Synthetic studies on pyrrolizidine alkaloids. II. Intramolecular additions of radicals and electrophiles to allylstannanes as methods for ring closure

The simple pyrrolizidine alkaloid (±)-isoretronecanol was efficiently constructed by a route involving the attachment of an allylstannane moiety to succinimide followed by appropriate reduction, activation, and cyclization by either “one-electron” or “two-electron” protocols.     

On the evaluation of ion source conditions for optimum sensitivity of chemical ionization

The best operating conditions that yield maximum sensitivity at minimum source pressure have been evaluated for the chemical ionization source in a Kratos MS-25 mass spectrometer. The best reagent gas pressure is shown to be different for each gas and is significantly lower than is usually reported in the literature.     

Halogenation of polyethylene. I. Bromination of single crystals

It has been demonstrated that the fold surfaces of polymers can be specific towards chemical attack, if the reaction is mild and nondestructive of the fold. Bromination of suspensions of single crystals of polyethylene in carbon tetrachloride has been shown to be such a system. This chemical modification of a fold surface is a powerful means of extending the applications of the physical methods available. Several methods were used, among them DTA, DSC, infrared spectroscopy and small-angle x-ray diffraction. Experimental results from these methods lead to the following conclusions. (a) Bromination takes place preferentially at the folds and is consistent with a regular adjacent reentry fold model. (b) Annealing of these brominated crystals demonstrates the major role played by the crystal surface in this process. (c) The preparation and properties of a novel copolymer system has been demonstrated. It is felt that this copolymer system may prove a useful addition to those systems presently available.