4a,b] Nach B3LYP/6-31 G**-Rechnungen [18] beeinträchtigt die vierte Cyclopropylgruppe in 7 a die Orientierung der drei anderen in der Weise, dass sich eine S 4 -Gesamtsymmetrie einstellt (Tabelle 1).…”