![]() Alcohols, ethers and highly branched alkanes generally show the greatest tendency toward fragmentation.The fragmentation of molecular ions into an assortment of fragment ions is a mixed blessing.The third diagram above displays a Grob-like fragmentation, favored by the relief of ring strain in the four-membered ring.Other examples of Grob fragmentations will be shown above in the second diagram.A Grob fragmentation takes place in the top example, because the orbitals of the bonding and non-bonding electron pairs participating in the reaction are aligned properly.Here a simple nucleophilic fragmentation at M is converted to an ethylagous analog by the insertion of a two carbon (ethyl) segment between the reacting moieties.An interesting and generally useful skeletal transformation, involving specific carbon-carbon bond cleavage with accompanying conversion of certain sigma-bonds to pi-bonds, is known as the Grob fragmentation.Spectrum diagrams are followed by the fragmentations leading to the chief fragment ions.As a rule, odd-electron ions may fragment either to odd or even-electron ions, but even-electron ions fragment only to other even-electron ions.Fragment ions themselves may fragment further.A less common fragmentation, in which an even-electron neutral fragment is lost, produces an odd-electron radical cation fragment ion.Also, the structure of most fragment ions is seldom known with certainty.Short segments of complementary DNA, called Okazaki fragments, are produced, and these are linked together later by the enzyme ligase.The Secondary & Tertiary Structures of DNA.The DNA fragments are joined by DNA ligase (not shown).Once the primers are removed, a free-floating DNA polymerase lands at the 3' end of the preceding DNA fragment and extends the DNA over the gap.The enzymes FEN1 and RNase H remove RNA primers at the start of each leading strand and at the start of each Okazaki fragment, leaving gaps of unreplicated template DNA. ![]() Eventually, the leading strand of one replication bubble reaches the lagging strand of another bubble, and the lagging strand will reach the 5' end of the previous Okazaki fragment in the same bubble. ![]()
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