The 13C spectra of 18 sets of aliphatic and alicyclic halides (F, C1, Br, I) have been obtained as 2 M solutions in C'DC13 and have been assigned. The differences in chemical shift with respect to the parent hydrocarbons (Ah) have been analyzed by the use of factor analysis. This technique leads to two sets of parameters: "intrinsic" substituent effects (a values) characteristic of the halogens and attenuation parameters (b values) which reflect the sensitivity of each molecular position to the substituent effects. In the present case it was found that only three-substituent-effect terms for each halogen are needed to correlate all of the data. The chemical shifts are related to the parameters by A6, = axlb, + a&, + ax3bs where x refers to the halogens and i refers to the molecular positions. The first substituent parameter (al) is essentially a constant for all of the halogens and appears to be related to the polar effect of halogen v i s -h i s hydrogens. The corresponding attenuation parameters (b,) represent the sensitivity of each molecular position to polar effects of the halogens. The second substituent parameter (az) increases approximately linearly on going from fluorine to iodine, controls the differences in A6for the series of halides, and appears to be related to the "freeness" of the valence electrons about the halogens. The third parameter (a3) is considerably less significant than the others. An analysis of the effect of the structural changes on the molecular attenuation parameters (bl-b3) reveals that the two most important substituent parameters are each transmitted to the a, 0, and y positions via the same or linearly related mechanisms. The a2 halogen factors are linearly related to a variety of non-NMR parameters characteristic of the halogens (reciprocals of the ionization potentials of CH&, wavelength of the first electronic transition of CH,X, C-X bond polarizabilities, and atomic contributions to molar diamagnetic susceptibilities) as well as the diamagnetic and paramagnetic susceptibiliities derived from NMR measurements.

Sir:Neolignansl are a group of secondary plant metabolites structurally characterized by the presence of two arylpropanoid units. In contradistinction to the related lignans the @ position of one arylpropane moiety is linked to one of three additional positions in the other. Within the class of neolignans substances with bicyclo[ 1.2.3]0ctane, hydrobenzofuran and spiro[5.5]undecane skeleton are encountered. Guianin ( 1)2 (from Aniba guianensis Aubl.), burchellin (2)3 (from Aniba burchellii Kosterm.), and futoenone (4)4 (from Piper futokadzura Sieb. Communications to the Editor

The reactions of normally unreactive bicyclic iodides such as 1-and 7-iodonorbornane with bromine has been found to occur readily with the formation of the corresponding bromide. The reaction involves the formation of the complex RI-X2 as an intermediate and is accelerated by polar solvents. The reaction of 1-iodobicyclo-[2.1.1]hexane with bromine led to rearranged products, showing that a cationic intermediate is involved. The data indicate that the IBr2" ion is one of the best of the known leaving groups for SN1 or SN2 reactions. The observation of a rapid reaction of the bridgehead bicyclo[2.2.2]octyl iodides with bromine has led to a reexamination of the reaction of 1,4-diiodobicyclo[2.2.2] octane with butyllithium. The previous report of the formation and trapping of the [2.2.2]propellane in this reaction was found to be incorrect.

No abstract

No abstract