关于假不对称碳原子

大学有机化学立体化学部分,多数教材未讨论“假不对称碳原子”。在教学中,同学们常提出一些涉及“假不对称碳原子”概念的问题。为此,本文就此问题做一些比较详细的讨论。现在以2,3,4-三羟基戊二酸为例,讨论几个在教学中常遇到的问题。一、光学异构体的数目 2,3,4-三羟基戊二酸的构造式为:     

替代M-型钡铁氧体纳米粒子的微波吸收性能

The microwave-absorbing behavior of substituted M-type barium ferrite nano-particles was investigated. The nano-particles were synthesized with coprecipitation-melted salt method. For the purpose of comparison, corre-sponding micro-particles were also prepared through direct coprecipitation and sintering. XRD and TEM of the nano-particles showed that the ferrite was hexagonal in structure and widely distributed in size with particle size being less than 100nm, the complex permittivity and permeability of a 1.50mm thick specimen and a 1.40mm thick specimen containing 60% by weight of substituted M-type barium ferrite nano-particles and micro-particles were measured respectively in X band (8.2～12.4GHz) range, from which the reflection loss (R.L.) of microwaves was calculated and two comparative absorption curves were given. The results showed that the synthetic nano-particles could well absorb microwaves in X band. The absorption was larger than 10dB in the range of 9.2～12.4GHz while the maximum absorption was 38.6dB at 10.6GHz.     

二氧化硅改性片状铁粒子的微波吸收性能

The preparation and microwave-absorbing behavior of micrometric silica-modified platelet iron particles (SMPLIP) were investigated. Through precipitation， hydrothermal reaction， silica-modification and reduction with hydrogen， micrometric porous SMPLIP were yielded. The permittivity values of SMPLIP had been significantly decreased due to the presence of silica. Measurements and calculations showed that a 1.93mm thick sample containing SMPLIP as much as 60% by weight was capable of absorbing X band(8.2～12.4GHz) microwaves with reflection loss being greater than -10dB within the frequency range of 8.2～11.36GHz， while the maximum re-flection loss was -14.8dB at 9.4GHz. The results had also shown that it was practicable to prepare thin， light-weight microwave absorbent with SMPLIP.     

α,β—二甲基脱水丙酮联苯酰的合成

用两种改进的方法，由联苯甲酰与３－戊酮反应制得α、β－二甲基脱水丙酮联苯酰（１），其结构由熔点、ＩＲ、ＨＮＭＲ确定，从ＨＮＭＲ谱推测：用乙醇作溶剂，加入ＫＯＨ、联苯甲酰及３－戊酮，于室温搅拌３ｈ后放置３天，所得ＩＡ为两对对映体；用苯作溶剂，加入适量聚乙二醇４００（ＰＥＧ４００），其它反应物同方法１，加热回流３ｈ，所得产物ＩＡ仅为一对对映体，改进的方法都缩短短了反应时间，上述两种方法得到的产物，经脱     

一种聚氯乙烯钙电极的研制

1967年 Ross 首先以二癸基磷酸钙溶于苯基磷酸二辛脂,并以此溶液为液体离子交换剂制成液态膜钙电极。1970年 Moody 等人用与上面相同的物质制成 PVC(聚氯乙烯)膜钙电极。其电阻为25兆欧,响应时间为6秒。我们找到了另外一种国产溶剂——甲基膦酸二(1-甲庚脂),并用二癸基磷酸钙作电活性物质,试制成一种 PVC 薄膜钙电极。这种电极内阻小,响应时间快。