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Please continue registration for this program without your LinkedIn profile or use a different LinkedIn account or email address. Are you sure you want to disconnect with account? If the hard drive has to do this for dozens of files each time it's opened, it can decrease the computers performance.
In the picture below is an example of file fragmentation, as can be seen the second example has other files and gaps in-between the continuous blue section. Disk utilities, such as Microsoft Defrag , is used to help clean or organize file fragmentation and help keep file access faster.
Contiguous , File , Microsoft defrag , Operating system terms. Under forcing conditions, the presumed intermediate 49 of fragmentation of oxime 50 underwent recyclization to give the product 51 of overall ring contraction, albeit in low yield Scheme 5.
Fragmentations may be governed by stereoelectronic factors. The oxime 54 , derived from dihydrocamphorquinone, fragmented under phase transfer conditions, with oxime OH activation presumably taking place via nucleophilic attack on dichlorocarbene equation Distal oxygen functionality may assist fragmentation. Basic ethanolysis of the bicyclic ketoxime 57 gave the acyclic unsaturated nitrile ester 58 as a single geometric isomer equation Adjacent sulfur substituents have been observed to promote fragmentation of oximes under Beckmann conditions.
Moody, in Comprehensive Heterocyclic Chemistry , Thermal ring fragmentation reactions often parallel the MS fragmentation in the cases where small stable molecules such as N 2 or CO can be extruded. An idea of the thermal stability of a given system can be gained by considering possible electrocyclic pathways, and the thermodynamic stability of the fragments obtained by such a process. The products are benzonitrile, dimethyl-cyanamide and the ring contraction product formed by extrusion of CO.
The thermolysis of 1,3,5-oxathiazines is more complex, the initial process being an electrocyclic extrusion of the carbonyl fragment.
Trifluoromethyl-substituted 1,3,5-oxadiazines behave similarly on thermolysis. Thus extrudes hexafluoroacetone to generate , which may be in equilibrium with a 1,3-diazete, and the reaction follows a course exactly analogous to that in Scheme 5. The examples of fragmentation reactions of radical cations discussed so far correspond either to direct bond cleavages or to bond cleavages preceded by H migration or intramolecular bond formation.
These rearrangements do not alter the connectivity of C and other atoms of the original molecules. The most familiar example is the interconversion of the radical cations of toluene and cycloheptatriene, which interchanges C atoms within the C skeleton and which gives rise to stable tropylium ions Scheme 13 after H loss.
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The rearrangement of C 7 H 8 radical cations has been studied in detail both by experimental methods and by theoretical calculations and the mechanism is well understood. The crucial feature is the initial generation of a distonic ion by a 1, 2-H shift from the methyl substituent to the aromatic ring.
Fragmented | Definition of Fragmented by Merriam-Webster
This is followed by cyclization to a bicyclic norcarane-like structure which eventually ring opens to the cycloheptatriene radical cation. This last step exhibits the highest activation barrier of the rearrangement and makes it a high energy process. However, a fragmentation of the toluene radical cation by a direct C—H bond cleavage also needs a large activation energy. Hence, the rearrangement competes successfully with this fragmentation, and a C 7 H 8 molecular ion may undergo several reversible toluene—cycloheptatriene rearrangements before the final fragmentation.
It often is assumed that this type of toluene—cycloheptatriene rearrangement applies to other polysubstituted alkylbenzenes, alkylarenes and even alkyl heteroarenes. Indeed, this rearrangement explains the abundant loss of a whole substituent from an arene molecular ion in spite of the normally strong bond to a C sp 2 atom of the arene, which has to be cleaved to detach the substituent. Misako Aida, Michel Dupuis, in Theoretical and Computational Chemistry , The present chapter has addressed the characteristics of pyrimidine dimers and the fragmentation reaction of thymine dimer radical cation.
Calculations at the level of CASSCF indicate that the fragmentation reaction of the thymine dimer radical cation is a stepwise process and may proceed easily with low energy barriers once an electron is removed from the thymine dimer. We have found that the puckering of the four-member ring in the thymine dimer determines the direction of the electron movement along the fragmentation.
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DNA and solvent environments. These effects undoubtedly will affect the quantitative findings from the present ab initio calculations of the small part of a large biological system. It is likely, however, that the essential characteristics of the processes are well captured by calculations such as the calculations described in this chapter. Time-dependent dynamics of these systems are also of great interest.
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Curran, in Comprehensive Organic Synthesis , 4.
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