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In a polar aprotic solvent, nucleophilicity increases up a column of the periodic table as there is no hydrogen bonding between the solvent and nucleophile; in this case nucleophilicity mirrors basicity. I − would therefore be a weaker nucleophile than Br − because it is a weaker base.
The terminology is typically applied to organometallic and coordination complexes, but resembles the Sn2 mechanism in organic chemistry. The opposite pathway is dissociative substitution, being analogous to the Sn1 pathway. Intermediate pathways exist between the pure associative and pure dissociative pathways, these are called interchange ...
Also, because the intermediate is partially bonded to the nucleophile and leaving group, there is no time for the substrate to rearrange itself: the nucleophile will bond to the same carbon that the leaving group was attached to. A final factor that affects reaction rate is nucleophilicity; the nucleophile must attack an atom other than a hydrogen.
Ligands in coordination complexes are susceptible to substitution. Both associative and dissociative mechanisms have been observed. [4] [5] Associative substitution, for example, is typically applied to organometallic and coordination complexes, but resembles the Sn2 mechanism in organic chemistry.
The Barton reaction involves a homolytic RO–NO cleavage, followed by δ-hydrogen abstraction, free radical recombination, and tautomerization to form an oxime. [3] Selectivity for the δ-hydrogen is a result of the conformation of the 6-membered radical intermediate. Often, the site of hydrogen atom abstraction can be easily predicted.
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Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. [44] Hydrogen bonds between water molecules have an average lifetime of 10 −11 seconds, or 10 picoseconds. [45]
The loss ruined BYU's undefeated season as Oregon, Indiana and Army are now the only remaining undefeated teams at the top level of college football. The Ducks stayed at No. 1 after a 16-13 win ...