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A CN bond is strongly polarized towards nitrogen (the electronegativities of C and N are 2.55 and 3.04, respectively) and subsequently molecular dipole moments can be high: cyanamide 4.27 D, diazomethane 1.5 D, methyl azide 2.17, pyridine 2.19. For this reason many compounds containing CN bonds are water-soluble.
Typical Ritchie N + values (in methanol) are: 0.5 for methanol, 5.9 for the cyanide anion, 7.5 for the methoxide anion, 8.5 for the azide anion, and 10.7 for the thiophenol anion. The values for the relative cation reactivities are −0.4 for the malachite green cation, +2.6 for the benzenediazonium cation , and +4.5 for the tropylium cation .
The two main mechanisms were the S N 1 reaction and the S N 2 reaction, where S stands for substitution, N stands for nucleophilic, and the number represents the kinetic order of the reaction. [ 4 ] In the S N 2 reaction, the addition of the nucleophile and the elimination of leaving group take place simultaneously (i.e. a concerted reaction ).
If looked at from the point of view of an S N 2 reaction this would seem counterintuitive, since the C-F bond is amongst the strongest in organic chemistry, when indeed the fluoride is the ideal leaving group for an S N Ar due to the extreme polarity of the C-F bond. Nucleophiles can be amines, alkoxides, sulfides and stabilized carbanions. [5]
A nitrogen bound to both a good electrofuge and a good nucleofuge is known as a nitrenoid (for its resemblance to a nitrene). [2] Nitrenes lack a full octet of electrons are thus highly electrophilic; nitrenoids exhibit analogous behavior and are often good substrates for electrophilic amination reactions.
The bimolecular nucleophilic substitution (S N 2) is a type of reaction mechanism that is common in organic chemistry. In the S N 2 reaction, a strong nucleophile forms a new bond to an sp 3-hybridised carbon atom via a backside attack, all while the leaving group detaches from the reaction center in a concerted (i.e. simultaneous) fashion.
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When a nucleophile X − adds to an alkene, the driving force is the transfer of negative charge from X to the electron-poor unsaturated-C=C- system. This occurs through the formation of a covalent bond between X and one carbon atom, concomitant with the transfer of electron density from the pi bond onto the other carbon atom (step 1). [ 1 ]