No abstract

The effect of pH on the gelation time of hexylene-bridged polysilsesquioxanes was determined with the sol−gel polymerization of 1,6-bis(trimethoxysilyl)hexane (1) in methanol. Gel times formed a crude bell curve plotted against pH with the longest gel times of 660 h near pH 5. This represents the first systematic study of the effects of pH on the gelation of polysilsesquioxanes.

Many students fail to develop a conceptual understanding of organic chemistry. Evidence suggests this failure goes hand-in-hand with a failure to grasp the techniques, meaning, and usefulness of curved arrow notation. Use of curved arrow notation to illustrate electrophilic addition appears to be a critical juncture in student understanding. Misconceptions arise because electrophilic addition is the first reaction where the curved arrow shows electrons from a pi bond forming a new bond that does not originate from a specific atom. This article describes a new technique (bouncing curved arrows) that addresses this stumbling block by designating which alkene carbon makes a bond to the electrophile. By removing this stumbling block and replacing it with a clear demonstration of the utility of curved arrows to describe regiochemistry of organic reactions, we encourage students to use curved arrows rather than rote memorization to deal with subsequent mechanisms. Student and faculty survey data are provided as evidence that both groups find bouncing curved arrows useful for describing electrophilic addition reactions, as well as electrophilic aromatic substitution reactions and carbocation rearrangements.