1. Unilever Research Port Sunlight Laboratory, Bebington, Wirral, L63 3JW, UK, Unilever Research Vlaardingen Laboratory, Olivier van Noortlaan 120, NL-3133AT Vlaardingen, The Netherlands, and Westfälische Wilhelms-Universität Münster, Organisch-chemisches Institut, Corrensstrasse 40, D-48149 Münster, Germany