Problems with mechanism

Eoint-source pump of limited capacity. Experience has indicated that earings are a serious problem with mechanical-aeration equipment. Wave action generated within the aeration tank tends to produce lateral stresses on the bearings and has resulted in failures and increased... 

An inherent problem with mechanical-draft cooling towers is the potential for recirculation. Normally, a high air velocity discharge provided by fans will eliminate this problem. 

Maintenance. Probably the most common problem with mechanical pumps in labs is inattention to the pump oil. More pumps have died because of LSETCOI (Let Someone Else Take Care Of It) than as a result of any heinous intentional act of destruction. The reason is simple Changing pump oil is not fun or glamorous. The proper maintenance of a mechanical pump, however, is as necessary as cleaning glassware, keeping a proper lab notebook, and backing up a computer hard disk. 

Pulsed columns are generally not used for column diameters greater than 180 cm because of problems with mechanical support and pulse generation. The great amount of backmixing also causes uncertainties in column performance. Small pulsed columns have been successfully used for the extraction of metals from slurries (Warwick, 1973). 

The reaction conditions, sodamide in ammonia, as well as the lack of electron-withdrawing groups directly attached to the aromatic ring, suggest the aryne mechanism (mechanism 2) rather than the nucleophilic aromatic substitution (mechanism 1). There are several additional problems with mechanism 1. 

The largest problem with mechanical mice is that they contain moving parts. These moving parts don t like dirt and dust. The mouse is designed to move on a flat surface. Most often, the mouse ball picks up dirt and dust and deposits it on the mouse rollers. When this dirt and dust combines with the oil from your skin, it forms a substance that sticks to the mouse rollers and forms a ring around the roller. 

The proposals for a dissociative transmetallation assume that the trans configuration of complex 44 to give a tranx-fPdR R Lj] complex 48 is preserved (Scheme 1.27). As the reductive elimination of R -R is well estabhshed to occur on cis-configured derivatives, a fast isomeri2ation of trans- to dx-fPdR R I ] needs to be postulated (Scheme 1.29). An important additional problem with mechanisms based on ligand dissociation is that this type of substitution is rare for Pd(ll) [224]. 

The advantage over Concept 1 is that the use ofperovskite membranes is circumvented (and the associated problems with mechanical and chemical... 

---