Structures of angrendiol, ferolin, and chimganidin
SummaryOn the basis of the results of a study of the products of chemical transformations and spectra, the structure of angrendiol has been established as 4,8-dihydroxygermacra-1(10), 5(6)-diene. It has been shown that ferolin and chimganidin are monoesters of angrendiol with parahydroxybenzoic and vanillic acids, respectively, at the secondary hydroxy group.
Stereospecific cope rearrangement of the germacrene-type sesquiterpenes
Abstract Stable, conformations of several germacrene-type sesquiterpenes in solution are deduced with the aid of intramolecular nuclear Overhauser effects (NOE) in the NMR spectra. From these conformations, stereochemical aspects of the Cope rearrangement as well as the stereochemistry of the elementype rearrangement products can readily be understood.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.