An Examination of the Relationship Between Transition State Geometry in Hydron Transfer Reactions and the Temperature Dependence of the Primary Kinetic Isotope Effect

Several recent papers by Kwart feature hydron transfer reactions in which the primary kinetic isotope effect is temperature independent over wide temperature ranges. It has been asserted (without theoretical justification) that this phenomenon is associated with transition state X….H….Y bond angles which are significantly less than 180°, whereas normal temperature dependence may be associated with transition states in which the angle is close to 180°. This work employs model calculations of isotope effects, principally for [1,5] H-shifts in 1,3-pentadiene, to examine Kwarts's hypothesis. No model tested yielded a temperature-independent isotope effect of substantial magnitude. The transition state (angle = 133°) was located on the MNDO potential energy surface and the isotope effect, calculated by a new and fast computational procedure, was again temperature dependent. Model calculations of secondary hydrogen isotope effects were carried out. When bending motions of the non-reacting hydrogens were coupled to C….H stretching modes in the force constant matrix, it was found that kH/kD was greater than the equilibrium secondary isotope effect, k_H/K_D, and that k_H/k_D for hydrogen transfer exceeded k_H/k_D for deuteron transfer when simple tunnel corrections were incorporated. A novel interpretation to account for the observation of some temperature-independent isotope effects is advanced.     

Aylesford新闻纸厂生产综述

Ａｙｌｅｓｆｏｒｄ新闻纸有限公司于 １９９３年由 ＳＣＡ森林产品和 Ｍｏｎｄｉ Ｅｕｒｏｐｅ建立的。随后，２．５亿英镑（合３．７５亿美元）的投资项目以新闻纸机（～＃１４机）和脱墨车间，还有１个完全自动化包装线和仓库、２个联合热电厂以及１个水和污水处理工厂的投产而宣告完成。 这一最新的发展只是Ａｙｌｅｓｆｏｒｄ众多造纸历史事件之一，早在１９２１年Ａｙｌｅｓｆｏｒｄ就已经开始制造新闻纸。在～＃１４机之前已有的新闻纸机（～＃１３机）已经运行了将近４０年，并于１９８２年成为英国第一台利用１００％脱墨纤维制造…     

A knowledge-based support system for mechanical ventilation of the lungs. The KUSIVAR concept and prototype

The KUSIVAR is an expert system for mechanical ventilation of adult patients suffering from respiratory insufficiency. Its main objective is to provide guidance in respirator management. The knowledge base includes both qualitative, rule-based knowledge and quantitative knowledge expressed in the form of mathematical models (expert control) which is used for prediction of arterial gas tensions and optimization purposes. The system is data driven and uses a forward chaining mechanism for rule invocation. The interaction with the user will be performed in advisory, critiquing, semi-automatic and automatic modes. The system is at present in an advanced prototype stage. Prototyping is performed using KEE (Knowledge Engineering Environment) on a Sperry Explorer workstation. For further development and clinical use the expert system will be downloaded to an advanced PC. The system is intended to support therapy with a Siemens-Elema Servoventilator 900 C.     

The hydrogenation of soybean oil

Journal of the American Oil Chemists' Society - 1