Imperfect synchronization

In connection with factors 2 and 3, it has been proposed that any factor that stabilizes the product (e.g., by resonance or solvation) lowers the rate constant if it develops late on the reaction coordinate, but increases the rate constant if it develops early. This is called the principle of imperfect synchronization. 

This year marks the 25th anniversary of the principle of nonperfect synchronization (PNS) it was introduced in 19851 as the principle of imperfect synchronization (PIS) but in later papers and reviews2 4 the name was changed due to the awkwardness of the acronym PIS. The foundations of the PNS rest mainly on a marriage between two fundamental concepts of physical organic chemistry, i.e., the concept of intrinsic barriers and that of transition state imbalances. 

One of the key goals of physical organic chemistry is to understand variation in reaction barriers resulting from reactant and solvent variation. In Chapter 8, Bernasconi uses his intriguing principle of imperfect synchronization to explain trends in intrinsic barriers resulting from substituent... 

Synchronization Team ability to work in synchronous and efficient way Imperfect synchronization events (nr)... 

In this section we shall look for evidence that imperfections in the synchrony, first of division then of DNA replication, reflect the fact that, in this system, cells can engage in DNA replication beyond a critical time limit antecedent to the time when most cells show synchronous division. In a preceding section it was reported that asynchronous entry of the cells into DNA replication continued for 40 or so minutes after the end of heat shocks. Also, evidence was presented that there is a time point 35 or so minutes before the shocks are ended, after which no cell that takes part in synchronous division at its peak can have entered into DNA synthesis. What is then the contribution to synchronous division of the fraction of cells that in fact enter DNA synthesis in the critical 1.25-hour interval between the two indicated times These cells will not have had time to finish S and normal G2 before they are supposed to participate in the first synchronous division. We shall see that in fact they contribute negatively to the synchrony, either by dividing later than at the time when synchronous division is at its peak or by not dividing at all. 

There are three experimental methods (Figure 8). The back-reflection Berg-Barrett camera is useful in examining imperfections near the crystal surface at depths of 10-100 um. A well-collimated monochromatic X-ray beam incident on the crystal is diffracted by planes [hkl) and recorded on film. Because of extinction effects, the diffracted intensity from imperfect regions exceeds that of the perfect regions. Dislocations appear as bands of contrasting darkness, 5-50 pro. wide. Film and crystal are moved in synchronization to map out... 

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