氢键对有机取代反应和加成反应的影响

取代反应和加成反应是有机化学中最基础、最重要、也是研究最多的反应。影响取代反应和加成反应的因素很多,文章从氢键的形成、类型、键能大小出发,分析讨论了其对饱和碳原子上亲核取代反应、苯环上C-F键的亲核取代反应、亲电加成反应及羰基化合物亲核加成反应的影响,所得结论对有机化学理论教学和有机合成具有一定的指导意义。     

溶剂化效应在有机反应中的作用

有机反应大多数都在溶剂中进行,溶剂对化学反应的中间体和产物有着不同程度的影响。在有机反应中,选择合适的溶剂十分关键。溶剂可以影响到溶质的解离,影响反应的立体选择性,同时溶剂可以影响有机反应的中间体,进而改变反应的结果。本文以溶剂对反应物和反应中间体的影响为重点,分析了分子内亲核取代,两可亲核试剂的亲核取代,以及亲核取代反应和消除反应的竞争的反应实例。     

应用电子效应判断有机化学反应主要产物

诱导效应和共轭效应是高等有机化学中两类重要的电子效应,贯穿了大学有机化学的学习,一直是大学有机化学中的重点难点。本文通过分类分析和总结这两类电子效应对π电子的极化作用和中间体稳定性两方面的影响,可确定反应的主要产物,有利于学生的学习和相关内容掌握,为有机化学知识在反应生产中判断主要产物提供了重要的基础保障。涉及的反应包括亲电加成反应、亲核加成反应和亲电取代反应等。     

亲核试剂的亲核性与碱性

文章以卤代烃的亲核取代反应为例,从亲核试剂的亲核性和碱性的定义入手,详细讨论了进攻试剂的亲核性与碱性的同和异,阐述了亲核试剂亲核性的影响因素,以便学生能够熟练掌握此知识点。     

反应条件对N-炔丙基-4-溴-1,8-萘酰亚胺与水合肼反应产物的影响

水合肼作为转移氢化试剂可选择性还原C=C双键和C≡C三键,亦可作为肼解试剂与邻苯二甲酰亚胺通过Gabriel反应制备伯胺;此外,由于水合肼是富电子基团,可对卤化物进行亲核取代反应.本文通过单因素实验研究了反应时间、反应温度、水合肼用量、溶剂、气体环境等因素对N-炔丙基-4-溴-1,8-萘酰亚胺与水合肼反应产物的影响.结果表明,影响Gabriel、转移氢化和亲核取代反应的主要因素分别是水合肼的用量、气体环境和反应温度.     

芳香亲核取代氢反应及4-氨基二苯胺的合成

芳香亲核取代氢反应是一种环境友好的有机合成反应。4-氨基二苯胺是一种重要的工业中间体,在它的合成过程中对环境污染严重。Flexsys公司将芳香亲核取代氢反应应用于4-氨基二苯胺的合成,解决了环境污染问题。并因此荣获1998年度美国总统绿色化学挑战奖。本文介绍了4-氨基二苯胺的传统合成方法,进而又介绍了芳香亲核取代氢反应的机理及其在4-氨基二苯胺合成中的应用。     

基于知识构建的化学反应机理教学探索

反应机理在现代有机化学课程中占有重要地位,用弯箭头表示法描述反应机理过程中电子流向是有机化学课程中最重要的表征方法之一。本论文借鉴国内外教学人员关于利用弯箭头表示法描述化学反应机理教学中的建议,选取亲电加成、亲核取代、双分子消除反应这几个章节为例,将知识构建教学策略应用于该内容的教学过程中,并进行了详细分析。     

3,4-二-O-乙酰基-D-鼠李糖的合成

标题化合物作为一种重要的有机合成中间体,在有机合成活性较高的天然产物中具有重要意义。以三-O-乙酰基-D-己烯糖作为起始原料,经脱乙酰基反应、磺酰化反应、乙酰化反应、亲核取代反应和还原反应合成目标产物。其中间体及目标产物的结构均经IR、~1HNMR和MS进行表征。对提高目标产物收率进行深入探索,结果表明,适当的反应时间、温度及投料的物质的量比分别能够有效提高乙酰化反应、亲核取代反应和还原反应的产品收率,总收率为63%。     

有机化合物的光取代反应及其在有机合成中的应用

本文简要介绍了脂肪族化合物的光卤化反应、氯磺化反应和亚硝化反应，以及芳香族代合物的光亲核取代、亲电取代和游离基取代反应的反应机理，并介绍了光取代反应在有机合成中的应用。     

硫醇作亲核试剂在有机合成中的应用

概括硫醇作为亲核试剂与环氧化合物和氮杂环丙烷类化合物加成反应、与酰氯、酸酐、酰胺、酯和羧酸的酰化反应及与醇和卤代烃的亲核取代反应。     

Reactions of histidine

The reactions of histidine were studied with the aim of converting this amino acid to 4-vinylimidazole, but a commercially attractive scheme could not be developed.     

