Crystal structure determination of the conformation of two bicyclo[3.3.1]nonan-ones

Abstract

The molecular structures of exo-7-methylbicyclo[3.3.l]nonan-3-one, 3, and the endoy-methyl isomer, 4, have been determined using X-ray. diffraction techniques. Compound 3 crystallizes in the space group 14 with a = 15.1 15 (l), c = 7.677 (2) A, and Z = 8 while 4 crystallizes in the space group P 2 1 , with a = 6.446 (I), b = 7.831 (I), c = 8.414 (2) A, P = 94.42(2)", and Z = 2. The structures were solved by direct methods and refined to final agreement factors of R = 0.041 and R = 0.034 for 3 and 4 respectively. Compound 3 exists in a chair-chair conformation and there is no significant flattening of the chair rings. However, in 4, the non-ketone ring is forced into a boat conformation.These results are significant in interpreting what conformations may be present in the related sp2-hybridized carbocations. JOHN F. RICHARDSON et TED S. SORENSEN. Can. J. Chem. 63, 1166Chem. 63, (1985.Utilisant des techniques de diffraction des rayons-X, on a determine les structures moleculaires de la methy]-7 exo bicyclo[3.3. I] nonanone-3, 3,0et de son isomhe methyl-7 endo, 4. Le compose 3 cristallise dans le groupe d'espace 14, avec a = 15,115(1)2 c = 7,677(2) A et Z = 8 alors que 4 cristallise dans le groupe d'espace P2,, avec a = 6,446(1), b = 7,831(1), c = 8,414(2) A, P = 94,42(2)" et Z = 2. On a resolu les structures par des methodes directes et on les a affintes jusqu'a des valeurs respectives de R de 0,041 et 0,034 pour les composCs 3 et 4. Le compose 3 existe dans une conformation chaise-chaise et il n'y a pas d'aplatissement notable des cycles en formes chaises. Toutefois, dans le compose 4, le cycle qui ne porte pas la cetone est force de prendre une conformation bateau. Ces rksultats sont importants pour interpreter la nature des conformations qui peuvent Ctre presentes dans les carbocations apparentes qui ont une hybridation sp2.[Traduit par le journal]A number of organic reactions, where a carbocation interrigid framework of the bicyclo[3.3. Ilnonane ring system and mediate is involved, undergo a rearrangement reaction characthe consequent difficulty in bringing C(3) and C(7) within terized by a n, 1-hydride shift, where position 1 is the carbo-"bonding" distance. cation centre and n is a C-H function located at a separationAs an aid in the study of the observable carbocations, we were interested in getting structural data on the related ketones In some recent examples where n = 5 and 6, it has been 3 and 4. Ketone 3 was expected to be a di-chair structure and 1 possible to directly observe a symmetrical p-hydrido-bridged our principle interest was in looking at the expected I carbocation 1, where p and q define a medium ring, i.e. p + "flattening" of the chairs because of transannular interactions. q = 6, 7, 8, or 9 (1 -3). In the case of p = q = 3, R = H, it On the basis of nmr work, ketone 4 had been proposed to have has also been possible to show the existance of 1 as an intera chair-boat structure (9). We were interested in confirming mediate in solvolysis or acid-catalysis reactions (4, 5).Like the simple r...