Overcrowding

Steric overcrowding associated with the interaction betw een the thiocarbonyl group and a bulky alkyl group gives a bathochromic shift. This has been interpretated as evidence for a smaller thiocarbonyl group" in the first excited state (73). 

Recently. Fourier transform technique allowed the determination in natural abundance of C chemical shifts for some 4-thiazoline-2-thiones. Substituent chemical shifts for methyl and phenyl groups have been collected and discussed (874). For the overcrowded polyalkyl-A-4-thiazoline-2-thiones. the evolution of these chemical shifts furnishes... 

Accurate low-temperature ( —150°C) X-ra determinations have been performed on a set of polyalkyl-A-4-thia2oline-2-thiones in order to determine ring geometry and deformations related to steric overcrowding (83. 84). The geometry of the ring is given in Fig. VII-1. 

The distances between all hydrogen atoms is approximately the same in this structure, so there is no problem with overcrowding. 

While not overcrowded, the polyethylene structure uses space with admirable efficiency, the atoms filling the available space with 73% efficiency. For contrast, recall that close-packed spheres fill space with 74% efficiency, so polyethylene does about as well as is possible in its utilization of space. 

Open areas around the operating units of a plant act as buffers to the surrounding community. Sufficient clearance should be allowed so that, if tall stmctures coUapse, other on-site buildings or equipment, or off-site properties are not affected. Adequate roadways providing entry to the plant are extremely important, and multiple entries and exits are advisable. An overcrowded plant can lead to damage or shutdown of adjacent units and may impede the movement of vehicles and materials in case of emergency (85). Another consideration is community fire-fighting assistance, first aid, and medical facihties. 

Because of signal overcrowding in the aliphatic range between Sh= 1.3 and 2.0, the HH coupling constants cannot be analysed accurately. Only the deshielded 3-/7 at Sh = 3.39 shows a clearly... 

Overcrowding issues should be noted. Future occupant density is estimated when the ventilation system for a building is designed. When the actual number of occupants approaches or exceeds this occupant design capacity, managers may find that lAQ complaints increase. At that point, the outdoor air ventilation rate will have to be increased. However, the ventilation and cooling systems may not have sufficient capacity to handle the increased loads from the current use of the space. 

It is extremely poor economic practice to fit the equipment layout too closely into a building. A slightly larger building than appears necessary will cost little more than one that is overcrowded, yet the extra cost will be small in comparison to the penalties that will result if, to iron out the kinks, the building must be expanded. 

Death replace a previously live cell with a dead one if either (1) the living cell ha.s no more than one live neighbor (i.e. it dies of isolation), or (2) the living cell has more than three neighbors (i.e. it dies of overcrowding). 

The transformation of the porphyrin intermediate 4 into a chlorin can be achieved after introduction of a C — C double bond into the 15-propanoate side chain of 4 to yield 5. The cyclization of 5 with participation of the 15-acrylic ester side chain under acidic conditions gives the chlorin 6 which is then transformed in a multistep reaction sequence into chlorophyll a. The driving force of chlorin formation from the porphyrin is believed to be the relief of steric strain at the sterically overcrowded porphyrin periphery which gives the desired trans arrangement of the propanoate side chain and the methyl group in the reduced ring. The total... 

Careful comparison of Pt-P bond lengths for the series trany-Pt(Pcy3)2X2 (X = H, Cl, Br, I) with those for p-any-Pt(PR3)2X2 (PR3 = PMe3 or PEt3) shows a more definite increase in Pt-P with anion size for the cyclohexyl-phosphine complexes (Table 3.16) believed to be owing to intermolecular X- H and X- C non-bonded interactions arising from overcrowding [151]. 

The reaction affords in variable yields (19-85%) a stabilized phosphonium yhde exhibiting two electron withdrawing substituents on the ylidic carbon a to the phosphorus atom, and requires apparently a dialkylarylphosphine oxide incorporating an overcrowded 2,4,6-trisubstituted aryl group. 

A typical laboratory that has been in operation for some time usually has run out of space for optimum operation. In some cases, the space may be there but cannot be utilized to full advantage. Work benches gradually get covered with permanent equipment set-ups, leaving little room for other work. Lack of storage space for supplies and samples becomes the rule rather than the exception. Adequate room for a desk, bookcase, or typewriter has often been overlooked. As more personnel is added, these problems become critical. Overcrowding also has a serious effect on safety. 

File drawers become overcrowded much too fast. Periodic cleanout of active files is a necessity, but very time consuming. Inexpensive cardboard file boxes are good for permanent storage of dead files. 

Sample shelves also become overcrowded quickly, but it is often required to keep samples for extended periods of time. Older samples can be stacked into cardboard cartons, clearly identified by laboratory project references or quality control numbers, and stored at a convenient location away from the laboratory. Periodically they should be inspected and the out of date ones eliminated. One word of caution, however. Under current pollution control rules, laboratory samples may not be indiscriminatly disposed of as garbage. The laboratory operator should call in a waste disposal service when in doubt. 

In addition to the telluration of a silylene, another unique synthetic route has been developed for the silicon-tellurium double bond system. Recently, it has been reported that the exhaustive reduction of an overcrowded dibromosilane Tbt(Dip)SiBr2 (61) with an excess amount (more than 4 equiv.) of lithium... 

If a live cell has one neighbor or none at all, it dies of isolation if it has more than three neighbors, it dies of overcrowding ("becomes unoccupied" might be a better description than "dies," as the cell may be reoccupied subsequently). 

Bulky substituents at tetravalent silicon centers are the structural key element of sterically overcrowded compounds with extraordinary properties Inter- and intramolecular interactions of the bulky ligands can be studied in detail and allow an assessment of the ligands influence on structure and reactivity. 

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