Noncanonical Reactions of Flavoenzymes

Enzymes containing flavin cofactors are predominantly involved in redox reactions in numerous cellular processes where the protein environment modulates the chemical reactivity of the flavin to either transfer one or two electrons. Some flavoenzymes catalyze reactions with no net redox change. In these reactions, the protein environment modulates the reactivity of the flavin to perform novel chemistries. Recent mechanistic and structural data supporting novel flavin functionalities in reactions catalyzed by chorismate synthase, type II isopentenyl diphosphate isomerase, UDP-galactopyranose mutase, and alkyl-dihydroxyacetonephosphate synthase are presented in this review. In these enzymes, the flavin plays either a direct role in acid/base reactions or as a nucleophile or electrophile. In addition, the flavin cofactor is proposed to function as a “molecular scaffold” in the formation of UDP-galactofuranose and alkyl-dihydroxyacetonephosphate by forming a covalent adduct with reaction intermediates.     

Reactions of azelaaldehydic esters

Alkyl azelaaldehydates and their acetals can undergo reactions at either the aldehyde or the ester group to form a variety of novel and reactive monomers and polymers. Pertinent reactions of the aldehyde group (and resultant products) include acetalization with pentaerythritol (diester-acetal), acetalization with glycerol (hydroxy ester-acetal), hydrogenation (hydroxy ester), reductive alkylation of ammonia (amino acid and imino diester), aldolization (dibasic acid) and hydrazone formation (azine dibasic acids). Reactions at the ester group include aminolysis (diacid amides) and hydrazinolysis (hydrazide acetal). These various products can undergo self-condensation or condensation with glycols or diamines to form polyesters, polyamides, poly (ester-acetals) and poly (amideacetals). Polymers with cyclic acetal structures in the polymer backbone have latent crosslinking capabilities. Presented at the AACC-AOCS Joint Meeting, Washington, D.C., April, 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Hypergolic Reactions of TNT

One way being considered to destroy trinitrotoluene (TNT) land or surf mines is to exploit its reactivity using darts containing chemicals, which, upon contact with TNT, cause instantaneous decomposition, but not detonation. To determine the best candidates to fill the darts, liquids, specifically amines, which react in a hypergolic fashion with TNT were examined for both the rate of reaction and amount of energy released. Micro‐calorimetry was used to measure heat release while spectroscopy and conventional peak intensity monitoring by chromatography were used to examine the rate of reaction. Calorimetry measurements showed little variation between different amines reacting with TNT (about 110–130 kJ mol⁻¹ TNT). TNT reaction with hydride actually produced more heat than with amines. Further, dinitrotoluene (DNT), which generates substantial heat, did not undergo a hypergolic reaction with amines suggesting that heat release is not the controlling factor for the hypergolic reactions. Rate constants, determined for the loss of TNT in dilute acetonitrile solution, clearly showed distinctions among the amines. The more primary amine functionalities in the amine compound, the faster it destroyed TNT. Hydrides or amine mixtures spiked with hydride decomposed substantially faster than the amines alone. However, a direct correlation between reaction rate and time‐to‐ignition was not observed.     

Reactions of Dimethyl Benzoylphosphonate

Reactions of dimethyl benzoylphosphonate (I) with various nucleophiles are described. The ester can serve simply as a useful benzoylation agent or it can undergo addition reactions to give substituted α-hydroxybenzylphosphonates. Its keto-group can be reduced to hydroxyl and can participate in the Wittig-Horner reaction. By the action of I with hydroxylamine in the presence of sodium formate, benzonitrile is obtained.     

Reactions between refractories

Glass and Ceramics -     

Reactions of trithiocyanuric acid with oxiranes. III. Reactions with epichlorohydrin

Reactions of trithiocyanuric acid with an excess of epichlorohydrin were investigated. Trifunctional polyetherols containing the s‐triazine ring were prepared. The structure of the products was verified using elemental analysis, ¹H‐NMR, and IR techniques. Some of the physical properties and the thermal stability of polyetherols were analyzed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1154–1160, 2002     

Photochemical Flow Reactions

The versatility of photochemical flow processes is rapidly expanding, and we suggest that this technique is capable of broadening the general appeal and impact of photochemistry similar or even to a greater extent to what microwave technology has done to thermal processes. This review highlights the recent developments that support this suggestion as well as the technological challenges that have yet to be resolved. Continuous photoflow reactions allow for better control over heating and mixing, are safer to operate on scale-up, in particular if LEDs are used in place of Hg lamps, they offer a higher surface/volume ratio and more efficient light penetration than batch mode photoreactions, and furthermore allow for the removal of products in-line to avoid secondary decompositions and poor conversions.