Problem-based learning, process-oriented guided inquiry learning, and peer-led team learning are student-centered, active-learning pedagogies commonly used in science education. The characteristic features of each are compared and contrasted to enable new practitioners to decide which approach or combination of approaches will suit their particular situation.

As a rule, a trans disubstituted alkene is more stable than the corresponding cis isomer. For cycloalkenes of fewer than eleven members, cis isomers are more stable than their trans counterparts. Although this exception to the normal rule is occasionally noted in beginning organic chemistry textbooks, it is often done without a careful analysis of the reasons behind it. The purpose of this article is to provide that analysis. In order for a cycloalkene to accommodate a trans double bond one or more of the following nonideal geometries must occur: a twisted π bond; pyramidal sp2-carbon atoms; nonideal sp3 bond angles; or longer than normal C–C single and double bonds. This article provides a list of experimentally determined relative energies of the cis and trans isomers within the series cycloheptene–cycloundecene, along with computationally derived energies at several levels of theory. It also examines the geometric distortions through which cycloalkenes relieve the strain introduced by a trans double bond.

Thioaldehydes containing virtually any -substitutent can be generated by photofragmentation of phenacyl sulfides. Donor-substituted derivatives are reactive toward electron-rich dienes and give 2 + 4 cycloadducts with regiochemistry corresponding to advanced C-C bonding in the transition state. Acceptor-substituted thioaldehydes react in the opposite regiochemical sense with C-S bonding advanced. A number of unusual thioaldehydes have been trapped, including the parent HCH=S, Me3SiCHS, Ph2P(0)CH=S, PhS02CH=S, and CNCH=S, as well as more conventional alkylor acyl-substituted derivatives.

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