Bicyclo hexenyl cations structure

If C(6) is substituted with very good carbonium ion stabilizers the transition-state structure [173] becomes more stable than the bicyclo[3.1.0]-hexenyl cation structure. Thus treatment of a series of 5-acyl-1,2,3,4,5-pentamethylcyclopenta-1,3-dienes with AlgCle produced cleanly the corres-... 

No other experimental structure determinations of bicyclo[3.l.0]hexenyl cations have been reported. Theoretical calculations have been undertaken by Hehre105 151 and Cremer and colleagues30. While in each of these instances the calculations were at a low level, the results are consistent with the presence of a short C(l)—C(5) and long C( 1)—C(6)/C(5)—C(6) internuclear distances for the parent cation. 

Bicyclo[2.1.0]pentene, 116, can be considered to be the prototype of a neutral homoantiaromatic molecule. The types of structural and bonding effects found for this molecule parallel in many respects those found for the bicyclo[3.1.0]hexenyl cation reported above. Further studies on both of these 4q systems will likely be rewarding in terms of fully understanding the nature of cyclopropyl homoconjugation and homoantiaromaticity. 

The structure of the l,2,3,4,5-pentamethylbicyclo[3.1.0]-hexenyl cation [170] was established by Childs et al. (1968) by H-nmr spectroscopy and a considerable delocalization of positive charge into the cyclopropane ring (112) was proposed. The structures have been extensively discussed by Childs et al. (1974 and references therein) for other bicyclo[3.1.0]hexenyl cations. 

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