A simple contactless impedance probe for determination of ethanol in gasoline

A contactless impedance probe with either a planar or a tubular detection cell has been developed and tested for rapid determination of the ethanol content in gasoline. The probe cell is connected as a capacitor determining the frequency of an electronic astable multivibrator. The multivibrator frequency depends on the permittivity of the test gasoline in the detection cell which is strongly influenced by the ethanol content as one of the major polar additives. The ethanol concentrations obtained with the impedance probe agree, within the reliability interval, with those obtained by GC-MS measurements and fall into the limits recommended by the appropriate European Standard. The gasoline samples are analyzed without any pretreatment.     

A DFT study on the (2 + 3) cycloaddition reactions of 2‐nitropropene‐1 with Z‐C,N‐diarylnitrones

B3LYP/6‐31G* calculations for competing (2 + 3)‐cycloaddition pathways for 2‐nitropropene‐1 (1) to Z‐C, N‐diarylnitrones ( 2a – e ) suggest a concerted reaction mechanism. However, the results point to the strongly asymmetric nature of transition complexes. Increasing polarity of the reaction environment and presence of electron‐donating substituents in the nitrone phenyl rings contribute to the higher asymmetry of these structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Enantioselective Synthesis of the Platensimycin Core by Silver(I)-Promoted Cyclization of Δ6-α-Iodoketone

A chiral-pool-based synthesis of the platensimycin core was achieved using (S)-lactic acid as an inexpensive starting material. The cyclohexenone ring was closed in a Mukaiyama–Michael domino sequence, while the quaternary stereocenter was created by a highly stereoselective decarboxylative allylation. The spirobicyclic skeleton was constructed by a RCM reaction. A new silver(I)-promoted cyclization reaction of Δ⁶- and Δ⁷-α-iodoketones was developed and applied for the pivotal carbon–carbon bond formation. The scope and limitations of this methodology are also presented.