Browsing by Subject "charge"

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    Electrostatically Enhanced Thioureas: Synthesis, Reactivity and Selectivity
    (2018-07) Fan, Yang
    Hydrogen bonding exhibits its importance in enzyme-catalyzed chemical transformations, naturally occurring three-dimensional architectures and molecular recognition. In recent years, synthetic chemists have successfully exploited hydrogen bonds and developed many enantioselective organocatalysts. As a result, small molecule hydrogen bond donors along with organometallic species and enzymes are now recognized as playing a major role in asymmetric synthesis. Thiourea derivatives are among the most common and widely-developed hydrogen bond catalysts. Impressive results in terms of both yields and enantioselectivities in asymmetric syntheses have been obtained. A key feature in their success is the ability of these compounds to simultaneously donate two hydrogen bonds to a substrate, despite their relatively weak acidity. This provides highly stereoconfined environments when chiral moieties are incorporated into the thiourea and has made them the subject of extensive research efforts. The work described in this thesis focuses on the development of a class of positively charged acidity-enhanced thiourea catalysts which make use of an alkylated pyridinium substituent and an appropriate non-coordinating counteranion to enhance their N‒H acidities and improve their catalytic activities by orders of magnitude in a variety of transformations. A series of these catalysts have been synthesized and their reactivities in both asymmetric and non-asymmetric transformations were explored. Simple and highly efficient synthetic schemes and excellent catalytic results have been discovered for these novel species.
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    Interim Policies and Procedures for the New College of Education and Human Development
    (University of Minnesota: College of Education and Human Development, 2006-05-10) Collins, Terry; Hogan, Jan; Yussen, Steven
    Thank you for agreeing to serve on the ad hoc faculty/staff committee to consider an interim governance and policy/procedure structure for the 2006-07 academic year. We expect that your recommendations will form the basis of the new CEHD operations until a new Constitution is developed and new policies and procedures are adopted. We ask you to meet as often as necessary in early June to review current practices in all three colleges and then make a recommendation to us on the topics listed below no later than June 13, 2006. We, in turn, will carefully consider your recommendations and forward them with our advice to the Provost. The Provost will advise the administration of the New College on how to proceed.